Response Of Soil Microbial Nutrients And Metabolism To Water Changes In Grasslands On The Western Slopes Of Helan Mountains

The low frequency of precipitation and low total precipitation in arid zones make grassland soils more sensitive to water changes.Natural precipitation is the main source of soil moisture in arid grassland,and the occurrence of precipitation events will produce a pulse effect and cause an explosive increase in the intensity of soil carbon and nitrogen mineralization,leading to the rapid completion of plant life histories.Currently,under the background of increasing global change,existing climate change models predict that future precipitation patterns will change in terms of both intensity and frequency.Arid areas may experience longer drought and the frequency of precipitation is more difficult to predict accurately,which will have an impact on soil moisture and soil microorganisms.It will also affect the decomposition of organic matter in soil and the transformation of soil nutrients,thus affecting the nutrient cycle of terrestrial ecosystems.In this study,soil samples of temperate steppe,temperate steppe desert,and temperate desert on the western slope of Helan Mountain were collected.By setting different water gradients（25%,30%,40%,and 50%of field water capacity）,laboratory incubation experiments were carried out to simulate the influence process of different precipitation events on soil microbial nutrients and metabolism.To explore the ecological stoichiometric mechanism of soil microbial nutrients and extracellular enzyme activities in response to soil water change,in order to clarify the soil microbial nutrient utilization strategy and the adaptation and evolution mechanism of rich soil microorganisms to the environment in arid areas,so as to provide scientific theoretical support for grassland restoration and productivity improvement in arid areas.The main findings are as follows:1.Soil moisture changes did not significantly affect microbial nutrient carbon（C）:nitrogen（N）:phosphorus（P）content and their stoichiometric ratios,and significantly affected nitrate nitrogen（NO₃^--N）and some soluble organic nutrients[dissolved organic carbon（DOC）,dissolved organic nitrogen（DON）and dissolved organic phosphorus（DOP）]and their stoichiometric ratios,as well as some C:N,C:P and N:P stoichiometric imbalances had a significant effect,while there was no effect on the ammonium nitrogen（NH₄⁺-N）content.The contents of microbial biomass carbon（MBC）,microbial biomass nitrogen（MBN）and microbial biomass phosphorus（MBP）were positively correlated with soil moisture content,and the microbiometric ratio and resource metering ratio fluctuated with the change of water.The above results indicate that there is a strong internal stability of soil microorganisms in the arid zone,but the process of water change caused changes in microbial demand for C,N and P nutrients,and microbial growth was affected by C restriction.2.Soil moisture changes had no significant effect on C-,N-,and P-acquiring enzyme activities and their stoichiometric ratios,and produced significant effects on soil microbial respiration,respiration entropy,nitrification rate and nitrogen mineralization rate in the 0-10 cm soil layer,but not on soil microbial entropy,ammonium rate,and phosphorus mineralization rate,indicating that microorganisms used more C sources for respiration,converted soil organic N mainly to NO₃^--N rather than NH₄⁺-N,and sequestered soil phosphorus.