Vertical pattern and its driving factors in soil extracellular enzyme activity and stoichiometry along mountain grassland belts

Abstract

Soil extracellular enzymes catalyze soil biochemical processes, and the geographical patterns of their activities and stoichiometry can reflect soil microbial functional dynamics. In previous research, latitudinal and longitudinal variations in soil extracellular enzyme activity (EEA) have been intensively investigated. However, its elevation patterns and depth variations (especially > 40 cm) received much less attention. Here, we measured potential activities of enzymes of carbon (C) (β-1,4-glucosidase), nitrogen (N) (β-1,4-N-acetylglucosaminidase; leucine aminopeptidase), and phosphorus (P) (acid phosphatase) up to 1 m soil depth along a vertical grassland belt in Xinjiang Uygur Autonomous Region, China. Soils were sampled from three elevation gradients (low, < 1000 m; mid, 1000–2000 m; high, 2000–3000 m) at five depths (0–10, 10–20, 20–40, 40–60, 60–100 cm). Soil EEA generally increased with elevation, while specific EEA normalized by microbial biomass C was lowest at mid-elevation. Both enzymatic C:N and C:P ratios were highest at mid-elevation. Soil EEA declined with depth but the extents varied with elevation. Depth variations in soil enzymatic stoichiometry also differed among three elevation gradients. Enzyme C:N and C:P ratios only decreased with soil depth at low elevation. From low to high elevation, enzyme N:P was highest at depths of 20–40 cm, 40–60 cm, and 0–10 cm, respectively. Key influential factors of soil EEA varied from low to high elevation. At low elevation, soil nutrient affected soil EEA indirectly through affecting microbial biomass. At mid-elevation, soil moisture influenced soil EEA directly and indirectly via pH. At high elevation, only soil pH impacted soil EEA directly.