Increased litter in subtropical forests boosts soil respiration in natural forests but not plantations of Castanopsis carlesii

Background and aims: Changes in net primary productivity in response to climate change are likely to affect litter inputs to forest soil. However, feedbacks between changes in litter input and soil carbon dynamics remain poorly understood in tropical and subtropical forests. This study aims to test whether the effects of litter manipulation on soil respiration differ between natural and plantation forests. Methods: Soil respiration, soil properties, fine root biomass and enzyme activity were measured in adjacent plots with doubling vs. eliminating litter input in both natural and plantation forests of Castanopsis carlesii in southern China. Results: After only 3 years of litter manipulation, the magnitude of change in soil respiration was greater in response to a doubling of the litter input (+24%) than to the elimination of litter input (−15%) in the natural forest, possibly due to a positive priming effect on decomposition of soil organic carbon (SOC). The quick and intense priming effect was corroborated by elevated enzyme activities for five of the six enzymes analyzed. In contrast, the response to litter removal (−31%) was greater than the response to litter addition (1%; not significant) in the plantation forest. The lack of positive priming in the plantation forest may be related to its lower soil fertility, which could not meet the demand of soil microbes, and to its high clay content, which protected SOC from microbial attack. The positive priming effect in the natural forest but not plantation forest of C. carlesii is also consistent with the significant declines in total soil carbon observed following litter addition in the natural forest but not the plantation forest. Conclusions: Increases in aboveground litter production may trigger priming effects and subsequently transfer more soil carbon to atmospheric CO₂ in the natural forest but not in the plantation forest with low fertility. Changes in litter inputs resulting from global change drivers may have different impacts on natural and plantation forests.