柳枝稷无性分株种群的密度依赖调节机制

Density-dependent regulation for ramet populations of Panicum virgatum

【目的】研究田间丛生克隆植物柳枝稷(Panicum virgatum)无性分株种群调节机制。【方法】于2005-2006年田间连续调查2~4年生规则行生柳枝稷固定长度种植行无性分株群内分株个体高度分布及分株群整体分株质量建成。同时在高低分株密集直立发生格局下,沿垂直方向以0.2m为固定空间间隔,对分株群垂直空间局部分株密度进行细分。【结果】证实了柳枝稷分株群整体密度依赖死亡机制的缺失;基于空间细化的密度界定,发现了无性分株种群内平均质量与密度异速关系的异化。分株高度均值层的分株数量与种群平均分株个体质量间的常用对数线性关系显著,并表现出对-4/3自疏轨迹的更好趋近。垂直填塞过程可能主导了上述异速关系的形成,即通过严格高度正态分布分株群垂直方向分株高度均值空间初始拥挤效应,伴随分株平均质量增长,分株群绝对高度不等性持续增加,同时围绕分株高度均值空间可能发生局部性的分株上下迁移过程,分株高度均值空间内分株密度相应下降,界定为拟自疏过程。【结论】相对于密度依赖死亡导致的水平填塞,柳枝稷无性分株种群的调节机制表现为亚种群尺度空间对数量的密度效应等价置换过程。

【Objective】This paper aimed to understand the regulation for ramet populations of field clonal Panicum virgatum plants.【Method】Height size patterns and total weight of Panicum virgatumramets at 2-4years old planted in regular row with fixed length during 2005-2006 were studied,and the local ramet densities in the vertical direction were fractionized by firm 0.2mheight.【Result】The absence of density-dependent mortality mechanism of Panicumvirgatum ramet populations was confirmed.Based on spatial definition of density,the alienation of relationship between average quality and density allometry within ramet population was observed.Significant log-linear relationship was found between number of ramets in mean-ramet-height space and average weight of whole ramets with an asymptote towards the-4/3self-thinning trajectory.Vertical packing process possibly dominated the formation of alienation.Through the initial crowding of strict height based normal distributed ramets in the mean-ramet-height space at vertical direction,the absolute height of ramets population increased continuously along with the increase of average mass.At the same time,locally up and down migration processes of ramets happened and the density of ramets in mean-ramet-height space decreased.This was defied as a 'similar self-thinning'process.【Conclusion】Comparing with the horizontal packing or density-dependent mortality in non-donal plant populations,the density-dependent population regulation of switchgrass ramet population presents the equivalent-density displacement of'number'by'space'.