AM Fungi Decompose Litter And Transport Nutrients To Their Host Plants In Karst Habitat

How arbuscular mycorrhiza fungi (AMF) utilize soil nutrients and supports host plant growth are intriguing. In the south Karst ecosystem with high soil erosion, mycorrhizal fungi can be extremely important for nutrient cycling. Researchers have been focused on the questions of saprotrophic ability on AMF for long. It has not been reported for the saprotrophic ability on decomposing organic matter and utilizing nutrients in Karst habitat to maintain nutritional balance of the ecosystem. How nitrogen mediates the process? How high diversity of AMF species maintains nutrients need of plant growth? How nutrients form and hypha affet plant growth and soil characteristics? It is important significance to know these questions for revealing mechanisms of nutrient cycle in Karst ecosystem. Therefore, two experiments were conducted in order to study the saprotrophic ability of litter decoompositon via AMF mycelium and the mixed effets of multiple AMF species to symbiotic development of host plant and soil property in this thesis. The experimental measurements are as follows.Experiment1:The effects of inoculation of Cinnamomum camphora seedlings with AMF were investigated. C.camphora seedlings were inoculated with Glomus etunicatum in isolated compartments with soils from a Karst area. Exogenous nitrogen of NH4NO3was added in rhizosphere soil and litter of15N Lolium perenne labeled with15N was applied in TEST soil in order to study the saprotrophic ability and the effects of exogenous nitrogen on decomposition. Experiment2:C.camphora seedlings were inoculated with two AMF species of G. etunicatum and G. mosseae, the adjacent compartment was applied (NH4)2SO4with15N labeled and planted Lolium perenne after12weeks in TEST. The aim was to test mixed inoculation with AMF species to host plant After15weeks treatments, the following was investigated:the colonized rate, mycelium density; photosynthesis and growth characteristics, plants and soil nitrogen and phosphorus status and815N;soil microbial nitrogen and carbon content, alkaline phosphatase and protease acitivity.(1) Exogenous nitrogen mediated litter decomposition and nutrient transportation for host plant by AMFExogenous nitrogen application increased mycelium density, plants photosynthesis rate and growth. It also increased N:P in root, stem and leaf. However, the total amount of nitrogen uptake was not affected. The application of exogenous nitrogen decreased utilization of15N from but increased soil microbial carbon, nitrogen, organic carbon, microbial C:N and alkaline phosphatase and protease activity in the neighbor compartments. The isolation interrupted mycelium extension and decreased mycelium density, plants height and stem diameter, leaf chlorophyll content and photosynthesis rate and consequently biomass accumulation. The isolation did not change the plants N:P remarkably, but decreased nitrogen and phosphorus uptake. It also decreased leaf815N value and soil microbial C:N. In conclusion, the results indicated that exogenous nitrogen application did not change the colonized rate of C.camphora seedlings, but did affected the mycelium density in the neighbor compartments significantly. The isolation altered root characteristics and plants growth. AMF was saprophytic, promoted soil litter decomposition and uptake and transphere the15N to the host plants. C.camphora seedlings preferred to utilize the rhizophere soil nitrogen. Under the conditions of low level nitrogen supply, the plants utilized more15N released from the neighbor compartments. Application of exogenous nitrogen promoted soil litter decomposition but decreased its utilization by the plants; in contrast, with high level of nitrogen supply, the plants uptake much more nitrogen and phosphorus and microbial carbon, nitrogen content and mycelium density were also increased in the neighbor compartments.(2) Mixed inoculation with AMF affected uptake and transportation of inorganic nutrients for host plants in Karst soilMixed inoculation did not significantly affect mycelium density in the neighbor compartments and colonized rate of Cinnamomum camphora seedlings in this experiment.It affected photosynthesis of C.camphora seedlings significantly, and also promoted growth, such as biomass accumulation, root length and volume, although not significantly. Mixed inoculation increased N:P in the roots, stems and the plants as a whole and total nitrogen uptake, but did not affect total phosphorus uptake. This treatments also increased δ15N value of the leaves, but decreased δ15N value of the soil and Lolium perenne leaves in the neighbor compartments. It also decreased soil microbial C:N, but increased alkaline phosphatase and protease activity significantly. The isolation affected the mycelium density in the neighbor compartments and it decreased biomass accumulation of root, stem and leaf and root length and volume, leaf chlorophyll content and photosynthesis rate, nitrogen and phosphours uptake and N:P value. The0.45um net isolation decreased significantly815N value of C.camphora seedlings leaves,but the815N value of the soil and the Lolium perenne leaves in the neighbor compartments was significantly much higher than in the other treatments. The net isolation also decreased the soil microbial carbon and nitrogen content and the C:N value. It also decreased significantly the content of total nitrogen, alkali soluble nitrogen and available phosphorous respectively. It increased alkaline phosphatase and protease activity in the neighbor compartments.In conclusion, the treatments did not affected the colonized rate of the C.camphora seedlings, but they significantly altered the mycelium density in the neighbor compartments. The isolation changed the root morphology and plants total biomass. Mixed AMF inoculation increased nutrients utilization and promoted plants growth, affected the root morphology, biomass and nitrogen and phosphorus accumulation and. The improvement was mainly the consequent of changed soil enzyme activity and microbial carbon and nitrogen and nutrients utilization. The mycelium affected significantly the plants nutrients utilization, and consequent photosynthesis and biomass accumulation. The mixed inoculation promoted utilization nutrients from distance farer away via mycelium uptake and transfer.(3) Effects of nutrients from and AMF mycelium on symbiotic development of host plant and soil characteristicsThe two-ANOVA indicated that the total amount of nitrogen and phosphorus uptake by the C.camphora seedlings was not affected significantly by the organic or inorganic nutrients, but the N: P uptake was. The net isolation did not changed N:P, though. The interaction of nutrients form (organic or inorganic) and net isolation affected nitrogen uptake but not phosphorus uptake. The significant effects on plant total biomass were mainly due to changes of stem biomass. The nutrients form did not affected root morphology remarkably which was mainly affected by net isolation. Both nutrients form (organic or inorganic) and net isolation affected the chlorophyll content and plants photosynthesis, soil available nitrogen and phosphorus and soil microbial carbon. The soil microbial nitrogen was mainly affected by the net isolation. In conclusion, the soil nutrients form affected the soil biochemical processes; both soil form and AM mycelium regulated plants nutrients utilization.In summary, AM fungi promoted soil organic matter decomposition; rhizosphere nutrients availability affected soil organic matter decomposition and plants nutrients utilization significantly. Mixed AM fungi species inoculation imposed positive effects on nutrients utilization and plants growth. Plants growth was affected by soil nutrients form and AM mycelium. Both factors contributed to the Plant-AM fungi-Soils system processes.