Studies On The Characteristics Of Crop Population And Soil Microbial Community Under The Mode Of Optimized Nutrition Managements

Large amounts of chemical fertilizers are applied to achieve high crop yield in modern agricultural production,which has not only caused a series of environmental problems but also lead to the decline of the farmland quality.In order to maintain the sustainable development of agriculture,it has become an urgent need for agricultural production to reduce input,improve efficiency and improve soil sustainable production capacity by optimizing nutrient management.Nutrient optimization managements can directly or indirectly affect soil microbes while achieving high-yield and high-efficiency of crops.Soil microorganisms play a decisive role in driving soil nutrient cycling,crop nutrient supply and soil fertility.Understanding the microbial community characteristics under the high-yield and high-efficiency of crops can provide scientific supports for sustainable management of soil.The field experiment was conducted in Rugao,Jiangsu Province,China from June 2014 to November 2016.The treatments mainly contain three nitrogen management approaches:without nitrogen(PK),farmers' fertilization practice(FFP)and optimized fertilization treatment(OPT).Three different fertilization regimes were set in the OPTs:O-NPK(only chemical fertilizer was applied),O-NPKM(using the organic manure substitute 20%of the total nitrogen used in O-NPK),OR-NPKM(Subtract 20%of the total nitrogen in O-NPK,and further using the organic manure substitute 20%of the remained amount of nitrogen).We had studied the effects of optimized nutrient managements on the yield and nitrogen use efficiencies of rice and wheat.Meanwhile,high-throughput sequencing was used to study soil bacterial and fungal community characteristics.In addition,under the laboratory incubation,DNA stable isotope probing(DNA-SIP)combined with high-throughput sequencing was applied to examine the effects of different fertilization regimes on the microbes involved in low molecular weight substrate(LMWOS),plant residues assimilation and nitrification.The results were listed as below:1.Optimized fertilization managements can achieve the same high yield level as the FFP treatment by optimizing population structure and coordinating grain development.In the year of 2015 and 2016,compared to FFP treatment,the rice yield of O-NPK was increased by 5.82%and 5.04%,respectively;the wheat yield was increased by 4.23%and 6.9%,respectively.There was no significant difference between the crop yields of O-NPKM and FFP treatments.However,the crop yield of OR-NPKM treatment was declined compared to FFP.The grain weight,filled grain rate,grain numbers on branches from 7 to 12 of rice panicle,and the grain weight of wheat was dramatically increased in O-NPK and O-NPKM.Moreover,the higher grain weight in the OPTs of rice was related to the higher sink activity of superior grain and faster grain filling rates than FFP tratement.2.Optimized fertilization managements impact the nitrogen use efficiency by regulating the absorption of nitrogen in different growth stages and the nitrogen allocation among different organs of rice and wheat.The dry biomass and nitrogen accumulation of FFP were significantly higher than the of OPTs before the booting stage,however,the differences diminished with the advance of crop growth till no significant differences in the mature stage between FFP and O-NPK,O-NPKM treatments.Compared to FFP treatment,the OPTs not only promoted the nitrogen translocation and recovery efficiency before anthesis,but also increased the nitrogen allocation rate from vegetative organs to panicles.The nitrogen partial factor productivity(PFPN),agronomic efficiency(AEN)and recovery efficiency(REN)were significantly enhanced in OPTs compared to FFP treatment in both rice and wheat.3.Different fertilizer managements had significant influences on the soil bacterial and fungal community structure,which were closely related to the changes of soil chemical properties.The contents of available phosphorus(AP)and available potassium(AK)were the dominant factors that significantly affected the soil bacterial and fungal community of both rice and wheat seasons.In addition,the changes in soil bacterial community structure in the wheat season were also significantly impacted by the soil NO3--N content.OPTs can improve crop nitrogen use efficiency by changing the relative abundance of microbes based on the phylum level,such as increasing the relative abundance of soil Chloroflexi,Cyanobacteria,and Acidobacteria in wheat season,and reducing that of Proteobacteria,Gemmatimonadetes,Verrucomicrobia,Gemmatimonadetes,and Chytridiomycota.In rice season,the reduced relative abundance of soil Proteobacteria and Firmicutes and the increased relative abundance of Nitrospirae and Basidiomycota were beneficial to the improvement of nitrogen use efficiency.The rice yield was affected by the shifts of bacterial community structure under different fertilization methods,however the wheat yield was influenced by the changes of both soil bacterial and fungal community structure4.Different fertilization regimes under optimized fertilization managements significantly influenced the bacterial and fungal community composition that involved in glucose assimilation.The results of DNA-SIP experiment have shown that 129 bacterial OTUs related to glucose assimilation were found in the NPK-treated soil(three years'application of chemical fertilizer),being more abundant than 59 in NPKM-treated soils(three years' application of chemical fertilizer and organic fertilizer);Moreover,10 and 11 glucose assimilation related OTUs of fungi were found in the NPK and NPKM-treated soils,respectively.Among bacteria,members of Firmicutes and Proteobacteria were the most active populations involved in the 13C-glucose assimilation in both NPK and NPKM treated soils.And Ascomycota,Basidiomycota,Glomeromycota were the dominant fungi that actively involved in the glucose assimilation.Bacterial genera containing Clostridium,Bacillus and fungal genera including Fusarium,Cylindrocarpon and Paralomus were the dominant ubiquitous glucose assimilators in both soils.Besides these,we also found different bacterial and fungal groups were existed in different fertilized soils,for expample,Paenibacillus and Sporomusa in NPK-treated soil and Azotobacter and Nectria in NPKM-treated soil.5.Different fertilization regimes under nutrient optimization management significantly affect the microbial community composition involved in rice straw utilization.(1)Proteobacteria and Actinobacteria that occupied approximately 94%of all the 13C-labeled bacteria community were the dominant bacterial phyla involved in rice straw assimilation.And members of Ascomycota also act as the predominant role in the degradation and assimilation of rice straw.(2)Different fertilization methods significantly shifted the community composition of bacteria and fungi involved in the straw assimilation.The relative abundance of Lysobacter was increased and Strepomyces of bacteria was decreased in the NPKM compared to the NPK treatment.For the fungi,the three years' application of organic manure increased the relative abundance of Syncephalis,but decreased that of Trichoderma.(3)Different fertilization regimes had no influence on the response strategies of dominant bacterial genus,but most of the genus of fungi in soil receive organic fertilizer respond faster than the soil received chemical fertilizer only.(4)The network of microbes involved in straw assimilation was more complex in NPKM treatment than that in NPK treatment.And short-term application of organic fertilizer changed the key microbial species that acted as module hubs and connectors.6.Different long-term fertilization regimes significantly influenced soil nitrification rate and the abundance of microbes related to nitrification.Compared to CK(no fertilizer was applied),long-term application of chemical fertilizer(CF)significantly reduced the potential nitrification rate(PNR)and abundance of ammonia oxidizing archaea(AOA),but significantly increased the abundance of ammonia oxidizing bacteria(AOB).The PNR and the abundance of AOA and AOB were remarkedly increased in soil long-term received organic fertilizer(OF).DNA-SIP was used to further identify the active nitrifiers,and the results have shown that both AOA and AOB contributed to ammonia oxidization in soils of CK and OF,whereas only AOB was detected in CF.In all test soils,nitrite oxidation was performed only by Nitrospira-like nitrite-oxidizing bacteria(NOB).Compared with CK,fertilization have shifted the active Nitrospira-like NOB composition,with the 97%-100%of 13C-labeled NOB was related to Nitrospira lineage ? in CF and OF treated soil.However,fertilization have few effect on the composition of active AOA and AOB community,e.g.nearly 91.6%and 90.6%of the 13C-labeled AOA were classified to Nitrososphaera subcluster 1.1 in CK and OF treated soil,respectively;Nitrosospira cluster 3a.1 accounted for 97.5%,98.4%and 99.4%of the total 13C-labeled AOB in the CK,CF and OF treatments,respectively.Regression analysis showed a significant positive relationship between PNR and active AOA(Nitrososphaera subcluster 1.1)and AOB(Nitrosospira cluster 3a.1)phylotypies,indicating that the abundance of the active ammonia oxidizers was the main determinant of the soil potential nitrification rate.In summary,the increases in crop yield and nitrogen use efficiency under the optimized nutrient managements were not only related to population growth characteristics of crops but also significantly related to soil microbial community characteristics.In addition,different fertilization regimes have changed the soil microbial groups associated with crop assimilates utilization and the abundance of active ammonia oxidizing microorganisms involved in the nitrification process,which will further affect soil ecological functions.