Soils contain the major reservoir of organic carbon (C) in terrestrial ecosystems, and decomposition of soil organic carbon (SOC) by microorganisms potentially affects global C cycling. The turnover of SOC is primarily regulated by extracellular enzymes secreted by the microorganism. Land use change greatly alters quantity and quality of soil organic matter (SOM), as well as environmental properties such as soil microclimates and pH. These changes lead to substantial variation in the SOC pool and microbial composition in various ecosystems, which can potentially impact soil extracellular enzyme activities. However, how soil C-decomposition enzymes respond to different land use change remains unclear. 

Supervised by Prof. CHENG Xiaoli, Zhang Qian, a doctoral student of Wuhan Botanical Garden, determined seasonal variations in C-decomposition enzyme activities including hydrolases and oxidases and C contents in woodland, shrubland, cropland, and adjacent uncultivated soils in central China. 

Compared with the uncultivated land, higher hydrolase activities in afforested land were related to higher soil dissolved organic C and labile C contents, whereas in cropland soils, it might be attributed to higher labile C, nitrogen (N) fertilization, tillage, and lower C: N ratios.  The highest oxidative enzyme activities in the cropland could be attributed to higher soil C recalcitrance Index and lower C: N ratio. Cropland increased specific enzyme activities compared with afforested land, indicating fast C turnover rates in cropland.  

This study suggested that afforestation could not only increase SOC content by increasing litter input but also enhance soil C sequestration and stabilization by reducing soil C turnover rate driven by the soil extracellular enzymes.

This research was financially supported by the National Natural Science Foundation of China and the Strategic Priority Research Program B of the Chinese Academy of Sciences. Results have been published in Land Degradation & Development entitled “Variations in carbon‐decomposition enzyme activities respond differently to land use change in central China”. 

Annual averages of soil hydrolytic enzyme activities under different land use type (Image by ZHANG Qian) 

Annual averages of soil oxidative enzyme activities under different land use type (Image by ZHANG Qian)