Stinson K A, Bazzaz F A
Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.
Oecologia. 2006 Feb;147(1):155-63. doi: 10.1007/s00442-005-0250-x. Epub 2005 Sep 15.
Plants growing in dense stands may not equally acquire or utilize extra carbon gained in elevated CO(2). As a result, reproductive differences between dominant and subordinate plants may be altered under rising CO(2) conditions. We hypothesized that elevated CO(2) would enhance the reproductive allocation of shaded, subordinate Ambrosia artemisiifolia L. (Asteraceae) individuals more than that of light-saturated dominants. We grew stands of A. artemisiifolia at either 360 or 720 muL L(-1) CO(2) levels and measured the growth and reproductive responses of competing individuals. To test whether elevated CO(2) altered size and reproductive inequalities within stands, we compared stand-level coefficients of variation (CV) in height growth and final shoot, root, and reproductive organ biomasses. Elevated CO(2) enhanced biomass and reduced the CV for all aspects of plant growth, especially reproductive biomass. Allocation to reproduction was higher in the elevated CO(2) than in the ambient treatment, and this difference was more pronounced in small, rather than large plant positive relationships between the CV and total stand productivity declined under elevated CO(2), indicating that growth enhancements to smaller plants diminished the relative biomass advantages of larger plants in increasingly crowded conditions. We conclude that elevated CO(2) stimulates stand-level reproduction while CO(2)-induced growth gains of subordinate A. artemisiifolia plants minimize differences in the reproductive output of small and large plants. Thus, more individuals are likely to produce greater amounts of seeds and pollen in future populations of this allergenic weed.
生长在密集群落中的植物可能无法同等程度地获取或利用在高浓度二氧化碳环境中增加的额外碳。因此，在二氧化碳浓度升高的条件下，优势植物和从属植物之间的繁殖差异可能会改变。我们假设，相较于光照充足的优势植物，高浓度二氧化碳会更显著地提高遮荫的从属豚草个体的繁殖分配。我们将豚草群落种植在360或720 μL L⁻¹的二氧化碳浓度水平下，并测量了相互竞争个体的生长和繁殖反应。为了测试高浓度二氧化碳是否改变了群落内个体大小和繁殖的不平等性，我们比较了高度生长以及地上部、根部和生殖器官最终生物量的群落水平变异系数（CV）。高浓度二氧化碳增加了生物量，并降低了植物生长各方面的CV，尤其是生殖生物量。在高浓度二氧化碳环境中，分配到繁殖的比例高于环境处理，且这种差异在小植株中比在大植株中更明显。在高浓度二氧化碳条件下，CV与群落总生产力之间的正相关关系下降，这表明较小植株的生长增加减少了在日益拥挤条件下较大植株的相对生物量优势。我们得出结论，高浓度二氧化碳刺激了群落水平的繁殖，而二氧化碳诱导的从属豚草植株的生长增加使小植株和大植株的繁殖输出差异最小化。因此，在这种致敏杂草的未来种群中，可能会有更多个体产生大量种子和花粉。
