Do stand density and month regulate soil enzymes and the stoichiometry of differently aged Larix principis-rupprechtii plantations?

Abstract

As essential components of soil properties and microbial processes, carbon (C), nitrogen (N), phosphorus (P), and extracellular enzymes play key roles in carbon and nutrient cycling in forest ecosystems worldwide. Forest management should include the development of healthy ecosystems to prevent soil degradation and nutrient loss and support productivity. However, it remains unclear how forest stand density and month impact extracellular soil enzymes, C, N, and P concentrations and their stoichiometry. A total of 486 soil samples were extracted from forest stand plots of different densities and ages, which were sampled continuously during the growing season (May-October). The soil organic C, total N, total P, β-1,4-glucosidase, β-N-acetyl Glucosaminidase, leucine aminopeptidase, and acid phosphatase were quantified. Higher levels of soil organic matter (e.g., C and N) was observed to accumulate in highly dense 27-year-old stands (27a) (2125–2425 trees ha−1). Moderate stand densities (36a, 925–1325 trees ha−1; 48a, 875–1150 trees ha−1) facilitated the procurement of C and N by microorganisms and C and Nsequestration in near-mature and mature forest soils due to an improved environment and more robust microbial activities. The soil contained more N during the mid-growing season, where in July it was ∼ 40 % higher than at the beginning and end of the growing season. Further, the soil microbes that acquired C and N were more robust. Monthly regulation caused the C:N:P acquisition ratio to deviate significantly from 1:1:1. Soil microbes absorbed C and N mid-growing season; however, they tended to absorb N and P at its onset and end. Monthly regulation may serve as a “switch” that adjusts the capacities of soil microbes to acquire C and N in 36a and 48a plantations. The regulation of stand density can promote extracellular enzyme activities through the accumulation and storage of soil organic matter during the growing season.