【目的】研究自然半干旱条件下杨树生长及叶片抗旱相关性状对不同造林密度的响应特征,为半干旱区杨树人工林品种与立地精准适配提供有益信息。【方法】在位于内蒙古达拉特旗的蒙鄂沙生植物园,以高(株行距2 m×3 m)和低(株行距3 m×3 m)两种造林密度栽植的5年生‘哲林4号’杨(Populus deltoides ‘Zhelin 4’)、‘汇林88号’杨(P. × simonii ‘Huilin 88’)和‘中雄4号’杨(P. deltoides × P. suaveolens ‘Zhongxiong 4’)为对象,观测分析其生长和叶片解剖结构、光合参数、脯氨酸等生理生化指标特征差异,并采用主成分分析和隶属函数综合法进行评价。【结果】①低造林密度下3个杨树品种的平均胸径和平均树高均显著大于高造林密度下,增幅均值分别为45.73%和20.52%,2种造林密度下‘中雄4号’杨生长表现均较好,且叶片厚度均显著高于其他品种。低造林密度下‘中雄4号’杨的叶片厚度和栅海比较高造林密度均显著增加,表明其具有更适应低造林密度的叶片结构;②从低造林密度到高造林密度,3个杨树品种的净光合速率(Pn)均显著下降,‘中雄4号’杨与‘汇林88号’杨Pn降幅分别为12.02%和16.05%,‘哲林4号’杨降幅最大,达48.26%,而‘中雄4号’杨和‘汇林88号’杨的蒸腾速率(Tr)、瞬时水分利用效率(WUEi)和气孔导度(Gs)在2种造林密度间差异均不显著。‘哲林4号’杨在高造林密度下的Tr和Gs显著下降且低于其他品种,综合表明低造林密度下杨树的光合能力更强;③高造林密度下3个杨树品种间的脯氨酸和可溶性糖含量差异不显著,‘中雄4号’杨的可溶性蛋白含量显著高于其他品种。而低造林密度下‘哲林4号’杨、‘汇林88号’杨和‘中雄4号’杨分别以可溶性糖、脯氨酸和可溶性蛋白含量显著最高,表明不同杨树品种可能以不同渗透调节物质适应干旱环境。【结论】自然半干旱条件下,低造林密度更有利于杨树生长,不同杨树品种通过不同性状指标特征响应造林密度以调节植株适应干旱环境;‘中雄4号’杨在两种造林密度下的生长及叶片抗旱性状表现更优,能适应半干旱区自然条件下更多造林密度的人工林营建。

【Objective】This study explored the growth and leaf drought resistance-related traits of poplar under natural semi-arid conditions in response to different plantation densities, thereby offering valuable insights for the precise matching of poplar varieties to site conditions in semi-arid regions.【Method】At the Meng’e Shasheng Plant Park in Dalate Banner, Inner Mongolia, three poplar varieties, Populus deltoides ‘Zhelin 4’, P. × simonii ‘Huilin 88’and P. deltoides × P. suaveolens ‘Zhongxiong 4’, planted in high plantation density (2 m×3 m) and low plantation density (3 m×3 m), at their five years old, were selected as the research objects, the characteristics of growth, leaf anatomical structure, photosynthetic parameters, proline and other physiological and biochemical indexes were observed and analyzed. Principal component analysis and membership function synthesis method were used to evaluate the differences.【Result】(1)The average DBH and average tree height of the three poplar varieties under low plantation density were significantly higher than those under high plantation density, with an average increase of 45.73% and 20.52%, respectively. The growth performance of ‘Zhongxiong 4’ under the two plantation densities was better, and the leaf thickness was significantly higher than that of other varieties. Under low plantation density, the leaf thickness and palisade to spongy ratio of ‘Zhongxiong 4’ were significantly increased compared with high plantation density, indicating that the leaf structure of ‘Zhongxiong 4’ was more suitable for low plantation density. (2)From low plantation density to high plantation density, the net photosynthetic rate (Pn) of the three poplar varieties decreased significantly. The Pn of ‘Zhongxiong 4’ and ‘Huilin 88’ decreased by 12.02% and 16.05%, respectively, while the Pn of ‘Zhelin 4’ decreased by 48.26%. The transpiration rate (Tr), instantaneous water use efficiency (WUEi) and stomatal conductance (Gs) of ‘Zhongxiong 4’ and ‘Huilin 88’ were not significantly different between the two plantation densities. Tr and Gs of ‘Zhelin 4’ decreased significantly under high plantation density and were lower than those of other varieties, indicating that the photosynthetic capacity of poplar was stronger under low plantation density. (3)At high plantation density, there was no significant difference in the contents of proline and soluble sugar among the three poplar varieties, the soluble protein content of ‘Zhongxiong 4’ was significantly higher than that of other varieties. However, at low density, ‘Zhelin 4’, ‘Huilin 88’, and ‘Zhongxiong 4’ exhibited the highest concentrations of soluble sugar, proline, and soluble protein. This suggests that different poplar varieties may adapt to drought environment with different osmotic regulatory substances.【Conclusion】Under natural semi-arid conditions, low plantation density is more conducive to poplar growth, and different poplar varieties respond to plantation density through differenttrait indicators to adjust the drought adaptability of trees. The growth and drought resistance of the leaves of ‘Zhongxiong 4’ were better under the two plantation densities, which could adapt to the construction of plantations with more plantation densities under the natural conditions of semi-arid region.