| Soil enzyme activities and microbial community composition vary with substratestoichiometric characteristics in the ecosystem,which profoundly affects nutrient turnover and substrate decomposition,and hence the nutrient cycling process in the ecosystem.In the mountain forest ecosystem,because of the change of elevation,the vegetation and soil will be differentiated,and the soil microorganism and enzyme activities will be further changed.However,most of the previous studies focused on the plant-soil-microbial relationship of large-scale elevation changes?within 530-3767 m?,and the conclusions were not unified due to the differences of vegetation types.Taking the micro elevation gradient plant soil as the research object,it can eliminate the differences brought by different vegetation types,and more accurately reflect the interaction among plants,soil and microorganisms in mountain forest ecosystem.Based on the theory of ecological chemometrics,this study takes the Quercus aliena var.acuteserrata forest system of Qinling Mountains at six elevations?1308 m,1403 m,1503 m,1603 m,1694 m and 1803m respectively?as the research object,through laboratory and field experiments,the changes of C:N:P ratios,the fractions of soil carbon and nitrogen and soil microbial index in the process of micro elevation changes were studied.The purpose of this paper was to clarify the overall response relationship of"plant soil microbial"system in Sharptooth oak forest belt of Qinling Mountains and provide theoretical support for further understanding the nutrient cycling mechanism of mountain forest ecosystem.The main conclusions were as follows:?1?Variation characteristics of C,N,P contents and stoichiometric ratios of plant-soil at different elevations in Quercus aliena var.acuteserrata forests in the Qinling MountainsIn the Quercus aliena var.acuteserrata forest belts of Qinglin Mountains,the contents of C,N,P and their stoichiometric ratios of plant-soil showed different trends etween1308-1803 m altitude.Among them,the contents of leaves N,P and fine roots P increased first and then decreased with the increase of elevation,while the contents of N in litters and fine roots decreased first and then increased with the increase of elevation.There was no significant difference between C:P ratio and N:P ratio of litters in the altitude gradients,the stoichiometric ratios of leaves,C:N ratio of litters and fine roots,with the increase of elevation,the general trend was upward,and the fine roots C:P ratio and N:P ratio showed the trend of decreasing first and then increasing;the soil C,N and P showed the trend of increasing first and then decreasing on the altitude gradient,but there was no significant difference between C:N ratio and N:P ratio with the changes of elevation.In the plant-soil system,the C:N ratio was more closely related,which showed that the C:N ratio can better reflect the mutual feed relationship of elements of the plant-soil system than the other two ratios in the Quercus aliena var.acuteserrata forest belts.?2?Variation characteristics of soil carbon and nitrogen components at different elevations in Quercus aliena var.acuteserrata forests in the Qinling MountainsThe contens of soil carbon and nitrogen fractions changed significantly in the Quercus aliena var.acuteserrata forest belts.Except ammonium nitrogen,soil microbial biomass carbon and nitrogen,dissolved organic carbon and nitrogen and nitrate nitrogen all increased first and then decreased with elevation.In addition,the content of soil ammonium nitrogen and nitrate nitrogen were 3.30-18.50 mg·kg-1and 0.20-0.41 mg·kg-1,respectively.The contents of ammonium nitrogen at six altitudes were significantly higher than that of nitrate nitrogen,which indicated that ammoniation was the main role of soil nitrogen mineralization in this area.The correlation analysis showed that the stoichiometric characteristics of plant-soil system have a significant impact on soil carbon and nitrogen fractions in the Quercus aliena var.acuteserrata forest belts,of which the stoichiometric ratios of plant has a greater impact,especially the C:N ratio of plant.?3?Variation characteristics of soil microbial indexes on different altitude gradients in Quercus aliena var.acuteserrata forests in the Qinling MountainsWith the increase of elevation,the change trend of enzyme activity in five soils was different.Among them,CBH and?G increased first and then decreased with the elevation,while?X was the opposite.NAG and AKP showed a downward trend at 1408 m-1694 m and increased at 1803 m.The total enzyme activity index exhibited a decreasing trend along the elevations,and compared with 1308 m altitude,the total enzyme activity of 1694m altitude soil decreased by 63.92%.The average activity ratio of soil enzyme C:N:P was about 1:1:0.8 in the Quercus aliena var.acuteserrata forest belts,which was limited in a relatively narrow range,but showed significant differences in different altitude gradients.In addition to the alpha diversity of fungi,the richness and diversity of soil microorganisms?bacteria and fungi?increased first and then decreased with the increase of elevation,and compared with 1803 m altitude,the bacterial alpha diversity of 1308 m,1408 m,1503 m,1603 m and 1694 m was 14.17%,15.01%,16.51%,16.07%,and 12.78%higher,respectively,while that of fungi was no significant difference between 1503 m,1603 m,1694 m and 1803 m altitude.There were obvious aggregation and separation effects of microbial beta diversity at different elevations.In the microbial community,Proteobacteria and Acidobacteria account for more than 70%of the bacterial community;Basidiomycota account for 50%-90%of the total relative abundance of fungal.In addition,the relative abundance of each phylum was significantly different in different altitude gradients.?4?Effects of plant-soil system and soil carbon and nitrogen fractions on microbial indexes at different elevations in Quercus aliena var.acuteserrata forests in the Qinling MountainsThe correlation analysis and the redundancy analysis showed that soil enzyme activities and its stoichiometric ratios,and soil microorganism?bacteria and fungi?were controlled by plant,soil C,N,P resources and the components of soil carbon and nitrogen in different degrees.Among them,the differences of soil enzyme activities and stoichiometric ratios were more closely related to soil microbial biomass?MBC,MBN?.However,for soil microorganisms,the components of soil active carbon and nitrogen were the main factors regulating their changes in the micro elevation scale. |
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