Department of Biological Sciences, University of Lethbridge, 4401 University Drive W., Lethbridge AB, Canada T1K 3M4.
Tree Physiol. 2018 Jun 1;38(6):789-800. doi: 10.1093/treephys/tpy019.
Heterosis or hybrid vigor is common in hybrid poplars, and to investigate its occurrence and physiological basis we compared narrowleaf cottonwoods, Populus angustifolia James, prairie cottonwoods, Populus deltoides Bartr. ex Marsh, and their native intersectional hybrids, P. × acuminata Rydb., from Alberta, Canada. Clonal replicates from 10 separate trees from each taxon were raised in growth chambers at different temperatures (T). Growth was similarly vigorous across the taxa at 20 and 24 °C, and morphological and physiological traits of the hybrids were generally intermediate between the parental species, or similar to the larger parent, demonstrating additive inheritance or dominance, respectively. Growth declined at 18 and 15 °C particularly in the parental species, and consequently hybrid vigor was displayed for root and especially leaf growth. Stomatal distributions and chlorophyll indices were intermediate in the hybrids and unaffected by T. Foliar nitrogen (N), net assimilation (Asat), stomatal conductance (gs) and transpiration (E) per unit of leaf area were lower in the hybrids, but the hybrids generally had larger leaf areas. Water-use efficiencies (Asat/gs) were similar across the taxa and reduced with warming, while nitrogen-use efficiencies (Asat/N) increased. δ13C was correlated with leaf mass per area, which varied across the taxa. Photosynthesis (Asat) was correlated with chlorophyll content index, N and/or gs in P. deltoides and the hybrids, but not in P. angustifolia, indicating different physiological limitations. We conclude that heterosis in P. × acuminata results from the compound benefits from multiple dominant traits, and superior growth particularly at suboptimal conditions. This indicates phenotypic stability or environmental adaptability, whereby heterozygosity provides metabolic diversity that allows hybrids to thrive across a broader environmental range.
杂种优势或杂种活力在杂交杨树中很常见，为了研究其发生和生理基础，我们比较了来自加拿大阿尔伯塔省的狭叶棉白杨（Populus angustifolia James）、草原棉白杨（Populus deltoides Bartr. ex Marsh）及其本地杂交种银白杨（P. × acuminata Rydb.）。从每个分类群的 10 棵单独的树上获得克隆复制品，并在不同温度（T）下在生长室中培养。在 20°C 和 24°C 下，所有分类群的生长都非常旺盛，杂种的形态和生理特征通常在双亲种之间处于中间位置，或者与较大的亲本相似，分别表现出加性遗传或显性遗传。在 18°C 和 15°C 下，生长明显下降，特别是在亲本种中，因此杂种表现出根和特别是叶生长的杂种优势。杂种的气孔分布和叶绿素指数处于中间水平，不受 T 的影响。单位叶面积的叶氮（N）、净同化（Asat）、气孔导度（gs）和蒸腾（E）较低，但杂种通常具有较大的叶面积。水分利用效率（Asat/gs）在所有分类群中相似，随温度升高而降低，而氮利用效率（Asat/N）增加。δ13C 与叶面积质量相关，叶面积质量在分类群之间有所不同。光合作用（Asat）与叶绿素含量指数、N 和/或 gs 在 P. deltoides 和杂种中相关，但与 P. angustifolia 不相关，表明存在不同的生理限制。我们得出结论，P. × acuminata 的杂种优势源自多个显性性状的综合优势，特别是在亚最优条件下具有更好的生长。这表明表型稳定性或环境适应性，杂种的杂合性提供了代谢多样性，使杂种能够在更广泛的环境范围内茁壮成长。
