How understory vegetation affects the catalytic properties of soil extracellular hydrolases in a Chinese fir (Cunninghamia lanceolata) forest

Abstract To study how the understory vegetation influences the catalytic properties of extracellular hydrolases, we established a paired treatment experiment, with understory vegetation and litter removed from one treatment (understory removal, UR) and litter removed and the understory vegetation left intact in the other (control, CK), in a subtropical Chinese fir ( Cunninghamia lanceolata ) plantation. We used fluorescent substrates to determine the maximum velocity ( V max ), the affinity of hydrolases to the substrates ( K m ), and the catalytic efficiency ( V max /K m ) of three extracellular hydrolases (β-1,4-glucosidase (βG), β-1,4-N-acetylglucosaminidase (NAG) and acid phosphatase (AP)). We found that the V max values for βG and NAG were 23.0% and 16.8% lower, respectively, in the UR treatment than in the CK treatment, and that the V max for AP was similar in both treatments. The K m and V max /K m for all the three hydrolases remained steady after the understory vegetation was removed. The soil C and N contents and the bacterial and fungal biomass were generally positively correlated with the V max values. Thus, understory vegetation had more influence on the activities ( V max ) than on the substrate affinities of extracellular hydrolases ( K m ). Microbes tended to concentrate on maintaining the catalytic efficiency when the SOC contents were between 15.8 and 20.3 g kg −1 when the understory vegetation was removed from a subtropical Chinese fir forest, and the catalytic efficiency could decrease under extremely low soil C contents. We suggest that understory vegetation should be maintained to sustain the potential microbial activity in subtropical Chinese fir forests.