Study On Soil Nitrogen-fixing Bacteria Of Different Vegetation In The Mountain Forests-the Arid Valley Ecotone In The Upper Reach Of Minjiang River

Soil nitrogen-fixing bacteria can not only break down dead organisms, but also affect availability and persistence of the soil nitrogen. It can be an important indicator of soil fertility and changing ecosystem function and important to restore and manage the deteriorate ecosystem and increase the productivity of different plants. We systematically studied the changing regularity of the rhizosphere soil nitrogen-fixing bacteria in the five different types of re vegetations:young plantation, mixed coniferous and broad-leaved forest, locust forest, scrub forest and Cyclobalanopsis secondary forest, in the Mountain Forests-the Arid Valley Ecotones, upper reaches of Minjiang River. We also discussed the effects of different vegetation restoration patterns on the diversity of soil nitrogen-fixing bacteria.The results showed:1 The numbers of rhizosphere soil nitrogen-fixing bacteria and non-rhizosphere soil nitrogen-fixing bacteria in different revegetation patters were significantly different and presented obvious seasonal dynamic change. The numbers of rhizosphere soil nitrogen-fixing bacteria is bigger than non-rhizosphere soil nitrogen-fixing bacteria's in all of the five revegetations. The number of rhizosphere soil nitrogen-fixing bacteria and non-rhizosphere soil nitrogen-fixing bacteria were both the biggest in summer, the order is GM>QG>CH>ZK>YL And the number in GM is the biggest in summer in five sample plots. The rhizosphere effect is between 2.23 and 4.35.2 The general changing regularity of both rhizosphere and non-rhizosphere soil nitrogen-fixing bacteria was almost the same in the culture process:the content of TN in nitrogen-fixing bacteria cultured soil was higher than no nitrogen-fixing bacteria cultured soil after a month, the content of TN in rhizosphere soil was higher than non-rhizosphere soil, the order of soil TN contents in seasons was:autumn>winter>spring>summer.3 PCR-DGGE(Polymerase Chain Reaction-denaturing gradient gel electrophoresis) was used to analyse the biodiversity of soil nitrogen-fixing bacteria. The results showed:in GM and CH, the number of 16Sr DNA band is visibly bigger than other three, the diversity of nitrogen-fixing bacteria community was rich. And the soil with higher vegetation coverage(GM) had higher richness degree, the Diversity Index is 2.88. From the phylogenetic trees analysis we could see soil nitrogen-fixing microorganisms from those plots had different degreed specificities, the 22 determined sequences belonged to 4 clusters, which were had higher similarity with Beta proteobacterium Bradyrhizobium sp,Enterobacter sp and Uncultured nitrogen-fixing bacterium from the different familily.4 The pH value was the biggest in young plantation,which is neutral, and decreased with the altitude. The pH value was higher in non-rhizosphere soil than rhizosphere soil. The contents of organic C, total N, alkali-hydrolyzable N, available P and available K in five types of plants were dramatically increased and the contents in rhizosphere was higher than non-rhizosphere. The contents in nature recovered forest (QG,GM) was higher than Planted forest(CH,ZK,YL). The soil nutrient component in young forest was the lowest.5 The biomass of soil microorganism in rhizosphere was dramatically higher than non-rhizosphere.There was a distinct seasonal dynamic both in microbial biomass C and microbial biomass N, and there was a almost same changing law in different forests:higher in summer and autumn, lower in spring and winter. In general, nature recovery forest> planted forest.6 Revegetation could improve the soil physicochemical condition to some degrees, promote stability of the community structure, increase the biomass of the soil microorganisms and the activily of the nitrogen-fixing bacteria, no matter in non-rhizosphere soil or rhizosphere soil, especially in scrub forest and locust forest. Low stinging shrub decreased the disturbance of to plants and ground in forests, so in the revegetation process, decreased the disturbance of grazing animals and blocked management is effective measures in revegetation. The locust forest performed best in the three young plantations, so it can be the dormant species in the future revegetation.