Differential Research Of Rhizospheric Soil Microorganism And Root Exudates Between Phyllostachys Edulis And Broad-Leaved Trees

The expansion of Phyllostachys edulis has seriously affected the process and function of the adjacent forest ecosystem.To analysis the expansion effect and mechanism is the basis of understanding the harm associated with the expansion of Ph.edulis.Previous research found,the expansion of Phyllostachys edulis to the adjacent secondary evergreen broad-leaved forest,enhanced the ammonification and inhibited the nitrification of soil,so we speculated that the differences of rhizosphere microorganism and root exudates between Ph.edulis and broad-leaved trees was the key reason of this phenomenon.Therefore,we collected the rhizosphere soils of Ph.edulis and broad-leaved trees（Castanopsis fargesii,Machilus thunbergii and Schima superba）in Guanshan National Nature Reserve of Jiangxi Province in summer of 2019.The soil nutrient content was analyzed by routine methods in the laboratory.The microbial composition and function of nitrogen transformation were analyzed by High-Throughput Sequencing technology.Meanwhile,GC-MS was used to analyze the components and relative abundances of plants root exudates.The aim of this study was to reveal the microbiological mechanism of changed soil nitrogen transformation caused by the expansion of Ph.edulis.The results show that:（1）The contents of organic carbon and total nitrogen in rhizosphere soil were Ph.edulis>S.superba>C.fargesii>M.thunbergii,but the contents of NH₄⁺-N and NO₃^--N were S.superba>C.fargesii>M.thunbergii;the soil p H was Ph.edulis>S.superba>C.fargesii>M.thunbergii.（2）The total microbial richness of Ph.edulis rhizosphere soil was similar to that of S.superba,which was significantly higher than that of C.fargesii and M.thunbergii,but the index of Shannon,Simpson diversity and Pielou evenness for Ph.edulis were significantly lower than the other three broad-leaved trees.（3）The abundance and diversity of ammonifying bacteria in Phyllostachys edulis rhizosphere were significantly different from those in broad-leaved trees.The number of ammonifying bacteria in rhizosphere soil was 1.01x10⁶,which was 17.72%higher than in M.thunbergii and 11.88%in C.fargesii,but the diversity index and evenness index of ammonifying bacteria were significantly lower than those in three broad-leaved trees.（4）The abundance of nitrobacteria and archaea in rhizosphere soil of Phyllostachys edulis is lower than that of broad-leaved trees,especially for the abundance of nitrobacteria community.Compared with M.thunbergii and S.superba,the number of AOB is reduced by 5.5%and 10.8%respectively,and the number of AOA is reduced by 28.9%and 147.1%,respectively.（5）The protein abundance of ammonification pathway in Ph.edulis was 25.08%and14.44%higher than that in Machilus thunbergii and Castanopsis fargesii,respectively,but6.95%lower than that in Schima superba;on the contrary,the protein abundance of nitrification pathway in Ph.edulis was significantly lower than that in broad-leaved trees.Importantly,there was not found ammonia monooxygenase in Phyllostachys edulis rhizosphere soil;while the ammonia monooxygenase abundance in Schima superba rhizosphere soil was as high as 10.91.（6）The ratio of AOB/AOA for Phyllostachys edulis rhizosphere soil is relatively higher than that of broad-leaved trees.The main reason for this result is that the ratio of AOB/AOA of rhizosphere soil has a positive correlation with p H.Influenced by the soil p H,the abundance of AOA community of Phyllostachys edulis decreases more significantly.（7）There was also a significant difference in root exudates between Ph.edulis and broad-leaved trees.The main components of Phyllostachys edulis are alcohols,accounting for 47.76%,and the relative content of methyl palmitate is the highest（27.22%）;the main components of C.fargesii,M.thunbergii and S.superba are esters,accounting for 35.15%,15.03%and 39.36%respectively.The main components of S.superba and C.fargesii are ethyl hexanoate,accounting for 13.99%and 11.13%,respectively.These results showed that Ph.edulis has more ammonification microbial community and higher ammonification pathway protease in rhizosphere soil than broad-leaved trees;on the contrary,it had less nitrobacteria,archaea and nitrosation pathway protease.These differences may be the key reason for the increase of ammonification and the inhibition of nitrification.The results of this study can further understand the influence of Phyllostachys edulis expansion on nitrogen biogeochemical cycle,and also has some enlightening effects on the development of N-microbial fertilizer of moso bamboo forest.