内蒙古草原锦鸡儿属重要物种的有性繁殖及其对气候干旱梯度和放牧管理的响应

Caragana Fabr. has become the important plant species in the Inner Mongolian grassland ecosystem with increasing thicketization. Although there are a number of biological and ecological studies on Caragana, the sexual reproduction of Caragana remains unclear. We propose to investigate: (1) the effects of climatic aridity gradient on the sexual reproduction (morphology of sexual organ, predation of sexual organ by insect, seed productivity, soil seed bank and seedling development) of important Caragana species; (2) the effects of grazing management measures on the sexual reproduction of important Caragana species; (3) the effects of the interaction between climatic aridity gradient and grazing on the sexual reproduction of important Caragana species; (4) the ability of sexual recruitment for Caragana through analyzing the characteristics of the sexual reproduction. To accomplish these goals, we will (1) observe the phenology of sexual reproduction, predation of sexual organ by insect, seed productivity and soil seed bank of Caragana species in the field; (2) study the morphology of sexual organ, seed germination and seed vigor for Caragana species using greenhouse experiments; (3) examine the development rates of seedlings under different habitat conditions using sowing experiments in the field. As the importance of Caragana species increases on the Inner Mongolian grassland, the results of this study will provide the scientific baseline for more appropriate exploitation of Caragana resources, for more effective conservation of the ecological function of Caragana species, and for understand the procedure of grassland thicketization dy Caragana species in the Inner Mongolian grassland ecosystem. And this study provide an example for the effects of the climatic aridity gradient and grazing management measures on the sexual reproduction of shrub species.

锦鸡儿属是内蒙古灌丛化草原生态系统中的重要物种，对其生物学和生态学研究正在广泛进行，但关于有性繁殖的研究极少。本项目拟通过①野外实地观测有性繁殖物候期、繁殖器官被昆虫取食率、开花数、结实数、种子数和种子库，②实验室测定繁殖器官形态指标和种子活力，③野外播种实验研究种子建成幼苗概率和消长情况三种研究手段，解决下列科学问题：（1）掌握气候干旱梯度和放牧管理（放牧强度和围封时长）及其联合作用对锦鸡儿属重要物种有性繁殖（包括繁殖器官形态、繁殖器官被昆虫取食率、种子产量和种子建成幼苗能力）的影响；（2）积累内蒙古草原锦鸡儿属植物有性繁殖基础数据，评估该属植物有性繁殖更新能力。该项目的研究成果为内蒙古草原锦鸡儿属植物灌丛化的解释提供生态学依据；为有效认识和利用锦鸡儿属植物资源，充分发挥其在草原生态系统中的作用提供理论依据；为阐明气候干旱和放牧对灌木有性繁殖的影响提供例证。

在内蒙古草原，研究了气候干旱和放牧管理对锦鸡儿属灌木繁殖特性的影响以及锦鸡儿属灌木扩张对草地生态系统结构和功能的影响。结论如下：(1)锦鸡儿属植物选择有性繁殖和克隆繁殖的主要驱动因素是繁殖代价和有性繁殖优先性，干旱对有性繁殖代价的影响远大于克隆繁殖。在繁殖方式选择中，有性繁殖具有优先性，然而，如果有性繁殖代价过高，植物将选择克隆繁殖，此时，二者的比例受繁殖代价调控。(2)放牧影响了有性繁殖和克隆繁殖相对重要性，从而影响了种群年龄结构、遗传多样性和分布格局，最终影响了种群增长率。(3)锦鸡儿属植物能通过不同开花对策和繁殖分配来适应气候干旱条件。在半干旱地带，开花采用K-对策，少而大的花，高繁殖效率；在强干旱地带，开花采用r-对策，多而小的花，低繁殖效率。在半干旱和干旱地区，有性繁殖分配高、能力强；在强干旱地区，有性繁殖分配很低、能力很弱。(4)锦鸡儿属成熟灌木对树苗建成有促进效应；促进效应包括了微环境改善效应和抗取食效应。促进效应、微环境改善效应和抗取食效应均受干旱胁迫、放牧强度和苗龄的影响；灌木扩张具有正反馈效应。(5)随着气候干旱和放牧强度的增加，繁殖能力大幅降低，放牧加强了气候干旱对种子生产和种群补充的负效应，气候干旱也增强了放牧的负效应。用有性繁殖无法解释随着气候干旱胁迫和放牧强度增加，灌丛逐渐增加的现象。(6)随着围封时间的增长，灌木有性繁殖能力降低；其原因是围封更有利于草本植物恢复，灌木的重要性降低；取食繁殖器官的昆虫数量增加；寄生植物感染增加。(7)在草地上，锦鸡儿属灌丛具有肥岛效应和改善微气候效应，气候干旱加强了这一效应，这些特征有利于其它生物在灌丛内部定居；因此，锦鸡儿属灌木扩张改善群落结构、提高物种多样性、提高生产力，并随着气候干旱胁迫的增加，促进作用增强。研究成果从有性繁殖的角度对草原灌丛化提供了一些解释；弄清了锦鸡儿属灌木在草原生态系统中的生态服务价值。