Aboveground litter input alters the effects of understory vegetation removal on soil microbial communities and enzyme activities along a 60-cm profile in a subtropical plantation forest

Abstract

Changes in litter input and understory vegetation due to climate change and human activities affect belowground processes in plantation forests. However, it is unclear whether and how aboveground litter interacts with understory vegetation for their effects on soil microbial communities and functions, especially in deep soils. A field manipulation experiment was conducted, including four treatments of understory vegetation removal plus aboveground litter removal (UVR + ALR), understory vegetation preservation plus aboveground litter addition (UVP + ALA), UVR + ALA, and UVP + ALR in a subtropical Chinese fir (Cunninghamia lanceolata) plantation. After seven years of continuous treatment, the soil samples along a 60-cm profile were used to evaluate microbial community compositions, major microbial enzyme activities, and several physicochemical properties in the four treatments. UVR resulted in significant negative effects on microbial biomass and enzyme activities at different soil layers with or without litter input, but it did not change the soil microbial communities such as F/B, G+/G−. Compared with ALR, ALA amplified the negative understory vegetation removal effects (UVREs) on β-D-cellobioside (CB), β-N-acetylglucosaminidase (NAG), and leucine aminopeptidase (LAP) activities, but did not affect UVREs on total soil PLFAs. Lesser negative UVREs on β-1,4-glucosidase (BG), LAP, and acid phosphatase (AP) activities were observed in top soils compared to deep soils in the ALR treatment. UVREs on soil microbial biomass were not significantly different among soil depths. These results indicate that aboveground litter and soil depth altered UVREs on soil physicochemical properties, primarily through soil microbial biomass and enzyme activities. UVREs were generally more sensitive to major enzyme activities than microbial biomass and were interactively influenced by aboveground litter and soil depth due to synergistic effects within soil ecosystems. This study highlights the integrated feedbacks of microbial structures and functions along soil profiles in response to litter and vegetation interactions in subtropical forests.