Effects Of Diffrent Agricultural Practices On Community Structure And Colonization Rate Of Arbuscular Mycorrhizal Fungi

Arbuscular mycorrhizal (AM) symbiosis is a plant-microbe association between some Glomeromycota fungi and the roots of more than80%of land plants. AM fungi (AMF) are rich in diversity in agricultural ecosystem, playing a vital role based on their unique community structure. AMF improve plant growth by increasing the supply of immobile soil nutrients, notably P, enhancing tolerance or resistance to soil pathogens and abiotic stresses, and by improving the soil structure. Agricultural management factors such as tillage methods, cultivated forms, types and amounts of fertilizers applied may have severe impacts on the AMF community structure. In this study, the micro-ecology theory and technology of mycorrhiza were adopted to investigate the effects of new agricultural practices, such as conservation tillage, rice cultivated in aerobic soil and use of harmless organic fertilizer, on community structures and inoculation rates of AMF. The experimental methods and main results were summarized as follows:1. In order to learn the community structure, spatial and temporal distribution of AMF in rice paddy soils, a field investigation was carried out in the experimental farm of Yancheng Academy of Agriculture Science, Jiangsu province from2006to2007. The soil samples were collected respectively from the plots of a waterlogged soil treatment and three aerobic soil treatments including the ground covered with plastic film, with rice straw mulching and without any mulching. Eighteen AM fungal species belonging to three genera were identified in the soil samples, including11species from Glomus,2species from Acaulospora,1specie from Scutellospora, and4unknown species. The most abundant species of AMF were G. geosporum, G. spurcum and G. mosseae. AMF diversity in aerobic paddy soil was higher than that of waterlogged paddy soil, but the dominant species of AMF, were not altered by water regime in the paddy field. However, the distribution of the dominant AMF species in the soil profile was altered by the water regime. G. geosporum, G spurcum and G. mosseae were the most abundant species in0-20cm layer of waterlogged soil and0-40cm layer of aerobic soil and G. aggregatum was the dominant species in 20-80cm layer of waterlogged and aerobic soil.2. AMF density was significantly higher in the aerobic soil than the waterlogged soil. Among three aerobic soil treatments, plastic film cover resulted highest AMF density. The density of AMF spores gradually decreased from upper layer to lower layer of soil. In waterlogged soil, the spores of AM fungi were mainly distributed in0-20cm soil layer, but the spores of AMF in the20-80cm soil layer in aerobic soil were significantly higher than that of waterlogged soil. It was also observed that both the water regime and plant species affected the root colonization rate. The rice root colonization of AMF was significantly higher in the aerobic soil compared to waterlogged soil. In addition, the colonization percentage of AMF in rice roots grown under aerobic condition was much higher in the treatment with plastic film than with straw mulching and no mulching. The AM colonization in barley roots was significantly higher than that in rice roots.3. The study on the different types of rice cultivated under non-flooded soil showed that the density of AMF spores in host plant rhizosphere correlated significantly with the infection rate of AMF. The cultivation methods significantly affected the contents of organic matter, available P and pH value in0-20cm layer of soils, which had very large effects on AMF’s growth and infection. The spore density and the infection rate of AMF showed a declining trend with the improvement of soil water content and soil organic matter. In contrast, the spore density and the infection rates of AMF to host plants were to some extent positively correlated with soil pH. Phosphorus (P) enrichment on the top layer of soil in plastic film treatment led to the inhibition of the reproduction and infection of AMF. Soil water content was the important influence factor on infection of AMF in aerobic soil.4. A field survey was conducted in a15-years long-term no-tillage wheat area in Linfen, Shanxi to study the effects of no-tillage without compaction, no-tillage with less compaction, no-tillage with subsoiling and traditional tillage on the diversity of AMF.12species from three genus of AMF were identified in the soil samples, including seven of Glomus, one of Acaulospora, two of Scutellospora, and two of unknown species. In addition, G. mosseae, G. versiforme and G. aggregatum were the dominant species in the no-tillage and conventional tillage treatments, G. mosseae and G. versiforme mainly were in the surface layer of soil, and G. aggregatum mainly was in the deep layer of soil.5. AM fungal species richnesses of conservation tillages were significantly higher than that of conventional tillage. There was no significant difference in AMF species richness among three no-tillage treatments. The species richness of AMF differed between different soil layers, and the species richness gradually decreased with the soil layer increases. The spore densities in no-tillage treatments were significantly higher than that of conventional tillage treatment. Especially, no-tillage with subsoiling treatment had the highest density of spores in the three conservation tillage treatments. The spore densities of AMF in different layers were also different, and the spore density of20-40cm layer was lower than that of0-20cm layer in the conventional tillage, but it was higher in the no-tillage treatments. The spore density of AMF of all treatments decreased with the increase of soil layer below40cm soil layer, and no AMF was founded below160cm soil layer. There was only one specie of AMF, identified as G. aggregatum in all the treatments below100cm soil layer.6. AM colonization and spore density at different growth stages of wheat in no-tillage soil were all significantly higher than that of conventional tillage soil, and the AM colonization and spore density in no-tillage with subsoiling were significantly higher than those of other two no-tillage treatments. The study results showed that the spore density and colonization of AMF in wheat soil had a seasonal variation. The AM fungal colonization reached the maximum in jointing stage of wheat, and the spore density had a highest value in mature period of wheat.7. The analysis on the relevance of soil environmental factors and the spore density and the infection rates of AMF in long-term no-tillage wheat field showed that the soil bulk density linking to the tillage management was negatively correlated with the spore density and the infection rates of AMF to wheat. In contrast, soil organic matter was positively correlated with the spore density and the infection rates of AMF to host plants.8. In order to evaluate the effect of G. mosseae on maize growth, a pot experiment was conducted by using different organic fertilizer rates (0.0,0.5,1.0,2.0and4.0g kg’soil). There were two AMF treatments (inoculation with G. mosseae,+AM and uninoculated control,-AM) at every organic fertilizer rate. Generally, both inoculated G. mosseae and organic fertilizer significantly improved plant growth. In the inoculated pots, the growth of plant and AM colonization varied with the rates of organic fertilization. The plant height, chlorophyll content, biomass, P uptake, and AM colonization were increased by the increasing of organic fertilizer rate up to2.0g kg1, but decreased or had no significant difference compared to the uninoculated plants at the highest fertilizer rate (4.0g kg-1). The results suggested that optimal organic fertilizer rate was needed to stimulate AM fungi and improve the maximal growth of plant in agricultural systems. 9. The comparative experiments between the organic fertilizer and inorganic fertilizer with the same amount of major nutrients (N, P and K) were conducted to understand the effect of organic matter on AM colonization and growth of maize. The results showed that organic matter played a significant role in promoting the infection rate of G. mosseae, plant height and biomass of maize. The infection rate of AMF and biomass of maize in the organic fertilizer treatments were higher than that of inorganic fertilizer treatment. At the early growing period of maize, the plant height was lower in organic fertilizer treatment than that of inorganic treatment, but it was significantly higher than that of inorganic fertilizer treatments at the late period of maize.Taking together, the effect of the agricultural practices on soil AMF community structure and infection rate was significant. The conservation tillage and non-flooded rice cultivation increased the infection and reproduction of AMF due to improved the soil aeration and water content. Increasing application of either organic or inorganic fertilizers containning P could inhibite the growth of AMF and AM rate in maize. The proper agricultural practices could thus promote the sustainable development of agriculture by moderately adjusting and controlling nutrition of top soil.