Research On Effects Of Arbuscular Mycorrhiza Fungi On Carbon And Nitrogen Balance In The Rice Field System

Nitrous oxide?N₂O?,carbon dioxide?CO₂?and methane?CH₄?emissions from rice paddies contribute a large part to global climate change.The fluxes of these greenhouse gases?GHGs?can be reduced by manual management of carbon?C?and nitrogen?N?flows in rice field ecosystem.In this study,we applied arbuscular mycorrhiza fungi?AMF?to rice production during growing season,and discussed the effects of AMF on C and N allocation,and the emissions of GHGs in rice field ecosystem using source-sink theory and path analysis method.The resuls could provide a potential mitigation measure for GHGs emitting from rice fields.Based on interaction effect analysis,we found there were synergies between traditional fertilizers and two kinds of AMF viz.Funnelliformis mosseae and Rhizophagus intraradices.Rhizophagus intraradices especially interacted with basal dressing significantly and therefore could reduce the application rate of fertilizer,which was the optimizing strain.Applying 27.4 kilogram of Rhizophagus irregularis per hectare could reduce 190 kilogram of basal dressing and 169 kilogram of top dressing.In addition,rice yield would reach 9824.9±159.1 kg·hm^-2 which was significantly higher than 9416.5±119.0 kg·hm^-2 under traditional fertilizer management.The utilization and distribution of N by different functional organs of rice were compared between traditional fertilizer application?control?and its combined application with the optimizing strain?AM inoculation?.Results show that AM inoculation promoted the growth of deeper roots and fibrous roots and expanded the absorption region of rice roots,which promoted N uptake and utilization efficiency.In addition,AM inoculation increased N concentration and accumulation in roots during growing season,and those in the vegetative parts?leaf blade,leaf sheath and stem?before grain-filling stage.N translocation from leaf blade,leaf sheath and stem to seeds was accordingly increased by 33.0%,33.7% and 107.8%,while the translocation efficiency was significantly increased.Accordingly,N concentration and accumulation of seeds were promoted by 18.8% and 39.0% at maturity.AM inoculation could promote photosynthetic capacity of rice,especially during the vegetative growth stage,significantly increased net photosynthetic rate by 13.6²5.5% comparing with control.Accordingly,AM inoculation significantly increased C accumulation in leaf blades,leaf sheaths and stems before grain-filling stage.The contributions of C translocation from the vegetative parts to seeds were ranked in descending order: leaf sheath > leaf blade > stem.AM inoculation significantly improved C translocation of leaf blades and stems to seeds by 61.4% and 58.6%,and C translocation efficiency of stems.At maturity,C concentration and accumulation in seeds of the inoculated rice were significantly promoted by 2.5% and 19.9%?p < 0.05?,while C/N was decreased by 13.7%,indicating a greater promotion on N than C allocation under AM inoculation.C accumulation in roots showed an increase trend during rice growth season,and the inoculated roots,as a main carbon sink,accumulated 52.3% more C than the control ones at maturity.During growing season,mycorrhizal symbiosis system played an important role in regulating the contents of C and N in soil.Compared to control,AM inoculation increased TN content of 20³0 cm soil,and TC content and C/N of 0¹0 cm and 20³0 cm soil.The variations of C and N would affect the emissions of GHGs from rice fields,and the influence pathways of AMF involved were investigated through complex factor path analysis.Results show that AMF varied the C and N distributions of rice and soil by affecting root morphology and plant physiological function.And this formed two main ways viz.Root Length-Soil TC-GHGs and Root Length-N Absorption-Soil TN-GHGs,which reduced the fluxes of GHGs by trade-off between the two pathways.The peak emissions of N₂ O appeared at midseason and end-of-season drainage,respectively.Compared to control,AM inoculation reduced the emission fluxes by 58.8% and 10.9% at the two stages,respectively.The peak emissions of CO₂ and CH₄ appeared at the two transition stages from flooding to midseason and end-of-season drainage,respectively.AM inoculation respectively reduced CO₂ emission fluxes by 55.4% and 66.4%,while reduced CH₄ emission fluxes by 52.5% and 29.4%.In rice production,AMF can reduce the amount of traditional fertilizer,and improve N assimilation and allocation to seeds.For C balance,AMF promoted CO 2 assimilation and allocation to roots.This regulatory mechanism mitigated the emission fluxes of N₂ O,CO₂ and CH₄ from rice fields.