Mediation Of Arbuscular Mycorrhiza Fungi On Plant Interaction Under Simulated Nitrogen Deposition

Enhanced nitrogen deposition simulates or reduces plants growth, impacts nutrient uptake, biodiversity in ecosystem and plant-microbial interactions such as plant-mycorrhizae symbiosis.To examine the responses of plant growth, nutrient uptake and mycorrhizae formation to enhanced nitrogen deposition and to investigate the influence of arbuscular mycorrhizal fungi (AMF) on the competition between crop and weeds under enhanced nitrogen deposition will contribute to the an effective weeds management and better utilization of weedy plant resources in agroecosystem. By means of pot experiments of simulated nitrogen deposition (4 g N m^-2year^-1), in the form of NH₄NO₃, effects of nitrogen deposition on plants of different functional group and plant species combination were conducted in environment-controlled growth chamber during 2002²005. Main results obtained in these experiments are as follows: 1 Response of plant growth to simulated nitrogen deposition among differentfunctional groupsFourteen native plant species in agroecosystem, Poa annua, Avena fatua, Lolium perenne, Oryza sativa, Eleusine indica, Echinochloa crusgalli var. mitis, Zea mays, Plantago virginica, Veronica didyma, Gnaphalium affine, Oxalis corniculata, Medicago lupulina, Trifokum repens and Amaranthus spinosus were used in the experiment, and they were divided into five different functional groups. Plants of C₄ grass , C₃ grass and C₃ legume responded in biomass much more significantly than those of C₃ forbs and C₄ forbs. Ratio of root biomass to shoot biomass of C₄ grass, Gnapbalium affine and Veronica didyma tended to reduce significantly, while Poa annua, Avena fatua and Plantago virginica increased significandy. There were no remarkable changes observed in N and P content of most plant species.Shoot and/or root N uptake of most plants were simulated significantly except Poa annua and Veronica didyma,while P uptake of most plants increased significantly except Oryza sativa, Veronica didyma and Amaranthus spinosus.Under enhanced nitrogendeposition ,mycorrhizal colonization was significantly reduced in Poa annua, Veronica didyma, Gnaphalium affine and Trifolium repens, but no remarkable changes were found in other plant species.2 Responses of co-existed C3 crop and C4 weed to simulated nitrogen deposition Three-years experiment indicated that biomass of C4 weed, Echinochloa crusgalli var. mitis, was simulated significantly by nitrogen deposition in both AMF-free condition and AMF-colonizing condition while biomass of C3 crop, Ory^a sativa, was simulated significantly only in AMF-colonizing condition. Under nitrogen deposition, biomass ratio of E. crusgalli var. mitis to 0. sativa declined significantly in no AMF condition, while no significant response was observed( in 2004 and 2005),or increased significantly(in 2003) in AMF-colonizing condition. In AMF-free condition, nitrogen deposition promoted N and P uptake of E. crusgalli var. mitis, but only promoted N uptake of 0. sativa, which N and P uptake both increased in AMF-colonizing condition (2003 and 2004).Mycorrhizal colonization of E. crusgalli var. mitis tended to increase under enhanced nitrogen deposition, and reponsed significantly in 2003, but mycorrhizal colonization of O.sativa had no significant change3 Mediation of AMF on co-existed species competitive interactionsThe different response of E. crusgalli var. mitis and O. sativa under simulated nitrogen deposition between AMF-free condition and AMF-colonizing condition indicated that mycorrhizea promoted the competitive ability of 0. sativa while reduced the competitivity of E. crusgalli var. mitis.