碳氮磷化学计量探讨同域分布的杨柳科植物性比失衡不同格局成因

An interesting ecological and evolutionary puzzle arises from the observations of male-biased sex ratios in the genus Populus, while in taxonomically related Salix, females dominated. In this project we selected two sympatric distributed species Populus kangdingensis and Salix paraplesia to investigate the contrasting patterns of sexual dimorphism from three aspects. 1) We hypothesize that high pollination intensity in Salix due to high density and pollination efficiency will cause sex chromosomes competition between pollen tubes of female- versus male-determining microgametophytes causes female-biased primary sex ratios. Through filed survey for the population density, pollination mode and manipulative pollination for different pollens can test the above certation hypothesis. 2) In gender dimorphic species, reproductive cost is usually predicted to be greater in female plants than in males. However, estimates of the relative reproductive investment made by each sex can vary, depending on the currency used. So we will use five currencies including biomass, carbon, nitrogen, phosphate and energy construction cost to precisely evaluate the reproductive costs in dioecious species. 3) We hypothesize that male Populus and female Salix possess higher growth rate and resistance to abiotic stress and herbivory damage. We will investigate the allocation of C, N, and P to test whether there is tradeoff between growth and defense; moreover. Scaling to the whole plant level, we will use N: P stoichimetry and Protein:RNA ratios to evaluate the growth rate hypothesis; and measure the energy gain and investment together for different gain-cost efficiency may contribute to the sexual dimorphism in growth rate and defense ability. Our results might lay a theoretical foundation for exploring the evolutionary tradeoffs in resource allocation among growth, reproduction and defense, and also conducive to revealing the inside mechanisms for sex ratio imbalance in Salicaceae. These will supply valuable information to predict the direction and rate for the dynamics in ecosystem structure, composition and function.

针对亲缘关系较近的杨柳科植物性比失衡时分别偏雄性和偏雌性这一独特的生态现象和科学问题，以碳氮磷的化学计量为指导，选择川西同域分布的康定杨和康定柳为材料，通过野外调查雌雄植株配置和传粉效率，并结合人工授粉，探讨花粉管竞生是否是柳树偏雌的重要原因；利用生物量、碳、氮、磷和能量建成成本五个通量来评价雌雄两性的繁殖成本，并从成本-收益角度阐释雌雄异株植物能量偿还策略的差异；整株水平上研究C:N:P和Protein:RNA对植物生长的调控机制，验证和完善生长速率假说；并考察雌雄异株植物碳氮磷资源在生长和防御之间的分配，以及碳氮磷间的最优防御分配，揭示生长和抗逆能力对性比失衡的贡献。研究结果有助于深入分析植物碳氮磷营养在生长、繁殖和防御间的权衡关系，拓宽化学生态计量学的应用，揭示杨柳科植物性比失衡呈现不同格局的内在机理。并可为探讨雌雄异株植物与天敌间的协同进化，预测未来种群结构动态变化提供参考。

针对亲缘关系较近的杨柳科植物性比失衡时分别偏雄性和偏雌性这一独特的生态现象和科学问题，选择青藏高原东缘贡嘎山不同海拔梯度上同域分布的冬瓜杨和川滇柳为材料，以碳氮磷的化学计量为指导，研究了雌雄植株配置、传粉效率、繁殖投入和竞争关系等，主要结果如下：[1]中海拔是冬瓜杨和川滇柳的适宜繁衍区，性比接近平衡，而在逆境生境条件下，冬瓜杨显著偏雄性，川滇柳则偏雌性。[2]高海拔上，杨树雄株抗逆能力更强，与偏雄性相吻合；而雌雄柳树间无差异，即柳树的偏雌不能用抗逆能力来解释；[3]川滇柳种群密度更高，传粉方式兼有虫媒和风媒，传粉效率较高，而容易产生花粉管竞争，从而更易偏雌性；[4]选择更多的通量指标，尤其是与能量代谢相关的“建成成本”和生长限制的“磷”元素能更准确的反映繁殖投入情况；综合考虑植物能量收支的光合-支出的偿还时间与性比失衡相吻合，这为杨柳科植物雌雄性比失衡提供有益的视角；[5]川滇柳对照条件下竞争更能力更强，而施氮时，冬瓜杨占优势。因而氮的可利用是调控杨柳竞争关系，促进植被演替的重要因子之一。本研究揭示了杨柳科植物性比失衡呈现不同格局的内在生理生态机理，可为预测未来种群结构动态变化提供参考。未来需在分子水平上，结合性别决定基因、性染色体和表观遗传学等进一步深入研究。