高寒退化草地狼毒种群不同海拔花大小-数量的权衡关系

Trade-off between the biomass and number of flowers in Stellera chamaejasme along an elevation gradient in a degraded alpine grassland

权衡关系是植物生活史对策理论的基础,花大小-数量的权衡关系对理解花的生物量分配具有重要的意义。该文利用实验生态学方法,研究了祁连山北坡高寒退化草地4个不同海拔狼毒(Stellera chamaejasme)种群花大小与花数量间的关系。结果表明:随着海拔升高,草地群落的高度、密度和地上生物量均呈先升高后降低的倒U型分布,狼毒花大小呈逐渐增大的趋势,而花数量呈相反的变化趋势;不同海拔样地狼毒花大小与花数量间的相关性存在差异,海拔2 700、2 900和3 000 m样地狼毒花大小和花数量之间均存在极显著的负相关关系(p<0.01),海拔2 800 m样地二者之间存在显著的负相关关系(p<0.05),狼毒植株分配给花大小与花数量的资源间存在着"此消彼长"的权衡关系;海拔2 800 m样地是狼毒植株花大小与花数量权衡关系由低海拔的花数量多而单花生物量低向高海拔的花数量少而单花生物量高转变的区域。狼毒植株通过合理权衡花数量和花大小的资源配置,以补偿在海拔梯度上不利因素对种群繁衍带来的影响,从而实现种群的繁殖成功,反映了毒杂草对异质性生境的表型可塑性机制。

Aims Trade-offs are the basis of the theory on plant life-history strategies, and the trade-off between flower size and flower number is an important determinant of flower biomass allocation. Our objective was to study the changes in the relationship between flower size and flower number in Stellera chamaejasme populations with ele-vation in Northwest China. Methods The study site was located in a degraded alpine grassland on the northern slope in Qilian Mountains, Gansu Province, China. Survey and sampling were carried out at four elevations at intervals of 100 m from 2 700 m to 3 000 m;a GPS was used to determine the elevation. Community traits were investigated and 45 individuals of S. chamaejasme were collected randomly at each elevation. The samples were cleaned and divided into differ-ent organs, and their biomass were then measured after being dried at 80 ℃ in an oven. Important findings With increasing elevation, the height, density, and aboveground biomass of the plant com-munities displayed a pattern of initial increase and then followed by a subsequent decline;the flower biomass in S. chamaejasme increased with increasing elevation, while the flower numbers decreased. The flower size was nega-tively correlated with the flower number, but the relationship varied along the elevation gradient; there was a highly significant negative correlation （p 〈 0.01） between the flower size and the flower number at elevations 2 700, 2 900, and 3 000 m, whereas the correlation only reached a significant level （p〈0.05） at the elevation of 2 800 m, indicating that there is a trade-off between the flower size and flower number. The elevation of 2 800 m appeared to be a switching point where the S. chamaejasme individuals with more but smaller flowers at the lower elevations were transformed into ones with fewer but bigger flowers with increasing elevation. Consequently, a change in the reproductive strategy with a trade-off between flower size and flower number ensures successful reproduction of the S. chamaejasme populations in adverse environments.