肉苁蓉种子休眠、萌发和寄生过程与环境的关系

Cistanche deserticola Ma is perennial, root holoparasitic plant distributing in temperate deserts and is a medicinal herb with high economic value. C. deserticola seeds have complex deep dormancy and low germination, at present the characteristics of seed dormancy and parasitic mechanism of C. deserticola are unclear. The objective of this project is to understand the ecological adaptation during seed stage of C. deserticola by the methods of experimental ecology. Main contents of this project include: (1) relationships between seed traits and environment will be explained by studying seed size, morphology, seed dormancy and germination; (2) relationships between embryo growth and morphological dormancy release and between seed physiological dormancy release and temperature will be discussed by studying the effect of alternating stratification simulating seasonal variation in temperature; (3) the response of seed dormancy release to seasonal changing temperature will be explained by studying the seed dormancy cycle of buried seeds; (4) the possible parasite induction mechanism between C. deserticola and its host will be discussed by extracting and identifying the chemicals that are exudated by root and possibly induce parasitic process during early stage of parasite between C. deserticola and roots of Haloxylon ammodendron/Haloxylon persicum. This project will deepen the understanding of seed biology and parasite of C. deserticola and enrich the theory of adaptive strategy of regional plants.

肉苁蓉是温带荒漠分布的一种根系全寄生多年生草本植物，具有药用经济价值。肉苁蓉种子具有复杂和深度的休眠特性而萌发困难，已有的研究对其种子特性和寄生机制仍不十分清楚。本项目利用实验生态学的方法，以理解肉苁蓉种子阶段对荒漠环境的生态适应性为目标，开展以下研究：1）肉苁蓉种子大小和形态结构、休眠和萌发特性，揭示种子大小和休眠与活力的关系，探讨种子性状与环境关系；2）通过模拟季节性变温的层积交替处理等方法，探讨种胚生长与形态休眠释放关系，以及形态生理休眠释放与环境温度的关系；3）研究土壤埋藏种子休眠循环随季节温度变化的规律，阐明土壤种子休眠的释放对温带荒漠环境的适应性关系；4）提取和鉴定在肉苁蓉与梭梭根系的寄生初期，由寄主根系分泌的、可能对寄生过程起诱导作用的化学物质的类别，探讨肉苁蓉与寄主之间的可能寄生诱导机理。该研究能够进一步深入理解肉苁蓉种子和寄生生物学特性，丰富和完善区域性植物适应对策理论。

肉苁蓉是列当科多年生草本植物，主要寄生于温带荒漠灌木梭梭的根部。在自然条件下肉苁蓉种子萌发率极低，严重制约了其人工繁育和资源保护。本研究探讨了肉苁蓉种子的形态结构特征、种子休眠和萌发特性；肉苁蓉结实格局以及结实期干旱对结实特性的影响；种子形态休眠释放对环境温度的响应；土壤种子生理休眠的季节性动态。主要研究结果如下：1、肉苁蓉具侏儒型种子，种子大小为0.2-1.0 mm。种子从外部向内部的结构依次为：透水的种皮、气腔、外胚乳、胚乳和未分化的球状胚。新成熟种子不能萌发，经过冷层积释放生理休眠以及高温释放形态休眠后，种子可在刺激物（氟啶酮）的诱导下萌发。种子萌发前胚需要生长到的关键长度为0.44 mm。肉苁蓉种子具有特殊的形态生理休眠，其休眠释放顺序为先生理休眠后形态休眠。这种种子的休眠类型在温带荒漠植物中尚属首次报道。2、肉苁蓉具有单次种子结实量大的繁殖特性。单株肉苁蓉的种子产量约占果序重量的44 %，单株结实种子总数量约为20.1万粒。种子发育期的干旱改变了单株肉苁蓉果序的结实特性。遮雨处理导致果序下部和中部大种子（0.8-1.0 mm）数量的降低以及果序上部小种子（0.4-0.6 mm）数量的增加。遮雨处理导致果序各部位种子具胚率降低。3、新成熟种子的形态休眠释放对季节性变温响应不敏感。30-40 ºC高温下种胚的生长速度较快。在35 ºC下培养6个月后，种胚即可生长到种子萌发的0.44 mm关键长度。4、新成熟肉苁蓉种子具有季节性的生理休眠动态。种子在成熟时具有初生休眠，散布后种子的生理休眠会在季节性变温的驱动下表现出休眠/状态性休眠之间的动态变化。早秋散布的种子，在经历冬季低温后种子的生理休眠逐渐释放，种子于次年早春获得较高的萌发潜力。次年春季随着温度的升高，种子逐渐丧失萌发潜力，随后于夏季重新获得生理休眠。肉苁蓉种子形态休眠和生理休眠的季节性释放动态的共同调节下确保种子在环境条件合适且可接触到寄主根系的情况下萌发，通过萌发管寄生到寄主上，是谨慎型萌发对策。