Variation of subtropical forest soil microbial biomass and soil microbial community functional characteristics along an urban-rural gradient

Abstract

Soil microorganisms, which are sensitive to environmental changes, affect soil nutrient cycling and play an important role in the biogeochemical cycling. To understand the changes of soil microorganisms in subtropical forest across the urban-rural environmental gradient, we analyzed the differences in soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial community functional diversitiy in Dashu Mountain National Forest Park (urban forest), Zipeng Mountain National Forest Park (suburban forest) in Hefei and Wanfo Mountain(rural forest) in Luan City. Results showed that soil MBC followed an order of rural natural forest (115.07 mg·kg-1) > suburban forest (101.68 mg·kg-1) > urban forest (82.73 mg·kg-1), soil MBN followed an order of rural natural forest (57.73 mg·kg-1) > urban forest (31.57 mg·kg-1) > suburban forest (29.01 mg·kg-1), soil microbial metabolic activities (AWCD), McIntosh index (U) were shown as rural natural forest > suburban forest > urban forest. The main carbon sources used by soil microbial communities in those forests were carboxylic acids, amino acids and carbohydrates, with weak utilization capacity for polyamines and polyphenols. The utilization capacity of soil microorganisms to amino acids, carboxylic acids, polymers and polyphenols followed the order of rural natural forest > suburban forest > urban forest. There were significant spatial variations in the functional characteristics of soil microbial communities under urban-rural environmental gradient, with Tween 80 and β-methyl-D-Glucoside being the characteristic carbon sources as the influencing factors. Soil pH was significantly positively correlated with the microbial McIntosh index and AWCD value, while soil ammonium nitrogen (NH4+-N) showed a significant positive correlation with microbial Shannon diversity index and AWCD value. There was a negative correlation between the microbial Simpson index and soil nitrate nitrogen (NO3--N). Soil pH, NH4+-N and NO3--N were the main factors affecting diversity index of microbial communities. The results suggested that there were significant differences in microbial community characteristics of forest soil in urban-rural environmental gradient forests, and that the metabolic potential and functional diversity of soil microbial community in urban forests were weaker than that of natural forests.