高硝酸盐盈余的设施菜地氮素高投入低利用率的机制研究

The continuous and higher rates of nitrogen applied to the vegetable soil to maintain the high yields even if in the soil with high nitrate concentration. Some previous studies indicated that, the absorption, transport and accumulation of the soil nutrients were inhibited by high humidity and salt stress, and lead to the degradation of the soil microbial population in intensive cultivation. It has been speculated that the special growing environment of high humidity, the response of nitrate stress on root structure and the effects of nitrate stress on key microbial functional diversity in nitrogen cycling may be the one of the mechanisms of low nitrogen use efficiency in high nitrogen input and high nitrate residual soil of greenhouse vegetable production system. To test the hypothesis, the laboratory simulation experiment and field experiment were conducted to study the effects of humidity and salt stress on nutrients uptake and accumulation, root growth and the change of the key microbial functional diversity in nitrogen cycling. So as to preliminary clarified one of the environmental impact mechanisms of high humidity lead to the decrease of nitrogen transport toward aboveground, to further reveal the root biology mechanism and soil microbiology mechanism of the low nitrogen use efficiency in high nitrogen input and high nitrate residual soil of greenhouse vegetable production system. The research achievements would provide a scientific basis for improving the nitrogen use efficiency, maintain the soil microbial function diversity and ensured the sustainable utilization of greenhouse soil.

在设施土壤硝酸盐大量盈余的情况下，仍需持续高量投入氮素来保证蔬菜高产，进而又加剧了硝酸盐累积，威胁设施蔬菜的可持续发展。研究表明，高湿和盐胁迫等抑制养分的吸收、转运和累积，集约化种植易导致土壤微生物种群退化。我们推测设施菜地特殊的高湿环境导致硝酸盐积累，产生盐胁迫，抑制根系生长和土壤氮循环关键微生物调控的供氮能力；且受根系-土壤微生物互作影响进一步降低根系对氮的吸收利用和土壤供氮潜力，这可能是导致设施菜地氮素高投入低利用率机制之一。为验证此科学假设，设计了室内模拟和田间试验，从湿度、硝酸盐供应水平对番茄养分吸收、根系生长及根系-土壤微生物互作、氮循环关键微生物数量和结构变化的影响等开展深入研究。以期初步阐明设施菜地高湿条件是导致氮素向地上部转运下降的环境影响机制之一，并进一步揭示其根系响应和根系-土壤微生物互作的机制。研究成果可为设施菜地提高氮肥利用率、保障设施土壤可持续利用提供科学依据。

在设施土壤硝酸盐大量盈余的情况下，仍需持续高量投入氮素来保证蔬菜高产，进而又加剧了硝酸盐累积，威胁设施蔬菜的可持续发展。通过室内水培试验发现，硝酸盐胁迫下，敏感性番茄品种SH根系生长受显著抑制，尤其是侧根生长，抑制率达90%，硝酸盐胁迫下，SH品种根尖NO3-离子外流值为876 pmol/cm/s，高出耐受性番茄品种YS品种1倍，根系无效耗能可能较少。选取连续种植15年不同化肥氮用量下的设施菜地土壤，通过加水密闭培养法研究表明：推荐施氮下矿化和硝化速率及土壤pH较较常规施氮处理分别增加了610.4%、75.9%和27.6%。长期高量化肥氮投入，显著降低了设施菜地土壤氮素矿化和硝化速率，而适量化肥氮投入，可维持土壤的供氮能力。长期施用化肥氮显著降低土壤中两种硝化细菌AOA和AOB的拷贝数，与AOB型硝化细菌相比，AOA型对长期施用化学氮肥更敏感，与推荐施氮处理相比，常规施氮下氨氧化细菌丰度下降75.6-99.8%，显著降低土壤反硝化细菌nirK和nirS的拷贝数，nirK型及nirS型反硝化细菌丰度分别下降59.1%-86.0%，83.5%-97.5%，nosZ型反硝化细菌丰度下降60.23%-93.92%。此外，设施大棚内的空气湿度明显高于露地，露地的平均空气湿度比大棚内的平均湿度低20%左右。番茄幼苗90±5%湿度处理18天后，地上部生物量明显降低，根的生物量也有所降低，但没有显著差异。90±5%高湿处理还显著抑制N、Ca、Mg在番茄体内的吸收累积量。初步阐明了设施菜地高湿的环境条件导致N素向地上部转运下降的环境影响机制，进一步揭示根系生物学和土壤微生物影响机制。为合理科学施用N肥、提高N肥利用率、维持土壤微生物功能、保证设施土壤可持续利用提供科学依据。