Responses of seedling performance to altered seasonal precipitation in a secondary tropical forest, southern China

Given the intensified global climate change, understanding the responses of seedlings in tropical forests to changing precipitation patterns is critical for predicting plant community regeneration. In a field study, we investigated the potential effects of changes in seasonal precipitation on seedling establishment and growth of Cinnamomum burmanni, a dominant tree species in a secondary tropical forest, southern China. The field precipitation treatments included ambient rainfall (CT), increased precipitation (IP) in the wet season, and extended dry (ED) season without change in annual rainfall. For the IP treatment, 25% of the mean annual precipitation was added in the wet season using pumps and sprinklers. For the ED treatment, 60% of incoming throughfall was removed in March and April to extend dry season for two months using transparent roofs, and re-added back in October and November with the total annual rainfall amount not changed. The results showed that the IP treatment increased seedling height growth in June and August when extra water was applied. By the end of experiment, stem biomass was significantly greater in IP plots than in ED plots. Precipitation treatments also affected biomass allocation. Seedlings in ED plots had a lower root/shoot ratio and root mass to total mass ratio. Compared to the control, the IP treatment significantly increased leaf and stem nitrogen concentrations of the seedlings. Nitrogen and phosphorus contents in stems and roots were much higher in IP plots than in ED plots, which might be explained by the increased NO3−-N and available phosphorus concentrations in soil. Our findings indicate that extended dry season without change in annual rainfall or increased precipitation in the wet season induced by climate change, is likely to affect soil nutrients, seedling biomass accumulation and partitioning, and nutrient uptake, and thereby impact regeneration dynamics and future community structure in tropical forests.