Effects Of A Precipitation Gradient On Soil Respiration And Soil Organic Carbon In An Alpine Meadow Of Qinghai-Tibetan Plateau

The global precipitation pattern is undergoing significant changes,which have an important impact on the carbon cycle of terrestrial ecosystems.However,we still lack in-depth understanding of the response and mechanism of soil carbon cycle processes to the precipitation gradient.In this study,the alpine meadow on the Qinghai-Tibet Plateau was taken as the research object,and the precipitation manipulation experiment was carried out.Six levels of precipitation change(1/12 times(1/12P),1/4 times(1/4P),1/2 times(1/2P),3/4 times(3/4P),1 time(P)and 5/4 times(5/4P)of the actual precipitation in the growing season of the year)were set to explore the effects of precipitation change on soil physical and chemical properties,soil respiration and its components,soil organic carbon and its fractions in the alpine meadow on the Qinghai-Tibet Plateau.The response mechanism of soil respiration and its components and the driving factors of soil organic carbon and its fractions under the precipitation gradient were revealed.Therefore,the findings could provide data support for accurately assessing the soil carbon cycle of the alpine meadow ecosystem on the Qinghai-Tibet Plateau,and provide theoretical guidance for the adaptive management of the alpine meadow on the Qinghai-Tibet Plateau for future precipitation pattern changes.The main results are as follows:(1)With the increase of precipitation amount,the aboveground biomass and standing litter biomass did not change significantly,but the aboveground litter biomass tended to decrease.Soil temperature decreased with the precipitation gradient,but did not change significantly.Drought significantly reduced soil water content in 040 cm soil layer and soil total nitrogen in 40-60 cm soil layer.And drought significantly increased the underground biomass of 20-60 cm soil layer.The content of free iron oxide and free alumina was the highest in 20-40 cm soil layer,but it was not affected by precipitation change.Only 1/12P treatment significantly increased iron-bound carbon in 40-60 cm soil layer by 153.6%.(2)There was a nonlinear response between soil respiration and precipitation amount,which showed that soil respiration increased first and then decreased with the increase of precipitation,and reached the maximum in 1/2P treatment.The autotrophic respiration rate increased significantly under 1/4P treatment and 1/2P treatment.The structural equation model showed that precipitation change indirectly affected autotrophic respiration by regulating soil water content,and there was a negative correlation between them,while aboveground biomass had a direct effect on heterotrophic respiration,and there was a positive correlation between them.(3)Soil total organic carbon(SOC)decreased with soil depth,and microbial biomass carbon(MBC)and dissolved organic carbon(DOC)also showed the same patterns.precipitation change did not significantly affect SOC,MBC and DOC in the 0-40 cm soil layer.However,1/4P,1/2P and 5/4P treatments significantly inhibited SOC in the 40-60 cm soil layer.1/12P treatment significantly increased MBC but inhibited DOC accumulation.Soil water content,soil total nitrogen,underground biomass,MBC and DOC were significantly positively correlated with SOC.(4)Further analysis of different fractions of SOC showed that drought inhibited particulate organic carbon(POC)in the 0-20 cm soil layer,but increased POC in the 20-60 cm soil layer.Unlike POC,drought reduced mineral-associated organic carbon(MAOC)in the whole soil profile.Soil water content,MBC,DOC and underground biomass were significantly and positively correlated with POC and MAOC.Except for free alumina,free iron oxide,iron-bound carbon and calcium-bound carbon were significantly positively correlated with POC and MAOC.Random forest results showed that POC was mainly regulated by underground biomass,while MAOC was mainly modulated by MBC.In summary,the effect of precipitation gradient on soil respiration is mainly related to the change of autotrophic respiration,and precipitation gradient directly or indirectly affects soil respiration components by changing aboveground biomass and soil water content.Although precipitation change did not significantly affect soil total organic carbon,microbial biomass carbon and dissolved organic carbon in the 0-40 cm soil layer,drought significantly inhibited the accumulation of total organic carbon in the 40-60 cm soil layer by reducing particulate organic carbon and mineralassociated organic carbon.The results of this study indicate that changes in deep soil organic carbon should be considered when exploring the feedback between soil carbon and precipitation changes.