Section of Ecology, Dept. of Biology, University of Turku, FI-20014 Turku, Finland.
Sci Total Environ. 2013 Feb 1;444:212-23. doi: 10.1016/j.scitotenv.2012.11.084. Epub 2012 Dec 27.
Although trees in polluted areas often exhibit modified growth habits, the immediate causes of changes in crown architecture and their consequences for persistence of plant populations in disturbed habitats are not well understood. We compared individuals of mountain birch, Betula pubescens ssp. czerepanovii, growing in severely disturbed habitats (industrial barrens) surrounding a nickel-copper smelter in north-western Russia, with birches growing in unpolluted habitats. They were found to have shorter heights, a shrubby growth habit, lower depth/width and surface/foliar mass ratios of the crown, higher numbers of dead branches and twisted trunks and higher branching resulting from increased numbers of long shoots and more densely spaced buds than individuals in unpolluted forests. The increased production of long shoots was enabled by their formation not only from the axillary buds of previous-year long shoots but also from the apical buds of short shoots. These latter long shoots develop in the inner part of the crown, thus increasing the crown density. Additionally, birches from industrial barrens better compensated for mechanical damage, such as trunk/shoot removal, compared to birches from unpolluted forest and mountain tundra habitats, presumably due to the larger number of buds formed annually. The specific crown architecture of these birches can be explained by the direct effects of pollution combined with changes in microclimate due to pollution-induced forest decline. The seed progenies of birches from an industrial barren reared in a benign environment produced higher numbers of long shoots than seedlings from other habitats, suggesting that adaptive changes in crown architecture are partially shaped by the selection imposed by long-term pollution impacts. Nearly spherical and compact crowns minimise the impacts of unfavourable environmental conditions on trees and are therefore adaptive. We concluded that the development of specific crown architecture allows mountain birch to dominate in habitats that are severely disturbed by pollution.
尽管受污染地区的树木常表现出生长习性的改变，但树冠结构变化的直接原因及其对受干扰生境中植物种群持续性的影响还不太清楚。我们比较了生长在俄罗斯西北部一个镍铜冶炼厂周围严重受干扰生境（工业荒地）中的高山桦（Betula pubescens ssp. czerepanovii）个体与生长在未受污染生境中的桦树。结果发现，它们的高度更矮、呈灌丛状、树冠深度/宽度和表面积/叶面积比更小、死枝和扭曲树干数量更多、分枝更多，这是由于长枝数量增加和芽间距更密所致。长枝的大量产生是由于它们不仅由前一年长枝的腋芽形成，而且由短枝的顶芽形成。这些后期长枝在树冠内部形成，从而增加了树冠密度。此外，与未受污染森林和山地冻原栖息地的桦树相比，来自工业荒地的桦树对机械损伤（如树干/树枝去除）的补偿能力更强，这可能是由于每年形成的芽数量更多。这些桦树的特定树冠结构可以用污染的直接影响与污染引起的森林衰退导致的小气候变化相结合来解释。在良性环境中饲养的来自工业荒地的桦树的种子后代比来自其他栖息地的幼苗产生了更多的长枝，这表明树冠结构的适应性变化部分是由长期污染影响所施加的选择塑造的。近球形和紧凑的树冠最大限度地减少了不利环境条件对树木的影响，因此是适应性的。我们得出结论，特定的树冠结构的发展使高山桦能够在受污染严重干扰的生境中占主导地位。
