Hummock-hollow microtopography affects soil enzyme activity by creating environmental heterogeneity in the sedge-dominated peatlands of the Changbai Mountains, China

Abstract

Soil enzyme activities play a pivotal role in ecosystem processes, such as organic carbon decomposition or nitrogen and phosphorus mineralization. Thus, enzyme activities measurements can provide insights into the rates of ecosystem-level processes in peatlands. Hummock-hollow microtopography is a common feature in boreal peatlands, but its influence on soil enzyme activity is not well understood. We investigated the effects of hummock-hollow microtopography on activities of three soil hydrolases (β-1,4-glucosidase (βG), 4-N-acetylglucosaminidase (NAG), and acid phosphatase (AP)) and one oxidase (peroxidase (PER)), as well as environmental variables in a sedge-dominated peatland in Changbai Mountains, in northeast China. We found that soil enzyme activities had large microtopographical and seasonal heterogeneity. During the growing season, the activities of three soil hydrolases (βG, NAG and AP) in hummocks were 6.6, 4.6 and 5.5 times higher than those in hollows, while the PER activity in hollows was 1.9 times higher than in hummocks. Soil enzyme activities in hummocks exhibited obvious seasonal variation, with the βG, AP and PER presenting minimum values in summer and peak values in spring and autumn. Principal component analysis (PCA) indicated that soil enzyme activity had larger microtopographical heterogeneity than seasonal variations. Water table position explained most variation (74.1%) in soil enzyme activity, followed by soil temperature (5.5%) and pH (3.1%) based on ordination analysis using RDA. We conclude that hummock-hollow microtopography creates heterogeneity in hydrologic conditions, soil temperature and nutrients, and thus influences soil enzyme activity involved in carbon and nutrient cycling in sedge-dominated peatlands. This information stresses the importance of hummock-hollow microtopography in regulating carbon and nutrient cycling in northern peatlands.