设施园艺栽培条件下退化土壤的氮素转化过程

The flower industry is one of the characteristic and pillar industries in Yunnan province. But continuous flower cropping under protective cultivation has caused serious soil degradation problem, which has seriously restricted the sustainable production of horticultural facilities. The mechanism research for continuous flower cropping obstacle under protective cultivation is the key scientific basis and important theoretical evidence for exploring soil quality restoration of continuous cropping obstacle, fertility reconstruction of degradated soil systems and developping technical measures for overcoming continuous cropping obstacles of flower soils. The aim of this study is to clarify the mechanism of continuous flower cropping obstacle under protective cultivation from the new point of view “soil nitrogen transformation processes”. The study will apply 15N isotopic dilution methods to determine the gross nitrogen transformation rates in lily soils with different continuous cropping years under protective cultivation, using isotope labeling experiments in the laboratory and in situ and calculating with the FLUZA model or the MCMC method. The nitrogen transformation will be focused on the processes and the gross transformation rates relating to nitrogen supply and conservation in order to evaluate the effect of different continuous cropping years of lily soils under protective cultivation on the conservation and supply capacity of soil nitrogen. The major factors and the mechanism influencing the nitrogen gross transformation rates will be illustrated by analyzing the soil physical and chemical properties, root exudates, enzymatic activity relating to nitrogen transformation, microbe community composition and function in the lily soils with different continuous cropping years under protective cultivation. It will help us to understand thoroughly the mechanism and the evolution process of the continous cropping obstacle in the lily soils with different continuous cropping years under protective cultivation from the essential aspect of nitrogen transformation processes and their reciprocal influencing factors in the rhizospheric micro-ecosystem.

长期连作及不合理的施肥管理导致的设施园艺土壤退化问题十分突出，已严重制约设施园艺可持续生产。阐明设施园艺土壤退化发生机理，是探索退化土壤质量恢复、系统肥力重建和开发土壤连作障碍治理改良技术措施的关键科学基础和重要理论依据。本项目将设施园艺土壤退化产生的机理研究首次集中到土壤氮素转化过程，采用15N稀释和富集法，通过室内标记培养试验方法和田间原位标记方法，利用FLUZA模型，以百合花卉土壤为例研究不同连作年限的设施百合土壤氮总转化速率，特别是控制土壤硝态氮消长、氮素供应与保蓄的转化过程及其总速率，评估设施花卉土壤连作年限对次生盐渍化程度、无机氮供应和保氮能力的影响；通过分析不同连作年限设施花卉土壤理化性质、氮转化相关微生物和酶活性、根系分泌物的差异，揭示土壤氮总转化速率的主要影响因素及机理；从土壤氮素转化过程本质及其互馈调控因素的视角揭示不同连作年限设施花卉土壤连作障碍的发生机理及演变过程。

设施土壤长期连作对土壤理化性质、微生物学性质和土壤氮转化的影响尚不十分清楚。本研究采用15N 稀释和富集法，运用 N转化模型测定了不同连作年限设施花卉土壤同时发生的10个关键氮转化过程的总转化速率。发现不同连作年限的设施土壤主要发生的氮转化过程是有机氮矿化、自养硝化和硝态氮同化过程，且转化速率随着连作年限的延长而升高，自养硝化速率和硝态氮同化速率之间的差值也随连作年限的延长而增大，这可能是长期连作设施土壤硝态氮累积的主要氮转化过程机理。采用实时荧光定量PCR、氯仿熏蒸培养法、二乙酸酯荧光素（FDA）等方法研究了不同连作年限设施土壤生物学特性和理化性质，及其与氮总转化速率的关系。结果表明，随连作年限的增加，土壤pH下降，速效养分和有机质累积；细菌数量和反硝化菌nirS型基因丰度呈现先下降后上升的趋势；而真菌数量和反硝化菌nirK型基因有上升趋势；与对照相比不同连作年限土壤AOA amoA基因拷贝数降低幅度达45.20%~99.46%，而AOB amoA基因拷贝数增加幅度达51.09%~112.40%；固氮基因nifH的基因拷贝数显著下降；微生物生物量碳氮含量显著增加，土壤中微生物总酶的活性呈现先增加后下降的趋势。研究结果揭示了长期连作土壤氮总转化速率变化的微生物学机理。 采用MiSeq高通量测序技术，研究了不同连作年限的设施土壤细菌和真菌群落组成和多样性变化及其与土壤环境因子的关系。Alpha多样性分析显示，与对照相比连作后设施百合红壤中细菌和真菌Shannon指数和Chao指数显著下降。真菌群落组成中子囊菌门占主导，子囊菌门镰刀菌属（Fusarium）丰度比例达 44.02%~58.83%，pH 与镰刀菌属显著负相关。长期连作土壤微生物群落多样性下降，土传病源菌镰刀菌属丰度的增长可能是引起设施土壤连作障碍的主要原因之一。本项目从氮总转化速率及其互馈调控因素的层面揭示了连作设施土壤以硝态氮累积为特征的次生盐渍化和以镰刀菌属数量累积为特征的土传病害加重的连作障碍发生机理和演变过程。