Soil aggregate mediates the impacts of land uses on organic carbon, total nitrogen, and microbial activity in a Karst ecosystem

Shuangshuang Xiao,Wei Zhang,Kelin Wang,Yingying Ye,Jie Zhao

doi:10.1038/srep41402

Abstract

Understanding the effect of land use on soil carbon, nitrogen, and microbial activity associated with aggregates is critical for thorough comprehension of the C and N dynamics of karst landscapes/ecosystems. We monitored soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC), and Cmic: Corg ratio in large macro- (>2 mm), small macro- (0.25–2 mm), and micro- (0.053–0.25 mm) aggregates to determine the changes in soil properties under different land uses in the karst area of Southwest China. Five common land-use types—enclosure land (natural system, control), prescribed-burning land, fuel-wood shrubland, pasture and maize fields—were selected. Results showed that pasture and maize fields remarkably decreased the SOC and TN concentrations in aggregates. Conversion of natural system to other land uses decreased MBC (except for prescribed-burning) and increased Cmic: Corg ratios in aggregates. The extent of the response to land uses of SOC and TN concentrations was similar whereas that of MBC and Cmic: Corg ratios differed across the three aggregate sizes. Further, the SOC concentrations were significantly higher in macro-aggregates than micro-aggregates; the MBC and Cmic: Corg ratios were highest in small macro-aggregates. Therefore, small macro-aggregates might have more active C dynamics.

Highlights

53.94 ± 6.62 b 30.29 ± 5.24 ab 6.12 ± 2.35 a lead to the differences in the distribution and availability of soil organic matter (SOM)[22,26]
Our study showed that macro-aggregates (>0.25 mm) were dominant in water-stable aggregates in all land uses, which is consistent with the results of Liao et al.[37], who conducted a study in the karst region
The response degree of SOC and TN concentrations to land uses was similar across the three sizes of soil aggregates

Summary

Introduction

53.94 ± 6.62 b 30.29 ± 5.24 ab 6.12 ± 2.35 a lead to the differences in the distribution and availability of soil organic matter (SOM)[22,26]. Previous studies have shown that land use can affect the C and N within aggregates, and the degree of its influence depends on soil texture and management measures[3,4,27]. The degree of the effects of soil disturbance on microbial activity within aggregates was shown to be mediated by fraction size[22]. How land uses affect the C, N, and microbial activity associated with aggregates in karst areas remains unclear. We chose five typical land uses (enclosure land, prescribed-burning land, fuel-wood shrubland, pasture and maize fields) in karst regions, and aimed to identify the effects of various land uses on the SOC, TN, and microbial activity (MBC and Cmic: Corg ratio) associated with aggregates. Considering different land uses had various vegetation management and soil disturbance regimes, we hypothesized that (1) conversion of the natural system to other land uses would decrease aggregate-associated SOC, TN, and microbial activity, and the extent of land-use effects would differ across the three sizes of aggregates; (2) SOC and TN concentrations and microbial activity would be higher in macro-aggregates as indicated by the aggregate hierarchical model; (3) different land uses would affect SOC, TN and microbial activity via various directly or indirectly pathways

Methods

Results

Discussion

Conclusion