胡杨枝芽生长特征及其展叶物候特征

以5个不同发育阶段的胡杨(Populus euphratica Oliv.)个体为研究对象,观测记录了枝芽展叶物候、枝芽生长特征和叶形变化的空间分布规律。结果表明:不同发育阶段的胡杨个体以及同一个体树冠的不同层次,其枝芽生长及其展叶物候期表现出不同的时空特征。随着树龄的增加和树冠层次的增高(由基向顶),当年新生枝条长度、枝条叶片数和叶形指数逐渐减小,但叶面积和叶片干重逐渐增大。5个不同发育阶段胡杨个体均表现出展叶物候始于树冠顶层,依次向下结束于树冠基部;展叶物候期共性表现在枝芽萌动期均在4月上旬,起始展叶期集中在4月中旬,展叶终期则在5月上旬到下旬;树龄较大的个体其枝芽萌动期、起始展叶期、展叶终期较树龄较小的个体早;其枝芽萌动期到展叶终期的时间进程较树龄较小的个体短;不同发育阶段的个体枝芽萌动期出现的时间较为离散,起始展叶期和展叶终期出现的时间较为集中。相关分析表明,出叶周期与枝条长度、枝条叶片数量和叶形指数呈极显著正相关,与叶面积和叶片干重呈显著负相关。

Investigation of bud burst, shoot growth and leaf expansion in Populus euphratica of different ages

Populus euphratica Oliv., a member in the subgenus populous, family Salicaceae, is the oldest and most primitive desert riparian forest species, mainly distributed in central Asia, west Asia and the Mediterranean region. Over 60% of natural P. euphratica forest is distributed in China, of which, 89.1% of P. euphratica is concentrated in the Tarim Basin of Xinjiang. Earlier research indicated that at different growth and development stages of P. euphratica individuals, leaf morphology was different, showing a clear heterophylly. Leaves of seedlings, saplings and young branches sprouted from adult trees are of linear and lanceolate, but with tree growth, ovate and broadly ovate leaves start to form giving the tree a unique look. In adult tree, the top canopy is dominated by broadly ovate leaves and the bottom canopy is of mainly linear and lanceolate leaves. This is known as exclusive or variant leaves of P. euphratica. Studies also shown that, in the same growing season of the same P. euphratica individual, it is always the case that the broadly ovate leaves on the top canopy start to burst first followed by the linear, lanceolate and ovate leaves at the bottom of the canopy, indicating a vertical inherent coordination of development. A clear relationship among branching, bud growth, leaf phenology and leaf shape change exist in this unique species worth detailed investigation. Most of the previous research was focused on flowering phenology, but the relationship among branching, bud growth, leaf phenology and leaf shape change and their vertical distribution have not been studied in detail at different developmental stages. We examined the development of these organs and their relationships and interactions using P. euphratica individuals at different developmental stages to lay a foundation for revealing the significance of leaf shape changes in P. euphratica life history. P. euphratica trees at five different development stages were investigated to study the characteristics of growth and the spatial distribution pattern of leaf shape changes. Results indicated that different growth pattern and leaf phenology were shown both in spatial distribution and phenological developmental stages at different individual canopy levels and trees of different ages. With the increase of tree age and canopy level (from base to top), new shoot length, leaf number per shoot and leaf shape index have decrease trend, but a gradual increase trend of leaf area and leaf dry weight were observed. Regardless of developmental stages, leaf expansion started on the top of the canopy and gradually moved to wards the base. Bud opened in early April, leaf expansion commenced in mid-April and finished from early to late May. Older trees showed earlier bud burst and leaf expansion than younger tress and they also finish leaf expansion early. Different bud burst and leaf expansion were observed on trees of different developmental stages but the commencement and termination of leaf expansion were relatively similar. Leaf emergence period was positively correlated with branch length, leaf number and leaf shape index but negatively correlated with leaf area and leaf dry weight and both correlations were significant.