Influences Of Biotic Factors On Alien Bacteria Invasion In Soil

Microbial invasions, which are occurring worldwide, have brought about widespread ecological, economic and social consequence. To understand ecological mechanisms underlying biological invasions could help to predict and control invaders. However,current models for biological invasions are predominantly based on macroorganisms, only few invasion model assumptions have been validated for microbial systems. Also, there is a lot of debates on the influences of biotic factors on alien invasion, especially on alien traits,native community characteristics as well as alien-natives phylogenetic distance.To address these knowledge gaps, in this study, we first used a soil micrcosom experiment to investigate the influences of the attributes of aliens and resident community on bacteria invasion separately. Alien traits included propagule pressure, cell size, growth rate and resource utilization capacitity and so on, while soil community characterics included protozoa number, bacterial sepcies diversity, bacterial functional diversity and so on. We then used Meta-analysis and an aquatic experiment to identify potentially general relationships between alien-native phylogenetic distance and invasion and the mechansim of pattern at the local scale.The results of this study are presented as follows:1) Compared the survival of alien bacteria having different propagule number in soil with heating disturbance or not, we found that the influence of propagule number on alien bacteria invasion depended on soil resource contents. In the soil under low available resource, survival of high propagule number bacteria was limted because of resource shortage, while low propagule nuber group did not. The does-response curve of propagule number and invasion potential showed almost horizontal line. In the soil under high available resource, which would not restrict the survival of high propagule nmber bacteria.And the survival of alien bacteria in soil showed expotential growth with propagule number increasing. Heating disturbance could make the dose-response curve to be expotential through increased soil available resource and weaken resident community competition.2) Compared the survival of four alien bacteria including Escherichia coli DH5α,Escherichia coli 0157:H7, Ralstonia solanacearum QL-Rs1115 and Bacillus amyloliquefaciens SQR9 in soil microcosms following heating disturbance, we found that alien bacteria invasion in soil was only significantly affected by the strain resource utilization capability. The survival of alien bacteria was positively correlated with their resource utilization capability for saccharose and glucose earlier in the experiment, while positively correlated with all resources types tested for strains’ utilization capability later in the experiment. Disturbance enhanced bacterial invasion via concomitant effects of increasing resource availability and decreasing native community resistance, but it also reduced the association between strains’ utilization capability and their invasion potential.3) Compared the survival of alien bacteria in four soil microsoms reconstructed by sterilizing two soils with different fertility and self or swap inoculation, we found that abundance of alien bacteria in soils were correlate with soil protozoa and the ratio of Gram negative to Gram positive bacteria, while ttd (time to detect limitation) were correlated with soil microbial respiration rate, bacterial species diversity and functional diversity. Also, soil protozoa and the ratio of Gram negative to Gram positive bacteria were determined by initial soil microbial inoculum composition, while soil microbial respiration rate, bacterial species diversity and functional diversity were determined by sterilized soil environmental condition.4) Using meta-analysis to elucidate the effects of alien-natives phylogenetic distance on invasion, we found that the predictive power of alien-naitves relatedness on invasion depended on both the invasion stage and spatial scale of the studies. On the one hand, we found that alien species more closely related to natives tended to be less successful at the local scale; invasion success, however, was unaffected by alien-native phylogenetic distance at the regional scale. One the other hand, alien species with stronger impacts on native communities tended to be more closely related to natives at the local scale, but less closely related to natives at the regional scale. These patterns were generally consistent across different ecosystems, taxa and investigation methods.5) An aquatic microsom experiment was conducted to distinguish the relative importance of niche difference and relative fitness difference on the relationship of alien-native relatedness and invasion. The results showed that invasion success of alien bacteria was only determined by niche difference, while invasion impact was determined by niche difference and relative fitness difference together. The effects of alien-native phylogentic distance on invasion success/impact both depended on the correlation between their phylogenentic distance and niche difference.Taken together, our study confirmed the influences of bitoc factors such as propagule pressure,alien species traits,resident community characteristics, alien-native relatedness,which indicates that mechanisms under microbial invasion might generally similar to invasions by maccroorgaims. However, the underlying process of biotic factors influencing invasion might be difference between microorganisms and macroorganisms. For example,propagule number promoted bacterial invasion by quorum sensing rather than allee effects.We propose increased use of microbial systems, which offer a simple and cost-efficient way, for experimental study of invasion scenarios.