Increased fine root production coupled with reduced aboveground production of plantations under a three-year experimental drought.

Climate change has led to more frequent and intense droughts. A better understanding of forest production under drought stress is critical for assessing the resilience of forests and their capacity to deliver ecosystem services under climate change. However, the direction and magnitude of drought effects on aboveground and belowground forest ecosystem components remain poorly understood. Here, we conducted a drought experiment including 30 % and 50 % throughfall reduction in a poplar plantation in the eastern coast of China to test how different drought intensities affected aboveground and fine root production. We further investigated the responses of soil physicochemical properties (e.g., soil moisture, soil pH, soil carbon, and soil nitrogen), and microbial properties (e.g., total microbial biomass, fungi:bacteria ratios, and Gram+:Gram- bacteria ratios) to drought. We found that the aboveground production decreased by 12.2 % and 19.3 % following 30 % and 50 % drought intensities, respectively. However, fine root production increased by 21.6 % and 35.1 % under 30 % and 50 % drought intensities, respectively. Moreover, all above- and belowground components exhibited stronger responses to 50 % compared with 30 % drought intensity. Our results provide some of the first direct evidence for simultaneous responses of forest above- and belowground production to moderate and intense droughts, by demonstrating that fine root production is more sensitive than aboveground production to both levels of drought stress.