Effects of plant traits on the regulation of water cycle processes in the Amazon Basin

Abstract. Plants play a key role in the soil-plant-atmosphere-climate hydrological continuum as they depend on water for their persistence and in turn affect water exchange processes. Changes in plant composition may affect these relationships through induced changes in cover, composition and functionality; however, detailed understanding on how feedbacks that involve plant traits develop are still seldom included in observational, experimental and modeling studies. To address this gap, here we make use of datasets derived from Earth Observation and models to examine the effect of plant traits on water cycle processes in the Amazon Basin. We used quantile regression to examine how plant traits (Specific Leaf Area (SLA), Leaf Dry Matter Content (LDMC), Leaf Phosphorus Content (LPC) and Leaf Nitrogen Content (LNC)), respond to parameters related to regulation of atmospheric water content (Evapotranspiration (ET), Potential Evapotranspiration (PET), Vapour Pressure Deficit (VPD)), land surface temperature (Land Surface Temperature (LST) day and night)), and soil moisture content (Soil Moisture (SM)) along their range of values. We found that SLA had the strongest relationships with parameters involved in the regulation of atmospheric water content and land surface temperature, but weak relationships with regulation of soil moisture content, for the Amazon basin and its sub-basins. Plant traits show even stronger relationships at the 5th and the 95th quantiles; this is particularly strong at low values of ET and PET and high values of VPD and LST. The associations remain strong and localised in some particular sub-basins. Our results highlight the role of plant traits in mediating hydrological processes, which are not yet included in current models. Further, the results suggest that if climate change induces shifts in water cycle parameters to more extreme values, the functional response of plants may exacerbate these effects and affect the resilience of the Amazon forest.