Soil nutrients and nutrient ratios influence the ratios of soil microbial biomass and metabolic nutrient limitations in mountain peatlands

Abstract

Soil microbes regulate the storage of carbon (C) in peatlands, which is facilitated by nutrients. To date, few researchers have examined the spatial distribution of soil microbial biomass, microbial community structure, and their metabolic nutrient limitations in mountain peatlands at different altitudes. This study aimed to improve the knowledge of how and why soil microbial biomass and their metabolic nutrient limitations varied with altitude. We investigated the phospholipid fatty acids (PLFAs) and enzymatic stoichiometry in surface (0–20 cm) and subsurface (20–50 cm) soil from peatlands with different types of vegetation in the Changbai Mountains. Overall, the soil microbial PLFAs were higher in the sedge-dominated peatlands than in the shrub/Sphagnum-dominated peatlands. The soil microbial PLFAs in the sedge-dominated peatlands were elevated at high altitudes but decreased with altitude in the shrub/Sphagnum-dominated peatlands. The soil fungal/bacterial ratios (F/B) in the surface soil increased with altitude in the sedge-dominated peatlands but not in the shrub/Sphagnum-dominated peatlands. The Gram-positive/Gram-negative bacteria ratios (G+/G−) in the surface soil decreased with altitude in the sedge-dominated and shrub/Sphagnum-dominated peatlands. The soil F/B ratios were higher, but the G+/G− ratios were lower in the shrub/Sphagnum-dominated peatlands than in the sedge-dominated peatlands. The soil pH and nutrient ratios explained most of the differences in soil bacterial and fungal PLFAs, respectively. However, the total nutrients of soil were the primary regulators of soil F/B and G+/G−. The soil microbial activities suffered from C- and phosphorus (P)- limitations in the mountain peatlands. The limitations were worse in the shrub/Sphagnum-dominated peatlands than in the sedge-dominated peatlands. The P limitations were greater at high altitude than at low altitude in both types of peatlands. The C and P limitations on soil microbial metabolism were primarily controlled by soil physical properties and nutrient ratios, respectively.