Soil Microbial Attributes At Different Spatial Scales In Deciduous Broad-leaved Forest In Qinling

Over the past few decades,there has been increasing concern about greenhouse gas emissions and their potential impact on climate change.Forest ecosystem is considered to reduce global greenhouse gas concentrations due to its huge above-ground and below-ground carbon sequestrations.Soil microbes are the main components of the terrestrial forest ecosystem,and can potentially impact the function and the ecosystem carbon dynamics.However,due to the heterogeneity of soil environment,the compositions of soil microbial community vary greatly at different scales.It is unclear whether there are differences in the dominant environmental factors affecting soil microbes at different spatial scales.In this study,we selected different scale(5 m × 5 m,1.25 m × 1.25 m and 0.31 m × 0.31 m)plots in Foping National Nature Reserve in Qinling to investigate soil microbial attributes and associated environments.We tried to explore the responses of soil microbial phospholipid fatty acids(PLFAs)biomass,community structure and respiration and related environmental factors at different scales.Our results were as follows:(1)The effects of tree species distribution on soil microbial attributes By calculating the tree influence potential(IP)of woody plants with a diameter at breast height(DBH)greater than 1 cm in the plot,and comparing with the physical and chemical properties of the soil and the attributes of soil microbial PLFAs,we found that the distribution of woody plant significantly affected the soil p H and fine root biomass and fine root carbon content,and there were differences between different woody plants.No significant correlation was found between soil microbial PLFAs biomass and IP,but there was a significant correlation between soil microbial community structure and IP,especially the fungal/bacterial ratios(F/B).The F/B had a certain negative correlation with other woody plants except the Meliosma cuneifolia Franch.,Quercus aliena Bl.var.acuteserrata Maxim.ex Wenz.,Rhamnus davurica Pall.and Acer tetramerum Pax.Tree species indirectly affected soil microbial community structure mainly by affecting soil p H,soil carbon and nitrogen.(2)The effects of soil carbon and nitrogen content on soil microbial respirationThe moisture,soil organic carbon(SOC),total soil nitrogen(TN),dissolved organic carbon(DOC)and dissolved total nitrogen(DTN),were significantly positively correlated with basic soil microbial respiration(BMR)(p <0.01);soil p H was significantly negatively correlated with BMR and basic soil microbial respiration per unit PLFAs(p <0.01).The DOC,SOC and TN were significantly positively correlated with the basic soil microbial respiration of pre PLFAs(p <0.01).Increased SOC and TN content significantly increased soil microbial CO2 emissions.Although DOC and DTN contents only accounted for about 0.1 % of soil C and N,it also significantly affected soil microbial respiration.BMR was mainly affected by the soil microbial community structure and SOC content.(3)Different factors affecting soil microbes at different spatial scalesOur results showed that soil microbial PLFAs biomass did not significantly change among three sampling scales except for the actinomycetes were higher at small scale compared to other scales(p < 0.05).Similarly,the soil microbial community structure was not significantly different except for the branched/monounsaturated PLFAs ratios were significantly higher in large scale than the small and medium scale(p < 0.05).Pearson correlation analysis indicated that there were significant differences in the correlation between soil microbial attributes and environmental factors at different spatial scales.Moreover,the results of redundancy analysis(RDA)showed that the interpretation of soil microbial attributes by environmental factors differed at different spatial scales.Namely,the most important controllers over soil microbial attributes were SOC,moisture and DTN at the large scale,and they were moisture,TN and DOC at the mid-scale,and they were soil p H,total phosphorus content and TN at small scales.Thus,our results showed that the interaction of environmental factors and the degree of spatial autocorrelation increased with small scale due to the existence of scale effect,leading to different effects of environmental factors.In summary,the distribution of species and DBH size of woody plants significantly affected the distribution and function of soil microbes.This effect was altered by the distance between the sampling point and the tree species and the DBH of the plant.Soil C and N,especially DOC and DTN significantly affected the distribution and community structure of soil microbes.In addition,there were differences in the impact of environmental factors on soil microbes at different scales.Thus,the study of soil microbial attributes on different scales will help us to understand the interaction between soil microbes and environment under global environmental change.