Responses Of Microbiota In Bean And Corn Root Zones To Fertilization Measures

Northeast China is the main grain producing area in China,with high soybean and maize yields and abundant straw resources.Straw has rich nitrogen,phosphorus and potassium nutrients,which can improve soil nutrient status,reduce chemical fertilizer input and increase the agricultural production.In addition,plant physiological traits are often related to resource acquisition strategies,and plant resource consumption and turnover are related to root microbial communities,thus,microbiota in root zones affect plant productivity.However,there are few studies on the effects of straw returning on bacteria,fungi and free-living diazotroph in different parts of crop root zones.Therefore,different fertilization measures were designed under field conditions in this study,including no fertilizer（CK）,NPK inorganic fertilizer（NPK）and straw returning with NPK inorganic fertilizer（NPKS）.We analyzed the responses of bacteria,fungi and diazotroph communities to fertilization in bulk soil,rhizosphere and endosphere of bean and corn,and identified significant enrichment of microorganisms and main influencing factors in crop root zones driven by fertilization measures,and we explored the effects of fertilization measures on the potential functions of root zones bacterial community,the ecological functional groups of fungi,and the nitrogen fixation potential of diazotroph.Main results were as follows:（1）Fertilization measures significantly affected bacterial community structure in bean and corn root zones（bulk soil,rhizosphere,endosphere,bean nodule）,but had no significant effect on bacterial diversity.Fertilization measures had no significant effect on the bacterial community structure and diversity of bean nodule.In addition,the influencing factors of bacterial community structure variation in crop root zones are different.Such as,soil ammonium nitrogen（NH₄⁺-N）was a key factor leading to bacterial community variation in bulk soil of bean and corn,soil available phosphorus（AP）was a key factor leading to bacterial community variation in rhizosphere of bean and corn;soil p H was a key factor leading to bacterial community variation in endosphere of bean and corn.The effects of fertilization on microbial community and function in bean and corn root zones were through the changing of soil and plant physical and chemical properties.Such as,straw returning（NPKS）significantly enriched beneficial bacteria such as Rhodanobacter,Pseudomonas,photoheterotrophy and nitrogen fixation bacteria function in crop root zones by increasing soil ammonium nitrogen,nitrate nitrogen,available phosphorus,plant nitrogen content,however,straw returning also significantly enriched harmful bacteria Ralstonia and function of human＿pathogens＿all and animal＿parasites＿or＿symbionts in bean root zones.NPK inorganic fertilizer significantly enriched beneficial bacteria such as Massilia and Streptomyces,and bacterial functions such as chemoheterotrophy and aromatic＿compound＿degradation,also significantly enriched harmful bacterial Ralstonia and harmful bacterial functional animal parasites or human＿pathogens＿all and animal＿parasites＿or＿symbionts in rhizosphere of bean and corn.（2）Fertilization measures significantly affected fungal communities in bulk soil,rhizosphere and endosphere of bean and corn,but had no significant effect on fungal community of bean nodule.In addition,fertilization measures significantly affected fungal diversity in bulk soil of bean and corn.Key impact factors varied according to niches,such as,soil available potassium was a key factor leading to fungal community variation in bulk soil of bean,soil total carbon was a key factor leading to fungal community variation in rhizosphere and endosphere of bean.In addition,fungal communities were more sensitive to fertilization measures than bacterial communities.Straw returning with NPK inorganic fertilizer enriched more saprotroph fungi in bean and corn root zones,such as Tausonia,Schizothecium,Tetracladium,no fertilizer and NPK inorganic fertilizer measures enriched more pathotroph fungi,such as Fusarium,Trichoderma,Metacordyceps,Drechslera.The main reason was that straw returning provided sufficient carbon,nitrogen,cellulose and other substances for saprotroph fungi to survive,and pathotroph fungi were more suitable to survive in low nutrient environments.（3）Fertilization measures had no significantly influence on soil nitrogenase activity and diazotrophic diversity in bean rhizosphere,but significantly influenced diazotrophic communities in bulk soil and rhizosphere of bean by changing soil respiration rate and ammonium nitrogen content.The bean nodules had the highest copies of nif H gene.Straw returning significantly increased soil nitrogenase activity and nif H gene copies of corn bulk soil.Fertilization measures significantly influenced the diazotrophic diversity in bulk soil of corn,and the diazotrophic communities in bulk soil,rhizosphere and endosphere of corn.Key impact factors also varied according to niches.Such as,soil total carbon led to the significant differences of diazotrophic community in bulk soil,and soil available potassium was the key factor for changing diazotrophic community of rhizosphere.The relative abundances of different enriched species under no fertilization measures was significantly and positively correlated with soil p H,and negatively correlated with soil total carbon,total nitrogen,ammonium nitrogen,available phosphorus,plant total nitrogen,soil nitrogenase activity and nif H gene copies.The relative abundances of different enriched species by straw returning combined with inorganic fertilizer was significantly and positively correlated with most environmental factors and negatively correlated with soil p H.Compared with no fertilization and NPK inorganic fertilizer,straw returning had the highest soil nitrogenase activity,which was mainly due to the increase of nif H gene copies,and the nif H gene copies was positively correlated with soil nitrogenase activity.On the other hand,straw returning provided good survival conditions for diazotroph by improving soil and plant nutrient properties.