Soil labile organic carbon and nitrogen and their relationship with enzyme activities in different vegetation zones along an altitudinal gradient on Mount Huangshan

Abstract

To understand the distribution characteristics of soil carbon and nitrogen and their labile fractions as well as their relationship with environmental factors (enzyme activities, soil pH, and understory vegetation diversity), soil samples were collected from four vegetation zones (evergreen broadleaf forest, mixed evergreen deciduous broadleaf forest Ⅰ and Ⅱ, and alpine meadow) along an altitudinal gradient (870-1 760 m) on Mount Huangshan. Three 10 m×10 m plots were arranged in each vegetation zones, and 10 sub-samples (0-10 cm depth) were randomly collected in each plot and mixed into one soil sample. Variables tested included soil total organic carbon (TOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), readily oxidization carbon (ROC), total nitrogen (TN), microbial biomass nitrogen (MBN), dissolved organic nitrogen (DON), soil urease activity, β-glucosidase activity, catalase activity, soil pH, Shannon-Wiener and Simpson diversity indices of the understory vegetation. Analysis included one-way ANOVA and Duncan multiple comparison, Pearson correlation, redundancy analysis, and Monte-Carlo permutation test. Results showed significant differences in soil MBC, DOC, TN, and MBN in different vegetation zones (P < 0.01). The soil microbial quotient (MBC/TOC) and DOC/TOC in different vegetation zones were significantly different (P < 0.01) and generally increased with elevation. The soil MBN/TN (5.79%) in alpine meadows was significantly higher than in other vegetation zones (P < 0.05). Soil urease activities generally decreased with elevation (P < 0.05); whereas, β-glucosidase and catalase activities generally increased with elevation (P < 0.01). The Pearson correlation and redundancy analysis showed that soil labile organic carbon and N fractions were not only dependent on TOC and TN, but also closely related to urease, β-glucosidase, catalase activities, and soil pH. Also, according to the Monte-Carlo permutation test DON had a significant effect (P=0.006) on the distribution of soil enzymes. In conclusion, soil labile organic carbon and N fractions in the Mount Huangshan Forest Ecosystem were directly and indirectly related to vegetation types, and greatly impacted soil enzyme activities.