Rainfall seasonality shapes belowground root trait dynamics in an Amazonian tropical rainforest: A test of the stress-dominance hypothesis

Valverde-Barrantes, O., Figueiredo Lugli, L., Fuchslueger, L., Hofhansl, F. ORCID: https://orcid.org/0000-0003-0073-0946, Martins, N., Cordeiro, A., Schaap, K., Andersen, K., Garcia, S., Grandis, A., Miron, A.C., Fleischer, K., Hoosbeek, M., Hartley, I., Oblitas Mendoza, E., Lapola, D., & Quesada, C.A. (2024). Rainfall seasonality shapes belowground root trait dynamics in an Amazonian tropical rainforest: A test of the stress-dominance hypothesis. 10.5061/DRYAD.0K6DJHBB0.

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Abstract

The stress-dominance hypothesis (SDH) predicts that trait variation at the community level increases with the availability of limiting resources, driving spatial and temporal patterns in aboveground plant functional trait expression. Here, we test the assumption that the SDH also applies to fine roots responding to spatial and temporal fluctuations in soil resource availability. We monitored fine root mass and functional root traits associated with resource acquisition, i.e., specific root length (SRL), specific root tip abundance (SRTA) and branching index (BI), and traits related to stress tolerance, like root diameter (RD) and tissue density (RTD) in a Central Amazonian tree community. To test for spatial differences in root traits we separated the uppermost organic (O-A horizon, 0-5 cm) and mineral soil (B horizon, 5-15 cm) layers, and for temporal fluctuations we investigated the relationship of precipitation on community-level root variation over a period of 27 months. In accordance with the SDH, we found that fine roots in the O-A horizon have on average 15% higher SRL, 23% higher BI, 32% higher SRTA, and 15% lower RTD than those in the B horizon. Similarly, precipitation shifted the community over time to higher mean SRL, BI, and SRTA (r= 0.92, 0.84 and 0.94, p<0.0001 respectively), although trait shifts occurred in the trimester after the rainy season onset, revealing a time-lag between rainfall patterns and community response. We also detected a positive increase in trait range for SRL and SRTA with lagged precipitation (r=0.90 and 0.79, p<0.0001). On the other hand, traits related to stress showed a weaker negative relationship with instantaneous precipitation (r =-0.7 and -0.57, p = 0.046 and p =0.1 for RD and RTD respectively). Our results supported the SDH predictions that root systems will become more acquisitive in areas with more resources, and that the community will shift to more acquisitive but also broader trait dispersion as hydric stress decreases. We conclude that although higher resource availability may increase competition for acquisition, trait overdispersion seems to promote species coexistence. Our results highlight how dynamic root systems can be in response to environmental cues, cautioning the common practice of making conclusions about root traits adaptations to environmental gradients based on a single sampling observation.

Item Type:	Data
Additional Information:	Creative Commons Zero
Uncontrolled Keywords:	FOS: Biological sciences, FOS: Biological sciences, root functional traits, tropical rainforest, root plasticity., trait temporal variation, Amazon tropical forest, Plant functional traits
Research Programs:	Biodiversity and Natural Resources (BNR) Biodiversity and Natural Resources (BNR) > Agriculture, Forestry, and Ecosystem Services (AFE) Biodiversity and Natural Resources (BNR) > Biodiversity, Ecology, and Conservation (BEC)
Depositing User:	Luke Kirwan
Date Deposited:	20 Jan 2025 12:53
Last Modified:	20 Jan 2025 12:53
URI:	https://pure.iiasa.ac.at/20356

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