The Researches About The Relation Between Exotic Plants And Soil Biota

Biological invasion have threaten the security of natural ecosystems, and been recognized as a global environmental problem. Many ecosystems are severely damaged or threatened by biological invasions, the damages include the changes the community or the structure of the community, the changes of large scale ecosystems process, the loss of biodiversity, etc. The success of biological invasions is related with the biological or ecological characters of alien species, the biotic resistance from native ecosystems, and the interaction effects of biotic and abiotic environmental factors in ecosystems. Release from natural enemies, the low stability of the community and the frequent environment disturbance often cause biological invasions. The invasion of alien plants is an important component in biological invasions, changes the local community structure via the competition with native plants, reduces the local biodiversity and ultimately affects the structure and function of ecosystems and the service offered. The researches about alien plants were mainly focused on the biodiversity in communities, the competition with native plants and the prey from herbivores and insects, while the effects from soil microbe were relatively ignored. Alien plants might escape the harmful soil pathogen and receive the benefit effect from local soil microbe, these are important to the dispersal, eruption and successful invasions of alien plants. Alien plants may change the structure and function of soil microbe community in the invasion process, and the new changed soil microbe may in turn have important effects on the alien and native plants. The effects of soil microbe on alien and native plants are extremely complicated interaction feedback processes, so it is very important to investigate the effect of soil microbe in the competition of alien and native plants. Particularly the studies of effect of soil microbe in the competition of alien and native plants are helpful to understand of the role of soil microbe in successful invasions of alien plants, and to predict the trends of alien plants in communities.The study investigated the effects of the invasive plant Coreopsis grandiflora on the functional diversity of soil microbial communities in Laoshan Mountain and found that the invasive species C. grandiflora enhanced the functional diversity of soil microbial communities where the habitat was invaded by the C. grandiflora. The study indicated that the successful invasive plants have profound effects on the function of soil microbial communities, the effects are site-specific.The study investigated the effects of the sterilization of the soil on the invasive weed Coreopsis grandiflora Hogg. at two irradiance levels and found that the negative effect of soil biota on the Fv/Fm of C. grandiflora at low irradiance may inhibit C. grandiflora to invade the forest canopy and other low light habitats which is in agreement with the observation from the field. Soil biota had negative effect on the leaf biomass, total biomass and the ability of photosynthesis of C. grandiflora at high irradiance. Soil biota contribute to the biotic resistance against invasive plants which is rarely studied before. Our study found that the effect of soil biota on invasive C. grandiflora varied with microhabitats with different light intensity and the effect of soil biota on the invasive plants is complex which needs more studies to understand the relationship between plant invasion and soil biota.The study investigated the effect of soil microbe on the competition of alien plant R. pseudoacacia and native plant Q. acutissima, and found that only leaf biomass of Q. acutissima was decreased because of the shade of R. pseudoacacia on Q. acutissima, the growth of Q. acutissima was not affected by R. pseudoacacia, and the existence of Q. acutissima obviously affected the growth of R. pseudoacacia in simulated natural condition. The conclusions can partly explain that native plant Q. acutissima coexist with the worst worldwide woody plant invader R. pseudoacacia in multi-habitats in North China. After the sterilization of the soil by benomyl, the growth of root nodules were benefited, and eventually the competition effect of Q. acutissima on R. pseudoacacia decreased and. the competition effect of R. pseudoacacia on Q. acutissima increased because of root nodules. The study suggested that native Q. acutissima has a negative effect on the growth and dispersal of R. pseudoacacia in natural soil, while after the sterilization of the soil, R. pseudoacacia was less inhibited by Q. acutissima and the competition of R. pseudoacacia on Q. acutissima was increased because root nodules were facilitated. The different responses of alien R. pseudoacacia and native Q. acutissima to soil sterilization suggested that alien R. pseudoacacia was more sensitive than native Q. acutissima to the change of soil microbe because of the symbiosis relationship between R. pseudoacacia and root nodules. Root nodule bacteria may be important in the dispersal and invasion process of nitrogen fixation alien plants like R. pseudoacacia.After the invasion of alien plants in local ecosystems, the soil microbe may be affected with the changes of vegetation. And the effects of changed soil microbe on alien plants vary with different environment conditions. In the competition of alien plants and native plants, the changed soil microbe may have different influences on the competition pattern. Neutral, positive, inhibitive effect varies with the different competition species. The effects of soil microbe on alien and native plants are extremely complicated interaction feedback processes, and the study in this field will contribute to understand the mechanism of invasions success of alien plants.