Harder Lawrence D, Aizen Marcelo A, Richards Shane A, Joseph Michael A, Busch Jeremiah W
Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4 Canada
Laboratorio Ecotono, INIBIOMA-CONICET and Centro Regional Bariloche, Universidad Nacional del Comahue, Quintral 1250, 8400 Bariloche, Río Negro, Argentina.
Am J Bot. 2016 Mar;103(3):484-97. doi: 10.3732/ajb.1500269. Epub 2016 Mar 1.
Pollen on a stigma represents a local population of male gametophytes vying for access to female gametophytes in the associated ovary. As in most populations, density-independent and density-dependent survival depend on intrinsic characteristics of male gametophytes and environmental (pistil) conditions. These characteristics and conditions could differ among flowers, plants, populations, and species, creating diverse male-gametophyte population dynamics, which can influence seed siring and production.
For nine species, we characterized the relations of both the mean and standard deviation of pollen-tube number at the style base to pollen receipt with nonlinear regression. Models represented asymptotic or peaked relations, providing information about the incidence and magnitude of facilitation and competition, the spatial and temporal characteristics of competition, and the intensity and relative timing of density-independent mortality.
We infer that pollen tubes of most species competed sequentially, their tips ceasing growth if earlier tubes had depleted stylar space/resources; although two species experienced simultaneous competition. Tube success of three species revealed positive density dependence (facilitation) at low density. For at least four species, density-independent mortality preceded competition. Tube success varied mostly within plants, rather than among plants or conspecific populations. Pollen quality influenced tube success for two of three species; affecting density-independent survival in one and density-dependent performance in the other.
The diverse relations of pollen-tube success to pollen receipt evident among just nine species indicate significant contributions of the processes governing pollen germination and tube growth to the reproductive diversity of angiosperms.
柱头上的花粉代表着一群本地雄配子体，它们竞相进入相关子房中的雌配子体。与大多数种群一样，非密度制约性和密度制约性存活取决于雄配子体的内在特性和环境（雌蕊）条件。这些特性和条件在花朵、植株、种群和物种之间可能存在差异，从而产生多样的雄配子体种群动态，进而影响种子的授精和产量。
对于九个物种，我们采用非线性回归来描述花柱基部花粉管数量的均值和标准差与花粉接受量之间的关系。模型呈现出渐近或峰值关系，提供了关于促进作用和竞争的发生率及强度、竞争的时空特征以及非密度制约性死亡率的强度和相对时间等信息。
我们推断，大多数物种的花粉管依次竞争，如果较早的花粉管耗尽了花柱空间/资源，其顶端就会停止生长；不过有两个物种经历了同时竞争。三个物种的花粉管成功率在低密度时显示出正密度依赖性（促进作用）。对于至少四个物种，非密度制约性死亡率先于竞争发生。花粉管成功率大多在植株内部存在差异，而非在植株之间或同种种群之间。花粉质量影响了三个物种中两个物种的花粉管成功率；在一个物种中影响非密度制约性存活，在另一个物种中影响密度制约性表现。
仅九个物种中花粉管成功率与花粉接受量之间就存在多样的关系，这表明控制花粉萌发和花粉管生长的过程对被子植物的生殖多样性有重大贡献。
