Litter decomposition is key to ecosystem carbon (C) and nutrient cycling, but this process is anticipated to weaken due to projected more extensive and prolonged drought. Yet how litter quality and decomposer community complexity regulate decomposition in response to drought is less understood. Here, in a five-year manipulative drought experiment in a Masson pine forest, leaf litter from four subtropical tree species (Quercus griffithii Hook.f. & Thomson ex Miq., Acacia mangium Willd., Pinus massoniana Lamb., Castanopsis hystrix Miq.) representing different qualities was decomposed for 350 ​d in litterbags of three different mesh sizes (i.e., 0.05, 1, and 5 ​mm), respectively, under natural conditions and a 50% throughfall rain exclusion treatment. Litterbags of increasing mesh sizes discriminate decomposer communities (i.e., microorganisms, microorganisms and mesofauna, microorganisms and meso- and macrofauna) that access the litter and represent an increasing complexity. The amount of litter C and nitrogen (N) loss, and changes in their ratio (C/N_loss), as well as small and medium-sized decomposers including microorganisms, nematodes, and arthropods, were investigated. We found that drought did not affect C and N loss but decreased C/N_loss (i.e., decomposer N use efficiency) of leaf litter irrespective of litter quality and decomposer complexity. However, changes in the C/N_loss and the drought effect on C loss were both dependent on litter quality, while drought and decomposer complexity interactively affected litter C and N loss. Increasing decomposer community complexity enhanced litter decomposition and allowing additional access of meso- and macro-fauna to litterbags mitigated the negative drought effect on the microbial-driven decomposition. Furthermore, both the increased diversity and altered trophic structure of nematode due to drought contributed to the mitigation effects via cascading interactions. Our results show that litter quality and soil decomposer community complexity co-drive the effect of drought on litter decomposition. This experimental finding provides a new insight into the mechanisms controlling forest floor C and nutrient cycling under future global change scenarios.

Mixed-species plantations generally exhibit higher ecosystem multifunctionality than monospecific plantations. However, it is unclear how tree species functional composition influences species mixture effects on ecosystem multifunctionality. We selected 171 monospecific and mixed-species plantations from nine regions across subtropical China, and quantified 13 key ecosystem functional properties to investigate how species mixture effects on ecosystem multifunctionality are modulated by functional diversity and identity. We found that ecosystem multifunctionality was significantly higher (p ​ < ​0.05) in mixed tree plantations than in monospecific plantations except the mixed-conifer species plantations. Across all regions, ecosystem multifunctionality was significantly higher (p ​ < ​0.05) in mixed conifer-broadleaf plantations than in monospecific plantations of the corresponding species, but not different between mixed and monospecific coniferous plantations. The magnitude of species mixture effects on ecosystem multifunctionality varied greatly with tree species compositions. Taking Cunninghamia lanceolata Lamb. as an example, the effects varied from a range of 2.0%–9.6% when mixed with a conifer species to 36%–87% when mixed with a broadleaf species. The functional diversity was the dominate driver shaping ecosystem multifunctionality, while functional identity, as expressed by community-weighted mean of specific leaf area, also had a positive effect on ecosystem multifunctionality through the increased below-ground nitrogen and phosphorus stocks regulated by specific leaf area of the mixing tree species. Our study highlights the important role of functional diversity in shaping ecosystem multifunctionality across region-wide environmental conditions. Mixed conifer-broadleaf tree plantations with distinct functional traits benefit the enhancement of ecosystem multifunctionality, and the magnitude of species mixture effects is modulated by the functional identity of tree species composition; those relationships deserve a special consideration in multifunctional management context of subtropical plantations.