Key message

Autumn flooding reduced nitrogen uptake and fine root mass. Leaf nitrogen resorption increased, but overall autumn nitrogen accumulation was negligible in flooded seedlings. Subsequently, spring survival and growth were decreased.

Abstract

Since nitrogen (N) is often limiting in terrestrial ecosystems, N is conserved in trees by resorption before leaf senescence. Bottomland forests are prone to flooding, which could reduce N uptake, and may decrease phloem transport, which is essential for N resorption. Therefore, we hypothesized that autumn flooding may diminish both N uptake and N resorption in trees, and this would reduce spring growth. Two-year-old Quercus texana seedlings either had no flood or had their complete root system flooded during dormancy induction, the period in autumn when trees prepare metabolically and physiologically for winter dormancy. We measured seedling growth and nutrient contents before flooding and after leaf fall and determined impacts of autumn flooding on growth during the subsequent spring. Autumn flooding resulted in a small increase in N resorption from leaves. In non-flooded seedlings, much more N accumulated in stems and roots than the amount resorbed from leaves, suggesting that there was substantial N uptake during the autumn dormancy induction period. However, flooding severely reduced accumulation of N in roots and stems during autumn, probably by directly reducing uptake and by increasing fine root mortality. Winter survival was reduced 50% by autumn flooding. Autumn-flooded seedlings that survived winter had greater new root growth in spring than non-flooded seedlings, but substantially decreased stem diameter growth. Our results indicate that Q. texana seedlings which are flooded during dormancy induction may be less competitive the following spring due to fine root mortality and reduced nutrient storage, which negatively impact spring growth.

中文翻译：

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秋季洪水破坏了季节性氮存储并影响了德克萨斯栎幼苗的春季生长

关键信息

秋季洪水减少了氮的吸收和细根质量。叶片氮的吸收增加，但淹水幼苗的秋季总氮累积微不足道。随后，春季生存和生长减少。

抽象

由于氮（N）通常在陆地生态系统中受到限制，因此在叶片衰老之前，氮通过吸收被保留在树木中。底层森林容易发生洪水，这可能会减少氮的吸收，并可能减少韧皮部的运输，这对于氮的吸收至关重要。因此，我们假设秋天的洪水可能会减少树木中氮的吸收和氮的吸收，这会减少春季的生长。两岁的德克萨斯栎幼苗在休眠诱导期间没有洪水或完全的根系被淹没。休眠期是秋天，在此期间树木通过代谢和生理学为冬季休眠做好准备。我们测量了洪水前和落叶后幼苗的生长和养分含量，并确定了秋季洪水对随后春季生长的影响。秋季洪水导致叶片对氮的吸收略有增加。在未淹水的幼苗中，茎和根中积累的氮要多于从叶片吸收的氮，这表明在秋季休眠诱导期有大量的氮吸收。但是，洪水可能会直接减少摄入量并增加细根死亡率，从而严重降低秋季氮素在根和茎中的积累。秋季洪水使冬季生存减少了50％。冬季存活的秋浸幼苗在春季比非浸苗具有更大的新根生长，但茎直径增长明显降低。我们的结果表明春季休眠后淹没的德州Q.幼苗由于较弱的根系死亡率和减少的养分储存而竞争力较差，这对春季的生长产生不利影响。