Effects Of Arbuscular Mycorrhizal Fungi On Soybean Growth And N₂O Emissions

Soybean is one of the important food and oil crops in the world,and its production plays an important role in ensuring food and nutrition security in China.The global warming potential of nitrous oxide（N₂O）,the third largest greenhouse gas,is 265 times that of carbon dioxide（CO₂）.Farmland,especially dry land,is the main source of N₂O emissions.Since soybean is one of the main dryland crops,the N₂O emission from its production cannot be ignored.Therefore,it is very significant to increase soybean production and income while reducing the N₂O emission.Arbuscular Mycorrhizal Fungi（AMF）are important soil microorganism,which can form mycorrhizal symbiosis with many plants and promote the absorption of nitrogen,phosphorus,and other nutrients by the host plants.Consequently,AMF has great potential in improving crop yield.However,recent studies have shown that AMF infection also affects soil N₂O emissions.Although soybean and other leguminous plants are one of the widely hosts of AMF,the comprehensive effects of AMF infection on soybean growth and N₂O emission and the underlying mechanism are still unclear.Thus,we conducted an integrated study through comparing crop types,regulating soil phosphate availability and inoculating AMF&rhizobium under both pot and field experiment conditions.Our objectives were to study the effects of AMF infection on soybean growth,soil carbon&nitrogen and phosphorus dynamics,soil N₂O emissions and relevant microorganisms,and to explore the underlying mechanisms.The main results are as follows:（1）AMF infection promoted soybean growth significantly.On the one hand,AMF promoted the growth of soybean by stimulating the absorption of nitrogen and phosphorus.On the other hand,AMF could enhance soybean growth by improving the symbiosis between soybean and rhizobia,which could enhance the biological nitrogen fixation of soybean for soybean growth.As compared to the non AMF inoculation,AMF inoculation significantly increased the aboveground biomass of soybean,the accumulation of nitrogen and phosphorus in shoot by 15.1%～36.7%,21.8%～48.3%and 99.4%～196.3%,respectively.And the soybean nodules number was significantly increased by 44.49%～189.66%with AMF inoculation.（2）The effect of AMF infection on soil N₂O emission was controlled by the inoculation of rhizobia.With the inoculation of rhizobia,AMF infection significantly increased N₂O emission by 33.5%,while reduced the N₂O emission by 31.5%if without rhizobia inoculation.AMF infection significantly increased soybean nodule number and promoted soybean biological nitrogen fixation.Strong biological nitrogen fixation ability could release more nitrogen into the soil through root exudates and root nodule decomposition,which provided more nitrogen substrates for denitrifying microorganisms（i.e.the higher abundance of nir S and nir K genes in the soil）so as to produce more N₂O.（3）Efficient absorption of soil phosphorus is one of the important mechanisms for the AMF effects on soybean growth and N₂O emission.The results of phosphate fertilizer regulation experiment showed that AMF promoted soybean growth through hyphae’s absorption of phosphate fertilizer.Compared with the phosphate-limited control,the aboveground biomass,root biomass and yield of soybean were significantly higher by 58.0%～145.6%,65.1%～79.8%and 75.1%～97.3%,respectively.Meanwhile,AMF significantly increased the soil N₂O emission by 39.3%～82.7%,and increased the soybean nodule number by 79.9%～312.5%.This study can improve the understanding of AMF effects on crop growth and soil N₂O emission,and provide theoretical support and technical approaches for green and sustainable soybean production.