Department of Ecology, Evolution and Behavior, University of Minnesota, 1987 Upper Buford Circle, Saint Paul, MN 55108, USA.
Tree Physiol. 2011 Jun;31(6):604-14. doi: 10.1093/treephys/tpr056.
Many willow species (genus: Salix) co-occur within habitats (α-diversity) and across the landscape (β-diversity) throughout North America. This high diversity is challenging to explain because closely related species often share similar functional traits and thus experience heightened competition and shared pest and pathogen susceptibility. To investigate whether traits related to drought survival are important in maintaining diversity, we conducted an experimental dry-down on six willow species in a greenhouse. We compared species' growth rates, stem and leaf hydraulics, leaf function and dieback and examined potential associations between their drought responses and habitat affinities. Habitat affinities were characterized based on species occurrence in randomly established field plots in central Minnesota. Overall, species that occur in drier, more seasonally variable habitats tended to have higher water-use efficiency, and faster growth rates than species from wetter habitats. However, the greatest difference in drought survival strategies was found between two species with similar habitat affinities. We conclude that differences in willow species could be important in both driving habitat differentiation and permitting temporal differentiation in resource utilization within habitats. Therefore, species' water-use strategies could be important in maintaining both α- and β-diversity across the landscape.
许多柳树物种（柳属：Salix）在北美生境中（α多样性）和跨越景观（β多样性）共存。这种高度的多样性难以解释，因为亲缘关系密切的物种通常具有相似的功能特征，因此会经历更高的竞争和共同的害虫和病原体易感性。为了研究与耐旱生存相关的特征是否对维持多样性很重要，我们在温室中对六种柳树物种进行了干燥处理实验。我们比较了物种的生长速率、茎和叶的水力、叶功能和枯萎情况，并研究了它们对干旱的反应与栖息地偏好之间的潜在关联。栖息地偏好是根据物种在明尼苏达州中部随机建立的实地调查点的出现情况来确定的。总体而言，与来自潮湿生境的物种相比，在较干燥、季节性变化较大的生境中生存的物种往往具有更高的水分利用效率和更快的生长速率。然而，在耐旱生存策略方面，两个具有相似栖息地偏好的物种之间存在最大的差异。我们的结论是，柳树物种的差异可能在驱动栖息地分化和允许生境内部资源利用的时间分化方面都很重要。因此，物种的水分利用策略对于维持景观范围内的α多样性和β多样性可能很重要。
