COS 155-1 - Reduced sensitivity of carbon and water exchange to soil moisture in temperate trees exposed to chronic throughfall removal

Abstract: Climatic change is projected to alter precipitation patterns and increase the risk of drought in substantial portions of Earth’s temperate biomes. Responses of plants to longer-term shifts in precipitation may have consequences for both short- and long-term land-atmosphere feedbacks, mediated by changes in rates of carbon and water exchange under a given set of environmental conditions. Here, we investigated the influence of long-term throughfall reduction on (1) diel and seasonal rates of transpiration, canopy conductance, and gross primary productivity, (2) responses of these processes to environmental conditions, including soil moisture, and (3) relationships of these processes with soil and atmospheric moisture during short-term natural dry periods. Using a 3-year throughfall exclusion experiment in US central hardwood forest, we examined co-occurring species responses to reduced precipitation and soil water availability by quantifying physiological process rates of three tree species under ambient rainfall, moderate (-45%), and severe (-80%) throughfall removal. Our results show that throughfall removal alters tree species’ relationships between shallow soil moisture and processes such as transpiration, canopy conductance, and gross primary productivity. During dry periods, transpiration, canopy conductance, and gross primary productivity slow down at any given soil moisture level and/or are less responsive to fluctuations in soil moisture. Thus, under future climatic conditions, drier growing seasons would decrease productivity at a given level of soil moisture, depending on species’ plasticity in physiological traits.