Abstract: We examined the interactive effects of soil warming and precipitation exclusion on understory vegetation biomass in Chinese fir (Cunninghamia lanceolata) plantation in subtropical China, with factorial treatments of soil warming (W, +5 ℃ above the ambient temperature) and 50% of precipitation exclusion (P) in a mesocosm experiment. The results showed that soil warming, precipitation exclusion and their interaction had significant effects on understory vegetation biomass. The above and belowground biomass increased significantly in the treatments of W and WP, with the increasing proportion being higher in W treatment. The P treatment significantly decreased belowground biomass. Root/shoot ratio decreased in the treatments of W, P and WP. The responses of above and belowground biomass and root/shoot ratio were primarily caused by the increase of soil temperature. However, the changes of dissolved carbon and nitrogen and mineral element concentrations of soil solution might directly affect undergrowth biomass. The increase in undergrowth biomass of different parts in the W treatment was significantly related to the decreases of the concentrations of Al³⁺, Fe³⁺ and Ca²⁺, while the increases of Al³⁺ and Na⁺ concentrations in P treatment might reduce belowground biomass. This study focuses on the main and interactive effects of increasing temperature and precipitation exclusion on the undergrowth biomass of Chinese fir plantation from the perspective of soil nutrient composition changes. The results can provide important theoretical basis for study of carbon cycling and forest management under the background of climate change.

Key words: warming, precipitation exclusion, undergrowth biomass, soil solution, mineral element concentration.