华北驼绒藜自然种群结实的花粉和资源限制

Pollen and resource limitations to lifetime seed production in a wild population of Ceratoides arborescens

运用人工授粉、补充无机营养、去叶处理以及疏花处理研究了华北驼绒藜自然种群花粉和资源有效性对结实的影响,并进一步探讨了该植物的选择性败育现象和繁殖对策。结果表明:花粉来源而不是花粉数量对华北驼绒藜结实存在显著影响;同枝授粉结籽率和结实率均低于自然授粉,异株授粉则显著高于同枝授粉和自然授粉;异株授粉种子千粒重显著高于自然授粉和同株异枝授粉,极显著高于同枝授粉。华北驼绒藜结实存在资源限制,补充施肥提高了单枝开花数和结籽率。随摘除叶片数量的增加,结籽率明显降低,摘除叶片处理与对照之间均形成显著差异,摘除1/2叶、3/4叶以及去全叶处理使种子千粒重显著低于对照。人工疏花实验表明华北驼绒藜存在选择性败育现象。华北驼绒藜可根据花粉和资源的可利用性来调整性分配、授粉方式和结实以获得最大适合度,具有复杂的繁殖对策,表现出较好的环境适应性。

Ceratoides arborescens （Losinsk） Tsien et C. G. Ma is an important forage in the northwestern arid and semi-arid regions of China. It has rich nutrient reserves, strong resistance to drought, and is also an excellent resource for ecological reconstruction and grassland improvement. In this study, the effects of pollen and resource availability on overall seed production in a natural population of C. arborescens were evaluated. The experimental material was taken from Siziwang Banner, Inner Mongolia, China. The plants were 4 years old, 60 × 60 cm in size, and 10-200 cm in height. Experimental treatments included artificial pollination from different pollen sources, fertilizer addition, and different degrees of defoliation and deflowering, and the resulting seed set （seeds per plant）, fruit set, and 1000-grain weight were determined. The selective abortion hypothesis and plant reproductive strategies were considered. The results were as follows： The pollen source and quality but not the total pollen numbers significantly affected the reproduction of this species. Pollens from different sources have significant impacts on fruit set, seed set, and 1000-grain weight. Self-fertilization with pollen grains from the same inflorescence yielded 10.04% fruit set, and fruit sets using pollen from a different inflorescence of the same plant and from different plants were 52.16% and 65.09%, respectively; the latter was significantly higher than in the control and the other treatments. The 1000-grain weight from fertilizations using pollen from different plants was 1.970 g, which was significantly higher than in the control and in self-fertilizations using pollen from different inflorescences of the same plant and from the same inflorescence. The seed set in this natural population was nutrient limited. Externally supplied fertilizer increased the numbers of flowers, and increased the seed set （89.96%） and 1000-grain weight （1.879 g） significantly compared with the unfertilized control, Better nutrition can enhance female reproductive function, improving both seed yield and quality. We performed five leaf cutting treatments, including the control. As increasing percentages of leaves were cut, the seed set decreased ; all of the leaf cutting treatments resulted in significantly lower seed set than in the control. As increasing percentages of leaves were cut, 1000-grain weight also decreased; cutting of half, three-fourths, and all of the leaves resulted in significantly lower 1000-grain weights than in the uncut control. The flower removal experiment indicated that seed set increased significantly but 1000-grain weight decreased significantly as more flowers were removed. There was selective abortion in C. arborescens. Ceratoides arborescens has adopted dichogamous reproduction to avoid inbreeding depression; in the absence of complete fertilization by pollen from a different plant, the flowers can be self- fertilized, which may function as a breeding safeguard mechanism to ensure reproduction when exogenous pollen is scarce. Plants of this species also improved their seed set （ to increase the potential number of offspring） and increased their seed size （to enhance the quality and competitiveness of their progeny） when resources were relatively abundant, both of which are strategies to improve fitness. The statistical analyses of fruit set, seed set, and seed weight indicated that C. arborescens has strongly plastic responses to pollen from different sources, to supplemental fertilization, and to the cutting of leaves and flowers. To maximize its fitness, plants of this species adjust their reproductive allocations, modes of pollination, and seed sets according to pollen and resource availability. Ceratoides arborescens has a complex reproductive strategy that provides it with great adaptability to its environment.