西藏高寒草原土壤团聚体有机碳变化及其影响因素分析

土壤结构的维持和稳定对高寒草原生态系统的稳定具有重要意义。为了探明高寒草原土壤结构的变化过程,研究了藏北正常、轻度和严重退化高寒草原表层(0～10cm)、亚表层(>10～20cm)不同粒径土壤团聚体有机碳(soil aggregates organic carbon,SAOC)的变化及对土壤结构的影响。结果表明:1)正常草地不同土层相同粒径团聚体有机碳质量分数均无显著差异,退化草地相同粒径SAOC质量分数随土层加深则呈显著提高的趋势;除轻度退化草地表层,不同状态草地各土层微团聚体(<0.25mm)有机碳质量分数显著高于大团聚体(>0.25mm)有机碳。2)退化草地表层、亚表层SAOC质量分数均呈显著下降,降幅随草地退化加剧却有所降低。但与轻度退化草地相比,严重退化草地表层大团聚体、微团聚体有机碳损失量分别增、减2.87、2.90g/kg,亚表层损失量则分别减少1.40、0.34g/kg,由于大团聚体有机碳损失量较大,其土壤抗蚀能力低于轻度退化草地。3)高原寒旱环境中,SAOC质量分数随SOC质量分数、土壤含水率的增加分别呈极显著(p<0.01)提高、显著(p<0.05)下降的趋势,土壤温度、土壤容重对SAOC质量分数的影响则均不显著。该文可为进一步探寻高寒草原生态系统维持与稳定的理论和方法提供参考。

Soil aggregates organic carbon change and its influence in Tibetan alpine steppe

Abstract: The alpine steppes, mainly distributed in cold and drought terrains in the Northern Tibetan Plateau at over 4,500 meters above mean sea level, is a grassland ecosystem with the largest area, most important ecological state, and most characteristic soil-forming process. In recent decades, its natural degenerative process of the steppe is taking a turn for the worse due to desertification. Thus, it is of great significance to explore the changing process of soil aggregates organic carbon (SAOC) and its impacts on soil structure, and to seek methods for maintenance and stability of soil structure in the alpine steppe. Three alpine steppes were selected randomly as research areas in this study, and each research area was spaced at 50-100 kilometers, and included three sampling areas, namely, normal steppe (vegetation coverage of 45%-65% and light surface layer desertification), light degraded steppe (vegetation coverage>20%-<45%, and significant surface layer desertification), and severely degraded steppe (vegetation coverage<20% and severe surface layer desertification). Three sampling micro-areas were set randomly in each sampling area, and each micro-area contained three sampling points. The soil samples were collected separately by surface layer (0-10 cm) and the subsurface layer (10-20 cm) at each sampling point. Three samples at the same layers in the same micro-area made up one mixing soil sample (the undisturbed sample was hard to collect because the tested soil was sandy soil). The mass fraction of soil aggregates in a different particle size was tested by the wet screening; the soil organic carbon (SOC) and soil aggregates organic carbon (SAOC) were determined by the potassium dichromate volumetric method - external heating method. The results show as follows: 1) The mass fraction is not significant for SAOC in the same grain diameter in different soil layers of the normal steppe, and the mass fractions for SAOC in the same grain diameter for the degraded steppe present an obvious increase with soil layer deepening. Except light degraded steppe surface layer, the mass fraction for organic carbon of microaggregates (<0.25 mm) is greater than that of macroaggregates (>0.25 mm) in different soil layers in different states of steppes. 2) The SAOC change for alpine steppe is special, and mainly shows SAOC mass fractions go down at 0-10 cm and 10-20 cm soil layers in the degraded steppe, but its decreasing amplitude becomes low with the aggravation of the grassland degradation. 3) Compared with the light degraded steppe, the loss of macroaggregates organic carbon increases by 2.87 g/kg, and the loss of microaggregates organic carbon decreases by 2.90 g/kg in the severely degraded steppe surface layer; the losses of macroaggregates and microaggregates organic carbon reduce by 1.40 and 0.34 g/kg respectively in the subsurface layer. It is seen obviously that the soil anti-corrosion in the severely degraded steppe is lower than that of the light degraded steppe, and soil environment in a severely degraded steppe becomes more unstable because of the bigger loss of its macroaggregates organic carbon. 4) The SOC mass fraction is extremely significant (p<0.01) and has a positive correlation with that of SAOC in different particle sizes; soil moisture content shows significant (p<0.05) and has a negative correlation with the mass fraction of SAOC in different particle sizes; and the volume weight and temperature of soil have a very slight impact on SAOC.