Variation patterns and their driving factors in soil extracellular enzyme activities and stoichiometry along a 49-years vegetation restoration chronosequence

Vegetation restoration by altering soil properties has far-reaching impacts on soil extracellular enzyme activities (EEAs) and stoichiometry (EES). However, the response of EEAs and EES to changes in various soil properties along long-term vegetation restoration chronosequences in metal mining areas is still unrevealed.

Soil organic carbon (SOC), nutrients such as total nitrogen (TN) and total phosphorus (TP), microbial biomass, physicochemical properties, heavy metals (Cd, Cr, Cu, Ni, V, and Zn), EEAs, and EES are appropriately analyzed along the chronosequence.

The EEAs exhibited an increasing trend at the early stage (0–15 years), which continued at high levels or increased thereafter at the late stage (16–49 years). The results also indicate that the enzyme C:P ratio increased linearly with time, whereas the enzyme C:N ratio lessened at the early stage and then grew at the late stage. Soil organic carbon, TN, and microbial biomass primarily controlled the variations in EEAs, and heavy metal contamination and SOC dominated the enzyme C:P ratio. Soil organic carbon and TN substantially regulated the variations in the enzyme C:N ratio at the early stage, and heavy metal contamination modulated the changes in the enzyme C:N ratio at the late stage.

The present study suggests the potential N and P co-limitations in soils, which were essentially caused by the low P and N availabilities at the early stage of restoration. Meanwhile, we also highlight the significance of treating soil heavy metal contaminations to reduce the limitation of microbial C metabolism at the late stage.