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

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 accordan..., Site description:
The study was carried out in the Cuieiras Reserve at ZF2, ca. 60 km north of Manaus, Amazonas, Brazil (latitude S 2° 35' 40'', longitude W 60° 12' 28''). The vegetation is an old growth lowland rainforest with a 40 m tall canopy dominated by the families Fabaceae, Sapotaceae, Burseraceae, and Lecythidaceae (Higuchi et al., 1998; da Silva et al., 2011). The mean air temperature is 26°C and the mean annual precipitation is 2400 mm (Araújo 2002; Figure 2). Soils are classified as Geric Ferralsols with a pH of 3.9 on average (Quesada et al., 2010). Nutrient availability in the mineral soil is low, particularly for P, with available P varying from 7 to 16 mg kg-1 (Schaap et al., 2021). The precipitation during the study period was obtained from a meteorological station located 2 km from the study site (Tower K34, Cordeiro et al., 2020). During the studied period, precipitation followed the climate seasonality of the area (Fontes et al., 2018; Cordeiro et al., 2020; Figure 2..., , # Rainfall seasonality shapes belowground root trait dynamics in an Amazonian tropical rainforest: A test of the stress-dominance hypothesis

[https://doi.org/10.5061/dryad.0k6djhbb0](https://doi.org/10.5061/dryad.0k6djhbb0)

## Description of the data and file structure

**Root** **morphological** **trait measurements**

Each selected fine root sample was scanned using a high-resolution flatbed scanner (600 DPI resolution, 256-level grayscale, TIFF format; Epson Scanner Perfection V700 Photo, USA) and analyzed using WinRhizo software (2007 Pro version, Instrument Regent, Quebec, Canada, details in Appendix S1) following Bouma et al. (2000). From the image analysis we extracted the total length, and total number of tips per root sample. Using the dry mass per root sample, we calculated SRL, SRTA, and BI as the trait positively associated with root acquisition function. In addition, using volume estimations from the software we estimated RTD as the trait positively associated with stress...