丛枝菌根真菌与有机肥配施对甜玉米根际土壤氮素转化及氮循环微生物功能基因的影响

Effects of AMF and Organic Fertilizer on N-transformation and Microbial N-cycling Genes in Rhizosphere Soil of Sweet Corn Field

【目的】研究丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)配施有机肥对甜玉米根际土壤氮素转化及氮循环微生物功能基因的影响,明晰AMF配施有机肥对甜玉米-土壤氮循环的微生物学过程,为氮肥利用率提高、化学氮肥减施增效提供技术支撑。【方法】采用大田区组试验,在磷(P2O5150 kg·hm^-2)、钾(K2O 225 kg·hm^-2)施肥水平一致的基础上设计7个施肥处理:(1)不施氮肥(CK);(2)优化施肥(OF);(3)有机氮肥替代10%化学氮肥(ORF10);(4)有机氮肥替代20%化学氮肥(ORF20);(5)有机氮肥替代10%化学氮肥+增施变形球囊霉(Glomus versiforme)(ORF10+AMF);(6)有机氮肥替代20%化学氮肥+增施变形球囊霉(ORF20+AMF);(7)不施氮肥+增施变形球囊霉(CK+AMF);每个处理3次重复。应用土壤常规理化指标分析方法和微生物功能基因芯片(GeoChip 5.0)技术,对不同施肥处理的甜玉米氮素利用率、氮代谢相关酶活性及氮循环功能基因进行分析。【结果】增施变形球囊霉能显著提高氮利用率。变形球囊霉配施有机肥对氮肥农学效率(NAE)、氮肥偏生产力(PFP)、氮肥吸收利用率(NRE)、硝酸还原酶(NR)、谷氨酸合酶(GOGAT)和谷氨酰胺合成酶(GS)活性具有极显著的正交互效应(P<0.001)。在所有处理中ORF20+AMF处理土壤氮素利用效率最高,农学效率(NAE)、氮肥偏生产力(PFP)、氮肥吸收利用率(NRE)、氮素生理利用率(NPE)较OF处理分别提高31.15%、28.08%、6.95%、10.41%。在氮循环微生物功能基因中,增施变形球囊霉处理组(ORF10+AMF、ORF20+AMF)NiR、narB、nasA、nirA、nirB、napA、nrfA、nifH、ureC基因相对强度显著高于对应未施菌处理组(ORF10、ORF20),ORF20+AMF处理的氨氧化基因hzo相对丰度比ORF20处理降低了20%,减少了氮素由N2释放途径损失的可能。【结论】增施变形球囊霉配施有机肥可显著调增同化氮还原基因(NiR、narB、nasA、nirA、nirB)、异化氮还原基因(napA、nrfA)、氮固定基因(nifH)、氨化作用基因(ureC)相对强度,降低硝化基因(hao)和氨氧化基因(hzo)相对丰度,驱动土壤氮素循环向植物氮高效利用的途径转化,提高氮肥农学效率(NAE)、氮肥偏生产力(PFP)、氮肥吸收利用率(NRE)和根系氮代谢酶活性,实现甜玉米化学氮肥减施增效的目标。

【Objective】Effects of AMF and organic fertilizer on nitrogen(N)transformation and microbial N-cycling gene in rhizosphere soil at sweet corn field were studied to improve the fertilization practice.【Method】In a field experiment,sweet corn was planted under various fertilization treatments,and the N-transformation between the plants and the soil monitored.The high-throughput sequencing platform,GeoChip 5.0,was used to determine the microbial community structure and N-cycling genes.Upon the base fertilization of P2O5150 kg·hm^-2 and K2 O 225 kg·hm^-2,7 modifications were applied with3 replicates for the soil treatments:(1)no N addition(CK),(2)optimized fertilization(OF),(3)organic N replacing 10%chemical N(ORF10),(4)organic N replacing 20%chemical N(ORF20),(5)ORF10 inoculated with Glomus versiforme(ORF10+AMF),(6)ORF20 inoculated with G.versiforme(ORF20+AMF),and,(7)CK inoculated with G.versiforme(CK+AMF).The physical and chemical analyses were performed on the plant and soil samples,and GeoChip 5.0 analyzed the community structure and N-cycling genes of the microbes in the rhizosphere soil under different treatments.【Result】The inoculation of G.versiforme in soil significantly increased the N utilization efficiency by the sweet corn plants as well as the activity of N metabolizing enzymes in the rhizosphere microorganisms.When AMF inoculation combined with organic N fertilization,significant effects were observed on increases of the efficiency of N fertilizer(NAE),partial productivity of N fertilizer(PFP),and absorption and utilization efficiency of N fertilizer(NRE)between the plants and the soil,as well as the activities of nitrate reductase(NR),glutamic acid synthetase(GOGAT),and glutamine synthetase(GS)in the microbes.Among all treatments,ORF20+AMF improved the N utilization by the plants the greatest—NAE,PFP,NRE,and NPE rose by 31.15%,28.08%,6.95%,and 10.41%,respectively,over those under OF.The relative signal intensities of NiR,narB,nasA,nirA,nirB,napA,nrfA,nifH,and ureC in ORF10+AMF or ORF20+AMF were significantly higher than those in ORF10 or ORF20.That of hzo in ORF20+AMF,in contrast,decreased by 20%compared with ORF20,which inviably caused a decreased N release by ways of N2.【Conclusion】The presence of AMF in soil enhanced the relative signal intensities of assimilating nitrogen reducing gene NiR,narB,nasA,nirA,and nirB,the N-reducing napA and nrfA,N-fixing nifH,ammonifying ureC,improved the NAE,PFP,and NRE,and increased the microbial N metabolizing enzyme activities.Meanwhile,the declined signal intensities on nitrifying hao,and ammoxidating hzo augmented the N-transformation from soil to plant.The application of AMF and organic fertilizer could,hence,be a promising approach to mitigate the dependency on chemical N fertilizer while promoting the crop yield of sweet corn in the field.