高寒草原土壤有机碳与腐殖质碳变化及其微生物效应

VARIATION OF ORGANIC CARBON AND HUMUS CARBON IN ALPINE STEPPE SOIL AND FUNCTIONS OF MICROORGANISMS THEREIN

基于多区域重复采样,研究了藏北高原不同状态(正常、轻度和严重退化)高寒草原表层(0～10 cm)、亚表层(10～20 cm)土壤有机碳(Soil organic carbon,SOC)、腐殖质碳(Humus carbon,HC)、胡敏酸碳(Humic acid carbon,HAC)和富里酸碳(Fulvic acid carbon,FAC)的变化,以及土壤微生物群落、微生物生物量碳(Microbial biomass carbon,MBC)、纤维素分解酶活性(Cellulolytic enzyme activity,CEA)对其产生的影响与作用。结果表明:高原寒旱环境中土壤的HC/SOC比例过低,但PQ值(HAC/HC)很高。随土层加深,不同状态草地SOC、HC、HAC含量、HC/SOC比例在总体上趋于不同程度的下降,PQ值则均呈一定程度的提高。相对于正常草地,随草地退化加剧,表层SOC、HC(HAC、FAC)增幅分别表现出略呈下降、大幅提高,亚表层降幅则均呈大幅下降。反映到0～20 cm土层,SOC、HC、HAC含量均表现出正常草地>严重退化草地>轻度退化草地,HC/SOC比例、PQ值则分别呈严重退化草地>正常草地>轻度退化草地、正常草地>轻度退化草地>严重退化草地,说明草地退化在促进表层SOC、HC(HAC、FAC)形成与积累的同时,更"激发"了亚表层的矿化,尤其是严重退化草地有机残体的分解过程,但腐殖质品质并未随土壤腐殖化程度的提高而得到相应改善。MBC、CEA与SOC、HC及组分高度一致的土体分布格局影响并决定了上述过程,草地退化有利于真菌、放线菌对土壤、尤其是亚表层土壤有机残体的分解与转化。

Based on repeated sampling in a number of areas, variations of organic carbon （SOC） , humus carbon （HC）, humic acid carbon （HAC） and fulvic acid carbon （FAC） in the surface （0 ～ 10 cm） and sub-surface （ 10 - 20 cm） layers of alpine steppes different in state （normal, slightly degraded and severely degraded） in the Northern Tibetan Plateau as well as influences arid effects of soil microbial community, microbial biomass carbon （MBC） and cellulolytic enzyme activity （CEA） on SOC, HC and HAC. Results show that the soil in cold and acid alpine environment is very low in HC/SOC ratio, but very high in PQ value （HAC/HC）. On the whole, the contents of SOC, HC and HAC and the pro- portion of HC/SOC in steppes different in state declines to a varying extent with soil depth in profile, while PQ value in- creases to a certain extent. Relative to normal steppes, the increase in SOC declines slightly and in HC （HAC, FAC） ri- ses dramatically in the surface soil layer, and both drop drastically in the sub-surface soil layer. In terms of contents of SOC, HC and HAC in the 0 - 20 cm soil layer, a decreasing ordeer of normal steppe 〉 severely degraded steppe 〉 slightly degraded steppe is found, and in terms of HC/SOC ratio and PQ value, a decreasing ordeer of severely degraded steppe 〉 normal steppe 〉 slightly degraded steppe, and of normal steppe 〉 severely degraded steppe 〉 slightly degraded steppe is re- spectively, which means degradation of a steppe promotes formation and accumulation of SOC and HC （ HAC and FAC） in the surface soil layer, and also ＂stimulates＂ mineralization of the sub-surface soil layer, and especially decomposition of organic debris in severely degraded steppes～ However, quality of the humus is not improved correspondingly along with the increasing degree of soil humification. The highly homogenous distribution MBC, CEA, SOC, HC and their components in the soil affects and decides the above-mentioned process. Steppe degradation is conductive to decomposition and transformation of organic debris in the soil by fungus and actinomycetes, especially in the sub-surface soil layer.