BG3.6

Carbon allocation in plants and ecosystems: mechanisms, responses and biogeochemical implications

Carbon allocation is a key process in ecosystems: it is coupled with plant growth, fuels metabolism and plays a crucial role for carbon sequestration in standing biomass and soil organic matter. While the importance of carbon allocation for plant and ecosystem functioning and the carbon balance is widely recognized, we still lack a comprehensive understanding of the underlying mechanisms, responses to global changes and wider biogeochemical implications. Open questions include: 1) what drives carbon allocation in plants and ecosystems?; 2) what is the fate of newly assimilated carbon?; 3) what determines the allocation of nonstructural carbon to growth, metabolism and storage?, 4) how does carbon allocation affect nutrient and water relations in plants and ecosystems?; and 5) how do allocation patterns change under changing environmental conditions and what are the consequences for biogeochemical cycles? This session invites contributions from observational, experimental and modelling studies.

Convener: Michael Bahn | Co-conveners: Henrik Hartmann, Mariah Carbone, Daniel Epron, Andrew Richardson
Presentations
| Wed, 25 May, 15:10–18:28 (CEST)
 
Room 3.16/17

Presentations: Wed, 25 May | Room 3.16/17

Chairpersons: Michael Bahn, Henrik Hartmann
C allocation in forests
15:10–15:20
|
EGU22-5943
|
solicited
|
Highlight
|
Virtual presentation
Flurin Babst, Andrew D Friend, Jingshu Wei, Georg von Arx, Dario Papale, and Richard L Peters

The data requirements of vegetation models are changing. For more than a decade, the community has been developing “next-generation” models that should be globally applicable and at the same time incorporate great process detail. The individual tree emerges from this development as the finest scale at which carbon, water, and nutrient dynamics can be realistically simulated. As such, precise tree-level observations of the relevant processes would ideally be available from across all forested biomes to inform and evaluate tree-centered vegetation models. This is not the case. Instead, we note a growing discrepancy between the demand for and the availability of highly-resolved measurements of carbon allocation in trees and forests.

To exemplify this discrepancy, we conducted a survey at 90 flux-tower sites from around the world that revealed priorities and deficiencies in existing data collections. We found that forest structure and aboveground carbon stocks have been ubiquitously inventoried, and that tree growth and foliage turnover have also been measured at many sites. By contrast, detailed information on water cycling, volume increment, and wood formation processes (especially belowground) are less common, as are records of tree mortality or terrestrial and airborne LiDAR that could help scale local observations. In addition, we found that the temporal resolution and length of existing time-series vary substantially across the current flux-tower network. Weighing the strengths and limitations of this and many other ecological monitoring networks, we conclude that the present data basis is insufficient to support accelerating vegetation model development.

Looking forward, we anticipate that not only the amount of tree-level observations needs to be increased – especially in tropical and boreal systems – but that the consistency, scalability, and predictability of forest carbon cycle observations needs to be improved. We also propose that intensive long-term monitoring sites be strategically paired with manipulative experiments at comparable sites to better connect past, present, and expected future dynamics. For this, we propose a versatile experimental framework and call for a community-wide discussion on the “yield on cost” of various field observations. We also list a number of key questions on how to best build and maintain cross-scale data archives in support of tree-centered vegetation modelling.

How to cite: Babst, F., Friend, A. D., Wei, J., von Arx, G., Papale, D., and Peters, R. L.: Observations of carbon allocation in the world’s forests must match pace with vegetation model development, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5943, https://doi.org/10.5194/egusphere-egu22-5943, 2022.

15:20–15:26
|
EGU22-2938
|
On-site presentation
Sebastian Doetterl, Benjamin Bukombe, Marijn Bauters, Pascal Boeckx, Landry Cizungu, Matthew Cooper, Peter Fiener, Laurent Kidinda, Isaac Makelele, Daniel Muhindo, Boris Rewald, and Kris Verheyen

The net primary productivity (NPP) of tropical forests is an important component of the global terrestrial carbon (C) cycle. The lack of field-based data, however, limits our mechanistic understanding of the drivers of NPP and C allocation. In consequence, the role of local edaphic factors for forest growth and C dynamics is unclear and introduces substantial uncertainty in estimating ecosystem C stock accrual. Here, we present data from field measurements on standing biomass as well as leaf, wood, and root production collected along topographic and geochemical gradients in old-growth African tropical mountain forests in the East African Rift System. We show that forests converge towards nutrient uptake more strongly when soil properties and parent material geochemistry indicate fertility constraints due to low amounts of rock-derived nutrients. In contrast, topography did not constrain the variability in C allocation and NPP fluxes. In consequence, aboveground:belowground biomass ratios and total NPP can differ greatly between geochemical regions for similar old-growth tropical forest types. Furthermore, soil organic carbon (SOC) stocks were not related to NPP C allocation and plant C input seemingly exceeding the maximum potential of these soils to stabilize C. We conclude that even after many millennia of weathering and the presence of deeply developed soils, tropical above and belowground C allocation, as well as soil C stocks, vary substantially due to the geochemical properties which soils inherit from parent material.

How to cite: Doetterl, S., Bukombe, B., Bauters, M., Boeckx, P., Cizungu, L., Cooper, M., Fiener, P., Kidinda, L., Makelele, I., Muhindo, D., Rewald, B., and Verheyen, K.: Soil geochemistry as a major driver of carbon allocation, stocks and dynamics in vegetation and soils of African tropical forests, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2938, https://doi.org/10.5194/egusphere-egu22-2938, 2022.

15:26–15:32
|
EGU22-422
|
ECS
|
On-site presentation
Ana Caroline Miron, Amanda L. Cordeiro, Nathielly P. Martins, Richard Norby, Iain P. Hartley, Raffaello Di Ponzio, Sabrina Garcia, Alacimar Guedes, Bruno T. T. Portela, Iokanam Pereira, Jéssica Campos, Amanda Damasceno, Erick Oblitas, Carlos Alberto N. Quesada, and Laynara F. Lugli

Seasonal phenological patterns in the Amazon Forest result from interactions among climate and turnover rates of different plant tissues. Changes in productivity rates and allocation are predicted to occur with climate change, particularly for dynamic tissues such as fine-roots and leaves. Accurate measurements of fine-roots and litterfall dynamics and their interactions with climate are key to understanding the fate of carbon and nutrients in these ecosystems, which will improve climate model predictions.

In this study we quantified fine-root dynamics up to 90 cm soil depth and asked if there were any differential allocation patterns between fine-roots and leaf litterfall productivity in a Central Amazon forest. We hypothesized that rainfall seasonality would affect such trends.

Fine-root (diameter <2mm) were measured monthly for 3 years (November 2016 – November 2019) using minirhizotrons cameras at the AmazonFACE site in a tropical rainforest in Central Amazonia near Manaus, Brazil. We divided root analysis in three soil layers: 0-30 cm (n=9), 30-60 cm (n=7) and 60-90 cm (n=6). Leaf litterfall was collected biweekly at the same site and period using 24 50 x 50 cm litter traps (0.25 m²) installed one meter above the ground.

The total fine-root biomass (0-90 cm) was 11.13 ± 0.2 Mg ha-1 and decreased with soil depth (0-30 cm: 4.97 ± 0.2; 30-60 cm: 3.43 ± 0.2; 60-90 cm: 2.73 ± 0.2 Mg ha-1). Fine-roots productivity also decreased with depth, ranging from 4.27 ± 0.31 Mg ha year-1 in the top 30 cm to 1.15 ± 0.18 Mg ha year-1 between 60 to 90 cm. As a result, turnover rates were faster in the first layer (1.08 year-1), and slower in the deeper layers (30-60 cm: 0.63; 60-90 cm: 0.45 year-1), being 0.78 year-1 for the whole soil profile.

Mean total fine-roots productivity up to 90 cm depth was 7.22 ± 0.82 Mg ha year-1 and mean leaf litterfall productivity was 5.94 ± 0.39 Mg ha year-1, with a marked seasonal trade-off between these two components. In the dry season (June to October) litterfall peaked, reaching 9.06 ± 0.22 Mg ha year-1 while fine-roots reached its lower values: 4.66 ± 0.54 Mg ha year-1. The opposite trend occurred in the wet season (November to May), when fine-roots reached 9.03 ± 1.18 Mg ha year-1 and litterfall dropped to 3.6 ± 0.08 Mg ha year-1. Rainfall was positively correlated with fine root productivity and negatively correlated with leaf litterfall, explaining 34% and 48% of the variation, respectively.

Our results show that, although commonly neglected, deep fine-roots account for a high proportion of forest productivity in the Amazon, once they are also very dynamic at deeper layers. Moreover, since new leaf production has been found to be temporally synchronized with litterfall production in this forest, such trends point to a possible shift in total plant carbon allocation between above and belowground compartments driven by the seasonal changes in rainfall regime. Deeper understanding of phenological mechanisms in the Amazon forest could therefore improve predictions of its long-term response and resiliency to changing climate. 

How to cite: Miron, A. C., Cordeiro, A. L., Martins, N. P., Norby, R., Hartley, I. P., Di Ponzio, R., Garcia, S., Guedes, A., Portela, B. T. T., Pereira, I., Campos, J., Damasceno, A., Oblitas, E., Quesada, C. A. N., and Lugli, L. F.: Asynchronous forest: the role of rainfall seasonality controlling fine-roots and litterfall productivity in Central Amazonia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-422, https://doi.org/10.5194/egusphere-egu22-422, 2022.

15:32–15:38
|
EGU22-10109
|
ECS
|
Virtual presentation
Giorgos Xanthopoulos, Kalliopi Radoglou, Gavriil Spyroglou, Delphine Derrien, Nicolas Angeli, and Mariangela Fotelli

The restoration of degraded land after mining with the establishment of forest plantations, contributes to climate change mitigation by enhancing carbon storage. For this purpose, around 2,570 hectares at the Lignite Center of the Hellenic Public Power Corporation in Western Greece were planted with black locust (Robinia pseudoacacia L.), since it is a fast-growing, drought-tolerant species with N-fixing capacity. The aim of this study, which was carried out within the COFORMIT project, was to estimate the C fluxes of litterfall, forest floor and fine roots (<2mm in diameter), and the C stocks of coarse roots (≥2mm in diameter) and soil in these plantations and to examine how they are affected by seasonal variability, canopy density, soil depth. Sampling was performed in 18 plots of higher and lower canopy density (36 plots in total). In each plot, litterfall and forest floor were sampled bimonthly, while soil samples were collected once at two depths (0-10cm, 10-30cm). To estimate carbon stocks in coarse roots, the root system of five black locust individuals, representative of the 5 classes of diameter at breast height (DBH) have been excavated. For the determination of carbon fluxes of fine roots, 12 cores were sampled around the perimeter of each selected tree. To assess fine root turnover, 48 in-growth cores had been placed around four trees with varying DBH. Carbon fluxes of litterfall and forest floor peaked from October till December in both pools. Total carbon sequestration in litterfall was 1.39 t ha-1 yr-1 and it significantly increased with increasing canopy density. Mean annual carbon in forest floor was 2.98 t ha-1 yr-1, which was not significantly affected by canopy density. The carbon sequestration in coarse roots was 12.89 t ha-1. Fine roots stored c. 0.27 t ha-1 of carbon, while no effect of soil depth (0-10 cm vs. 10-30 cm) was detected. Fine root turnover was 0.17 t ha-1 yr-1 and it also did not differ with soil depth. Soil organic carbon (SOC) increased greatly with depth (from 19.57 t ha-1 in 0-10 cm to 33.19 t ha-1 in 10-30 cm) and in total (52.75 t ha-1) was higher than the SOC levels reported in literature for black locust plantations of the same age, possibly due to the presence of lignite mining residues. Our results support the significant carbon sequestration potential of the studied restoration plantations and are discussed in relation to findings from other black locust restoration schemes.

Keywords: CO2 sequestration, black locust, post-mining rehabilitation, soil organic carbon, forest floor, litter, below-ground biomass.

How to cite: Xanthopoulos, G., Radoglou, K., Spyroglou, G., Derrien, D., Angeli, N., and Fotelli, M.: Carbon sequestration in litterfall, forest floor, roots and soil in Robinia pseudoacacia restoration plantations., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10109, https://doi.org/10.5194/egusphere-egu22-10109, 2022.

15:38–15:44
|
EGU22-11351
|
ECS
|
Virtual presentation
Ido Rog, Hagar Fox, and Tamir Klein

Mixed forests are typically more productive and are faster to recover from drought compared to monospecific forests. Disentangling the contribution of each species to the overall success of the forest requires observations at the individual tree level. In this study, we measured a complete set of carbon (C) pools and fluxes at the tree-level in five tree species, two conifers and three broadleaf, co-existing in a mature evergreen mixed Mediterranean forest. Our study period included a drought year, followed by an above-average year. Across species, C sinks of 38-91 kg tree-1 year-1 were 16-32% larger than C source of 27-77 kg tree-1 year-1 in the dry year, with larger belowground C investment of the shallow-rooted species. Overall, respiration was the largest sink across species and years, accounting for 26-62% of all assimilated C, followed by growth (16%) and root exudation (19%). Non-structural carbohydrates accumulation was similar between the wet and the dry year. These detailed tree-level observations expose large interspecific differences in C allocation among fluxes and tissues and specifically in response to varying water availability. These insights become useful for forest management under ongoing change.

How to cite: Rog, I., Fox, H., and Klein, T.: Tree-scale carbon allocation dynamics in a mature mixed forest using long-term mass balance approach , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11351, https://doi.org/10.5194/egusphere-egu22-11351, 2022.

15:44–15:50
|
EGU22-13561
|
ECS
|
On-site presentation
Bruno Montibeller, Michael Marshall, Ülo Mander, and Evelyn Uuemaa

Global heating is affecting the gross primary production (GPP; i.e., amount of CO2 assimilated by plants) and evapotranspiration (ET; i.e., water loss from surface evaporation and transpiration) across forests in the northern hemisphere. Increasing temperatures have induced a prolonged growing season that has enhanced GPP during the spring and autumn seasons. In the summer season, it has resulted in higher ET. Although these findings are reported in multiple studies, we lack investigations that specifically analysed long-term regional scale changes in GPP and ET in undisturbed core forest areas, which play an important role in the carbon and water fluxes. Analyses of GPP and ET changes across undisturbed forest areas are essential to understand how these areas are adapting to new climate conditions and contribute to the mitigation of human greenhouse gas emissions. In our study, we used Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data to investigate the trends and changing rates of GPP, ET and water-use-efficiency (i.e., quantity of carbon assimilated by litre of water; WUE=GPP/ET) across undisturbed forest areas in Europe from 2000 to 2020 at monthly basis. We used the Mann-Kendal test to identify the significance of trends and the Theil–Sen estimator to quantify the monthly rate of change. The results indicated that during early spring and late autumn, approximately half of the total undisturbed core forest areas (3601.5 km2), mostly located in eastern Europe, showed an increase in GPP and ET. These areas also showed an increase in WUE because the increase in GPP was greater than the ET. However, most forest areas showed a decrease in GPP during summer, which was not compensated by the GPP increase during spring and autumn. These uncompensated forest core areas were spatially scattered across different forest types in Europe and were responsible for offsetting 20% of the total GPP increase in all European forest core areas. Our results provided evidence that certain forest core areas have limitations to act as carbon sinks, therefore, reducing the capacity to mitigate human carbon emissions. Moreover, by identifying the location of these forests, our results can support the application of management strategies that enhance carbon assimilation. 

 

How to cite: Montibeller, B., Marshall, M., Mander, Ü., and Uuemaa, E.: Carbon assimilation and water use efficiency increases in undisturbed core forest areas may not compensate carbon losses, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13561, https://doi.org/10.5194/egusphere-egu22-13561, 2022.

Tree C metabolism
15:50–15:56
|
EGU22-2861
|
ECS
|
On-site presentation
Cedric Zahnd, Lia Zehnder, Ansgar Kahmen, and Günter Hoch

Leaves in tree crowns experience different microclimates depending on their vertical positions, particularly in light availability. This leads to different rates of carbon assimilation. Additionally, leaf phenology potentially varies along the same gradient. Therefore, it can be assumed that the size and seasonal dynamics of the non-structural carbohydrate (NSC) pool are different in sunlit and shaded twigs of individual trees.

Here we test how microclimatic gradients and leaf phenology influence the NSC dynamics of young twigs along the vertical gradient of individual tree crowns. Throughout the year 2020, we measured the NSC concentration in twigs from the top and bottom crown parts of mature trees from 9 species in a temperate mixed forest at the Swiss Canopy Crane II facility near Basel, Switzerland. We recorded the timing of budbreak along the canopy depth of those trees and continuously measured the light environment with loggers in various canopy positions in three consecutive seasons (2019-2021).

The timing of budbreak showed barely any difference between top and bottom crown parts in broadleaved species. However, in the conifers Abies alba and Picea abies, buds opened ca. 7 days earlier in the bottom crowns than the top. Light availability throughout the growing season in the lower crown parts was around 30 % of that at the top. In most species, the NSC pools were strikingly similar in sunlit and shaded twigs, both quantitatively and in terms of their seasonal dynamics. Only the two ring-porous species Quercus petraea and Fraxinus excelsior showed differences: in both, the lower twigs reached their minimum starch levels after budbreak about a week later than the top twigs, and took longer for the subsequent refilling. However, even in species that showed slight differences in the seasonal NSC dynamics between upper and lower canopy, the end of season NSC concentrations in late autumn were identical between top and bottom twigs.

The very similar NSC dynamics and pool sizes between twigs from upper and lower crown parts, despite stark differences in light availability, are surprising. Further analyses of carbon assimilation and the ratio of carbon source to sink tissues along these vertical canopy gradients will allow to better interpret those results and to get an improved understanding of how carbon storage is controlled in mature trees.

How to cite: Zahnd, C., Zehnder, L., Kahmen, A., and Hoch, G.: How do leaf phenology and microclimate influence carbon storage dynamics along the vertical canopy gradient of mature trees?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2861, https://doi.org/10.5194/egusphere-egu22-2861, 2022.

15:56–16:02
|
EGU22-6539
|
ECS
|
On-site presentation
David Herrera, Christine Römermann, Henrik Hartmann, Susan Trumbore, Jan Muhr, Paulo Brando, Divino Silvério, and Carlos A. Sierra

Trees store most of the nonstructural carbon (NSC, mainly sugars and starch) in the stem wood to support metabolism and growth. For many species, NSC concentration decreases radially with sapwood depth. Spatial distribution of NCS also varies with wood anatomical traits, as NSC is dispersed in the wood living-fibers or concentrated  in parenchyma cells. These distributions may  influence temporal changes in NSC and are related to mortality and growth. Observed relations between NSC storage and wood traits thus are associated with differences in the time scales of NSC cycling in  trees and in the ability of trees to survive and recover from stressful conditions such as drought or mechanical damage.  

Here we focus on the following questions: i) what are the radial mobilization rates of NSC across the sapwood for tropical trees with different NSC spatial distributions? and ii) how old is the NSC stored in these trees and the NSC that they access for respiration and wood growth?

To answer these questions we measured NSC content through a radial path in the sapwood (from bark to pith) in eight tropical tree species, four fiber and four parenchyma-storing species, in a seasonal dry forest in Brazil during 2019. We measured the 14C in the soluble carbon extracted from wood segments corresponding to two depth ranges of each radial path (0-2cm and 2-4cm) and in the respired CO2 from 6cm wood core segments. We estimated the age of the wood by counting tree rings and measuring the 14C in the cellulose.  

We found significant seasonal changes in the starch content at different sapwood depths in all trees evaluated, indicating that NSC is metabolically active across all depths where starch is stored. Radiocarbon data indicate that fiber-storing trees retained NSC in the wood for decades. In some cases NSC was even older than the wood that contained it, indicating the mixing of old NSC coming from deeper layers of wood. Irrespective of the stored NSC ages, trees always used younger NSC for respiration, indicating that our water extraction includes both reserves being used for metabolism and older C that may be less available at the moment of sampling. However, trees accessed older NSC when they faced stressful conditions, e.g. when in negative C balance, requiring a larger contribution of the old stored NSC to support respiration. Thus, tree species with low mortality and slow growth such as fiber-storing species may remobilize older NSC from deeper layers of wood to survive stressful conditions for longer time than parenchyma-storing species.

These findings highlight the diversity of NSC storage and remobilization strategies in tropical trees. These strategies have important implications for our understanding not only of how trees will respond to future climatic changes but also about the mechanism of carbon cycling in tropical trees and ecosystems. 

How to cite: Herrera, D., Römermann, C., Hartmann, H., Trumbore, S., Muhr, J., Brando, P., Silvério, D., and Sierra, C. A.: Nonstructural carbon age and lateral mixing in the stem wood of tropical trees, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6539, https://doi.org/10.5194/egusphere-egu22-6539, 2022.

16:02–16:08
|
EGU22-1931
|
ECS
|
Virtual presentation
Boaz Hilman, Emily Solly, Frank Hagedorn, Iris Kuhlman, David Herrera-Ramírez, and Susan Trumbore

The bomb radiocarbon approach allows to estimate the time elapsed since carbon (C) fixation and thus to study the use of stored C. Previous studies show that fine roots (≤ 2 mm), a large and dynamic C pool in trees, are constructed from C that was fixed years to more than a decade previously. In comparison, aboveground tissues grow from C mostly < several years old. Our current understanding is that 14C ages of tree tissues mainly reflect the 14C content of the C substrate which supports their growth. We addressed the question – what explains the variations in 14C age of C supporting growth among tissues and between trees?

We compared tissue chronological ages determined from annual-ring count (roots) or observations (needles, branches) with 14C-based C ages along an elevational gradient near the Alpine tree line (Stillberg, Davos, Switzerland). Previous studies have shown that decreasing temperatures along this gradient limit tree growth. Carbon assimilation via photosynthesis is less sensitive to low temperatures, resulting in accumulation of storage compounds in tree line trees. We therefore expected stored C in trees at the tree line to have the slowest turnover rates and oldest C; i.e. that the age difference between 14C and chronological age would increase with elevation.

While needles and branch wood tissues were produced from 0-2 yr C, fine roots were produced from C fixed up to a decade ago. Contrary to our prediction, the C age in the roots decreased from 9.5 yr 150 m below the tree line to 4.5 yr at the tree line. Relatively unstressed trees in a site located 600 m lower used the youngest C to build roots (1.5 yr). But the old C ages cannot be explained by a complete decoupling from fresh C, as the roots contained a metabolically active pool with ages of 0-1.5 yr used for root respiration. Previous studies showed that root growth commences before shoot growth and mostly occurs earlier in the growing season. It is therefore plausible that during root growth the reliance on old stored C is greater than at the end of the summer when sampling took place. Yet, the timing of root growth alone cannot explain the elevation trend in the age of C used to build fine roots. The carbon allocation model we adopted suggested that roots are built from older C when the turnover time of the root storage declines. In agreement, the soluble storage compounds below the tree line had the oldest 14C ages and the slowest turnover times.

Overall, the oldest belowground C reserves were found at intermediate elevations, where growth limitation was slightly eased, and perhaps a larger proportion of fresh C assimilates were used for the growth of aboveground tissues rather than fine roots. Larger amounts of fresh C are allocated to the belowground when C availability is in surplus either when conditions are favorable (at the lowest elevation) or when growth rates are small compared to C assimilation (at treeline). 

How to cite: Hilman, B., Solly, E., Hagedorn, F., Kuhlman, I., Herrera-Ramírez, D., and Trumbore, S.: Role of storage reserves in new tissue growth quantified using bomb 14C at the alpine treeline, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1931, https://doi.org/10.5194/egusphere-egu22-1931, 2022.

16:08–16:14
|
EGU22-10463
|
ECS
|
On-site presentation
Thomas Guzman, Pierre Petriacq, Josep Valls Fonayet, Sabrina Dubois, Nicolas Devert, Cedric Cassan, Amelie Flandin, and Lisa Wingate

During the process of photosynthesis, leaves capture CO2 from the atmosphere and rapidly convert it into a diverse array of primary and secondary metabolites. Plants maintain a core set of metabolic pathways that ensure the basic building blocks of life that are available for each plant species to function. However, as plants evolved on land, they began to allocate this carbon (C) to innovative secondary metabolites and organs (cuticles, roots, wood) that protected them from abiotic stress (UV radiation, aridity, freezing) and biotic attack (fungal pathogens and insect/animal herbivory). As plants expanded over the land surface and occupied different niches, the amount of C fixed by plants varied and the types of secondary compounds synthesised by plants began to differ. Little is known about the metabolic profiles of the dominant European tree species and how variable the metabolomes of individual tree species are to changes in site conditions such as nutrient availability or soil moisture status. This study took advantage of recent advances in high-resolution mass spectrometry (HRMS) and bioinformatic tools to compare the leaf metabolomes of 14 commercially important tree species grown across three common gardens. Alongside the metabolic profiles, important chemical and morphological data were also collected from the trees during sampling, including targeted analysis of specific leaf metabolites such as proteins and phenolic compounds to obtain quantitative information on how their concentrations varied between tree species and site. Our analysis showed that the metabolomes of each tree species statistically differ from one another, and this dissimilarity was highly conserved at all three sites, even though tree growth and mortality rates varied between species and site. Our analysis also clearly highlighted distinct metabolome shifts between angiosperm and gymnosperm tree species, with angiosperms displaying greater concentrations of chlorophyll and amino acids alongside lower C/N ratios. These differences were also accompanied by discrepancies in an important set of secondary metabolites detected with the metabolomic technique. Furthermore, we also found that certain secondary compounds were essential in distinguishing between deciduous and evergreen species or families where targeted analysis could not detect significant differences. Our results indicate that temperate tree species may have conserved chemical 'fingerprints' that provide information on fundamental differences in the activity of certain plant metabolic pathways. This thus provides a promising tool to investigate how and why different plant species allocate C differently over the growing season and defend themselves against diverse abiotic and biotic pressures.

How to cite: Guzman, T., Petriacq, P., Valls Fonayet, J., Dubois, S., Devert, N., Cassan, C., Flandin, A., and Wingate, L.: The metabolic 'toolkits' of temperate trees are species-specific and vary little with modest soil moisture variability., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10463, https://doi.org/10.5194/egusphere-egu22-10463, 2022.

16:14–16:20
|
EGU22-4213
|
ECS
|
On-site presentation
Juliane Helm, Roberto Salomón, Jan Muhr, Kathy Steppe, Boaz Hilman, and Henrik Hartmann

We lack a detailed understanding of tree carbon flux dynamics to quantify stem respiration correctly. Stem CO2 radial diffusivity and vertical CO2 transport with the xylem sap produce uncertainties in respiration estimates based on stem CO2 efflux measurements. Two independent approaches have been applied for comparison to assess such uncertainties: (1) the mass balance approach accounts for CO2 efflux from the stem to the atmosphere, CO2 transport through the xylem and CO2 stored within the stem to estimate total respiration rates, and (2) measurements of stem O2 consumption as a more robust proxy for stem respiration than stem CO2 efflux, because O2 is less soluble than CO2 in the sap solution and hence less  affected by vertical transport.

In this study, we compare these two approaches and study CO2 and O2 flux dynamics along the stem height to capture CO2 transport. During summer 2019, we measured vertical CO2 and radial CO2 and O2 fluxes, sap flow, stem temperature and xylem sap pH from twigs. Stem CO2 and O2 fluxes were calculated along 4-m stem segments on mature beech trees in a managed forest in Germany.

We found that xylem [CO2] and CO2 and O2 fluxes did not vary with stem height. Interestingly, stem CO2 efflux was a poor predictor of stem respiration in the monitored mature trees. O2 influx was always higher than CO2 efflux (on average CO2-to-O2 ratios was 0.72), resulting in an underestimation of stem respiration when using CO2 measurements only, which is standard practice.

Preliminary results of the implementation of this dataset into a biophysical stem respiration model (TReSpire) suggest that CO2 respired in the xylem of mature trees encounter a relatively long diffusive pathway to reach the bark tissues, so that a significant fraction of CO2 dissolves in the sap and is transported upwards before being detected by traditional approaches. Our study provides insights into stem carbon flux dynamics in large trees, and thus helps to improve estimation of ecosystem carbon cycling.  

How to cite: Helm, J., Salomón, R., Muhr, J., Steppe, K., Hilman, B., and Hartmann, H.: Observed and modelled stem respiration CO2 and O2 fluxes in mature beech trees, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4213, https://doi.org/10.5194/egusphere-egu22-4213, 2022.

16:20–16:26
|
EGU22-7527
|
ECS
|
On-site presentation
Olga Dombrowski, Cosimo Brogi, Harrie-Jan Hendricks Franssen, Damiano Zanotelli, and Heye Bogena

Carbon allocation is a major driver of plant growth and plays a key role in shaping ecosystem processes and the global carbon (C) cycle. In contrast to annual crops, fruit trees store and remobilize C in their perennial plant components, have long canopy durations, relatively low respiratory costs, and remain productive for decades. To predict C dynamics in fruit tree orchards under global change, it is essential to expand the understanding of carbon allocation in fruit trees and to improve its representation in comprehensive modelling environments such as land surface models (LSMs). LSMs simulate the exchanges of matter and energy between the terrestrial biosphere and the atmosphere. They are widely used in C cycle and climate change studies, and typically include representations of various types of natural vegetation and annual crops. Despite the importance of fruit orchards in regions that are strongly affected by climate change, such as the Mediterranean, they are rarely considered in LSMs, thus leaving an important gap in the representation of C allocation and related biogeophysical and biogeochemical processes of these agro-ecosystems. In this work, we present the new fruit tree sub-model CLM-FruitTree within the Community Land Model version 5 (CLM5). Herein, a fruit tree is described by a perennial deciduous phenology with C allocation to standing woody biomass components and annual organs such as leaves, fine roots, and fruits that are either shed or harvested within the yearly cycle. Two different pools, the storage and the photosynthetic pool, contribute to tree growth while C allocation to the individual plant components is based on allocation coefficients that vary depending on the specific phenological phase. CLM-FruitTree was tested using multiple years of field measurements of above- and belowground biomass components, leaf area index (LAI), yield, soil respiration, and eddy covariance (EC) data from an apple orchard in South Tyrol, Italy. We found that biomass allocation was captured within 1-5 % of the measured values, with about half of the assimilated C allocated to fruits. Growth from C storage thereby played a significant role in shaping initial leaf development and growth of fine roots. Simulated ecosystem C fluxes showed a high correlation (r > 0.84) with the EC measurements and the seasonal dynamics were well represented. Average annual gross primary productivity was predicted within 1.5 % of the measured values while net carbon uptake was overestimated by on average 21 % mostly due to an underestimation of soil respiration in the orchard caused by necessary simplifications in the microbial respiration, orchard structure, and management practices. Overall, the new sub-model CLM-FruitTree allows the exploration of the dynamics of C allocation and fluxes in fruit orchards, and may advance C cycle and climate change studies of such agro-ecosystems at larger scale.

How to cite: Dombrowski, O., Brogi, C., Hendricks Franssen, H.-J., Zanotelli, D., and Bogena, H.: Introducing CLM-FruitTree to model carbon allocation in fruit orchards with the Community Land Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7527, https://doi.org/10.5194/egusphere-egu22-7527, 2022.

Coffee break
Chairpersons: Michael Bahn, Henrik Hartmann
Drought responses
17:00–17:06
|
EGU22-11269
|
Virtual presentation
Marta Galvagno, Mirco Migliavacca, Edoardo Cremonese, Gianluca Filippa, Giorgio Vacchiano, Consolata Siniscalco, Silvio Oggioni, Umberto Morra di Cella, and Ludovica Oddi

Projections of future climate change indicate that extreme events will be larger in frequency and intensity, with an increased risk of ecosystem transition from carbon sinks to carbon sources. In particular, warming is occurring at a higher rate in the Alps, with important impacts for tree species acclimated to a strong climate seasonality and a short growing season.

In this study, we investigated the ecosystem responses to heatwave and drought at a high-altitude Larix decidua (Mill.) forest in the western Italian Alps (IT-Trf, 2050 m asl), by coupling direct measurements of ecosystem-scale surface-atmosphere fluxes and tree-based observations. Ecosystem fluxes were monitored by means of the eddy covariance technique, measuring water and carbon fluxes (i.e., gross primary production, net ecosystem exchange, and evapotranspiration). From 2015 to 2017 additional observations were carried out at tree level, including stem growth and its duration, direct phenological observations, sap flow, and tree water deficit.

Results showed that the warm spells observed in 2015 and 2017, caused the advance of the larch phenological development and, thus, of the seasonal trajectories of many processes. However, we did not observe significant quantitative changes in the C sequestration at the ecosystem level, whereas in 2017 we found a reduction of 18% in larch stem growth and a contraction of 45% of the stem growth period. The growing season in 2017 was indeed characterized by different drought events and by the highest water deficit during the study years. By combining tree- and ecosystem-based observations, we demonstrated that larch growth decrease was not driven by a reduction of the photosynthetic activity.

We formulate two contrasting hypotheses to explain our results: i) a shift in C allocation within the plants towards the prioritization of NSC storage within leaves and roots over growth processes, which question the C-source limitation hypothesis, usually applied in vegetation modeling; ii) the ‘Insurance Hypothesis’, which can be used to explain the stability of the whole ecosystem gas exchanges, where the negative effects of climatic fluctuations on larch growth might have been buffered by the asynchrony responses of the understory species that can benefit from the higher temperatures.

How to cite: Galvagno, M., Migliavacca, M., Cremonese, E., Filippa, G., Vacchiano, G., Siniscalco, C., Oggioni, S., Morra di Cella, U., and Oddi, L.: Contrasting responses of forest growth and carbon sequestration to heat and drought in the Alps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11269, https://doi.org/10.5194/egusphere-egu22-11269, 2022.

17:06–17:12
|
EGU22-11285
|
ECS
|
On-site presentation
Johannes Ingrisch, Angelika Kübert, Jianbei Huang, Kathiravan Meeran, Joost van Haren, Lingling Shi, Ines Bamberger, Jürgen Kreuzwieser, Marco Lehmann, Michaela Dippold, Laura Meredith, Nemiah Ladd, Michael Bahn, and Christiane Werner

Drought exerts a major control on the carbon (C) cycle of terrestrial ecosystems worldwide. However, the mechanisms and processes underpinning ecosystem responses remain uncertain, in particular in diverse, tall-growing ecosystems like tropical rainforests. In such ecosystems, trees are a predominant driver of ecosystem C cycling, as they link the major ecosystem fluxes, photosynthesis and ecosystem respiration through allocation and utilisation of recent assimilated C. Trees respond dynamically to drought, generally by reducing C assimilation and altering investments of recent C into metabolism, defence, growth and storage, which has consequences for the fate of C in the system. However, to date most of our understanding is derived from experiments on small trees and we lack an understanding of how whole-tree C allocation responds in diverse, stratified forest ecosystems.

To address this knowledge gap, we implemented a 9.5-week experimental drought in the world’s largest controlled growth facility, the Biosphere 2 Tropical Rainforest in Arizona, US. We continuously measured isotopic CO2 fluxes of leaves, stem and soil as well as leaf and phloem non-structural carbohydrates across a range of canopy and understory forming trees during pre-drought and drought conditions. To study drought effects on the fate of recent photoassimilates, we labelled the entire ecosystem with a 13CO2 pulse during pre-drought and drought conditions and traced the carbon flow in leaf, stem and soil fluxes and non-structural carbohydrates of leaves and phloem.

Across all studied trees, drought generally reduced CO2 uptake and metabolic activity in leaves, stems and soil. The phloem transport rates slowed down and the turnover of recent photoassimilates declined. As drought progressed respiration was increasingly fuelled by C reserves, as indicated by isotopic flux dynamics and a depletion of starch pools, particularly in leaves. Drought response patterns of fluxes, carbohydrate pools and C allocation dynamics were highly variable among trees. Interestingly, response diversity was not primarily explained by species identity, but likely related to a combination of functional and structural traits and the trees’ microenvironment within the forest. We conclude that the structural and functional composition of a forest is an important driver for tree C allocation and needs to be considered for understanding the mechanisms underpinning forest C dynamics in response to drought.

How to cite: Ingrisch, J., Kübert, A., Huang, J., Meeran, K., van Haren, J., Shi, L., Bamberger, I., Kreuzwieser, J., Lehmann, M., Dippold, M., Meredith, L., Ladd, N., Bahn, M., and Werner, C.: Drought effects on whole-tree C dynamics in an enclosed tropical rainforest, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11285, https://doi.org/10.5194/egusphere-egu22-11285, 2022.

17:12–17:18
|
EGU22-1638
|
Virtual presentation
Arthur Gessler, Jobin Joseph, Frank Hagedorn, Shengnan Ouyang, and Leonie Schönbeck

It is getting more and more clear that the sink activity in trees strongly determines carbon (C) uptake and within-plant C distribution. Here we show that short- and long-term changes in water availability impacted the belowground (mycorrhizosphere) C sink strength, which however, not only affected C transport to the roots but also nitrogen (N) uptake by tree roots and the N allocation to aboveground tissues. The negative drought impact on N uptake might be a result of reduced root growth and the lower availability of recent assimilates for mobilizing inorganic N in the soil as the physiological N uptake capacity of the roots was not clearly affected. On the other hand, we show that increased N availability in the soil can have positive effects on C allocation to the rooting system of trees under drought and consequently can reduce drought induced growth impairment and mortality. Our results show that the strong interaction between nutrients and carbon needs to be taken into account to understand the resilience of trees and forests towards drought events projected to occur more frequently in future.

How to cite: Gessler, A., Joseph, J., Hagedorn, F., Ouyang, S., and Schönbeck, L.: The interaction of carbon and nutrient relations in trees exposed to drought, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1638, https://doi.org/10.5194/egusphere-egu22-1638, 2022.

17:18–17:24
|
EGU22-2100
|
ECS
|
Virtual presentation
Shengnan Ouyang, Weijun Shen, Matthias Saurer, Honglang Duan, Guijie Ding, Liehua Tie, Maihe Li, and Gessler Arthur

Severe drought acutely impairs plant hydraulic functioning and impedes processes of carbon (C) and nutrient as well as their allocation. However, how fertilization would modify the allocation of C and nutrient between sink and source organs during drought stress remains largely unknown.

We used three-year old potted seedlings of sessile oak and Scots pine in a greenhouse experiment where they were subjected to three different fertilization treatments (non-fertilized, moderate and high fertilization) and two water regimes (well-watered and severe drought) across two consecutive growing seasons. 13C and 15N labeling were labeled to trace the C and nitrogen (N) allocation. Leaf gas exchanges and predawn water potential, biomass of the different plant organs and NSC concentration, as well as relative 13C and 15N allocation to root, stems and leaves were assessed in the two growing seasons.

Our results showed that sessile oak grown under fertilization suffered faster from drought and showed earlier death than unfertilized seedlings. Fertilization significantly improved aboveground growth, increased shoot: root ratio and reduced NSC storage in sessile oak. This leads to drought-induced C depletion and increased mortality under severe drought. Progressing drought altered C and N translocation strategies in sessile oak by prioritizing C allocation to and N retention in the roots under moderate fertilization, but not in high fertilization. In sessile oak, seasonal dynamics of C and N allocation is coupled and independent of drought and fertilization. By contrast, fertilization and drought, both had only minor impacts on Scots pine C allocation and the tradeoff of C allocation between growth and reserves, as well as the uptake of added N by root. Severe drought strongly decreased NSC in stem and root of Scots pine, while NSC concentrations in leaf and fine root kept stable and high and at the status of mortality.

We conclude that sessile oak shows a more plastic response to environment changes than Scots pine by adjusting its C and N relations on the whole plant level. The impact of fertilization on tree seedlings drought responses seems to be species-specific and is also modified by the degree of drought and fertilization.

How to cite: Ouyang, S., Shen, W., Saurer, M., Duan, H., Ding, G., Tie, L., Li, M., and Arthur, G.:  Fertilization effects on drought responses in sessile oak and Scots pine seedlings , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2100, https://doi.org/10.5194/egusphere-egu22-2100, 2022.

17:24–17:30
|
EGU22-509
|
ECS
|
On-site presentation
Alice Orme, Markus Lange, Simon Andreas Schroeter, Marcus Wicke, Georg Pohnert, and Gerd Gleixner

Drought is an ever-increasing threat; its negative effects on ecosystems and their functioning directly impact our food security. It is therefore critical to understand the mechanisms that affect drought resilience of ecosystems. Many ecosystem functions depend on plant-soil interactions and are mediated by dissolved organic molecules, which are then recorded in the dissolved organic carbon (DOC) that leaches from plants and soils. In particular, DOC properties during and after rewetting can reveal if and how ecosystems are affected by drought. We therefore investigated the concentration of DOC in four different plant communities on sandy soils in Germany over three years that differed in drought intensity, including the extreme 2018 drought. We also analysed the molecular composition of DOC using ultrahigh-resolution mass spectrometry to identify the carbon sources during the rewetting period. A linear mixed effect model revealed that drought intensity significantly affected DOC concentration. DOC concentration in soil leachate was slightly increased following medium drought intensity, but was significantly reduced following high drought intensity. This suggests that medium intensity drought may stimulate DOC release, however, high intensity drought reduces DOC release. Molecular composition analysis of the DOC present during the rewetting period revealed an initial release of plant-derived carbon followed by an increase in soil organic matter-like compounds. Our findings indicate that the initial release of plant-derived carbon into soil leachate might be crucial for the ability of ecosystems to quickly recover from drought. High intensity drought may interrupt plant functioning to the point of preventing the accumulation and subsequent release of plant-derived carbon during drought, and therefore hamper ecosystem recovery. This suggests the presence of tipping points with respect to the ability of ecosystems to recover from drought. As such, monitoring DOC concentrations could lead to better assessements of the drought resilience of ecosystems.

How to cite: Orme, A., Lange, M., Schroeter, S. A., Wicke, M., Pohnert, G., and Gleixner, G.: Increased Drought Intensity Reduces Release of Plant Carbon into Dissolved Organic Carbon Pool, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-509, https://doi.org/10.5194/egusphere-egu22-509, 2022.

17:30–17:36
|
EGU22-10760
|
ECS
|
On-site presentation
Matthew Worden, Caroline Famiglietti, Alexandra Konings, Paul Levine, and Anthony Bloom

Drought affects carbon fluxes by influencing photosynthesis, respiration, and disturbance, as well as by impacting the size of the different vegetation and soil pools. Changes to how much photosynthetic carbon is allocated to foliage, woody components, roots, and more persist even after meteorological conditions have returned to normal. These shifts in carbon allocations in turn affect future photosynthesis through changes in leaf area and water uptake ability, for instance. However, the magnitude of post-drought recovery effects on terrestrial carbon fluxes are often overlooked and poorly modeled. This is especially the case in tropical ecosystems as there are large uncertainties in the tropical ecosystem sensitivity to climate forcing such as drought. We hypothesize that a key driver of carbon flux predictive error in land surface model simulations is their representation of changes in carbon allocation during and after water stress. Most models use static carbon allocation schemes which, given their assumption of uniformity through time, do not account for the impact of drought. Those that do have dynamic allocation are often poorly parameterized due to the difficulty of in situ carbon allocation measurements. We investigate first whether it is possible to constrain dynamic carbon allocation based on observations of fluxes and model data fusion. We then investigate whether the constrained dynamic carbon allocation model has improved predictions of modeled net biosphere exchange (NBE) during drought and drought recovery. To do so, we implement a dynamic carbon allocation scheme within the CArbon DAta MOdel fraMework (CARDAMOM) data assimilation system, which robustly optimizes the parameters and carbon cycle states of an intermediate-complexity ecosystem model based on a suite of observational data on carbon fluxes and pools. We test the dynamic allocation scheme at a wet tropical (French Guiana) and a dry tropical (Cumberlands Plain) flux tower site. We find at the Cumberland Plains flux tower that the dynamic allocation model outperforms the static allocation model in predicting NBE. Furthermore, we retrieve significant carbon allocation shifts during drought periods at this site with increasing allocation to autotrophic respiration, wood biomass, and labile biomass and decreasing allocation to foliage biomass and fine root biomass relative to non-drought conditions. Our results demonstrate the importance of accounting for stress-induced carbon allocation shifts in land surface models as well as the ability to infer carbon allocation shifts from flux measurements.



How to cite: Worden, M., Famiglietti, C., Konings, A., Levine, P., and Bloom, A.: Accounting for carbon allocation shifts after drought improves NBE predictions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10760, https://doi.org/10.5194/egusphere-egu22-10760, 2022.

Belowground C allocation
17:36–17:46
|
EGU22-1943
|
solicited
|
Highlight
|
Virtual presentation
Cindy Prescott

I propose that patterns of belowground carbon flux observed under various environmental conditions can be largely explained by plant production of ‘surplus carbon’. Under common environmental conditions such as moderate deficiencies of water, nitrogen or phosphorus, high light, low temperatures, or elevated atmospheric carbon dioxide concentrations, plant leaf cells produce more photo-assimilates than they are able to use for primary metabolism, and so have surplus fixed carbon. Accumulation of surplus carbohydrates can damage leaf cells and so must be either transformed to other compounds or removed from the leaf. Active carbohydrate sinks are essential for the transport and removal of surplus C. Moderate deficiencies of N or P do not interfere with phloem loading, so much of the surplus C can be transported through the phloem, eventually reaching the roots. Active sinks for surplus carbon in roots include phosphorylated and non-phosphorylated respiration, conversion to starch, transfer to mycorrhizal fungi, or carboxylation to malate which is exuded or taken up by bacteria both inside and outside the root. These active sinks prevent metabolite accumulation and feedback inhibition of photosynthesis. The foundational benefit of belowground C fluxes and transfers to root-associated organisms may be assisting with the removal of surplus fixed carbon.

 

How to cite: Prescott, C.: Plant surplus carbon underlies belowground carbon fluxes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1943, https://doi.org/10.5194/egusphere-egu22-1943, 2022.

17:46–17:52
|
EGU22-2332
|
ECS
|
Virtual presentation
Israel Oren, Bertrand Muller, and Xavier Draye

Establishment of a seminal root system in maize is a crucial step in supporting the growth of nascent seedlings, until the adventitious root system is established. Nonetheless, little is known about this process in maize due to the hidden nature of roots and the difficulty to precisely assess the complicated architecture of a tangled root system in soils. The dynamics of root growth and of the concomitant carbon (C) allocation during this initial step can affect seedlings’ survival chances, growth, and yield at later stages over the life course of maize plants. Assimilated C is allocated to different competing sinks in the plant, such as the shoot and different roots, as a function of C availability and the size of the different sinks (the larger the sink size, the more C is allocated to it). Changes in roots’ C supply or sink size may affect the competition for C supply between the different sinks, and may re-shape C allocation patterns and thus root architecture. Such changes can happen due to decreased photosynthesis or stomatal closure (or both), thus affecting C supply, or due to the potential effect of heterogenous soil, that can lead to some roots outperforming others, and thus affecting the different roots’ sink size within a root system. Architectural differences in the seminal root system in maize, which consists of one primary and a few seminal roots, can result from changes in the density along the main root’s axis, diameter, length, growth rate, and the diversity of the lateral roots of the primary and seminal roots. We used aeroponics and high temporal and optical resolution monitoring to test the effect of changes in C source and sink sizes on maize seminal root architecture, and more specifically, on lateral root density, dimensions, growth, and diversity. Shading and excision of roots were used to manipulate C source and sink size, respectively. Root system images were taken every 2.5 hours, and root growth was assessed by repeatedly measuring dimensions of individual roots over a 2-3 days period using ImageJ software, combined with the SmartRoot plug-in. Under high-light conditions, the growth of the primary root’s laterals was more vigorous compared to the seminal roots’ laterals. Shading led to decreases in lateral root growth, density, and diversity, compared to well-lit seedlings. Root excision lead to changes in root architecture, probably due to changes in C allocation patterns, with increased growth of the laterals in the remaining roots (either the primary or the seminal roots). Selection for maize genotypes that are able to maintain seminal root system growth under limited water and nutrient availability conditions by maintaining (a) C allocation to the root system even when its sink size decreases, and (b) plasticity of C allocation patterns within the root system in such a way that the proportion of water and nutrient gain to C investment in constructing and maintaining roots is maximized, will contribute to increased seedling survival and crop yield under unpredicted and unfavorable conditions, typically experienced in low-input agriculture.

How to cite: Oren, I., Muller, B., and Draye, X.: Carbon source and sink size affect seminal root system architecture in maize, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2332, https://doi.org/10.5194/egusphere-egu22-2332, 2022.

17:52–17:58
|
EGU22-5798
|
ECS
|
Virtual presentation
Emmanuella Onyinyechi Osuebi-Iyke, Stanislaus Schymanski, Oliver O'Nagy, and Frank Minette

A large part of photosynthetically fixed carbon is translocated below-ground in order to construct and maintain the roots needed to supply the shoot with adequate water and nutrients. However, the amount of carbon translocated below-ground is not easily quantified, as an unknown part is lost as root respiration, which is not easily distinguished from microbial soil respiration.

Here we present a novel plant growth chamber enabling continuous and separate monitoring of above-ground and below-ground gas exchange. The above-ground compartment is separated from the soil compartment by an impermeable fat layer, and a custom-developed carbon-free soil substrate is used to eliminate CO2 release due to microbial decomposition of pre-existing soil carbon. Each compartment of the growth chamber is connected to an infrared gas analyzer, enabling simultaneous monitoring of above-ground and below-ground fluxes. A novel experimental approach using chemical agents was employed to test if CO2 uptake and release was adequately quantified in each compartment over several days.

In a pilot experiment performed to identify a suitable carbon-free soil, maize plants grown at a 20% volumetric water content, 1.3g/cm3 bulk density and a 14h/10h day/night regime showed a correlation between evapo-transpiration and root length but not with root biomass, suggesting that the cost/benefit ratio of root allocation may be more related to root respiration and mechanical energy expenditure than accumulated root biomass. In fact, our preliminary results suggest that cumulative root respiration over 2 weeks was of a similar order of magnitude as the carbon stored in the root system at the end of the experiment, and that root respiration rates were relatively similar to nocturnal shoot respiration rates. A detailed analysis is underway and will be presented during the conference.

How to cite: Osuebi-Iyke, E. O., Schymanski, S., O'Nagy, O., and Minette, F.: A novel plant growth chamber for separate and continuous monitoring of above-ground and below-ground gas exchange, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5798, https://doi.org/10.5194/egusphere-egu22-5798, 2022.

17:58–18:04
|
EGU22-5349
|
ECS
|
Virtual presentation
Richard Nair, Martin Strube, Marion Schrumpf, Tarek El-Madany, and Mirco Migliavacca

Root dynamics and allocation belowground are a major uncertainty in ecosystem studies because roots are hard to measure in comparison to leaves, which can be assessed at fine timescales using a variety of remote sensing approaches. We built an automated minirhizotron system capable of taking root images on a sub-daily scale and analyzed all high frequency images from this with a neural network approach. We pair this with a daily series of above-ground vegetation indexes of the same plants from standardized ‘phenocam’ digital camera methods. Here we will demonstrate, from a mesocosm experiment that 1) in a mixed species mesocosm, root and shoot production (i.e. rate of change of indexes) as not synchronized on short (multi-day) timescales and 2) root growth rate was more important than overall biomass and leaf growth rate in determining variability in soil CO2 efflux. Hence this efflux was likely driven by root growth respiration rather than maintenance respiration. We also show the first results from applying similar principles to ecosystem measurements. 

How to cite: Nair, R., Strube, M., Schrumpf, M., El-Madany, T., and Migliavacca, M.: Short-term asynchrony of root and shoot growth links to soil carbon flux dynamics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5349, https://doi.org/10.5194/egusphere-egu22-5349, 2022.

18:04–18:10
|
EGU22-1634
|
On-site presentation
Oleg Menyailo, Roman Sobachkin, Mikhail Makarov, and Chih-Hsin Cheng

Forest stand density has been shown to have different albeit small effects on soil carbon. We hypothesized that the absence of density effect on soil carbon (C) storage can be explained by a loss of old soil C. This replacement of old by fresh C results in zero net C sequestration by soils but could alter the quality of soil organic matter.   We used one afforestation experiment in Siberia, in which three tree species (spruce, larch and Scots pine) were grown for the last 30 years at 18 levels of stand density, ranging originally from 500 to 125,000 stems per ha. We selected five density levels and studied C and nitrogen (N) contents in mineral soils at 0-5 cm depth. The age of soil C was measured under larch and spruce for three levels of density by radiocarbon (14C) dating. In all soil samples we determined stability of soil organic matter (SOM) to mineralization (decomposability) and to elevated input of readily decomposable C – glucose (primability).  Stand density affected soil C and N contents differently depending on the tree species. Only under spruce both C and N contents were increasing with density, under larch and pine the covariation was insignificant, while N tended even to decline with density increase.  With the 14C data we were able to show strong dilution of old SOM by fresh C derived from the trees, the effect was stronger with higher density. This provides first evidence that density increase increases the fractions of new C versus old C and this can happen without altering the total C contents like under larch. While stand density altered soil C and N contents only under spruce, it altered C decomposability under all tree species: with density increase the C decomposability (per unit of C) declined under spruce but increased under larch and pine. This is relevant to predicting C losses from forest soils with different tree species and densities.  Higher losses would occur under larch and pine with higher densities, but increase of density under spruce would reduce the C losses from soil. Furthermore, while no significant covariation of stand density with C primability was detected, we first observed strong tree species effects on C primability. Twice as much C is lost from soil under larch than under spruce and pine by equal addition of C-glucose.  This indicates that elevated C deposition from roots and exudates to soil as predicted due to elevated CO2 concentration would most strongly accelerate soil C turnover and C losses under larch than under spruce and pine. Overall, tree species altered the susceptibility of soil C to elevated C input and stand density had strong effect on the decomposability of SOM, which is important parameter of C stability. The effect of stand density is thus important to consider even if stand density does not affect total soil C content. 

How to cite: Menyailo, O., Sobachkin, R., Makarov, M., and Cheng, C.-H.: Tree species and stand density: Effects on soil organic matter content, decomposability and susceptibility to microbial priming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1634, https://doi.org/10.5194/egusphere-egu22-1634, 2022.

18:10–18:16
|
EGU22-10059
|
ECS
|
Virtual presentation
Andrea Koplitz-Weissgerber, Alix Vidal, Carsten W. Mueller, Franz Bruegger, and Tarquin Netherway

The type of tree mycorrhizal association, together with the leaf type of the host, can influence carbon (C) pools and thus potentially C persistence in forest soils. In arbuscular mycorrhizal (AM) systems, litter tends to decompose rapidly with high C mineralization, thus favoring the formation of mineral-associated organic matter (MAOM). In ectomycorrhizal (EcM) systems, the litter decomposition is slower, which tends to result in the accumulation of particulate organic matter (POM). Yet, the effect of different mycorrhizal types associated with broadleaf trees on soil organic matter pools, and especially different fractions of POM (free: fPOM and occluded: oPOM), have rarely been explored. We quantified and characterized the soil organic matter (SOM) fractions within AM-associated and EcM-associated systems, on various sites. We collected soil samples (1-10 cm) on four sites in Sweden. Each site included broadleaf EcM-associated trees (Betula pendula), AM-associated trees (Fraxinus excelsior), and crop fields. We combined density and soil particle size fractionation to separate the soil into five organic matter (OM) fractions: fPOM, oPOM, oPOMsmall (< 20 µm), MAOM (> 53µm), and MAOMsmall (< 53 µm). We measured the C and N content, as well as δ13C values in all soil fractions and characterized the chemical composition of the POM fractions using 13C CP-MAS NMR spectroscopy. We also analyzed the fungal communities in the bulk soil using a sequencing approach.  As expected, forest soils contain higher amounts of POM, especially fPOM, than crop field soils. The fPOM in crop fields was less decomposed as in forest soils, as reflected by the lower alkyl C : O/N alkyl C ratio in the NMR spectra. Regardless of the vegetation and mycorrhizal types, the four sites presented oPOM and fPOM with similar chemical characteristics. Yet, the chemical composition of oPOMsmall varied across sites, as reflected by contrasting alkyl C : O/N alkyl C ratio. While the vegetation type (forest versus crop field) tends to be an essential driver of SOM fraction mass distribution, site-specific variations, rather than vegetation and mycorrhizal types, seem to drive the chemical composition of oPOMsmall fractions. As fungi are key decomposers of SOM we expect that differences in SOM fractions between vegetation types and sites will also be reflected in different fungal communities. However, we expect that differences in fungal communities between mycorrhizal types and vegetation types will be larger than between sites.

How to cite: Koplitz-Weissgerber, A., Vidal, A., Mueller, C. W., Bruegger, F., and Netherway, T.: How do arbuscular vs. ectomycorrhizal trees and site-specific variations affect soil organic matter pools?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10059, https://doi.org/10.5194/egusphere-egu22-10059, 2022.

18:16–18:22
|
EGU22-6667
|
ECS
|
Virtual presentation
Zhen Li, Songlin Wu, Longbin Huang, and Yuanfang Huang

Eco-engineering Fe ore tailings into technosols (i.e., soil-like growth substrates) has been advocated to be a promising technology for sustainable rehabilitation of tailings with native plant communities 1-3. Arbuscular mycorrhizal (AM) symbiosis has been found to be able to colonize tailing technosol eco-engineered through exogenous plant biomass input, and contributed to aggregate development and organic matter stabilization in the tailings4. However, the AM performance and their eco-functionality usually varies depending on water conditions and tailing technosols developed from different plant biomass residue (PBR) input, which has yet been addressed in previous studies. Therefore, the present study aimed to investigate the role of AM symbiosis in aggregate development and association of organic carbon (C) and nitrogen (N) with mineral phase of aggregates in the developing technosols eco-engineered from Fe ore tailings, in relation to low water supply and plant biomass residues of contrasting nutrient quality (e.g., C:N ratios). The results showed that AM symbiosis did not influence aggregate development, but stimulated organic carbon and nitrogen stabilization  in tailings-technosol. In particular, AM symbiosis enriched organic C (rather than N) sequestration in minerals of tailings-technosol amended with Lucerne hay containing high N and low C:N ratio. Comparatively, AM symbiosis seemed to have enriched significantly N (rather than organic C) in aggregate minerals in tailings-technosols amended with Sugarcane mulch (with low N and high C:N ratio). This increased N sequestration may have resulted from N-rich AM fungal exudates or fungal biomass. AM symbiosis enhanced organic matter sequestration through enhancing associations between carboxyl-rich organics and key Fe-rich phyllosilicates and/or Fe(oxy)hydroxides. Drought stress limited AM symbiosis role in organic C and N sequestration in the tailing-technosol. In summary, the study indicated that plant biomass of different C:N ratio could influence AM role in organic matter stabilization in Fe ore tailings-technosol, and further studies are required to unravel implications of different organic C and N sequestration in aggregate minerals of tailings-technosols, in relation to long-term pedological development and sustainability of soil functions.

  • Wu, S.; Liu, Y.; Bougoure, J. J.; Southam, G.; Chan, T. S.; Lu, Y. R.; Haw, S. C.; Nguyen, T. A. H.; You, F.; Huang, L., Organic Matter Amendment and Plant Colonization Drive Mineral Weathering, Organic Carbon Sequestration, and Water-Stable Aggregation in Magnetite Fe Ore Tailings. Environ Sci Technol 2019, 53, (23), 13720-13731.
  • Huang, L.; Baumgartl, T.; Zhou, L.; Mulligan, R. In The new paradigm for phytostabilising mine wastes–ecologically engineered pedogenesis and functional root zones, Life-of-Mine Conference, 2014; 2014; pp 16-18.
  • Huang, L.; Baumgartl, T.; Mulligan, D., Is rhizosphere remediation sufficient for sustainable revegetation of mine tailings? Ann Bot 2012, 110, (2), 223-38.
  • Li, Z.; Wu, S.; Liu, Y.; Yi, Q.; You, F.; Ma, Y.; Thomsen, L.; Chan, T.-S.; Lu, Y.-R.; Hall, M.; Saha, N.; Huang, Y.; Huang, L., Arbuscular mycorrhizal symbiosis enhances water stable aggregate formation and organic matter stabilization in Fe ore tailings. Geoderma 2022, 406.

How to cite: Li, Z., Wu, S., Huang, L., and Huang, Y.: Arbuscular mycorrhizal colonization enhanced organic carbon and nitrogen sequestration in technosols eco-engineered from Fe ore tailings with different plant biomass residues, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6667, https://doi.org/10.5194/egusphere-egu22-6667, 2022.

18:22–18:28
|
EGU22-8986
|
Presentation form not yet defined
Increasing Microbial Biomass is the Key to Sequestering Carbon in Soil. 
(withdrawn)
Judith Fitzpatrick