Community Structure And Diversity Of Phosphorus-solubilizing Microorganism In Biological Soil Crusts And Its Function

Desertification has seriously hindered the sustainable development of global economy and society.The environmental problems caused by desertification has become one of the most serious problems on Earth.At present,desertification has affected one fifth and one third of the world's population and land,respectively.In China,Inner Mongolia is one of the provinces which is most seriously affected by desertification.Biological soil crusts(BSCs)are one of the natural landscapes in desert ecosystem and play an important role in the restoration of desert ecosystem.Total phosphorus is exile and the content of Bio-available phosphorus(BAP)is very low either in BSCs.The lack of BAP greatly limits the formation and development of BSCs.Phosphorus-solubilizing microorganism(PSM)plays a vital role in driving phosphorus solubilization and mineralization and may significantly affect the development of BSCs.So far,the research on phosphorus-solubilizing microorganism mainly concentrated on rhizosphere soil,the study on phosphorus-solubilizing microorganism in BSCs and its effect on the formation and development of BSCs is still unclear.In this study,BSCs was sampled from the major deserts in Inner Mongolia,the community structure and diversity of phytate-mineralizing bacteria in the BSCs were analyzed based on high-throughput sequencing or culture-dependent method..The factors affecting the community structure and composition of phosphorus-solubilizing microorganism were elaborated.Keystone species phytate-solubilizing bacteria were predicted by CoNet.The effect of PSM on the formation and development of BSCs were validated by simulation experiment of inoculation.The possible mechanism of PSM was explored at nutritional level and microbial interaction.The results as follows:1.The richness and diversity of phytate-mineralizing bacteria in BSCs in the eastern Kubuqi Desert are low.Moss crusts are the highest with richness and diversity index being 1214.89 and 4.64,respectively.Most of the phytatc-mincralizing bacteria can not be cultured(90%);besides that,Proteobactcria and Actionnobacteria are also dominant.Among Protcobacteria,alpha-Proteobactcria arc major,beta-Protcobactcria and gamnma-Protcobactcria arc relative low.29 genus such as Brevundimoncis,Microvirga,Pseudomonas,Novosphingobium,Streptomyces and Spengomonas are included.Microvirga,Brevundimonas and Streptomyces are dominant in algae,lichen and moss crusts,respectively.The relative abundance of Brevundimonas,Microvirga,Streptomyces and Phingomonas in the three types of BSCs was higher than the corresponding soil.Novosphingobium,Singulisphaera,Streptomyces and Eromicrobium are the keystone species in the phytate-solubilizing bacteria.AP is a major factor affecting the community structure and composition of phytate-mineralizing bacteria.2.We isolated 230 bacteria and 25 fungi which could solubilize calcium-phosphate from BSCs.Bacillus,Sphingomonas,Pseudomonas and Trichoderma were dominant.The ability of calcium-phosphate solubilization and calcium-phytate-phosphorus mineralization were 0.15?38.05 ?g/mL and 2.83?78.89 IU/mL,respectively.The fungal calcium phosphate-phosphorus dissolving ability and calcium phytate-phosphorus dissolving ability were 0.43?7.31 g/mL and 89.00?96.32 lU/mL,respectively.The ability of fungi to solubilize calcium-phosphate is weaker than that of bacteria,but the ability of mineralize calcium-phytate is stronger than bacteria.Bacillus,Sphingomonas,Pseudomonas and Trichoderma have the ability to solubilize calcium-phosphate and mineralize calcium-phytate simultaneously.This may be one of the reasons why these species being dominant.3.13 bacteria and 1 fungi obviously promoted the development of BSCs.Further analysis showed that PD3,Bbqt10,NJT15-9,Bbqz14 and TZ1-1(TZ1-1 belong to fungi,others are bacteria)acted on the surface of sandy with different types of phosphorus,which strongly promoted the development of BSCs.These strains belonged to Bacillus,Sphingomonas and Trichoderma.After inoculated PD3,Bbqt10,NJT15-9,Bbqz14 and TZ1-1,the thickness of BSCs increased by 12.11%?130.10%compared with CK and the contents of OM,Chl a,AP and AN in soil increased by 25.78%?218.34%,12.11%?89.22%,16.18%?61.67%and 34.18%?365.86%compared with CK,respectively.Soil phosphatase and phytase increased by 34.56%?81.86%and 26.79%?31.40%,respectively.Meanwhile,the relative abundance of Proteobacteria(57.59%?89.19%),Ascomycota(70.94%?99.15%)and Ochrophyta(0,03%?37.79%)increased.At the genus level,the relative abundance of Methylophilus(3.61%?20.37%),Meyerozyma(0.08%?89.86%),Ochromonas(0.03%?43.61%)and Filamoeba(0.18%?38.56%)also increased;the copies of 16S rRNA gene and nifH gene increased after inoculation of PSM as to indicate the biomass enhancement of bacteria,cyanobacteria and nitrogen-fixing bacteria resulting in promoting the development of BSCs.In conclusion,the diversity of calcium-phytate-mineralizing bacteria in BSCs of Inner Mongolia is low and most of them are uncultured bacteria;while the diversity of calcium-phytate-mineralizing bacteria is high and the dominant spceices have the ability of calcium-phosphate solubilizing and calcium-phytate mineralizing at the same time,while they obviously promote the development of BSCs.This study laid a foundation for understanding and utilization of PSM in BSCs.