西藏退化高寒草原土壤团聚体有机碳的变化特征

Characteristics of Soil Aggregates Organic Carbon in Degraded Alpine Steppes in Tibet

为进一步了解高寒草原土壤碳动态变化特点与变化过程,采用湿筛法对藏北高原未退化、轻度退化和严重退化高寒草原表层(0~10 cm)、亚表层(>10~20 cm)不同粒级w(SAOC)(SAOC为土壤团聚体有机碳)进行研究.结果表明,与未退化草地相比,不同程度退化草地w(SAOC)均呈下降趋势,但严重退化草地表层、亚表层中w(SAOC)、>0.25 mm粒级w(SAOC)、<0.25 mm粒级w(SAOC)降幅均显著低于轻度退化草地;不同程度退化草地表层、亚表层中>0.25、<0.25 mm粒级w(SAOC)在总体上趋于下降,且亚表层的降幅明显高于表层的降幅,但退化草地亚表层中w(SAOC)仍高于表层(未退化草地、轻度和严重退化草地亚表层较表层分别增加51.84%、31.34%、6.83%),w(SAOC)的土层差异随草地退化加剧而大幅缩小;轻度、严重退化草地不同粒级w(SAOC)的土层分布特征仍与未退化草地一致,其表层、亚表层中>0.25 mm粒级w(SAOC)均明显较高;与未退化草地相同,退化草地表层、亚表层w(SAOC)贡献率亦均呈|2~0.25 mm|>|<0.25~0.053 mm|>|>2 mm|>|<0.053 mm|粒级;退化草地环境对团聚体与w(SAOC),以及w(SOC)(SOC为土壤有机碳)与w(SAOC)间的关系具有重要影响.研究显示,高原冷干环境下不同粒级SAOC及其变化受草地退化程度、土层深度等的深刻影响,需要从影响土壤有机碳形成与转化的土壤机制等方面进行深入研究.

Alpine steppe is the most important steppe ecosystem in Tibetan Plateau.Important problems in alpine steppes degrading process are explored,including soil aggregates organic carbons(SAOC)change characteristics,change process,etc.,which has important significance for further predicting soil carbon dynamic change trend,and seeks the theory and method for restoring and reconstructing degraded alpine steppe ecosystem.Wet screening method is adopted for studying surface(0-10 cm)and subsurface(>10-20 cm)soil in light degraded and severely degraded alpine steppe in the south of Northern Tibet Plateau.It is obvious that SAOC in dry and wet plateau environment with different grades and changes thereof are deeply affected by steppe degradation degree,soil depth,etc.It is embodied in the following aspects:(1)The SAOC content decreases in the steppes in different degraded degrees,but the SAOC content,and macroaggregates(>0.25 mm)and microaggregates(<0.25 mm)SAOC content in surface and subsurface layers in seriously degraded steppe are higher than that of the light degraded steppe.This may be related to the decomposition and transfer ability of microbes to the soil organic residual bodies,which plays an important role in the stability of soil ecological system with the microbes′adaptation to gradually deteriorative soil environment.(2)In the cold and draught environment of the alpine steppes,both macroaggregates(>0.25 mm)and microaggregates(<0.25 mm)SAOC contents degrease in surface and subsurface layers in the steppes in different seriously degraded degrees as a whole,where the degree of reduction in subsurface layer is obviously higher than that the surface layer.However,the SAOC content in the subsurface layer is still higher than that of the surface layer.The SAOC contents increase by 51.84%,31.34%and 6.83%respectively in the subsurface layer of non-degraded steppe,light and seriously degraded steppes,and the difference of SAOC in soil layers is significantly lessened with steppe degeneration intensified.(3)In the cold and draught environment of the alpine steppes,the SAOC distribution characteristics in different size fractions in light and seriously degraded steppes are still consistent with that of the non-degraded steppe;the macroaggregates SAOC content is significantly higher than the microaggregates SAOC in their surface and subsurface layers.(4)Similar to non-degraded steppes,the degraded surface and subsurface layers show the SAOC contribution rate decreases dramatically at the size fractions of 2-0.25,<0.25-0.053,>2 and<0.053 mm successively.The size fractions at 2-0.25 and<0.25-0.053 mm determine the SAOC contribution rates at the size fractions of>0.25 and<0.25 mm.(5)The degraded steppe environment has an important effect on the relation between aggregates and SAOC as well as soil organic carbons(SOC)and SAOC.