Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
Am J Bot. 2011 Sep;98(9):1437-45. doi: 10.3732/ajb.1100123. Epub 2011 Aug 24.
The distribution of species is determined in part by their functional traits. One important function is the ability of xylem to supply water to leaves and withstand water-stress-induced cavitation. These hydraulic traits are hypothesized to have evolved in response to selection by precipitation and temperature. •
We grew 26 species in the genus Pinus in a common environment and used phylogenetic comparative methods to examine whether the evolution of seedling hydraulic and wood density traits were associated with the climate of the extant geographic range of the species. We also examined whether these traits were correlated with each other, with integrated water-use efficiency (WUE), and with plant growth. •
Contrary to predictions from a hydraulic model, we found no association between stem hydraulic conductivity (K(S)) and precipitation, even though there was substantial variation for K(S) in the genus. Nevertheless, K(S) was positively correlated with temperature, plant biomass, and WUE. Wood density was infrequently associated with climate or correlated with other traits except for plant biomass. •
Reduced K(S) in cold climates, if associated with reduced conduit diameter, likely evolved to increase resistance to freezing-induced xylem cavitation. The absence of a K(S)-precipitation relationship among Pinus seedlings suggests that associations between hydraulic traits and precipitation found in adult trees arise through plastic responses to moisture availability and/or develop over ontogeny. The weak association among wood density, climate, and other traits suggest that this trait does not contribute to climate adaptation in Pinus.
物种的分布部分取决于它们的功能特征。一个重要的功能是木质部向叶片供水和承受水分胁迫诱导空化的能力。这些水力特征被假设是为了应对降水和温度的选择而进化的。
我们在一个共同的环境中生长了 26 种松树属物种，并使用系统发育比较方法来检验幼苗水力和木材密度特征的进化是否与物种现存地理范围的气候有关。我们还检验了这些特征是否相互关联，与综合水分利用效率（WUE）和植物生长有关。
与水力模型的预测相反，我们发现茎水力传导率（K(S)）与降水之间没有关联，尽管在该属中 K(S)存在很大的变化。尽管如此，K(S)与温度、植物生物量和 WUE呈正相关。木材密度很少与气候有关，也与其他特征无关，除了植物生物量。
在寒冷气候下，K(S)的降低，如果与导管直径的降低有关，可能是为了增加对冻融引起的木质部空化的抵抗力而进化的。松树幼苗中 K(S)-降水关系的缺失表明，在成年树木中发现的水力特征与降水之间的关联是通过对水分可用性的可塑性反应产生的，或者是在个体发育过程中形成的。木材密度、气候和其他特征之间的弱关联表明，该特征对松树的气候适应没有贡献。
