复杂地形条件下根系对土壤有机碳的贡献

Contribution of Root Biomass to Soil Organic Carbon Under Complex Landforms Conditions

在地形条件复杂的地区,量化根系对土壤有机碳的贡献对科学评价水土流失区的土壤碳储量具有重要意义.本研究在黄土高原丘陵沟壑区的砖窑沟小流域内,基于地貌类型(梁峁坡、沟坡和沟谷)和植被措施(农田、林地和草地措施)两大因素采集土壤和根系样品,在流域尺度上研究根系密度(FRD)对土壤有机碳密度(SOCD)的贡献.在砖窑沟小流域内,地形、植被措施和土层厚度及其交互作用显著影响SOCD和FRD的空间分布. SOCD和FRD在不同地形部位下均呈现出沟谷>沟坡>梁峁坡的趋势,在不同植被措施下均呈现出林地措施>草地措施>农田措施的趋势,在不同土层厚度上均呈现出表层(0～20 cm)大于下层(20～100 cm)的趋势.此外,FRD对SOCD的影响显著(P <0. 05),SOCD随着FRD增加呈现出对数增加的趋势,且不同地形和植被措施下的根系-碳转化效率差异显著(P <0. 05).在农田措施下,沟谷(0. 87)的根系-碳转化效率均是沟坡(0. 43)和梁峁坡(0. 43)的2. 0倍;在草地措施下,沟坡(0. 57)的根系-碳转化效率分别是沟谷(0. 45)和梁峁坡(0. 27)的1. 3倍和2. 1倍;在林地措施下,梁峁坡(0. 56)的根系-碳转化效率是沟坡(0. 44)的1. 3倍.因此,在砖窑沟小流域内,从增加根系-碳转化效率的角度而言,沟谷适合进行农业生产,沟坡适宜进行退耕还草,而梁峁坡适合进行退耕还林.

Quantifying the contribution of fine root density( FRD) to soil organic carbon density( SOCD) under extremely complex landforms is of great significance for the evaluation of carbon storage at an eroded small catchment in hilly regions of the Loess Plateau.Soil and root samples were collected from typical landforms( a ridge slope,gully slope,and valley bottom) and different vegetation types( cropland,grassland,and woodland) to investigate the contribution of FRD to SOCD at the Zhuan Yaogou watershed The spatial distribution of SOCD and FRD was influenced significantly by landforms,vegetation type,soil depth,or their interactions. SOCD and FRD tended to go in the following order: valley bottom > gully slope > ridge slope on different landforms,Woodland > grassland >cropland on different types of vegetation,and surface > lower depths at different soil depths. Additionally,FRD had a significant effect on SOCD( P < 0. 05),SOCD increased logarithmically with FRD,and there was a significant difference in root-carbon conversion efficiency between different landforms and types of vegetation( P < 0. 05). The root-carbon conversion efficiency on the valley bottom( 0. 87) was 2. 0 times higher than those on ridge slopes( 0. 43) and gully slopes( 0. 43) on cropland;the root-carbon conversion efficiency on gully slopes( 0. 57) were 1. 3 and 2. 1 times greater than those in valley bottoms( 0. 45) and ridge slopes( 0. 27),respectively,on grassland;and the root-carbon conversion efficiency on ridge slopes( 0. 56) was 1. 3 times greater than that on gully slopes( 0. 44). Therefore,from the perspective of increasing root-carbon conversion efficiency at the Zhuan Yaogou watershed in the hilly region of the Loess Plateau,valley bottoms are suitable for agriculture,gully slopes are suitable for returning farmland to grassland,and ridge slopes are suitable for returning farmland to woodland.