| Ecological stoichiometry is one of the important tools to reveal the nutrients cycling and balance in terrestrial ecosystems and their dynamic changes in ecological process.The stoichiometry ratios of soil nutrient and microbial biomass is also considered an effective method to reflect the rates of C,N,and P elements formation and mineralization in soil following human management.Therefore,studying the stoichiometric characteristics of soil and microorganisms might prove our understanding of the biogeochemical cycle process.In this study,we selected Larix principis-rupprechtii plantations with different thinning intensity treatments,plantation ages and mixed ratios as the research object in Haodifang farm,Taiyue Mountain,Shanxi province.Combined with relevant analysis,stepwise regression model and Structural equation model to further explore the impact of different human management on soil physical and chemical properties and microbial community and its driving mechanism on the stoichiometric characteristics of soil and microbial biomass carbon,nitrogen,and phosphorus,and explore the key regulator of the soil and microbial biomass carbon,nitrogen and phosphorus stoichiometric ratios of Larix plantation with different thinning intensity treatments,forest ages and mixed ratio.Our results demonstrated that:(1)The effect of different intensity thinning treatments had significant impact on soil water content,temperature,and nutrients concentrations in plantations.Compared with control site,the soil water content,temperature,organic carbon,total nitrogen,total phosphorus,nitrate nitrogen,ammonium nitrogen and available phosphorus content in the soil under moderate or high density thinning treatments were relatively higher.However,the difference in p H value among the four different density plantation soils did not reach a significant level.Density adjustment also played a positive role in promoting the diversity of understory vegetation,as well of the decomposition efficiency of surface litter and underground roots.However,these environmental factors did not increase with the increase of density regulation.Medium intensity thinning are more conducive to improving these environmental factors.After analyzing the relationship between soil physical properties,nutrient indicators,microbial community and soil and microbial biomass stoichiometric characteristics,we found that p H value,water content,nitrate nitrogen content and ammonium nitrogen content are important factors affecting the soil carbon : nitrogen ratio;soil p H value,moisture content,nitrate nitrogen content and available phosphorus content are the main driving factors of soil carbon : phosphorus ratio;while soil moisture content,soil temperature,nitrate nitrogen content,ammonium nitrogen content and available phosphorus content mainly affect soil nitrogen : phosphorus ratio.In addition,the results of the structural equation model showed that the physical and chemical properties of the soil and the microbial community explained 24%,41%,and 32% of the total variance of the soil microbial biomass carbon :nitrogen ratio,carbon : phosphorus ratio,and nitrogen : phosphorus ratio,respectively.(2)The variation of age gradient and sampling season have significant effects on soil water content,temperature and nutrient elements in Larix plantation.Specifically,compared with the 30 a plantation,the soil p H,moisture content,temperature,organic carbon,total nitrogen,total phosphorus,nitrate nitrogen and ammonium nitrogen content in the soil of the 40 a or 50 a plantation are relatively higher.However,the soil available phosphorus content in plantations of different ages from high to low is 30a>40a>50a.There is no significant difference in the diversity of understory vegetation in plantations of different ages,but with the growth of plantation ages,the decomposition efficiency of surface litter and underground roots of different diameters shows an increasing trend.In addition,the results of the structural equation model showed that the physical and chemical properties of the soil and the microbial community explained 28%,45%,and 35%of the total variance of the soil microbial biomass carbon : nitrogen ratio,carbon :phosphorus ratio,and nitrogen : phosphorus ratio,respectively.Among them,soil temperature,water content,total nitrogen,total phosphorus,available phosphorus,grampositive and gram-negative bacteria abundance are the direct or indirect driving factors that affect the soil microbial biomass carbon : nitrogen ratio;soil p H,the concentrations of soil organic carbon,total nitrogen,available phosphorus,bacteria abundance and actinomycetes abundance are the direct or indirect driving factors that affect the soil microbial biomass carbon : phosphorus ratio;while the soil microbial nitrogen : phosphorus ratio is affected by soil temperature,organic carbon,available phosphorus,and the abundance of gram-positive bacteria and fungi.(3)The increasing of the proportion of broad-leaved trees in Larix plantations has a significant impact on soil moisture content,temperature and nutrient elements concentration.Specifically,compared with pure forest,the soil p H value,water content,temperature,organic carbon content,total nitrogen content,total phosphorus content,nitrate nitrogen content,ammonium nitrogen content and available phosphorus content of 0-20% or 20-40%mixed ratio plantations is relatively high,i.e.the increase in the proportion of broad-leaved tree species might improve the physical and chemical properties of the soil and nutrient level.The diversity of understory vegetation of Larix plantation with different mixed ratios is generally higher than that of pure plantation.At the same time,the increasing the proportion of broad-leaved tree species may also helps to improve the decomposition efficiency of surface litter and underground roots of different diameter levels,thereby accelerating the return of nutrients to the soil nutrient pool.After analyzing the relationship between soil physical and chemical properties,nutrient indicators,microbial community and soil and microbial biomass stoichiometric characteristics,we found that mixed ratios have a leading role in affecting the stoichiometric characteristics of soil and microbial biomass by improving soil physical and chemical properties and soil microbial activity.In addition,the results of the structural equation model showed that the physical and chemical properties of the soil and the microbial community explained 29%,43% and 40% of the total variance of the soil microbial biomass carbon :nitrogen ratio,carbon : phosphorus ratio and nitrogen : phosphorus ratio,respectively.Among them,soil temperature,organic carbon,total phosphorus,bacteria abundance and fungi abundance are the direct or indirect driving factors that affect the soil microbial biomass carbon : nitrogen ratio;soil moisture content,organic carbon,nitrate nitrogen,fungi,bacteria abundance and actinomycetes abundance are the direct or indirect driving factor that affects the soil microbial biomass carbon : phosphorus ratio;the soil microbial nitrogen :phosphorus ratio is affected by soil temperature,organic carbon,total phosphorus,bacteria abundance and fungi abundance.In summary,the results of this study indicate that the medium-intensity thinning treatment in this study could be used as a reference for density control of Larix plantations in subalpine areas,and management strategies for plantations of different ages should be based on the nutrient requirements of plantations.To improve the soil fertility,it is appropriate to promote the nutrient cycling of plantations through fertilization and other methods.In addition,through natural protection to promote the formation of coniferous and broad-leaved mixed forests,it may help improve soil nutrient levels and microbial activity. |
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