Study On Influence Factors And Changes In Organic Carbon Fraction Of Grassland Soils At The Southern Foot Of Qilian Mountains In Different Restoration Years

With global climate change and increased disturbances from human activities in recent years,grasslands have become one of the world’s most severely degraded types of terrestrial ecosystems.The high altitude,temperature differences,and radiation on the Qinghai-Tibet Plateau make it a sensitive and fragile feature,and because the region has been affected by human activities(grazing)for a long time as a pastoral area,grasslands are also showing varying degrees of degradation trends.The Qilian Mountains,located on the Tibetan Plateau’s northeastern edge,are not only one of China’s six natural pastures,but also an important water-conserving area in China’s northwest inland arid zone,arching the source of three rivers in the south and preventing the Bataan Tengri Desert in the north,with a very important ecological status.Since 2000,the Chinese government has launched a series of restoration projects to address the threat of grassland degradation,including grazing rest,fallowing,artificial planting and replanting,and various other restoration measures.Fencing(natural sequestration)is one of the most widely promoted restoration projects and is often considered to be one of the most effective practices.This paper takes the restoration of grass on the southern foot of the Qilian Moutains as the researth area,and uses the combination of field experiment and indoor analysis to the main factors affecting the change of soil organic carbon fraction in the study area,including soil water content,soil bulk density,total soil porosity and soil carbon to nitrogen ratio.It is important to establish a scientific and reasonable organic carbon grouping method to understand the changes of soil carbon stock and carbon sequestration mechanism by different organic carbon components.The study of the characteristics and formation of soil components under the ecological restoration model provides a theoretical reference basis for an in-depth understanding of the reconstruction of soil functions after grassland restoration,improving the quality of ecological restoration and improving the soil.The following main conclusions were drawn.(1)With increasing restoration age,the soil capacity gradually decreases and the soil water content gradually decreases;the porosity(Pt)of each site generally tends to increase slightly with increasing restoration age,and this trend is more obvious in the surface layer(0～20 cm).POC/MOC values show a decreasing trend compared to natural grassland,with small POC/MOC values,soil organic carbon is more stable and not easily decomposed and used by organisms;MWD and GMD show a gradually increasing trend,the larger the value,the better the stability of the agglomerates.The carbon to nitrogen ratio of soil sand grains is higher than the carbon to nitrogen ratio of other soil organic carbon fractions,and in general the carbon to nitrogen ratio decreases as the soil grain size becomes smaller.(2)Among the different fractions of soil organic carbon,sand and chalkare the main fractions,and the fraction of organic carbon allocated to clay particles fluctuates in the restored grassland;the organic carbon content of soil sand,coarse chalk and fine chalk is greatest in the surface layer(0～10 cm)of the restored sample site.(3)Soil water content,soil bulk density,soil porosityand soil organic carbon fraction are significantly positively correlated(P<0.05);mean weight diameter and geometric mean diameter are positively correlated;p H and carbon to nitrogen ratio and soil organic carbon fraction are significantly negatively correlated(P<0.05).