Rapid Leaf Deployment Strategies in a Deciduous Savanna
Rapid Leaf Deployment Strategies in a Deciduous Savanna
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DOI：
10.1371/journal.pone.0157833
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发表时间：
2016-06-16
期刊：
影响因子：
3.7
通讯作者：
Higgins, Steven Ian
中科院分区：
文献类型：
--
作者：
February, Edmund Carl;Higgins, Steven Ian
落叶植物避免了在不利季节维持叶子的成本，但每年都要承担长新叶的成本。因此，在具有明显季节性和低叶结构成本的生态环境中，预计会发生落叶。在我们的研究系统中，一个季节性干燥的热带稀树草原，许多树木是落叶的，这表明叶片的建造成本一定很低。然而，先前的研究表明，氮在这个系统中是有限的，这表明叶片的构建成本很高。在这里，我们使用土壤水分有效性、叶片物候和树冠中氮分布的时间序列来研究这个难题，以说明树木如何在叶子脱落之前吸收氮，并在生长季节开始时利用储存的氮和碳储备来构建新叶。我们的研究结果表明，树木在第一场降雨之前不久就展开了叶子，并预期会出现氮矿化的相关脉冲。我们的研究结果还表明，树木在第一场雨的两周内迅速形成了一个完整的树叶冠层。我们检测到叶片氮含量的增加与第一次降雨和氮向更远端的分支移动相对应，这表明储存的氮储备被用来构建叶片。此外，这些叶片的稳定碳同位素比率（δ C-13）表明储存的碳用于叶片结构。我们的研究结果表明，利用储存的氮和碳储备及早部署叶片是一种与第一场雨的开始有内在联系的策略。这一策略可能会赋予那些在雨季开始时或之后展开树叶的物种竞争优势。
Deciduous plants avoid the costs of maintaining leaves in the unfavourable season, but carry the costs of constructing new leaves every year. Deciduousness is therefore expected in ecological situations with pronounced seasonality and low costs of leaf construction. In our study system, a seasonally dry tropical savanna, many trees are deciduous, suggesting that leaf construction costs must be low. Previous studies have, however, shown that nitrogen is limiting in this system, suggesting that leaf construction costs are high. Here we examine this conundrum using a time series of soil moisture availability, leaf phenology and nitrogen distribution in the tree canopy to illustrate how trees resorb nitrogen before leaf abscission and use stored reserves of nitrogen and carbon to construct new leaves at the onset of the growing season. Our results show that trees deployed leaves shortly before and in anticipation of the first rains with its associated pulse of nitrogen mineralisation. Our results also show that trees rapidly constructed a full canopy of leaves within two weeks of the first rains. We detected an increase in leaf nitrogen content that corresponded with the first rains and with the movement of nitrogen to more distal branches, suggesting that stored nitrogen reserves are used to construct leaves. Furthermore the stable carbon isotope ratios (delta C-13) of these leaves suggest the use of stored carbon for leaf construction. Our findings suggest that the early deployment of leaves using stored nitrogen and carbon reserves is a strategy that is integrally linked with the onset of the first rains. This strategy may confer a competitive advantage over species that deploy leaves at or after the onset of the rains.