Soil organic matter dynamics under different land use in grasslands in Inner Mongolia (northern China)

[摘要] We examined bulk soil properties and molecular biomarker distributions insurface soils from Inner Mongolian grasslands in order to understand theresponses of soil organic matter to different land use. A total of 16 soilswere collected from severely degraded grassland by overgrazing (DG), nativegrassland without apparent anthropogenic disturbance (NG),groundwater-sustaining grassland (GG) and restored grassland from previouspotato cropland (RG). Compared to NG, soil organic carbon content was lowerby 50% in DG, but higher by six-fold in GG and one-fold in RG. Theδ¹³C values of soil organic carbon were–24.2 ± 0.6‰ in DG, –24.9 ± 0.6‰ in NG,–25.1 ± 0.1‰ in RG and –26.2 ± 0.6‰ in GG,reflecting different degradation degrees of soil organic matter or differentwater use efficiencies. The soils in DG contained the lowest abundance ofaliphatic lipids (n-alkanes, n-alkanols, n-alkanoic acids, ω-hydroxylalkanoic acids and α-hydroxyalkanoic acids) and lignin-phenols, suggesting selectiveremoval of these biochemically recalcitrant biomarkers with grasslanddegradation by microbial respiration or wind erosion. Compared to NG, thesoils in GG and RG increased ω-hydroxylalkanoic acids by60–70%, a biomarker for suberin from roots, and increased α-hydroxylalkanoic acids by 10–20%, a biomarker for both cutin andsuberin. Our results demonstrate that the groundwater supply andcultivation–restoration practices in Inner Mongolian grasslands not onlyenhance soil organic carbon sequestration, but also change the proportions ofshoot- versus root-derived carbon in soils. This finding has importantimplications for the global carbon cycle since root-derived aliphatic carbonhas a longer residence time than the aboveground tissue-derived carbon insoils.

[学科分类] 地球化学与岩石