EGU22-2703, updated on 27 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

The effects of elevated CO2 and phosphorus limitation shaping fine root functioning in Central Amazon forests

Laynara F. Lugli1,2, Carlos Alberto Quesada2, and the AmazonFACE team*
Laynara F. Lugli and Carlos Alberto Quesada and the AmazonFACE team
  • 1Technical University of Munich, School of Life Sciences, Freising, Germany
  • 2National Institute for Amazonian Research, Biogeochemical cycles, Manaus, Brazil (
  • *A full list of authors appears at the end of the abstract

One of the most important questions that remain open in terrestrial ecology refers to how the Amazon rainforest, the largest tropical forest in the world, will respond to elevated atmospheric CO2. Since a large part of the Amazon grows in soils with very low phosphorus (P) availability, understanding how potential nutrient limitation could impact forests in a changing world becomes crucial. There is strong evidence for a positive effect of elevated CO2 on plant growth but sustaining such a response in the Amazon would require plants to increase their access to P, making it important to understand the effects of elevated CO2 on root P-uptake strategies. To this end, we installed eight Open Top Chambers (OTC) in an understory forest in Central Amazon in Manaus, Brazil, being four control with ambient CO2 (aCO2) and four treatment with +200 ppm CO2 (eCO2). Inga edulis, a common N-fixing tree in the area, was chosen as study species. In each OTC, I. edulis was grown in six pots, three containing control soil from the study area and three containing control soil with 600 mg/kg of P added as triple super phosphate. After two years, plants were harvested and total soil respiration, total root dry mass, root nodulation, root morphological traits (mean diameter, specific root length – SRL, specific root area – SRA and root tissue density – RTD) and potential root phosphatase activity were measured. Total soil respiration was significantly higher in both treatments with eCO2 when compared to treatments with aCO2. Total dry root biomass followed a similar pattern, and root biomass in the eCO2 and P+eCO2 treatments were twice that of the other two aCO2 treatments. Plants invested in more fine roots (< 1 mm diameter) than in coarse roots with eCO2-only, whilst in P+eCO2, both fine and coarse roots biomass increased. No nodules were detected in control plants, whilst almost 75% of plants growing in P+eCO2 and 30% of plants growing in eCO2-only and P-only displayed nodulation. Mean fine root diameter for plants growing in eCO2-only was significantly higher than all other treatments, leading to a significant decrease in SRL and RTD, with no changes in SRA. In both treatments with eCO2, fine root phosphatase activity (expressed per root dry mass and specific area) significantly decreased in comparison to aCO2. However, when extrapolating root phosphatase activity for total fine root biomass, pot-level phosphatase exudation was twice as high in eCO2 than in aCO2 treatments. Our results clearly point to a shift in plant belowground strategies, suggesting an even stronger control of nutrient acquisition mechanisms by eCO2 than P addition. With eCO2, plants allocated much more biomass to fine roots and nodules, rather than increased phosphatase exudation per root-unit. Such trade-off suggests that in this scenario, plants might acquire P directly by exploring higher soil volumes, whilst allocating extra C to N-fixing bacteria. We demonstrate how eCO2 and P availability can shape belowground plant traits pointing to important trade-offs that could determine ecosystem-scale changes in future climate scenarios.

AmazonFACE team:

From the National Institute of Amazonian Research, Manaus, Brazil: Bachega, Luciana R.; Martins, Nathielly P.; Leite, Pamella; Pereira, Ana Caroline, M.; Pereira, Iokanam; Guedes, Alacimar; Garcia, Sabrina; Santana, Flavia; Aleixo, Izabela; Portela, Bruno T. T.; Damasceno, Amanda; Menezes, Juliane C. G.; Ushida, Gabriela; Ferrer, Vanessa; Santos, Yago R.; Souza, Cassio; Moraes, Anna C. M. From the Universidade Estadual do Amazonas, Manaus, Brazil: Vinicius F. Souza. From the University of Vienna, Centre of Microbiology and Environmental Systems Science, Vienna, Austria: Fuchslueger, Lucia. From Florida International University, Department of Biological Sciences, Miami, United States: Valverde-Barrantes, Oscar. From College of Life and Environmental Sciences, University of Exeter, UK: Hartley, Iain P. From the University of Campinas, SP, Brazil: Lapola, David. From Technical University of Munich, School of Life Sciences, Freising, Germany: Rammig, Anja. From Department of Ecology and Evolutionary Biology, University of Tennessee, United States: Norby, Richard.

How to cite: F. Lugli, L. and Quesada, C. A. and the AmazonFACE team: The effects of elevated CO2 and phosphorus limitation shaping fine root functioning in Central Amazon forests, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2703,, 2022.

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