| In order to investigate the effects of organic-inorganic fertilizer ratio on the structure and function of denitrifiers community in wheat rhizosphere at the jointing stage, a long-term positioning experiment with combined application of organic and inorganic fertilizers was conducted. Four treatments were set up:single application of chemical fertilizer(T1), 15% sheep manure combined with chemical fertilizer(T2), 30% sheep manure combined with chemical fertilizer(T3), and 45% sheep manure combined with chemical fertilizer(T4).The soil samples were collected at early and late jointing stage.The abundance and community structure of nirS-type and nirK-type denitrifiers were explored using real-time PCR and high-throughput sequencing technology, and laboratory culture experiment was conducted to investigate denitrification capacity and soil respiration in wheat rhizosphere at jointing stage. The results showed that,compared with early jointing stage, the soil DC, SR, dissolved organic carbon(DOC) and NO-3-N were significantly decreased at late jointing stage in wheat rhizosphere.Soil pH and nirS-type denitrifier abundance were significantly increased at late jointing stage. Correlation analysis showed that DC was significantly positively correlated with DOC(P< 0.01) and NO-3-N(P<0.05) contents,but negatively correlated with pH(P<0.01) and nirS-type denitrifier abundance(P<0.05),and no significant correlation with nirK-type denitrifier abundance. Compared with inorganic fertilizer alone,the soil DC and SR of organic-inorganic combined application were significantly reduced at late jointing stage.Under the treatment of applying organic fertilizer, the abundance of soil DC, SR and nirK-type decreased with the increase of the proportion of organic fertilizer, and the abundance of nirS-type increased.Compared with the application of inorganic fertilizer only, combined application of organic-inorganic fertilizer improved the α-diversity index of nirK-type denitrifier community.However,there was no significant difference among different organic fertilizer ratios. The abundance of nirS-type denitrifier decreased with the increase of organic fertilizer ratio. RDA analysis showed that, pH and NO-3-N were the main factors affecting nirK-type denitrifier community structure, while NO-3-N and NH+4-N were the main factors affecting nirS-type denitrifier community structure. Correlation analysis showed that DC treated with organic fertilizer was significantly positively correlated with nirK-type denitrifier abundance(P<0.01) and Chao1 index of nirS-type denitrifier community(P<0.01). However, there was a negative correlation between DC and nirS-type denitrifier abundance(P<0.01). At late jointing stage, wheat reduced rhizosphere denitrification capacity and reduced nitrogen loss by reducing rhizosphere soil DOC and increasing pH. Increasing the application ratio of organic fertilizer caused the change of the NO-3-N in wheat rhizosphere soil, reduced nirK-type denitrifier abundance, and changed community structure of denitrifiers, and thus reduced the denitrification capacity, and alleviated the adverse effects of low nitrogen stress on the growth of wheat at jointing stage. |
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