Characteristics of different aged plantations of Ormosia hosiei with regards to soil microbial biomass and enzymatic activities

Stand age is an important indicator of tree growth and life cycle, and has implications for ecological and biological processes. This study examined changes in soil microbial biomass (SMB) as well as enzyme activities of different aged plantations and revealed their relationship to soil properties. SMB, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorous (MBP) and enzyme activities (β-1,4-glucosidase (β-G), β-1,4-xylosidase (β-X), cellobiohydrolase (CBH), leucine aminopeptidase (LAP), β-1,4-n-acetylglucosamine (NAG) and acid phosphatase (ACP)) were measured in Oromosia hosiei plantations of different ages. The soil quality index (SQI) model assessed soil quality. SMB contents significantly decreased in young (7-year-old) and mature plantations (45-year-old) compared to middle-aged (20-year-old) plantations. Activity of soil β-G, β-X, CBH and NAG in the 20-year-old plantations was markedly higher than in the other plantations except for β-G, CBH and NAG in the 45-year-old plantations. Soil organic carbon (SOC), total potassium (TK), total porosity, dissolved organic carbon, nitrate nitrogen (NO₃⁻-N) and non-capillary porosity were key factors affecting SMB, while soil bulk density, pH, SOC, NO₃⁻-N, TK and forest litter (FL) were the main factors affecting soil enzyme activities. SQI decreased in the order: middle-aged > mature > young. The efficiency of soil organic matter conversion, the effect of nitrogen mineralization and fixation by microorganisms, and the better efficiency of phosphorus utilization in mid-age plantations, which improves soil physical properties, better facilitates tree growth, and further improves the buffering of the soil against acidity and alkalinity. FL quality was the only soil biological factor affecting soil enzyme activity. Our findings demonstrate that different aged plantations affect soil microbial biomass, enzyme activity, and soil quality.