Effects Of Rainfall Variation On Organic Carbon Formation In Stipa Breviflora Shrub Desert Steppe

Rainfall variability is an important component of global climate change,which will significantly affect terrestrial ecosystem function and regional soil organic carbon pools.As water is a major limiting factor in shrub desert grassland ecosystems,it is necessary to investigate the mechanisms of rainfall variability on soil organic carbon formation in shrub grassland.In this study,four rainfall gradients(natural rainfall(CK),30% decrease in rainfall,30% increase in rainfall and 50% increase in rainfall)were set up by anthropogenic control.The distribution characteristics of organic carbon,lignin phenols and amino sugars in soil of scrub patches and herbaceous matrix were analyzed by biomarker analysis technique to elucidate the contribution of plant-derived carbon and microbial residual carbon to the formation of soil organic carbon(SOC)in Stipa breviflora shrub desert steppe under different rainfall,by analyzing the distribution characteristics of soil organic carbon,lignin phenols and amino sugars in shrub patch and herbaceous matrix.Through analyzing the relationship between plant community structure characteristics and soil physical and chemical properties with the content of soil organic carbon,lignin phenols and amino sugars,we revealed the factors affecting the changes in organic carbon from plant and microbial sources,and explored the influence and underlying mechanisms of rainfall changes on soil organic carbon composition in Stipa breviflora shrub desert steppe.The results can provide data support for the accurate assessment of soil carbon pools in shrub grasslands,and also be able to provide theoretical guidance for adaptive management of shrub grassland in response to global change.The main findings of the study were as follows:(1)The cover and species number of shrub patches and herbaceous matrix increased with the increase of rainfall.Under the same treatment,the cover of shrub patches was higher and the number of species was smaller than that of herbaceous matrix.The importance value of shrubs and perennial bunch grasses decreased with increasing rainfall,while that of semi-shrubs and annual and biennial herbs tended to increase with rainfall.Both increased and decreased rainfall increased the importance value of perennial forbs.(2)Increasing or decreasing rainfall increased the SOC content in the shrub nebkhas,but increasing rainfall only increased the SOC content in the 0-30 cm soil layer below the nebkhas.The SOC content in the nebkhas was higher than under nebkhas and herbaceous matrix in all rainfall treatments,and tended to decrease with increasing soil layer.(3)The increase of rainfall by 50% significantly increased the total amount of soil lignin in the nebkhas and under the nebkhas,and the contents of vanilla,syringyl and cinnamon phenolic monomers and the ratio of total lignin to total organic carbon in soil also showed the same characteristics,which indicated that the increase of rainfall by 50% promoted the contribution of plant derived carbon in shrub patches to total organic carbon in soil,while the increase of rainfall had no significant effect on the contribution of plant derived carbon in herb matrix.Under each rainfall treatment,the contribution of plant derived carbon in nebkhas was higher than that under nebkhas and herb matrix.The contribution of plant derived carbon to soil total organic carbon in different rainfall treatments and different matrix decreased with the increase of soil depth.(4)The total amount of soil amino sugar in the nebkhas,under the nebkhas and herbaceous matrix increased with the increase of rainfall,and the decrease of rainfall had no significant effect on the total amount of soil amino sugar,but had a certain decreasing trend.The ratio of soil total amino sugar/soil total organic carbon content(TAS/SOC)in and under nebkhas increased with the increase of rainfall,and the soil TAS/SOC increased with the increase and decrease of rainfall in herb matrix.The ratio of glucosamine content to cell wall acid content(Glu N/Mur A)in shrub nebkhas and 0-20 cm soil layer under nebkhas and of herb matrix increased with the increase of rainfall.These results indicated that increasing rainfall enhanced the contribution of microbial residue carbon to soil organic carbon,especially the contribution of fungal residue.The total amount of soil amino sugar in nebkhas was higher than that under nebkhas and herb matrix under the treatment of rainfall reduction,and the total amount of soil amino sugar in nebkhas was lower than that in herb matrix.The total amount of soil amino sugar in both nebkhas and herb matrix decreased with the increase of soil depth,and the TAS/SOC also showed similar variation characteristics.These results indicated that the contribution of microbial residual carbon to soil organic carbon showed a trend that the contribution in nebkhas was higher than that under nebkhas and of herb matrix,and decreased with the increase of soil depth in herb matrix.(5)Rainfall variation contributed the accumulation of microbial residual carbon to soil organic carbon by influencing soil temperature,and promoted the accumulation of microbial residual carbon and plant derived carbon in soil by influencing community cover.The contribution of plant derived carbon to soil organic carbon was greater than that of microbial residue carbon under different rainfall treatments.