Soil Enzyme Activity and Stoichiometry Change with Perennial Mugwort Cropping Cultivation Year in Central China

Our understanding of how intensified land use changes (such as conversion of annual to perennial crops) influence soil extracellular enzymes is still limited, especially at the spatio-temporal scales. In this study, we investigated the spatio-temporal patterns of five soil hydrolytic enzymes (i.e., α-glucosidase (AG), β-glucosidase (BG), N-acetyl-glucosaminidase (NAG), L-leucine aminopeptidase (LAP), and acid phosphatase (AP)) and their stoichiometry with different perennial mugwort cropping cultivation years (mugwort cropping for 0 (control), 3, 6, and 20 years). The results revealed that the activities of AG, BG, LAP, and AP first increased and then decreased with increasing mugwort cropping cultivation year, indicating the nutrient limitation under long-term mugwort cropping. Except for the activity of NAG, the activities of AG, BG, LAP, and AP showed close relationships with biotic (aboveground and root biomass) and abiotic factors (especially soil organic carbon, N content, P content, and their stoichiometry). Across the soil depths, the ecoenzymatic C:P ratio ranged from 0.81 to 0.91 and N:P ratio ranged from 0.93 to 1.03. The random forest model showed that biotic and abiotic factors contributed 59% and 78% of vector length and angle changes, respectively. The observations suggest the long-term mugwort cropping could increase soil nutrient limitation, which may not benefit for sustainable development of perennial cropping systems. The findings increase our understanding on the impacts of soil management practices (conversion of annual to perennial crops) on soil enzyme activities and thus nutrient cycling.