Effects of Amaranthus palmeri Invasion on Soil Extracellular Enzyme Activities and Enzymatic Stoichiometry

Soil extracellular enzyme activities (EEAs) and enzymatic stoichiometry (ES) play essential roles in plant invasion processes. Nevertheless, how soil EEAs and ES respond to Amaranthus palmeri invasion and what their driving mechanisms remain poorly understood. We compared 22 pairs of A. palmeri–invaded plots and native vegetation plots in North China. Soil physicochemical properties and the potential activities of C-acquiring enzyme (β-1,4-glucosidase, BG), N-acquiring enzyme (β-N-acetyl-glucosaminidase, NAG), and P-acquiring enzyme (alkaline phosphatase, AKP) were determined. Compared with native vegetation soil, invasion by A. palmeri significantly altered the soil total C, ammonium nitrogen (N-NH4) content, and C:N ratio. Pearson’s correlation and random forest analysis showed that soil EEAs and ES were mostly correlated with soil pH, total N, total C, and available phosphorus (P-PO4). Redundant analysis demonstrated that soil total C was the major factor significantly explaining the variations in soil EEAs and ES of A. palmeri. Our findings highlight the effects of invasive species (A. palmeri) on soil chemical and biological properties, and enhance the understanding of soil microbial nutrient limitation; they also serve to reveal the mechanism of nutrient cycling and underground ecosystem processes mediated by A. palmeri invasion.