灌丛化对干旱区草地土壤有机碳化学结构和热稳定性的影响

土壤有机碳(soil organic carbon,SOC)的稳定性是指其抵抗微生物降解的能力,它决定着C循环和周转。灌丛化是指灌木的盖度、密度和生物量在草地中显著增加的现象,这种现象在干旱区尤为普遍。研究灌丛化对草地SOC稳定性的影响对于理解全球C循环、气候变化及其两者之间相互作用有着重要的意义。本研究在典型的干旱区新疆,选取沿海拔分布的4类草地,使用固态_¹³C核磁共振技术与热分析技术间接而又完整地揭示灌丛化对草地SOC稳定性的影响。结果表明：灌丛间的芳香碳的比例沿海拔从温性荒漠到山地草甸逐渐降低。在温性荒漠、温性草原化荒漠、温性荒漠草原和山地草甸,烷基C/烷氧C的比值分别增加了0.07、0.12、0.03、0.20。低海拔的温性荒漠和温性草原化荒漠的指标热易分解的SOC质量(较低温度下分解的SOC)与SOC总质量的比值(%Exo₁)、SOC分解一半时的温度(TG-T₅₀)和SOC在能量释放一半时对应的温度(DSC-T₅₀)显著低于高海拔的温性荒漠草原和山地草甸。在草原化荒漠、荒漠草原和山地草甸中,灌丛下的%Exo₁和DSC-T₅₀均高于灌丛间,而TG-T₅₀低于灌丛间。在温性荒漠,从灌丛间到灌丛下,低温时SOC燃烧释放出的能量占总燃烧能量(Q)的比例的减小而高温时SOC燃烧释放出的能量增加。本研究结果表明灌丛化增加了干旱区SOC化学结构的稳定性和热稳定性。

Effects of Woody Proliferation on Chemical Structure and Thermal Stability of Soil Organic Carbon in Arid Grasslands

The stability of soil organic carbon (SOC) refers to its ability to resist microbial degradation, which determines the C cycle and turnover. Shrubbery refers to the significant increase of shrub coverage, density and biomass in grassland, which is particularly common in arid grassland. The study of the impact of shrub on grassland SOC stability is of great significance for the study of global C cycle, climate change and the interaction between them.In this study, four types of grassland distributed along the altitude were selected in the typical arid area of Xinjiang, and the effects of shrub on the stability of grassland SOC were revealed indirectly and completely by using solid-state 13C nuclear magnetic resonance technology and thermal analysis technology. The results showed that the proportion of aromatic carbon among shrubs decreased gradually from temperate desert to mountain meadow along the altitude. In temperate desert, temperate grassland desertification, temperate desert grassland and mountain meadow, the alkyl C/O-alkyl C value increased by 0.07, 0.12, 0.03 and 0.20 respectively. The index of low altitude temperate desert and temperate grassland desertification, the ratio of the mass of SOC easily decomposed by heat (SOC decomposed at lower temperature) to the total mass of SOC (% Exo₁), the temperature at half of SOC decomposition (TG-T₅₀) and the corresponding temperature at half of SOC energy release (DSC-T₅₀) are significantly lower than those of high altitude temperate desert grassland and mountain meadow. In grassland desertification, desert grassland and mountain meadow, the% Exo₁ and DSC-T₅₀ under shrub were higher than those between shrubs, while TG-T₅₀ was lower than that between shrubs. In temperate desert, from shrub to shrub, the proportion of energy released by SOC combustion in total combustion energy (Q) decreases at low temperature, while the energy released by SOC combustion increases at high temperature.The results showed that shrub increased the stability of SOC chemical structure and thermal stability in arid area.