Carbon storage capacity of semi‐arid grassland soils and sequestration potentials in northern China

Abstract

Organic carbon (OC) sequestration in degraded semi-arid environments by improved soil management is assumed to contribute substantially to climate change mitigation. However, information about the soil organic carbon (SOC) sequestration potential in steppe soils and their current saturation status remains unknown. In this study, we estimated the OC storage capacity of semi-arid grassland soils on the basis of remote, natural steppe fragments in northern China. Based on the maximum OC saturation of silt and clay particles <20 μm, OC sequestration potentials of degraded steppe soils (grazing land, arable land, eroded areas) were estimated. The analysis of natural grassland soils revealed a strong linear regression between the proportion of the fine fraction and its OC content, confirming the importance of silt and clay particles for OC stabilization in steppe soils. This relationship was similar to derived regressions in temperate and tropical soils but on a lower level, probably due to a lower C input and different clay mineralogy. In relation to the estimated OC storage capacity, degraded steppe soils showed a high OC saturation of 78-85% despite massive SOC losses due to unsustainable land use. As a result, the potential of degraded grassland soils to sequester additional OC was generally low. This can be related to a relatively high contribution of labile SOC, which is preferentially lost in the course of soil degradation. Moreover, wind erosion leads to substantial loss of silt and clay particles and consequently results in a direct loss of the ability to stabilize additional OC. Our findings indicate that the SOC loss in semi-arid environments induced by intensive land use is largely irreversible. Observed SOC increases after improved land management mainly result in an accumulation of labile SOC prone to land use/climate changes and therefore cannot be regarded as contribution to long-term OC sequestration.

Rebuilding soil carbon in degraded steppe soils of Eastern Europe: The importance of windbreaks and improved cropland management

“…The SOC decrease in cultivated soils was not accompanied by a loss of the fine fraction induced by erosion, indicated by similar fine fraction contents in cropland and natural grassland soils (Table ). Under semiarid conditions, cultivated steppe soils of Northern China revealed a substantial loss of the fine fraction by wind erosion, which resulted in a substantially lower potential for C sequestration despite strong SOC losses (Steffens, Kölbl, & Kögel‐Knabner, ; Wiesmeier et al, ; Wiesmeier, Munro, et al, ). As long‐term cultivation did not affect soil texture of the investigated sites, the observed decline of fine fraction OC is associated with a relatively low mean SOC saturation of 49% in cropland soils.…”

“…Topsoil samples (0–10 cm) were fractionated into free particulate organic matter (fPOM), aggregate‐occluded POM (oPOM), coarse mineral‐associated organic matter (MOM >20 μm), and fine mineral‐associated organic matter (MOM <20 μm), referred to as the fine fraction. Details on the fractionation approach can be found in Wiesmeier, Munro, et al (). The OC concentrations of fractions were measured using a VarioMax CNS elemental analyzer (Elementar, Hanau, Germany) and an EA3000 CN analyzer (Hekatech, Wegberg, Germany) for oPOM with limited amount of material.…”

SOC storage and potential of grasslands from 2000 to 2012 in central and eastern Inner Mongolia, China

“…The results indicated that the SOC storage in 2000-2012 tended to increase in general. The results of other studies have also showed that climate change would affect SOC storage at large scale , and the SOC loss in semi-arid environments induced by intensive land use was largely irreversible (Wiesmeier et al, 2015). Therefore, the mechanism of effects of long-term climate change on soil carbon accumulation in grasslands is still worthy of attention.…”

Reviewing our options: Managing water‐limited soils for conservation and restoration

“…Grazing exclusion therefore significantly enhances SOM storage, particularly in the topsoil (Wiesmeier, Kreyling, et al, ; Yong‐Zhong, Yu‐Lin, Jian‐Yuan, & Wen‐Zhi, ). However, grazing exclusion predominately results in enrichment of labile POM whereas more stable silt and clay fractions are close to C saturation, even in degraded soils (Steffens et al, ; Wiesmeier et al, ).…”