EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Initial responses of fine root dynamics of understory plants to elevated CO2 in a Central Amazon rainforest

Nathielly Martins1, Laynara F. Lugli1, Oscar J. Valverde-Barrantes2, Bruno Takeshi1, Maria Pires1, Juliane G. Menezes1, Iokanam Sales Pereira1, Alacimar Guedes1, Vanessa R. Ferrer1, Yago R. Santos1, Gabriela U. Neves1, Anna C. M. Moraes1, Ana Caroline Miron1, Iain P. Hartley3, Richard J. Norby4, Carlos A. Quesada1, Lucia Fuchslueger5, and the AmazonFACE team*
Nathielly Martins et al.
  • 1National Institute of Amazonian Research, Coordination of Environmental Dynamics (CDAM), Aleixo, Manaus, Brazil (
  • 2Florida International University, Department of Biological Sciences, Miami; United States (
  • 3University of Exeter, Amory Building, Rennes Drive, Exeter (
  • 4Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN, USA (
  • 5Centre of Microbiology and Environmental Systems Sciences, University of Vienna, Vienna, Austria (
  • *A full list of authors appears at the end of the abstract

In large parts of the Amazon rainforest low soil phosphorus availability may prevent the stimulation of forest growth in response to elevated atmospheric CO2 (eCO2). One strategy of plants could be to increase the relative allocation of the extra C belowground to their root systems to enhance nutrient acquisition and alleviate the potential phosphorus limitation, but little is known about the responses of tropical lowland forest species. We hypothesized that in tropical understory plants will trigger a first a fast upregulation of fine root phosphatase activities, followed by changes in fine root productivity and adaptions of morphological parameters, such as specific root length (SRL), specific root area (SRA) and root tissue density (RTD) to enhance phosphorus mobilization, increase its availability and exploit a larger soil and litter volume.

We tested our hypothesis in the first CO2 enrichment experiment in Central Amazonia at a low soil phosphorus site, increasing CO2 levels by 200 ppm relative to CO2 ambient (aCO2) concentrations using open top chambers (OTC) in the forest understory. We monitored potential root phosphatase activity, root productivity, and morphological traits in the soil with ingrowth cores (0-15 cm) and in the litter layer, as well as root biomass stocks in 0-5 and 5-10 cm of depth.

In contrast to our hypothesis, we observed a reduction in fine root productivity (<1mm diameter), from 0.038 ± 0.01 mg cm2 day-1 under aCO2 to 0.013 ± 0.004 mg cm2 day-1 after 12 months of eCO2. On the other hand, the fine root biomass stock (<2mm diameter) increased at 5-10 cm from 0.86 ± 0.18 at aCO2 to 1.74 ± 0.65 mg-1 cm2 with eCO2, but there was no effect of eCO2 on fine root biomass in the litter layer. However, roots growing in the litter layer significantly increased their SRL and showed a strong tendency of higher SRA in response to eCO2 (SRL: 4.66 ± 1.08 and 9.58 ± 2.12 cm mg-1; SRA:  0.63 ± 0.18 and 1.0 ± 0.25 cm2 mg-1 with aCO2 and eCO2, respectively), but we did not observe changes in root morphological parameters in the soil, only a tendency towards decreasing RTD. Moreover, we found a strong trend towards an increase in potential root phosphatase activity with eCO2 in the litter by 20.0 % (aCO2: 66.16 ± 10.4; eCO2: 79.39 ± 20.8 nmol mg-1 dry root h-1) and soil by 45.61% (aCO2: 97.42 ± 30.76; eCO2:141.86 ± 34.04 nmol mg-1 dry root h-1).

Our initial results suggest that understory plants intensified the investment in fine root dynamics in litter layer as response to eCO2 (e.g., increase in SRL and potential root phosphatase activity) Furthermore, with a potential increase in root phosphatases exudation (litter and soil) in the first year with eCO2, our results reinforce the importance of this mechanism to mobilize inorganic P. Our results provide an initial understanding of nutrient mechanisms acquisition under eCO2 in a tropical forest, which can be incorporated into ecosystem models to allow more reliable predictions of forest productivity under eCO2.

AmazonFACE team:

Katrin Fleischer; Sabrina Garcia; Flavia D. Santana; Amanda Damasceno;Anja Rammig; David Lapola; Bart Kruijt

How to cite: Martins, N., F. Lugli, L., J. Valverde-Barrantes, O., Takeshi, B., Pires, M., G. Menezes, J., Sales Pereira, I., Guedes, A., R. Ferrer, V., R. Santos, Y., U. Neves, G., C. M. Moraes, A., Caroline Miron, A., P. Hartley, I., J. Norby, R., A. Quesada, C., and Fuchslueger, L. and the AmazonFACE team: Initial responses of fine root dynamics of understory plants to elevated CO2 in a Central Amazon rainforest, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-426,, 2022.

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