Effects Of Simulated Warming And Precipitation Increasing On Soil Carbon Composition And Respiration Of Abandoned Grassland In The Loess Hilly Region

The project of returning farmland to grassland is an important measure for ecological restoration in the Loess Plateau.Exploring the changing characteristics of soil carbon components and respiration of abandoned grasslands under climate change and their interaction with soil extracellular enzymes has important ecological significance for understanding the soil carbon pool components of fragile habitats under the background of climate change.In this study,abandoned grassland for 12 years in the loess hilly region was taken as the research object,and the interaction between climate warming and precipitation increase and their interaction was artificially simulated.The method of combining field detection and indoor analysis was used to analyze the effect of soil carbon composition and soil respiration rate.The response characteristics of warming and precipitation and the process of enzyme activity clarified the direction and extent of the impact of climate change on the soil carbon pool components and soil respiration rate of the abandoned grassland ecosystem in the loess hilly region.The main findings are as follows:(1)Warming has significantly increased the surface temperature of the soil,with an average increase of 1.47°C in 2018 and an average increase of 1.27°C in 2019.The precipitation increasing treatment significantly reduced the soil temperature,with an average decrease of 0.76°C in 2018 and an average decrease of 0.68°C in 2019.In terms of soil moisture,the precipitation increasing significantly increased the soil moisture content,and the soil moisture content of the 50%precipitation increase treatment was the highest,which was0.99%and 2.1%higher than the control in 2018 and 2019,respectively.The interaction of warming and precipitation has no significant influence on soil temperature and moisture content.(2)50%precipitation increase significantly increases soil organic carbon,while warming reduces soil organic carbon content.Warming and precipitation increase 50%have an antagonistic interaction with organic carbon content,of which 50%precipitation increase is the main regulation factor.There is no significant difference between soil total nitrogen and phosphorus between different treatments.In 2019,the soil C:N and C:P of the 50%precipitation increase treatment were significantly higher than other treatments,and the N:P change was not significant.In terms of available nutrients,both temperature increase and precipitation increase increase the content of dissolved organic carbon,of which 50%increase in precipitation has a significant impact.(3)Warming significantly increased the content of soil microbial biomass carbon and phosphorus,and precipitation increasing significantly the content of microbial biomass phosphorus.Warming and increased precipitation played a synergistic role in the process of affecting soil microbial biomass carbon and phosphorus..In terms of soil carbon components,50%precipitation increase significantly increases the content of easily oxidized organic carbon in the soil,and the synergistic interaction of warming and precipitation increasing promotes a substantial increase in easily oxidizable organic carbon.Warming increases the content of recalcitrant organic carbon,while precipitation increases the content of labile organic carbon.The interaction of the two has no significant effect on active and inert organic carbon.(4)The main environmental factor affecting soil respiration in this area is soil moisture content.Due to the abundant precipitation in the growing season in 2019,the soil respiration rate has increased by 2.2 times compared with the same period in 2018.This includes the effect of rain-induced dry and wet alternation on soil respiration.The effect of warming on soil respiration mainly depends on the current season's precipitation and temperature.Seasonal warming with abundant rainfall has a very significant promotion effect on soil respiration.Warming at winter also significantly increases the soil respiration rate.Warming reduces the temperature sensitivity of soil respiration(Q₁₀),while increasing precipitation increases Q₁₀.Linear regression analysis showed that soil easily oxidizable organic carbon,labile organic carbon,and total soil organic carbon were all significantly positively correlated with soil respiration rate,indicating that the increase in available carbon sources for soil microorganisms would significantly increase soil respiration rate.(5)Changes in soil hydrothermal environment will significantly affect the activity of soil extracellular carbon degrading enzymes.In terms of hydrolytic enzymes,warming and precipitation and the interaction of the two significantly reduce soil BG and CBH enzyme activities.Among them,precipitation increasing has a stronger negative impact on soil BG and CBH enzyme activities.Warming and precipitation increasing have a synergistic inhibitory effect on BG and CBH enzyme activities.Contrary to the above two cellulase activities,increase Temperature significantly increases the key enzyme activity of soil hemicellulase(BX),and the effect of warming and increasing rainfall on BX enzyme activity is mainly caused by the positive effect of warming.In terms of oxidase,warming significantly increased soil oxidase activity,and the rain enhancement treatment in 2019 significantly reduced soil PER and PPO enzyme activities.The results of correlation analysis between soil carbon pool and soil enzyme activity show that the content of soil carbon components and soil enzyme activity have a close mutual regulation relationship.Redundancy analysis and variance decomposition analysis show that soil physical and chemical properties,biological properties are highly correlated with changes in soil respiration rate and enzyme activity.In summary,the climate prediction of abandoned grassland tending to warm and wet in the loess hilly region will accelerate soil carbon emissions in the region.Soil carbon sequestration mainly depends on the ratio of water and heat.The future climate change dominated by temperature rise will change the structure of the soil carbon pool in the region,and the distribution relationship between activated carbon and inert carbon will further change,and this change may not be conducive to carbon sequestration.In addition,soil enzyme activity can be used as an effective indicator for in-depth understanding of changes in soil carbon pools.