Litter chemical quality strongly affects forest floor microbial groups and ecoenzymatic stoichiometry in the subalpine forest

Abstract

Litter chemical quality regulates the distinct composition of the main microbial groups and ecoenzymatic stoichiometry. Microbes in spruce ( Picea asperata Mast.) and fir ( Abies faxoniana Rehd.) rather than birch ( Betula platyphylla Suk.) and rhododendron ( Rhododendron lapponicum (L.) Wahl.) can more easily adjust their physiological metabolism to acclimate to low N resources. Litter decomposition is the main pathway of nutrient cycling that bridges aboveground and underground material circulation and energy flow. Microorganisms are essential for the regulation of organic carbon decomposition and nutrient cycling. We sought to reveal whether litter chemical quality predominates forest floor microbial structure and function in different species and how their characteristics vary with litter decomposition stages. We measured litter substrate quality, microbial community structure, microbial biomass carbon (MBC) and nitrogen (MBN), extracellular enzyme activities and stoichiometric homeostasis of fresh litter (L), and fermentative (F) and humus (H) layers for these tree species. Overall, the enzyme activities and microbial biomass of birch and rhododendron were greater than those of spruce and fir. The microbial abundances of birch and rhododendron decreased with decomposition. Forest floor microbial nutrient limitation is generally restricted by N in subalpine forests, and ecoenzymatic stoichiometry is affected mainly by dissolved C/N/P stoichiometry. Stronger microbial C:N homeostasis (H′) was observed for spruce (5.56) and fir (4.17) than that for birch (1.82) and rhododendron (1.33). We conclude that litter chemical quality led to the disparity in forest floor microbial groups and ecoenzymatic stoichiometry for different tree species.