Effects of Mycorrhizal and Extraradical Hyphae of Subtropical Native Tree Species on Soil Enzyme Activities and Their Stoichiometric Ratios

We aimed to study the effects of mycorrhizal and extraradical hyphae on soil physical and chemical properties and enzyme activity characteristics in a subtropical plantation and to explore its indicative effect on the effectiveness of soil nutrients. In this study, three native afforestation tree species, Cunninghamia lanceolata, Schima superba, and Liquidambar formosana, with different biological characteristics, root functional traits, and nutrient acquisition strategies in subtropical regions were selected as the research objects. Based on the method of in-growth soil cores, the nylon mesh with different pore sizes was used to limited the root system and hypha into the soil column. The soil physical and chemical properties of five kinds of hydrolase related to the carbon (C), nitrogen (N), and phosphorus (P) cycles were determined in this study. The correlation of different tree species, roots, and mycelia with soil physicochemical properties, enzyme activity, and stoichiometric ratios was analyzed. The results revealed that mycorrhizal treatment significantly affected the soil total carbon (TC) and pH but had no significant effect on hydrolase activity and its stoichiometric ratio. Tree species significantly affected soil physical and chemical properties, soil β-1,4-N-acetylglucosaminidase (NAG), β-1,4-glucosidase (βG), and cellobiohydrolase (CB) activities and soil enzyme stoichiometric ratios. The soil enzyme activity and stoichiometric ratio of the Chinese fir forest had higher values than in monoculture broad-leaved stands of both Schima superba and Liquidambar formosana. There was no significant interaction effect of mycorrhizal treatments and tree species on all soil properties, enzyme activities, and stoichiometric ratios. In addition, the soil enzyme activity and stoichiometric characteristics were mainly affected by the pH. In this study, the soil enzyme activity ratios In(BG + CB):In(AP) and In(NAG + LAP):In(AP) were lower values than the global scale, while the ratios of In(βG + CB):In(NAG + LAP) were higher than the average, indicating that the soil microorganisms in this area were limited by C and P. Moreover, the soil enzyme activity and chemical metrology characteristics were mainly affected by the pH change. In conclusion, differences in litter quality and root functional traits of tree species affected the soil enzyme activity and its stoichiometric characteristics through the shaping of the forest environment by organic matter input, and the influence of pH was the main regulating factor.