Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Stellenbosch, 7602, South Africa.
Department of Geoscience and Geography, University of Helsinki, Helsinki, FI-00015, Finland.
New Phytol. 2013 Oct;200(1):241-250. doi: 10.1111/nph.12349. Epub 2013 Jun 6.
Environmental conditions and plant size may both alter the outcome of inter-specific plant-plant interactions, with seedlings generally facilitated more strongly than larger individuals in stressful habitats. However, the combined impact of plant size and environmental severity on interactions is poorly understood. Here, we tested explicitly for the first time the hypothesis that ontogenetic shifts in interactions are delayed under increasingly severe conditions by examining the interaction between a grass, Agrostis magellanica, and a cushion plant, Azorella selago, along two severity gradients. The impact of A. selago on A. magellanica abundance, but not reproductive effort, was related to A. magellanica size, with a trend for delayed shifts towards more negative interactions under greater environmental severity. Intermediate-sized individuals were most strongly facilitated, leading to differences in the size-class distribution of A. magellanica on the soil and on A. selago. The A. magellanica size-class distribution was more strongly affected by A. selago than by environmental severity, demonstrating that the plant-plant interaction impacts A. magellanica population structure more strongly than habitat conditions. As ontogenetic shifts in plant-plant interactions cannot be assumed to be constant across severity gradients and may impact species population structure, studies examining the outcome of interactions need to consider the potential for size- or age-related variation in competition and facilitation.
环境条件和植物大小都可能改变种间植物-植物相互作用的结果，在胁迫生境中，幼苗通常比较大个体更容易受到促进。然而，植物大小和环境严重程度对相互作用的综合影响还知之甚少。在这里，我们首次通过在两条严重程度梯度上检查草类 Agrostis magellanica 和垫状植物 Azorella selago 之间的相互作用，来检验交互作用的个体发育转变是否会因环境条件越来越严重而延迟的假设。A. selago 对 A. magellanica 丰度的影响，但不是生殖努力，与 A. magellanica 的大小有关，在环境严重程度较高的情况下，交互作用向更负面转变的趋势延迟。中等大小的个体受到的促进作用最强，导致 A. magellanica 在土壤和 A. selago 上的大小类分布存在差异。A. magellanica 的大小类分布受 A. selago 的影响大于环境严重程度，表明植物-植物相互作用对 A. magellanica 种群结构的影响大于生境条件。由于不能假设植物-植物相互作用的个体发育转变在严重程度梯度上是恒定的，并且可能影响物种的种群结构，因此研究相互作用的结果需要考虑竞争和促进作用中可能存在的大小或年龄相关的变异。
