咸水滴灌棉田土壤氮素转化关键微生物过程与机理

The shortage of water resources of good quality is becoming an important issue in the arid and semi-arid regions of the world. For this reason, the availability of saline water resources has become an important consideration. Irrigation with saline could supply water for crops, but also load salts in soil. The high concentrations of soluble salts in soil cause osmotic stress, which can inhibit microbial activity and biomass, or even kill, soil microorganisms and therefore affect nutrient cycling. The nitrogen cycle is an important component for the soil ecosystem. The transformation process and cycle of nitrogen were driven primarily by microorganisms. The response of the soil microbial community to various environmental stresses is of current interest because of its pivotal role in nutrient cycling, soil organic matter turnover and maintenance of plant productivity. However, key microbial processes and mechanisms of soil nitrogen transformation under saline environment are not well understood by far. Irrigation with saline water is an inevitable trend and practical issues in the arid region of Xinjiang. The present study attempted to determine the effect of water salinity on soil nitrogen transformation characteristics in cotton field under drip irrigation with saline water, and to determine the microbial process and key microorganisms of soil nitrogen transformation. The objectives of this study were to reveal the intrinsic link between soil nitrogen transformation and key microbial in cotton fields under drip irrigation with saline, and to promote the saline water resources utilization and nitrogen effective management in arid region.

干旱地区淡水资源匮乏，应用咸水和微咸水进行农业灌溉是一个必然趋势。咸水灌溉在供应作物水分的同时也增加了土壤盐分，导致渗透胁迫，抑制土壤微生物活性甚至导致死亡，进而影响养分循环。氮循环是土壤生态系统元素循环的核心之一, 其循环转化过程主要由微生物所驱动。土壤微生物在土壤养分循环、有机质周转以及维持植物生产力等方面都起着关键作用，土壤微生物群落对环境胁迫的响应已成为当前的研究热点。但目前盐渍环境下土壤氮素转化的关键微生物过程和机制还未能被清楚地揭示。本项目针对新疆干旱区微咸水灌溉的必然趋势和现实问题，研究咸水滴灌棉田土壤氮素转化特征，探讨咸水滴灌对土壤氮素转化微生物过程和关键微生物的影响，揭示咸水滴灌棉田土壤氮素转化与关键微生物之间的内在联系，为干旱区咸水资源的合理利用以及氮素的有效管理及调控提供科学依据。

干旱区由于淡水缺乏使得咸水微咸水成为重要的替代灌溉水资源。咸水微咸水灌溉会导致盐分积累进而改变土壤理化和生物学性质，这将直接影响氮素矿化、硝化等循环转化过程（土壤微生物驱动）。合理的水氮管理对于提高咸水灌溉作物产量和水肥利用率，降低环境污染风险至关重要。然而，关于滴灌条件下咸水灌溉和施氮肥对土壤微生物和氮素转化的影响效应还不清楚。因此，揭示咸水滴灌土壤氮素转化和关键微生物之间的关系对于促进干旱区咸水资源利用和氮素管理具有重要的科学意义。研究表明：咸水灌溉显著增加土壤NH4-N含量，NO3-N含量显著降低。棉花15N回收率为38%-54%，土壤15N回收率为20%-29%。15N总回收率微咸水灌溉显著高于淡水和咸水灌溉。在适宜的灌水和施氮量下，微咸水灌溉对作物的负面影响较小，而咸水灌溉显著降低棉花产量和氮肥利用率。氮素淋洗损失量为5.0 -25.5 kg/hm2，占施氮量的1.81%-4.79%。氮淋洗随灌水量、灌溉水盐度和施氮量的增加而增加。土壤氨挥发损失在一个滴灌施肥周期（7 d）的前1-2 d达到最大，随后迅速降低。氨挥发损失量为9.0 -33.7 kg/hm2，占施氮量的3.20%-4.80%。咸水灌溉土壤氨挥发显著高于微咸水和淡水灌溉。N2O排放量在一个滴灌施肥周期的前3 d占总排放量的80.6%–89.7%。微咸水和咸水灌溉显著增加N2O排放，微咸水灌溉N2O累积排放量最高。长期微咸水咸水灌溉降低土壤微生物量、活性和功能多样性，导致土壤质量恶化。微咸水和咸水灌溉显著增加氨氧化古菌（AOA-amoA）丰度和多样性，而氨氧化细菌（AOB-amoA）、反硝化细菌（nirK、nirS）丰度和多样性显著降低。施氮肥显著增加氨氧化细菌丰度和多样性，对氨氧化古菌没有影响。土壤N2O排放量与硝化微生物 (AOA-amoA、AOB-amoA) 和反硝化微生物（nirK、nirS）丰度均呈正相关，表明N2O排放来源于硝化作用和反硝化作用。但是，硝化作用对N2O排放的相对贡献率为69%-100%，说明硝化作用是咸水滴灌土壤N2O排放的主要来源。进一步分析表明，硝化作用与氨氧化细菌丰度和多样性呈显著正相关，而与氨氧化古菌无相关性。说明氨氧化细菌是咸水滴灌土壤硝化作用的主要驱动者。