设施番茄连作条件下土壤硝化作用对土壤酸度的响应机制

The abnormal soil nitrification often appeared under protected vegetable continuous mono-cropping and this phenomenon always accompanied by soil salt accumulation and soil acidification. Many studies suggested that it has some correlation between soil acidification and soil nitrogen cycle. Not merely excess of soil nitrogen could result in soil acidification, but also soil acidification has some influence on soil nitrogen metabolism. However, the influence and its mechanism of soil acidification on soil nitrogen nitrification which is the key step of soil nitrogen cycle are not clear yet. In our study, we take three kinds of soil samples as research objects, including soil with excess fertilization and significant acidity under protected different tomato continuous mono-cropping crops, soil with balanced fertilization and non-significant acidity under protected different tomato continuous mono-cropping crops and protected tomato soil with simulative different acidity. Firstly, the change rule of the various form nitrogen in nitrification of all these three kinds different acidity soil will be analyzed with 15N tracer technique. Then, Illumina Miseq high throughput sequencing techniques and Q-PCR will be used to investigate the change rule of the nitrifying microbial community and abundance of nitrifying enzymatic functional genes amoA, nxrA. On this base, to reveal the response mechanism of soil nitrification to soil acidity under protected tomato continuous mono-cropping. The results will provide a theoretical basis for the regulation of soil acidification and the efficient utilization of nitrogen in protected tomato continuous mono-cropping.

设施蔬菜连作土壤常出现硝化作用异常，而这种异常多伴随着土壤盐分积累和土壤酸化等多种因素。有研究表明，土壤酸化与土壤氮循环有一定的相关性，不仅土壤氮素过量会导致土壤酸化，而且土壤酸化对土壤氮代谢也有一定影响，但有关土壤酸化对土壤氮循环关键步骤-氮素硝化作用的影响及其机制尚不得而知。本项目拟以过量施肥的设施番茄不同连作茬次差异酸度土壤、平衡施肥的设施番茄不同连作茬次未有显著差异酸度土壤和设施模拟不同酸度土壤为研究对象，首先通过15N同位素示踪技术，研究三类不同酸度土壤硝化作用过程中各种形态氮素的转化规律；然后采用Illumina Miseq高通量测序技术和Q-PCR技术，解析设施酸化土壤硝化菌群群落结构及硝化关键酶功能基因amoA、nxrA丰度变化规律；在此基础上，分析揭示设施番茄连作条件下土壤硝化作用对土壤酸度的响应机制；为设施番茄连作土壤酸化调控及氮素高效利用提供理论依据。

土壤硝化作用是土壤氮循环的关键步骤，但有关土壤酸化对土壤氮素硝化作用的影响及其机制尚不得而知。本项目以过量施肥的设施番茄不同连作年限差异酸度土壤、平衡施肥的设施番茄不同连作年限未有显著差异酸度土壤和设施模拟不同酸度土壤为研究对象，首先，明确了平衡施肥和过量施肥的设施番茄土壤连作均导致土壤pH的显著降低，其中平衡施肥CMY13比CMY1降低0.49个单位，而过量施肥CY13比CY1降低0.78个单位；其次，发现了平衡施肥设施番茄土壤硝化潜势在较长连作年限内保持稳定（CMY1到CMY11），而过量施肥设施番茄土壤硝化潜势在较短连作年限下急剧增加（CY1到CY6），然后长期过量施肥（≥CY11）又出现土壤硝化潜势的显著降低。然后，采用Illumina Miseq高通量测序技术和Q-PCR技术，指出平衡和过量施肥连作土壤硝化作用的氨氧化过程均有土壤AOA和AOB菌群共同主导，平衡和过量施肥连作土壤AOA群落结构和土壤pH呈显著负相关，AOB群落结构则是主要和土壤pH呈显著正相关。平衡施肥连作土壤亚硝酸氧化过程主要由nxrB-NOB主导，而过量施肥连作土壤亚硝酸氧化过程主要由nxrA-NOB主导。整体来看，施肥方式的不同引起了设施土壤硝化菌群群落结构和硝化关键酶功能基因的变化。和平衡施肥稳定土壤硝化潜势相比，短期过量施肥引起的设施连作土壤硝化潜势的快速提高可能加快了土壤氮素的流失，引起了氮素对环境污染的加重，不利于土壤氮素的有效利用；然而，长期过量施肥引起的土壤硝化潜势的显著降低可能和土壤pH的大幅度降低有关，因为前人研究结果认为土壤pH低于6.0时硝化作用速率显著下降，设施模拟酸化土壤研究结果也进一步验证了土壤过度酸化抑制土壤硝化作用。由此可见，在设施番茄周年连作生产过程中，适当减少化肥施用量，缓解土壤酸化是维持土壤氮素高效利用和促进设施番茄产业可持续发展的有效手段之一。