| Arbuscular mycorrhizal(AM)fungi are a kind of endophytic fungi which can form a good symbiosis with 80%terrestrial plants.In AM symbiosis,the host plants supply carbohydrates to AM fungi,AM fungi can absorb mineral elements and transport them to their host plants by hyphae,such as phosphate,nitrogen.This trade is regulated by both plant and fungal transport components.The uptake and transport of phosphorus and nitrogen in AM symbiosis are closely related.Arginine as a transport carrier of nitrogen could transfer from ERM to IRM with polyphosphates for nitrogen transport.The carbon supply of host plants also affected the nitrogen and phosphorus transport of AM fungi.However,it is not clear how interact with each other.This study uses cotton as study object.The effects of different nitrogen,carbon and phosphorus sources on the colonization rate of AM fungus,arginine formation and the nitrogen and phosphorus nutrition of host plants were studied in this paper.It establishes the basis for the further study on the relationship between nitrogen metabolism and carbon and phosphorus metabolism in AM symbiosis.The main contents and results of this study are summarized as follows:(1)In order to determine the effect of AM fungus colonization and nitrogen and phosphorus nutrition of cotton under different nitrogen sources,a three-compartment culture system was adopted and different nitrogen sources(potassium nitrate,ammonium sulfate,arginine,urea)were added to the extraradical compartment.The results showed that there was no significant effect of AM fungus on the biomass of cotton plants under different nitrogen sources,but exogenous nitrogen could increase the colonization rate of AM fungus and the nitrogen content in the overground part of cotton plants.But inorganic nitrogen could promote AM fungus to colonize the host plants,increase arginine level and nitrogen content in the overground part the host plants,except urea,other treatments could significantly increase the content of phosphorus in the overground part of cotton plants,the supplying of arginine was the most significant.It shows that different nitrogen sources have no significant effect on the biomass of the host plants but it is beneficial to the colonization of AM fungus.Inorganic nitrogen can promote arginine formation and the absorption and transport of nitrogen in AM symbiosis more than organic nitrogen.(2)Supplying different forms of phosphorus sources(potassium dihydrogen phosphate,calcium superphosphate,sodium phytate,lecithin)to the extraradical compartment to explore the effects of AM fungus colonization,arginine formation and the nitrogen and phosphorus nutrition of cotton plants under different phosphorus sources.The results showed that inoculation of AM fungus had no significant effect on the biomass of cotton plants under different phosphorus sources,and the addition of phosphorus to ERM inhibited the colonization of AM fungus,indicating that exogenous phosphorus inhibited the growth and development of AM fungus.Different phosphorus sources increased arginine content of mycorrhizal arginine and nitrogen content in the overground part of cotton plant.Compared with organic phosphorus,inorganic nitrogen can increase arginine content and nitrogen content of mycorrhizal,and is more favorable for AM to absorb and transfer nitrogen to host plants.On the contrary,organic phosphorus is better than inorganic nitrogen.(3)To investigate the effects of different concentrations of nitrogen and phosphorus combinations on the growth of AM infected host plants and host plants,we added different concentrations of nitrogen and phosphorus to the extraradical compartment,The results showed that different concentrations of nitrogen and phosphorus combinations significantly increased the colonization rate of AM,but there was no significant difference between different combinations of nitrogen and phosphorus,among which high nitrogen and low phosphorus contributed to AM colonization of cotton plants,mycorrhizal colonization rate reached 71.4%,According to the biomass status of mycorrhizal cotton,AM fungus had no significant effect on the growth of mycorrhizal cotton under low nitrogen and low phosphorus levels,but only increased the growth of mycorrhizal cotton plants at high phosphorus or high nitrogen levels.(4)Different carbon sources(glycerin,glucose,sucrose)were added to the extraradical compartment to explore the effects of AM fungus colonization,arginine formation and the nitrogen and phosphorus nutrition of cotton plants.The results showed that different carbon sources significantly increased the biomass of non-mycorrhizal cotton plants,but had no significant effect on the growth of mycorrhizal plants,and different carbon sources had different effects on nitrogen and phosphorus nutrition of AM fungus and host plants.Glycerol and glucose increased the colonization rate of AM fungus,sucrose decreased the colonization rate of AM,and the three carbon sources decreased arginine level and nitrogen content of mycorrhizal fungi,and inhibited arginine biosynthesis by AM fungus.The addition of glycerol and sucrose to AM fungus increased the content of phosphorus in the overground part of cotton,while glycerol and glucose increased the content of phosphorus in the underground part.The results showed that different carbon sources have no significant effect on the growth of host plants,and the effects of three kind of carbon sources on arginine formation and nitrogen and phosphorus content are complex,and the specific reasons need to be further studied. |
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