BG3.14

Silicon (Si) is widely recognized as an important regulator of the global carbon (C) cycle via its effect on diatom productivity in oceans and the weathering of silicate minerals on continents. Si is also a beneficial plant nutrient, improving resistance to herbivory and pathogens and mitigating the negative effects of several abiotic stresses, including nutrient limitation. However, changes in Si sources and cycling during long-term development of terrestrial ecosystems remain poorly understood. We studied Si in soils and plants along two 2-Ma coastal dune chronosequences in southwestern Australia (Jurien Bay and Guilderton). Soil development along these chronosequences includes carbonate leaching in Holocene soils, formation of secondary Si-bearing minerals in Mid-Pleistocene soils, followed by their loss via dissolution, to yield quartz-rich soils of Early-Pleistocene age. The chronosequences also exhibit an extreme gradient of soil fertility in terms of rock-derived nutrients, and shifts from nitrogen (N) to phosphorus (P) limitation of plant productivity as soils age. Along each chronosequence, we quantified the pools of reactive Si-bearing phases and plant-available Si in the soils, and physically extracted soil phytoliths (amorphous silica formed in plant tissues). We also quantified Si, macronutrients and total phenols in the most abundant plants growing along the best-studied of the two chronosequences (Jurien Bay). We found that plant-available Si was lowest in young and carbonate-rich soils, because carbonates weathering reduces the weathering of silicate minerals by consuming protons, and Si is strongly sorbed by secondary minerals in alkaline soils. Plant-available Si increased in intermediate-age soils during the formation of secondary minerals (kaolinite), and finally decreased in old, quartz-rich soils, due to continuous desilication. As pedogenic Si pools became depleted with increasing soil age, Si availability was increasingly determined by soil phytoliths. At Jurien Bay, foliar Si increased continuously as soils aged, in contrast with foliar macronutrients that declined markedly in strongly weathered soils. Finally, foliar phenol concentrations declined with increasing soil age and were negatively correlated with foliar Si at the community and individual species level, suggesting a tradeoff between these two leaf defense strategies. Our results highlight a nonlinear response of plant-available Si to long-term pedogenesis, with an increase during carbonate loss and a decrease in the silicates weathering domain. They also demonstrate that the retention of Si by plants during ecosystem retrogression sustains its terrestrial cycling by leveraging the high reactivity of soil phytoliths compared with soil-derived aluminosilicates. Moreover, the continuous increase of plant Si concentrations as rock-derived nutrients are depleted suggests important plant benefits associated with Si in P-impoverished environments. This is in line with the resource availability hypothesis, which predicts that plants adapted to infertile soils have high levels of anti-herbivore leaf defenses. In particular, old and P-depleted soils increased the relative expression of Si-based defenses, while young soils where plant productivity is limited by N promoted leaf phenol accumulation. Overall, our results demonstrate that long-term ecosystem and soil development strongly influence soil-plant Si dynamics, with cascading effects on plant ecology and global Si and C biogeochemistry.

How to cite: de Tombeur, F., Turner, B., Laliberté, E., Lambers, H., Mahy, G., Faucon, M.-P., Zemunik, G., and Cornélis, J.-T.: Long-term silicon dynamics in terrestrial ecosystems: insights from 2-million years soil chronosequences, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1105, https://doi.org/10.5194/egusphere-egu21-1105, 2021.

Forest ecosystem has a high carbon sequestration capacity and plays a crucial role in maintaining global carbon balance and climate change. Phytolith-occluded carbon (PhytOC), a promising long-term biogeochemical carbon sequestration mechanism, has attracted more attentions in the global carbon cycle and the regulation of atmospheric CO₂. Therefore, it is of practical significance to investigate the PhytOC accumulation in forest ecosystems. Previous studies have mostly focused on the estimation of the content and storage of PhytOC, while there were still few studies on how the management practices affect the PhytOC content. Here, this study focused on the effects of four management practices (compound fertilization, silicon fertilization, cut and control) on the increase of phytolith and PhytOC in Moso bamboo forests. We found that silicon fertilization had a greater potential to significantly promote the capacity of carbon sequestration in Moso bamboo forests. this finding positively corresponds recent studies that the application of silicon fertilizers (e.g., biochar) increase the Si uptake¹ to promote phytolith accumulation and its PhytOC sequestration in the plant-soil system². Of course, the above-mentioned document² also had their own shortcomings, i.e., the experimental research time was not long, lacking long-term follow-up trial and the bamboo forest parts were also limited, so that the test results lack certain reliability. We have set up a long-term experiment plot to study the effects of silicon fertilizer on the formation and stability of phytolith and PhytOC in Moso bamboo forests. But anyway, different forest management practices, especially the application of high-efficiency silicon-rich fertilizers¹, may be an effective way to increase the phytolith and PhytOC storage in forest ecosystems, and thereby improve the long-term CO₂ sequestration capacity of forest ecosystems. Research in this study provides a good "forest plan" to achieve their national voluntary emission reduction commitments and achieves carbon neutrality goals for all over the world.

Refences:

¹Li et al., 2019. Plant and soil, 438(1-2), pp.187-203.

²Huang et al., 2020, Science of The Total Environment, 715, p.136846.

How to cite: Xu, L., Shi, Y., Lv, W., Niu, Z., Yuan, N., and Zhou, Y.: Effect of forest management on the formation and stability of phytolith and PhytOC in forest ecosystem, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-573, https://doi.org/10.5194/egusphere-egu21-573, 2021.

Silicon is important as a nutrient for phytoplankton (diatom, radiolarian, silicoflagellates and sponges) and for the phytolith production by terrestrial vegetation. Silicon also contributes in removing carbon dioxide from the atmosphere through silicate weathering.  Hence it is important to understand the behavior of the silicon cycle throughout earth history. Silica is the second most abundant element in the earth's crust and the concentration of silicic acid in the marine environment has not changed since the past 10,000 years. Phytolith plays an important role in the silicon cycle. While the phytoplankton in marine environment bioengineers silica within the water column, phytolith transports terrestrial biogenic silica into the marine environment and act as a silicon sink. Though astonishingly, very few researches have been carried out in the field of marine phytolith sink and also on the phytoliths in the marine environment.

For this study, we have chosen the world highest terrestrial sediment receiving submarine fan, the Bengal fan. The core sample was extracted at a water depth of 3520m at 85.960985 N, 9.99351 E. 24 phytolith types were identified and all the morphotypes were counted dividing into three size classes. These size classes were specific to considering morphotypes. Most related simple geometries were used to calculate the volume of phytolith cells and these volume data were used in calculating the total volume of phytolith in one gram of sediment by combining with an absolute abundance of phytolith data for each size class, which were later used to calculate the total weight of phytolith in one gram of marine sediment. According to the results in deep oceanic sediment at the core, the location contains ⁓0.15mg/g phytolith during the low phytolith flux periods (ex. Late Holocene) and ⁓2.678mg/g of phytolith during the high phytolith flux periods such as 25ka to 30ka B.P. and around the beginning of deglaciation. After removing 10% from the total weight as phytolith occluded carbon (PhytOC), phytolith derived biogenic silica content in sediment varies from ⁓0.135mg/g - ⁓2.41mg/g. Thus, phytolith in marine sediment contributes as a permanent silicon and carbon sink. By considering average marine sediment density as 1.7g/cm³, in a 1cm thick, one square km sediment layer contains ⁓2 to 40 metric tons of biogenic silica derived from phytolith, during low and high phytolith flux periods. This study serves as the pioneer of this field of study and further it is important to investigate the release of biogenic silica in to marine environment by phytolith and PhytOC content in different morphotypes and in different geological regions, for better understanding the contribution of phytolith to the biogenic silicon cycle in the marine environment.

Keywords: Marine phytolith, Deep oceanic sediment, Silicon cycle, Phytolith Flux, Silicon sink.

Acknowledgements

This work was funded by the National Natural Science Foundation of China (NSFC 41876062) and Key Special Project for Introduced Talents Team of Southern Marine Science and EngineeringGuangdong Laboratory (Guangzhou) (GML2019ZD0206).

How to cite: Thilakanayaka, V., Chuanxiu*, L., and Xiang, R.: Contribution of terrestrially derived phytolith as a marine silicon sink, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3989, https://doi.org/10.5194/egusphere-egu21-3989, 2021.

1) Crop loss due to insect herbivory is one of the largest challenges facing the agricultural industry. As herbivore populations continue to grow in light of global change, securing crop resources is becoming increasingly critical. Silicon (Si) has been shown to effectively mitigate the adverse effects of herbivores such as the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae), in crop species (namely grasses), that have evolved the ability to uptake large amounts of Si through their roots and accumulate it in aboveground tissues. Nevertheless, the effectiveness of Si accumulation as a plant defence against herbivory in the short term, and its consequential effects on alternative defence responses, remain unclear.
2) We conducted two discrete experiments to determine the short-term dynamics of Si, chemical defences and resistance to herbivory in the model grass, Brachypodium distachyon: 1) Both Si-supplemented (+Si) and control (-Si) plants were treated with methyl jasmonate (MeJA) as a form of simulated herbivory and we measured the interplay of Si accumulation, the phytohormones jasmonic acid (JA) and salicylic acid (SA), and carbon-based defences over 24 hr. 2) We exposed H. armigera larvae to B. distachyon plants grown under three conditions: +Si, -Si, or treated with Si only once H. armigera feeding began. We measured the effect of short-term plant exposure to Si on H. armigera performance and plant resistance.
3) MeJA-induced Si accumulation occurred as early as 6 hr after treatment via increased JA concentrations. Si supplementation decreased SA concentrations, which could have implications on additional downstream defences. We show a trade-off between Si and phenolics in untreated plants, but this relationship was weakened upon MeJA treatment. Although foliar Si concentrations remained lower, within 72 hr of exposure to Si, plants obtained virtually the same level of resistance to H. armigera as plants exposed to Si for over 30 days. H. armigera feeding also accelerated Si deposition after 6 hr of exposure to Si, however, in as little as 24 hr, levels of Si deposition were similar to plants exposed to Si long term.
4) In addition to its well-documented role as a long-term defence against herbivores, we demonstrate that, over short-term temporal scales, Si accumulation responds to herbivore signals and impacts on plant defence machinery. Further, we provide novel evidence that plants can rapidly incorporate Si into their tissues to mitigate the adverse effects of herbivory as effectively as plants exposed to Si long term.

How to cite: Waterman, J., Cibils-Stewart, X., Hall, C., Mikhael, M., Cazzonelli, C., Hartley, S., and Johnson, S.: Rapid silicon accumulation affects carbon-based plant defences and enhances plant resistance to a global insect pest, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3733, https://doi.org/10.5194/egusphere-egu21-3733, 2021.

Grasses accumulate large concentrations of silicon (Si) which alleviates a range of stresses including defence against herbivores. Likewise, grasses symbiotically associate with foliar Epichloë-fungal endophytes which provide herbivore defence, mainly via the production of alkaloids. Some Epichloë-endophytes increase foliar Si concentrations, particularly in tall fescue (Festuca arundinacea) but also in perennial ryegrass (Lolium perenne); it is unknown whether this impacts herbivores. Likewise, while Si is primarily a physical defence against herbivores, it can also affect defensive secondary metabolites; Si supply might therefore also affect alkaloids produced by Epichloë-endophytes, however, this remains untested. We grew tall fescue and perennial ryegrass in a factorial combination with or without Si supplementation, in the absence or presence of a chewing herbivore; Helicoverpa armigera. Grasses were associated with four different Epichloë-endophyte strains (tall fescue: AR584; perennial ryegrass: AR37, AR1, or wild type) or as Epichloë-free controls. Specifically, we assessed how Si supply and Epichloë-endophyte presence impacts plant growth and chemistry, and how their interaction with herbivory affects foliar Si concentrations and alkaloid production. Subsequently, their effects on H. armigera relative growth rates (RGR) were evaluated. In Fescue, the AR584-endophyte increased constitutive (herbivore-free) and induced (herbivore-inoculated) silicon concentrations when Si was supplied. In perennial ryegrass, AR37-endophyte increased constitutive and induced silicon concentration, meanwhile, AR1-endophyte increased constitutive levels only. Si supply and herbivory did not affect alkaloids produced by AR584- or AR1/Wt-endophyte in tall fescue and perennial ryegrass, respectively. However, Si suppressed herbivore-induced production of alkaloids in the AR37-endophyte perennial ryegrass association. Si was a more effective defence in tall fescue than perennial ryegrass, significantly reducing H. armigera RGR. Our results suggest that Si reduced herbivore performance to such an extent in tall fescue that it was operating at maximum effect and endophyte-mediated increases in Si concentration made no further difference. Si had a more modest impact on herbivores in perennial ryegrass, potentially linked to silicon decreasing herbivore feeding and thus, suppressing herbivore-induced alkaloids. We provide novel evidence that increased Si concentrations in some cases interact with endophyte-produced chemical defences, which could ultimately impact plant resistance to herbivores.   

How to cite: Cibils-Stewart, X., Mace, W. J., Popay, A. J., Hartley, S. E., Lattanzi, F. A., Hall, C. R., Powell, J. R., and Johnson, S. N.: Epichloë-endophytes increase constitutive and herbivore-induced silicon defences in grasses but do not directly increase grass resistance to a chewing insect herbivore, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10431, https://doi.org/10.5194/egusphere-egu21-10431, 2021.

In recent years, silicon (Si) has been increasingly linked to biotic stress management in plants including insect herbivory. The effectiveness of Si against chewing insects is now well recognized. Silicification of plant tissues makes them abrasive and tougher, reducing their masticability and digestibility to insect herbivores. This can cause mandibular wearing of chewers and affect their growth and feeding. Although there has been extensive research on the effects of Si on plant defences (i.e. antixenosis and antibiosis), it remains unclear how feeding on silicified plants affects insect defences to their natural enemies. Insect herbivores show morphological and behavioural defences when encountering predators and parasitoids. For example, lepidopteran larvae can regurgitate, twist the body, or even drop off the plants when attacked by natural enemies. Moreover, insects possess innate immunity (physiological defence) against the attackers, demonstrating cellular and humoral responses upon attack. Notably, there could be potential trade-offs between different defence and immunity traits. Given that feeding on Si-rich plants affects insect growth rates, this could impact their relative investment in different defences, thereby making insects more susceptible to their enemies. We are investigating the effects of Si on plant resistance and tolerance to herbivory and its cascading effects on insect defences to their enemies. We have been growing the model grass, Brachypodium distachyon, a high Si-accumulator, hydroponically with or without Si and examining the effects of Si against the global insect herbivore, Helicoverpa armigera. Our preliminary results suggest that Si supplementation enhances plant antixenotic and antibiotic traits and increases plant tolerance to herbivory. We are currently exploring insect defence and immunity traits when fed on silicified versus non-silicified plants. Our study would shed light on the impacts of Si on insects’ susceptibility to biocontrol agents and provide a better understanding of the effects of Si on insect-plant-natural enemy interactions.

How to cite: Islam, T., Moore, B. D., and Johnson, S. N.: Is silicon a double-edged sword against insect herbivores?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10497, https://doi.org/10.5194/egusphere-egu21-10497, 2021.

Abstract: Being an important carbon (C) sink on Earth, phytolith occluded carbon (PhytOC) has been investigated in various soil-plant systems. Yet, the environmental factor (i.e., drought) is less studied on the variation of phytolith, its relative depositions in plant tissues, morphology variations, and occluded carbon in the soil-plant systems. In this study, we analyzed the monthly variations of phytolith production and phytolith-occluded carbon (PhytOC) in the leaves of Dendrocalamus ronganensis grown on a karst mountain in southwestern China. This study aimed to understand the drought factors influencing phytolith formation, morphology variation and carbon sequestration in plants. Our results showed that the phytolith assemblages and PhytOC between new and old leaves were significantly different, and varied with plant growth stages. The average PhytOC of old leaves and new leaves was 3.2% and 2.2%, respectively. In particular, both PhytOC and proportions of elongate, cuneiform and stomata phytolith in new leaves significantly decreased during drought months (from September to November). This study suggests that PhytOC in plants is closely related to phytolith morphologies, and significantly affected by growth stage and hydrologic conditions of the growth environment. This indicates that we can improve the efficiency of phytolith carbon sequestration in plants and potentially reduce the atmospheric carbon dioxide content by improving the soil water conditions required for plant growth.

Keywords: Dendrocalamus ronganensis; phytolith; phytolith-occluded carbon; soil drought

How to cite: Li, R., Wen, M., Tao, X., Vachula, R. S., Tan, S., Dong, H., and Zhou, L.: Drought influences the phytolith morphology variation and its occluded carbon of leaves in Dendrocalamus Ronganensis during growing season, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-180, https://doi.org/10.5194/egusphere-egu21-180, 2021.

Decomposition of plant leaves is influenced by multiple traits, however, discrete structures of Si such as silicious trichomes on the leaf surface have been overlooked, although similarly to defense against insect herbivores, trichomes are thought to protect leaves from decomposers. This study hypothesized that silicious trichomes slow down leaf decomposition by soil meso- and macrofauna. We used two mesh bags (<0.2 mm and 5 mm) and examined ash-free mass loss of green leaves of Broussonetia papyrifera and Morus australis, closely related Moraceae species apparently different in trichome size and density, after 25 days of decomposition in a common garden. We also measured 10 traits of initial leaves and performed microscopic observation of the leaf surface with an energy dispersive X-ray analyzer. Of the leaf traits, trichome density on the lower leaf surface differed greatly between the two species. Our microscopic observation showed that short trichomes densely arranged on the lower leaf surface of B. papyrifera were highly silicified and that some of long trichomes were also composed of calcium. Ash-free mass loss of M. australis was greater in 5-mm mesh bag than in <0.2-mm mesh bag, while that of B. papyrifera did not differ by mesh size, which represents a suppressive effect of silicious trichomes on decomposition by meso- and macrofauna. The trichomes of B. papyrifera remained apparently intact on the decomposed surface, supporting a view of their continuously deferring influence on the large decomposers during the experimental period. For the meso- and macro-detritivore community, three taxa (Acari, Collembola and Isopoda) showed high population density in the common garden. Overall, our results suggest that distinct forms of Si bodies in plants such as trichomes are worth considering in better understanding of leaf decomposition by meso- and macrofauna.

How to cite: Nakamura, R., Amada, G., Kajino, H., Morisato, K., Kanamori, K., and Hasegawa, M.: How do silicious trichomes influence leaf decomposition by meso- and macrofauna?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-643, https://doi.org/10.5194/egusphere-egu21-643, 2021.

Returning crop straw into soil is an important practice to balance biogenic and bioavailable silicon (Si) pool in paddy, which is crucial for rice healthy growth. However, it remains elusive how straw return affects Si bioavailability, its uptake, and rice yield, owing to little knowledge about soil microbial communities responsible for straw degradation. Here, we investigated the change of soil Si fractions and microbial community in a 39-year-old paddy field amended by a long-term straw return. Results showed that rice straw-return significantly increased soil bioavailable Si and rice yield to from 29.9% to 61.6% and from 14.5% to 23.6%, respectively, compared to NPK fertilization alone. Straw return significantly altered soil microbial community abundance. Acidobacteria was positively and significantly related to amorphous Si, while Rokubacteria at the phylum level, Deltaproteobacteria and Holophagae at the class level were negatively and significantly related to organic matter adsorbed and Fe/Mn-oxide combined Si in soils. Redundancy analysis of their correlations further demonstrated that Si status significantly explained 12% of soil bacterial community variation. These findings suggest that soil bacteria community and diversity interact with Si mobility via altering its transformation, resulting in the balance of various nutrient sources to drive biological silicon cycle in agroecosystem.

How to cite: Song, A., Li, Z., and Fan, F.: Soil bacterial communities interact with silicon fraction transformation and promote rice yield after long-term straw return, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-760, https://doi.org/10.5194/egusphere-egu21-760, 2021.

  Phytolith provides a new preconstruction and interpretation of palaeovegetation in either forest or grassland regions. In particular, the phytolith reliability records in both vegetation types should be assessed when they are employed on palaeovegetation reconstruction in north temperate region. Yet this issue has not been clearly investigated. Being two vegetation types (including forest and grassland) in northeast China (NE China) where it is an integrated physical geography unit, they provide some crucial references regarding the phytolith reliability. Thus, we firstly focused the study site of NE China to collect 108 topsoil samples from five dominant community types in forest region and 154 topsoil samples from four dominant community types in grassland region, respectively, to their phytolith assemblages. This study was to establish the reference databases of modern soil phytolith to demonstrate their record reliability. These phytolith data thus better serve palaeovegetation reconstruction in sedimentary sequences using their corresponding vegetation types in two selected regions.

    Analytical results showed that topsoil phytolith assemblages and their phytolith indices (Iw, Ic and W/G) varied substantially with different vegetation types in NE China; phytolith indices were also variations aligned with vegetation compositions. These finding suggest that phytolith is a reliable proxy using reconstructing palaeovegetation.

  The palaeovegetation reconstruction based on these phytolith reference databases indicated that NE China had experienced substantial vegetation changes since the late-glacial period. Community types in forest region may have experienced a succession sequence from the open Larix mixed forest to the open woodland, then turning to the closed broadleaf forest, and finally to the closed Pinus koraiensis mixed forest. In particular, we found that vegetation types in grassland region was dominated by a flourish C3 grass steppe since late-glacial period, with a total coverage higher than 50%. The coverage of C3 grass and C4 grass were higher than 25% and 16%, respectively.

  The palaeovegetation interpretation using these phytolith reference databases since the late-glacial period were consistent with that reconstructed using pollen assemblages in the same stratigraphic profile, confirming the phytolith reliability for reconstructing vegetation type and community type in the NE China. Phytolith record analysis also provided some detailed vegetation information such as the vegetation composition of the understory and Larix abundance in forest region, and the proportion of C3/C4 grass, their biomass and community coverage in grassland region.

  Thus, this study demonstrates the phytolith reliability to provide new perspectives on palaeovegetation reconstruction in northern temperate regions. Furthermore, this finding acts as a potential reference for exploring the relationship between phytolith and (palaeo)vegetation in other temperate regions.

(Supported by the National Natural Science Foundation of China (Grant No.41971100,41771214 )

How to cite: Jie, D., Gao, G., and Li, D.: Reliability of phytoliths for reconstructing vegetation dynamics in northeast China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-308, https://doi.org/10.5194/egusphere-egu21-308, 2021.

Crop dispersal has long been recognised as an important topic in agricultural archaeology and food globalisation. One of most pressing questions facing archaeologists is determining when and where millet arrived in the South China Coast. Our study focused on the millet phytoliths remains from three Neolithic sites in southeast coastal Fujian. Multiple dating methods, including charred carbon dating, phytolith carbon dating, and optically stimulated luminescence were used to construct the chronologies of the sites. The dating results showed that BTS was initially occupied at approximately 5,500 cal a BP. The millet phytoliths recovered in this study are likely the earliest millet remains found in Fujian, suggesting that millet arrived in the South China Coast at least 5,500 years ago. However, questions about whether millet agriculture in northern China dispersed southward through the inland or coastal routes remain unanswered. Given that millet remains were found in Jiangxi and northern Fujian – two important gaps in the inland route – no earlier than 5,000 cal a BP, it seems that the millet remains recovered from the coastal sites of Fujian might have dispersed following a coastal route from northern China. Nevertheless, Fujian is an important junction of the coastal route for the dispersal of millet from northern China. These findings not only provide new insights to millet dispersal routes in China, but also have significant implications for crop communications between Taiwan and mainland China during the Neolithic age.

How to cite: Dai, J., Cai, X., Jin, J., Ge, W., Huang, Y., Wu, W., Xia, T., Li, F., and Zuo, X.: Millet arrived in the South China Coast around 5,500 years ago, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8311, https://doi.org/10.5194/egusphere-egu21-8311, 2021.

Silicon oxides are the most abundant mineral group in soils. Therefore, plant roots are always exposed to some silicic acid (Si(OH)₄), which is the soluble form of silicates. Monosilicic acid molecules are taken up by roots, carried in the xylem, and subsequently polymerize to silica in varied silicifying target sites. This biogenic silica (SiO₂·nH₂O) can constitute several percent by dry weight in certain plant taxa. However, the mechanisms of its formation remain mostly unknown. In the roots of sorghum (Sorghum bicolor), silica aggregates form in an orderly pattern along the cell walls of endodermis cells. To investigate the structure and composition of root silica aggregates, we studied their development along roots of hydroponically grown sorghum seedlings. By using Raman micro-spectroscopy, auto-fluorescence, and scanning electron microscopy, we found that putative silica aggregation loci could be identified in roots grown under Si starvation. These micrometer-scale spots were constructed of tightly packed modified lignin and were capable of nucleating trace concentrations of silicic acid. Substantial variation in cell wall auto-fluorescence between roots grown with and without silicic acid demonstrated the impact of silicon on cell wall chemistry. Taken together, this work demonstrates a high degree of control over lignin and silica deposition in cell walls. Such regulation implies an important, yet unknown, function for silicon in plant biology.

How to cite: Zexer, N. and Elbaum, R.: Silica formation in sorghum (Sorghum bicolor) roots, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12176, https://doi.org/10.5194/egusphere-egu21-12176, 2021.