长期施肥对旱地红壤细菌群落的影响

Effects of Long-Term Fertilization on Bacterial Community in Upland Red Soil

为探讨长期不同施肥对旱地红壤细菌群落的影响,以中国农业科学院祁阳红壤实验站的冬小麦—夏玉米定位试验为研究对象,选取不施肥(CK)、单施氮肥(N)、施化学氮磷钾肥(NPK)和化学氮磷钾+有机肥配施(NPKM)4个处理,于试验开展25年(2015年)小麦收获后采集各处理0~20 cm的土壤样品,利用Illumina MiSeq高通量测序技术对土壤细菌群落进行测定,并深入揭示影响旱地红壤细菌群落的关键因素。结果表明:(1)长期不同施肥显著改变了旱地红壤的化学性质,N和NPK处理的土壤pH显著降低至4.02和4.15,而NPKM处理的土壤pH显著上升至5.99。NPK和NPKM处理均显著改善土壤肥力,但后者效果明显优于前者,而N处理对土壤肥力的提升效果微弱。(2)长期不同施肥改变了旱地红壤优势菌的相对丰度,非度量多维度分析(NMDS)和相似性分析(ANOSIM)表明不同处理的土壤细菌群落发生显著变化。(3)与CK相比,N处理的4种多样性指数(物种丰富度、Chao1指数、系统发育多样性和香农指数)显著降低了21.4%~49.4%,而NPKM处理显著增加了7.0%~66.9%,NPK处理也会使系统发育多样性和香农指数显著降低10.3%和13.0%。(4)逐步回归分析表明土壤pH是决定优势菌相对丰度及4种多样性指数的首要因素,多元回归树分析(MRT)探明土壤pH共解释了83.1%的细菌群落变异,不同处理间细菌群落转变均由土壤pH驱动。(5)STAMP分析发现,N、NPK和NPKM处理与CK分别有11、14和8个显著差异细菌属。综上所述,长期施肥后旱地红壤细菌群落主要受土壤pH的影响,而土壤肥力的作用相对较弱,长期施用化学氮肥造成的红壤酸化的负面效应已远超肥力改善的正面效应。因此,旱地红壤施肥应以防治土壤酸化为前提,长期化肥有机肥配施是一项适宜的施肥措施。

【Objective】Fertilization is an effective measure to improve soil fertility and increase crop yield in red soil.As important components of a soil ecosystem,soil microorganisms play an essential role in soil fertility formation,organic matter decomposition,and nutrient biogeochemical recycling as well.However,though soil microorganisms are very sensitive to fertilization,limited information is available in the literature about effects of fertilization on the microbial community in upland red soil.The objective of this study is to investigate responses of the bacterial community in upland red soil to long-term fertilization varying in strategy,and to provide a theoretical basis for rational fertilization and sustainable utilization of the red soil in South China.【Method】In this study,a long-term field fertilization experiment(established in 1990)on winter wheat–summer maize rotation at the Qiyang Red Soil Experimental Station of the Chinese Academy of Agricultural Sciences was carried out.The experiment had four treatments,i.e.no fertilizer(CK),only application of chemical nitrogen fertilizer(N),application of chemical nitrogen,phosphorus and potassium fertilizer(NPK),and application of NPK plus manure(NPKM).Except CK,all the treatments received N 300 kg·hm–2·a–1,and the N in Treatment NPKM had 30%coming from chemical fertilizer and the rest from manure.Samples of surface soil(0~20 cm)were collected in May 2015(after wheat was harvested and before maize was planted).The technology of high-throughput sequencing of the V4-V516S rRNA gene region were used to determine composition and diversity of the soil bacterial community in the samples,and then to identify key factors affecting the bacterial community in the upland red soil.【Result】Results show:(1)Long-term fertilization significantly changed chemical properties of the upland red soil.Compared with CK,Treatments N and NPK declined significantly or down to 4.02 and 4.15,respectively,in soil pH,while Treatment NPKM increased significantly or up to 5.99.Both NPK and NPKM significantly improved soil fertility,but the effect of the latter was much better than the former.However,Treatment N only increased soil TN content,which was not conducive to soil fertility;(2)Long-term fertilization affected relative abundance of the soil dominant bacteria at the phylum level.Non-metric multidimensional scaling(NMDS)and similarity analysis(ANOSIM)shows that soil bacterial communities in the treatments varied significantly;(3)Compared with CK,Treatment N was 21.4%~49.4%lower in the four diversity indices(observed species,Chao1 index,phylogenetic diversity and Shannon index),while Treatment NPKM was 7.0%~66.9%higher.Besides,Treatment NPK was 10.3%and 13.0%lower,respectively in phylogenetic diversity and Shannon index;(4)Stepwise regression analysis shows that soil pH was the primary factor determining relative abundance of the dominant soil bacterial phyla and four diversity indices of the soil bacterial community.Furthermore,multivariate regression tree(MRT)analysis shows that soil pH explained 83.1%of the detected variation of the soil bacterial communities between the treatments,and differentiation of the bacterial community was driven by soil pH;and(5)Compared with CK,statistical analysis of metagenomic profiles(STAMP)shows that Treatment N,NPK and NPKM had 11,14 and 8 treatment-specific bacterial genera,respectively.【Conclusion】In conclusion,the bacterial community in the upland red soil following long-term fertilization is mainly affected by soil pH,and the negative effects of soil acidification induced by long-term fertilization may have far exceeded the positive effects of fertility improvement.Therefore,fertilization in upland red soil should be based on the premise of prevention of soil acidification,and combined application of chemical fertilizer and manure is a suitable fertilization measure.