Dynamics of Soil Organic Carbon and Aggregate Stability with Grazing Exclusion in the Inner Mongolian Grasslands

Ding Wen,Jinjing Zhang,Nianpeng He,P.C Abhilash

doi:10.1371/journal.pone.0146757

Abstract

Grazing exclusion (GE) has been deemed as an important approach to enhance the soil carbon storage of semiarid grasslands in China; however, it remains unclear how different organic carbon (OC) components in soils vary with the duration of GE. Here, we observed the changing trends of different OC components in soils with increased GE duration in five grassland succession series plots, ranging from free grazing to 31-year GE. Specifically, we measured microbial biomass carbon (MBC), easily oxidizable OC (EOC), water-soluble OC (WSOC), and OC in water stable aggregates (macroaggregates [250–2000 μm], microaggregates [53–250 μm], and mineral fraction [< 53 μm]) at 0–20 cm soil depths. The results showed that GE significantly enhanced EOC and WSOC contents in soils, but caused a decline of MBC at the three decade scale. Macroaggregate content (F = 425.8, P < 0.001), OC stored in macroaggregates (F = 84.1, P < 0.001), and the mean weight diameter (MWD) of soil aggregates (F = 371.3, P < 0.001) increased linearly with increasing GE duration. These findings indicate that OC stored in soil increases under three-decade GE with soil organic matter (SOM) stability improving to some extent. Long-term GE practices enhance the formation of soil aggregates through higher SOM input and an exclusion of animal trampling. Therefore, the practice of GE may be further encouraged to realize the soil carbon sequestration potential of semi-arid grasslands, China.

Highlights

Some management practices, such as the promotion of native vegetation growth, sowing of legumes and grasses, and decreasing grazing intensity may enhance soil organic carbon (SOC) storage in grasslands [1,2,3]
The results showed that SOC, easily oxidizable OC (EOC), water-soluble OC (WSOC), and microbial biomass carbon (MBC) significantly differed among the five plots (F = 18.73, P < 0.01 for SOC; F = 5.09, P < 0.05 for MBC; F = 125.61, P < 0.01 for EOC; F = 6.82, P < 0.01 for WSOC) (Table 1)
SOC, EOC, and WSOC linearly increased with increasing Grazing exclusion (GE) duration (Fig 2)

Summary

Introduction

Some management practices, such as the promotion of native vegetation growth, sowing of legumes and grasses, and decreasing grazing intensity may enhance soil organic carbon (SOC) storage in grasslands [1,2,3]. Grazing exclusion (GE) represents as an important approach to improve grasslands in Inner Mongolia, China, and has been widely implemented since 2000. Previous studies have demonstrated that typical grasslands subjected to GE have an enormous capacity to enhance SOC storage at decadal scale [3,4,5,6,7,8], and the stability of newly formed SOC under GE has been explored using soil aggregates [9] and soil particle-size fractions [10]. Soil Organic Carbon Dynamics and Aggregate Stability in Grasslands

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Discussion

Conclusion