Changes Of Soil Organic Carbon And Microbial Properties In Pinus Taiwanensis Forest At Different Altitudes In Daiyun Mountain Of Subtropical

The soil is the largest active carbon pool in the Earth system.The forest carbon pool is an important part of the soil carbon pool,and its small changes will have a strong feedback effect on climate warming.There are many studies on soil organic carbon at different altitudes,among which microbe is an essential factors affecting SOC changes.However,the current research mainly focuses on the influence of altitude on single soil carbon pool or single microbial community.How the microbes affect the SOC pool is still unknown.Pinus taiwanensis,a Chinese Endemic Tree species.Daiyun Mountain is the largest genetic base of Pinus taiwanensis in China.It has been found that the dwarfing of high-altitude Pinus taiwanensis plants affects the return of litter and may change the input process of soil organic matter.Therefore,this study studied the three altitudes?1300 m?L?,1450 m?M?,1600 m?H??of Pinus taiwanensis in the mid-subtropical Daiyun Mountains,and explored the response of SOC and microbial characteristics to altitude gradients.The main results are as follows:a.SOC content and most physicochemical properties were significantly different at different altitudes,including soil water content,total nitrogen,total phosphorus,NO₃^--N,carbon/nitrogen?C/N?and Labile carbon pool I?LPI-C?,labile carbon pool II?LPII-C?,acid resistant carbon pool?RP-C?decreased significantly with the increase of altitude.The poor vegetation growth at the altitude leads to a decrease in litter return and a lack of nutrients.Compared with L altitude,the proportion of LPI-C at H altitude increased significantly,while the proportion of RP-C decreased significantly.With the increase of altitude,the stability of soil organic carbon decreased gradually.More RP-C was decomposed into LPI-C,and the nutrient turnover at H altitude was maintained.b.Except for microbial biomass carbon?MBC?content in A horizon,MBC,the contents of microbial biomass nitrogen?MBN?and microbial biomass phosphorus?MBP?in soil decreased significantly with increasing altitude.Altitudinal gradient have significant effect on soil enzyme activity in the A horizon,but the effect of altitude on enzyme activity was generally weak in the B horizon.The activity of?-glucosidase??G?,cellulose hydrolase?CBH?and peroxidase?PEO?decreased significantly with increasing altitude in the A horizon,while the activity of acid phosphatase?ACP?increased significantly.The study site is a phosphorus-restricted area.With the increase of altitude,the phosphorus contents are significantly decreased,and the phenomenon of phosphorus deficiency is intensified.MBP is often used as an effective reservoir of phosphorus and has a decisive effect.It can supplement the available phosphorus in the soil,and thus MBP is a key role in determining enzyme activity in the region.c.The dominant bacteria and fungi community composition at level of phylum at different altitudes were consistent.The dominant bacterial phyla across 3 altitudes soils were Proteobacteria,Acidobacteria,Chloroflexi and Actinobacteria.The dominant fungi phyla across 3 altitudes soils were Basidiomycota,Ascomycota,Zygomycota and Chytridiomycota.Different altitudes had no significant effect on the Alpha diversity of bacteria and fungi,but the Beta diversity of L altitude bacteria was significantly higher than that of M and H.In addition,there are also significant differences in microbial functions at different altitudes.At L altitude,lipid,vitamin and other nutrients and energy metabolism increased,the functional abundance of degraded activated carbon increases,and microbial synthesis of functional proteins increased.However,a variety of amino acids,and citric acid metabolism were stronger at H altitude.d.The main environmental factors affecting the structure and function of soil microbial community at different altitudes are the content of soil available nutrients.MBP and C/N ratio are the most important factors determining soil bacterial structure at different altitudes.DON is the most important factor determining soil fungal structure at different altitudes,and MBN and C/N are the most important factors determining soil microbial function.Nitrogen is the most important factor determining soil microbial function.The dominant species of Proteobacteria,microbial community function?NAG?and metabolism?synthetic protein function?all affect the transformation of nitrogen and change C/N.Low C/N at high altitude accelerates the decomposition rate of microorganisms on the substrate.Therefor,C/N is the main factor affecting the SOC component at different altitudes.