Native broadleaf tree species stimulate topsoil nutrient transformation by changing microbial community composition and physiological function, but not biomass in subtropical plantations with low P status

Abstract

Microbial communities and their associated enzyme activities affect carbon (C), nitrogen (N), and phosphorus (P) metabolism in soils. We used phospholipid fatty acids (PLFAs) analysis and extracellular enzyme activity assays to evaluate the effects on topsoil microbial community and nutrient transformation of converting Chinese fir (CF) plantations to native broadleaf (Castanopsis hystrix [CH] and Mytilaria laosensis [ML]) plantations in this study. We found that CH and ML plantations had significantly higher soil organic C (SOC), total N (TN), NH4+-N, soil C/N ratios (C/Nsoil), soil C/P ratios (C/Psoil) and soil N/P ratios (N/Psoil) but significantly lower total P (TP) compared to CF plantations. A distinct shift in soil microbial community composition, but not microbial biomass was evident 23 years after stand conversion. Redundancy analysis (RDA) showed that soil microbial community composition was substantially influenced by litterfall mass (LF), TP, N/Psoil, SOC, fine root biomass (FR), C/Nsoil, TN, litter C/N ratios (C/Nlitter), and C/Psoil; of these, LF appeared to be the primary driver of differences in soil microbial community composition (p < 0.05). In addition, the total activity of hydrolytic enzymes involved in C metabolism (β-glucosidase and cellobiohydrolase), N metabolism (N-acetyl-glucosaminidase), and P metabolism (acid phosphatase) increased significantly in the two native broadleaf plantations, whereas the total activity of oxidase (phenol oxidase) decreased significantly. Furthermore, the change trends of specific enzyme activity (i.e., enzymes per unit microbe) were similar to total enzyme activity. The dynamics of soil microbial enzymatic activity after stand conversion provide a functional link between changes in microbial community composition and soil nutrient transformation. Our findings suggest a mechanism in native, non-N2-fixing broadleaf tree species that stimulates soil nutrient transformation in subtropical planted forests with low P via increases in the quantity and quality of litter and the physiological function per unit of microbial biomass.