Long-Term Grazing Exclusion Improves the Composition and Stability of Soil Organic Matter in Inner Mongolian Grasslands

Abstract

Alteration of the composition of soil organic matter (SOM) in Inner Mongolian grassland soils associated with the duration of grazing exclusion (GE) has been considered an important index for evaluating the restoring effects of GE practice. By using five plots from a grassland succession series from free grazing to 31-year GE, we measured the content of soil organic carbon (SOC), humic acid carbon (HAC), fulvic acid carbon (FAC), humin carbon (HUC), and humic acid structure to evaluate the changes in SOM composition. The results showed that SOC, HUC, and the ratios of HAC/FAC and HAC/extractable humus carbon (C) increased significantly with prolonged GE duration, and their relationships can be well fitted by positive exponential equations, except for FAC. In contrast, the HAC content increased logarithmically with prolonged GE duration. Long-term GE enhanced the content of SOC and soil humification, which was obvious after more than 10 years of GE. Solid-state 13C nuclear magnetic resonance spectroscopy showed that the ratios of alkyl C/O-alkyl C first decreased, and then remained stable with prolonged GE. Alternately, the ratios of aromaticity and hydrophobicity first increased, and then were maintained at relatively stable levels. Thus, a decade of GE improved the composition and structure of SOM in semiarid grassland soil and made it more stable. These findings provide new evidence to support the positive effects of long-term GE on soil SOC sequestration in the Inner Mongolian grasslands, in view of the improvement of SOM structure and stability.

Effect of Grazing Exclusion on Vegetation Characteristics and Soil Organic Carbon of Leymus chinensis Grassland in Northern China

“…Grazing exclusion has been reported to be an effective practice to restore degraded grassland, as vegetation characteristics and soil properties have been shown to improve under long-term grazing exclusion [26,27]. In this study, we selected the biomass, cover, richness, DS, and SHDI to examine the effect of long-term grazing exclusion on vegetation characteristics.…”

A Molecular Investigation of Soil Organic Carbon Composition across a Subalpine Catchment

“…Then, 200 µL of solution was drop-deposited onto a crystal quartz sample holder and air-dried. Soil samples were loaded into the diffractometer with the X-ray generator set to 40 We developed a method that combines FT-IR and bulk C XAS results to quantify SOC functional group abundance (the SOC-fga method) using the Beer-Lambert Law:…”

“…Both the consumption (removal) of plant materials and the input of cattle excrement may further influence the composition of SOC entering the soil at these sites [39][40][41]. For example, Wang et al [40] reported that the content of aromatic C increased while O-alkyl C (polysaccharide) decreased after 4 years of grazing exclusion in inner Mongolian grasslands. Although we did not quantify cattle grazing pressure, BC is consistently under higher grazing pressure than RCM and RCF based on our field observations.…”

Latitudinal patterns and influencing factors of soil humic carbon fractions from tropical to temperate forests

“…Soils were immediately passed through a 2-mm sieve to remove visible roots, gravel, and stones. Soil samples that were used to determine humic carbon fractions and texture were air-dried, while other subsamples that were used to determine soil microbe were stored at 4ºC, following an established protocol (Wang et al, 2015).…”

“…As one of the most important fractions of SOM, soil humus has many important functions, such as the slow release of plant nutrients, cation exchange, pH buffering, and interactions with micronutrients, toxic metal ions, and xenobiotic organic molecules (Fabbri et al, 1996;Brunetti et al, 2007). Some studies, using a variety of techniques, have compared soil humus between different ecosystems (Watanabe et al, 2001) and investigated the effects of land-use changes (or management types) on the soil humic fraction (Yang et al, 2004;Wang et al, 2015). Martin et al (1998) investigated changes in soil humic fractions with altitude, and found that the fractions increased with increasing altitude.…”