Drought stress mitigation by nitrogen in boreal forests inferred from stable isotopes
Drought stress mitigation by nitrogen in boreal forests inferred from stable isotopes
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DOI：
10.1111/gcb.15813
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发表时间：
2021-08-02
影响因子：
11.6
通讯作者：
Hauck, Markus
中科院分区：
文献类型：
--
作者：
Dulamsuren, Choimaa;Hauck, Markus
北方大部分地区的森林生长最初受到低温和低氮有效性的限制。由于高纬度气候迅速变暖，越来越多的森林面积正在转向干旱限制，特别是在大陆和北方森林的南部地区。处理这一问题的研究大多是树状年代学和遥感分析，侧重于气候影响，但没有回答干旱是单独有效还是与氮素短缺结合在一起限制森林生产力和活力的问题。在这里，我们通过对蒙古落叶松森林的案例研究，结合稳定同位素分析、树木年轮分析和利用附生地衣对当地牲畜密度变异性的生物指示表明，在所研究的位于内蒙古北方森林南缘的高度干旱的森林中，树木对干旱的脆弱性被饲养在附近和森林边缘的牲畜的氮肥所改变。这种干旱-氮素相互作用背后最可能的机制是气孔导度的降低，这是已知的由植物中低氮水平引起的。因此，家畜施氮可以缩短气孔关闭的时间，从而增加树木的生长，我们测量的是径向树干增量。尽管迄今为止在被子植物中研究的潜在机制应该在针叶树上进行实验测试，但我们的结果表明，仅关注水不足以理解干旱有限的北方针叶林对气候变化的反应。
Forest growth in most parts of the boreal zone is originally limited by low temperatures and low nitrogen availability. Due to the rapid climate warming at high latitudes, an increasing forest area is switching to drought limitation, especially in continental and southern parts of the boreal forest. Studies addressing this issue were mostly dendrochronological and remote-sensing analyses focusing on climatic effects, but not answering the question whether drought is effective alone or in combination with nitrogen shortage at limiting the forests' productivity and vitality. Here we show in a case study from larch forests of Mongolia with a combination of stable isotope analyses, tree-ring analysis and bioindication of the local variability of livestock densities using epiphytic lichens that, in the studied highly drought-prone forests at the southern fringe of the boreal forest in Inner Asia, the trees' vulnerability to drought is modified by nitrogen fertilization from livestock kept in the vicinity and the edge of the forests. The most likely mechanism behind this drought-nitrogen interaction is the reduction of stomatal conductance, which is known to be induced by low nitrogen levels in plants. Nitrogen fertilization by the livestock could, thus, shorten the times of stomatal closure and thereby increase tree growth, which we measured as radial stem increment. Even though the underlying mechanisms, which were so far examined in angiosperms, should be experimentally tested for conifers, our results indicate that focusing on water alone is not enough to understand the climate change response of drought-limited boreal forests.