连续施氮对马铃薯根际细菌群落结构及反硝化作用的影响

为了揭示连续施用不同氮量对半干旱地区马铃薯根际细菌群落结构及反硝化作用的影响。通过大田试验设置了6个不同施氮量处理:N₀(对照,不施氮)、N₇₅(施氮量75 kg·hm^-2)、N₁₅₀(施氮量150 kg·hm^-2)、N₂₂₅(施氮量225 kg·hm^-2)、N₃₀₀(施氮量300 kg·hm^-2)和N₃₇₅(施氮量375 kg·hm^-2),研究了连续5年不同施氮量对半干旱地区马铃薯根际细菌群落结构及反硝化作用过程中编码亚硝酸还原酶的关键酶基因nirK和nirS丰度的影响。结果显示:各处理土壤中$NO_{3}^{-}$ -N含量随施氮量的增加显著增加,最高施氮量处理(N₃₇₅)土壤中$NO_{3}^{-}$-N含量高达80.41 mg·kg^-1,分别比其他处理增加了86.87%~856.12%;土壤亚硝酸还原酶活性随着施氮量的增加随之增强,高氮处理显著高于低氮处理。高通量测序结果显示,大量施氮降低了细菌群落的Alpha多样性,显著改变了土壤细菌群落的物种组成;与N₀处理相比,其他各施氮处理根际土壤中变形菌门和厚壁菌门的相对丰度增加了1.66%~26.53%和22.59%~85.52%,放线菌门和酸杆菌门的相对丰度降低了3.48%~34.63%和4.21%~37.12%,高氮处理显著低于不施氮及低氮处理;高量施氮显著提高了根际土壤中Lactococcus、Bacillus和Lysobacter的相对丰度。根际土壤中nirK和nirS相对丰度随施氮量的增加随之增加,高氮处理中nirK和nirS相对丰度分别比N₀处理增加了116.26%、101.49%和28.24%、8.47%。Person相关性分析表明,nirK相对丰度与土壤$NO_{3}^{-}$-N含量呈显著正相关关系,pH与nirK和nirS的丰度呈显著负相关关系。大量施氮造成土壤剖面中$NO_{3}^{-}$-N积累量的增加以及pH值降低是引起根际细菌群落结构以及nirK和nirS丰度变化的主要原因。

Effects of continuous nitrogen application on bacterial community structure and denitrification in the rhizosphere of potato

A five-year field experiment was conducted at Dingxi in the Gansu Province of China from 2013 to 2018 to determine the effects of continuous application of different nitrogen rates on bacterial community structure and denitrification mechanisms. The experiment had six nitrogen application rates, namely: No nitrogen application (control, N₀), 75 kg N·ha^-1 (N₇₅), 150 kg N·ha^-1 (N₁₅₀), 225 kg N·ha^-1 (N₂₂₅), 300 kg N·ha^-1 (N₃₀₀) and 375 kg N·ha^-1 (N₃₇₅). It was found that nitrate ($NO_{3}^{-}$-N) content and nitrite reductase activity significantly increased with increasing nitrogen application rates. Treatment N375 increased $NO_{3}^{-}$-N content by 86.87%-856.12% when compared with the other treatments. Results from high-throughput sequencing showed that N375 significantly reduced the Alpha diversity of the bacterial community and changed the bacterial community composition of the rhizosphere. The control increased the relative abundance of Proteobacteria and thick-walled bacteria by 1.66%-26.53% and 22.59%-85.52%, respectively when compared with the nitrogen treatments. The relative abundance of nirK and nirS increased with increasing nitrogen application rates. Treatment N375 increased the relative abundance of nirK and nirS by 116.26% and 28.24%, respectively when compared with the control. Pearson correlation analysis showed that the relative abundance of nirK was significantly and positively correlated with $NO_{3}^{-}$-N while soil pH was negatively correlated with the abundance of nirK and nirS. The accumulation of $NO_{3}^{-}$-N and the reduction of soil pH due to the high nitrogen application rate changed the bacterial community structure and nirK and nirS abundance.