Effects Of Phyllostachys Pubscens Invasion Of Native Broadleaf Forest On Community Characteristics Of Soil CO₂-fixing Bacteria And Its Mechanism

Moso bamboo ?Phyllostachys pubscens? mainly distributed in the tropical and subtropical regions,is an important economic bamboo species in the south of China,and they rely on the bamboo whips constantly spread to the surrounding.Plant invasion potentially alters the carbon cycle and soil microbial community in terrestrial ecosystems,and soil autotrophic microorganisms play an important role in fixed CO₂.However shifts in CO₂-assimilating bacterial communities and their driving environmental factors during bamboo invasion remain largely unknown.Real-time quantitative?qPCR?,terminal restriction fragment length polymorphism?T-RFLP?and clone library were employed to examine the effects of moso bamboo?Phyllostachys pubscens?invasion into native broadleaf forest on CO₂-assimilating autotrophic bacteria community and their function in Tianmu Mountain and Lushan Nature Reserve.Reundancy analysis?RDA?was used to analyse factors affecting CO₂-assimilating bacterial community structure in soil.The purpose of this study was to reveal the characteristics of CO₂-assimilating bacterial community structure and the driving environmental factors during bamboo invasion in nature reserves of subtropical region.The two field sites ?Shi Mendong and Jin Shanmen? in Tianmu Mountain Nature Reserve studies showed that moso invasion increased the abundance of cbbL genes and RubisCO enzyme activity.Bamboo invasion increased the cbbL gene copies by 72% and 105%,and increased RubisCO enzyme activity by 140% and 80%,as compared to the broadleaf forest,at two field sites,respectively.The correlation analysis indicated that cbbL gene copies correlated positively with soil pH.RubisCO enzyme activity correlated positively with available phosphorus,available potassium,EC and nitrate nitrogen.Gene copies of cbbL correlated positively with RubisCO enzyme activity?r=0.80,P=0.016?.The multi-response permutation procedures?MRPP?analysis displayed there were significant differences in community composition between the mixed forest and the broadleaf forest at the SMD site,and between the bamboo forest and the mixed forest at the JSM site.The principal coordinate analysis?PCoA?and cluster analysis?UPGMA?analysis revealed site was the main factor to influence the CO₂-assimilating bacterial community structure.RDA showed that pH?P=0.029?,SOC?P=0.001?,C/N ratio?P=0.001?,nitrate nitrogen?P=0.011?and ammonia nitrogen?P=0.035?explained the community variation in cbbL-containing bacteria at the Shi Mendong site.In Jin Shanmen site soil pH,nitrate nitrogen and available potassium were the main factors to influence the community structure of cbbL-containing bacteria,only available potassium content?P=0.043?was significantly correlated with the community structure of cbbL-containing bacteria.The multivariate regression tree?MRT?analysis revealed that readily oxidizable carbon?ROC?content was the critical factor determining geographic variation in the diversity,abundance and activity of autotrophic bacteria community.The cbbL-containing bacterial communities were dominated by the order Rhizobiales,such as Blastochloris viridis,Starkeya novella,and Bradyrhizobium sp.The two field sites ?Huang Longsi and Bi Yunan? in Lushan Nature Reserve studies showed that the abundance of cbbL gene and the activity of RubisCO enzyme in different soils varied from geographical location.The gene copies of cbb L in mixed forest of bamboo and broadleaf forest was significantly higher than moso bamboo forest,and RubisCO enzyme activity was significantly lower than evergreen broadleaf forest and moso bamboo forest at Huang Longsi site.The cbbL gene copies in mixed forest of bamboo and broadleaf forest was significantly higher than moso bamboo forest and evergreen broadleaf forest at Bi Yunan site.The cbbL gene and RubisCO enzyme activity in three forest stands in Bi Yunan site were all higher than Huang Longsi site.The correlation analysis indicated abundance of cbbL gene copies correlated negatively with nitrate nitrogen?r=-0.612,P<0.01?and available nitrogen?r=-0.348,P=0.026?,RubisCO enzyme activity correlated negatively with oxidizable carbon?ROC?content?r=-0.314,P=0.046?.MRPP and non-metric multi-dimensional scaling?NMDS?revealed that there were significant differences in community composition among the three stand types at Bi Yunan site,and samples under three forest types were grouped together at Huang Longsi site.RDA showed that available phosphorus?P=0.001?,pH?P=0.002?and SOC?P=0.002?content explained the community variation in cbbL-containing bacteria at the Huang Longsi site.In addition to above factors,total nitrogen content?P=0.029?and EC?P=0.024?were also the main factoers to affect community variation in cbbL-containing bacteria at the Bi Yunan site.MRT analysis revealed that nitrate nitrogen content was the critical factor determining diversity,abundance and activity of autotrophic bacteria community.The clone library showed that Rhizobiales were the dominant strain,and there were a small amount bacteria,such as Nitrobacter and Azospirillum.The population and distribution of CO₂-fixing autotrophic microorganisms were different in Lushan and Tianmu Mountain field sites.Geographical differences affected the biogeographic distribution of CO₂-fixing autotrophic microorganisms communities,and the content of avilible nitrogen was the main factor driving the geochemical differentiation of CO₂-fixing autotrophic microorganisms.