Warming and drought modify belowground interactions for water among coexisting plants

International audience

English. Background/Question/Methods Understanding how climate alters plant-soil water dynamics, and its impact on physiological functions, is critical to improved predictions of vegetation responses to climate change. Here we analyzed how belowground interactions for water shift under warming and drought, and associated impacts on plant functions. In a semi-arid woodland, adult trees (piñon and juniper) and perennial grasses were exposed to warming and precipitation reduction. After six years of continuous treatment exposure, soil and plant water isotopic composition under natural- and tracer-conditions were measured to assess community-level water source partitioning and hydraulic redistribution. Results/Conclusions Warming and drought modified plant water uptake depths. Shifts in water uptake depths under warming resulted in reduced water source partitioning. Under drought, plants maintained similar water source partitioning among species compared to ambient conditions. Trees showed higher water stress, reduced water use and photosynthesis in response to warming and drought. No evidence of hydraulic redistribution was observed for any species independent of the treatments. This study demonstrates that coexisting plants can modulate their partitioning of water sources under prolonged warming and drought but these adjustments do not systematically mitigate climate extremes. Additionally, hydraulic redistribution is not necessarily a significant process compensating climate change impacts in this semi-arid ecosystem.