Study On The Ecostoichiometric Characteristics Of Litter-soilmicrobes And Their Relationships At Different Elevations In Helan Mountains

Mountain ecosystem is an important biodiversity center and ecological functional area of terrestrial ecosystems,and its altitudinal gradient effects are exceptionally sensitive to global climate change.To this end,based on the ecological chemometrics theory,this study was conducted in five vegetation types:desert steppe(HMCY),shallow mountain scrub(QSGC),Pinus tabuliformis forest(YSL),Picea crassifolia forest(QHYS),and subalpine scrub(YGSGC)at different altitudes(1350-2600 m)in the Helan Mountains of Ningxia to analyze the variation of ecostoichiometric characteristics of C,N,and P in litter,soil,and soil microbes along the altitude,and the relationship between each of the two components.Our results can provide a reference basis for the study of nutrient cycling in mountain ecosystems.The main results of the study are as follows.1.With increasing elevation,litter C content,litter C/N,N/P,C/P ratios showed a trend of first increasing and then decreasing,while litter N and P content showed a trend of first decreasing and then increasing.The C content of litter at different elevations was highest in shallow mountain scrub(1815m),N content in desert grassland(1350 m)and P content in Picea crassifolia forest(2450 m),all peaking at middle and low elevations,which were favorable to the accumulation of litter nutrients;litter C/N,C/P and N/P ratios were generally low,the decomposition rate of litter was faster,and the decomposition of litter was mainly limited by N and P elements.2.With increasing elevation,soil organic carbon(SOC),total nitrogen(TN)content,TN/TP and SOC/TP ratio showed a gradually increasing trend,soil total phosphorus(TP)content showed a trend of first increasing and then decreasing,and SOC/TN ratio as a whole showed a gradually decreasing trend.The content of SOC,TN and TP decreased with increasing soil depth,and SOC/TN and TN/TP ratios were low,while SOC/TP ratio was high,indicating that soil nutrients in this study area have an obvious "surface aggregation" and nutrients are easily limited by N and P elements.Elevation significantly affected soil ecological stoichiometry and chemical properties;mean annual temperature(MAT),soil water content(SW)and soil microbial biomass nitrogen(MBN)content were the main ecological factors affecting soil ecological stoichiometry.3.The content of soil microbial biomass carbon,nitrogen and phosphorus(MBC,MBN and MBP)showed a gradual increase with increasing altitude,the soil MBC/MBN ratio showed a trend of decreasing and then increasing,and the soil MBN/MBP and MBC/MBP ratios showed a trend of increasing and then decreasing.The variation pattern of the content of soil MBC,MBN and MBP with the soil layer was the same as that of the content of SOC,TN and TP,and the environmental conditions in the soil surface layer were favorable to the accumulation of soil microbial biomass nutrient content;the overall low soil MBC/MBN and MNB/MBP ratios and the high MBC/MBP ratio indicated that soil microbial biomass nutrients were easily limited by N and P elements.The interaction of altitude,soil layer and elevation with soil layer significantly affected the ecostoichiometric characteristics of soil microbial biomass;soil fast-acting phosphorus(AP)content and MAT were the main ecological factors affecting the ecostoichiometric characteristics of soil microbial biomass.4.There is a correlation between each two of the litter-soil-soil microbial biomass ecostoichiometric characteristics.The correlations between the ecostoichiometric characteristics of litter,surface soil and soil microbial biomass were weak,indicating that litter could not directly characterize the nutrient content of soil and the growth activity of soil microbes.The correlation between soil and soil microbial biomass ecostoichiometric characteristics was significant.The content of SOC and TN was both significantly correlated with soil microbial biomass ecostoichiometric characteristics,but the soil TP content was only negatively correlated with soil MBN/MBP and MBC/MBP ratios.In summary,the C and N content of litter,soil,and soil microbial biomass between different elevations showed that litter > soil > soil microbial biomass,the P content showed that soil > litter > soil microbial biomass,with an overall pattern of high C content and low N and P content.Litter,soil and soil microbial biomass nutrients are susceptible to the synergistic effects of N and P elements.Therefore,we should improve the chemical quality of litter in Helan Mountains,focus on the supply of N elements or N and P complex elements to improve the soil quality,and effectively realize the circulation and flow of nutrients between litter-soil-soil microorganisms in mountain ecosystems.