Leaf shedding increases the photosynthetic rate of the canopy in N2-fixing and non-N2-fixing woody species
Leaf shedding increases the photosynthetic rate of the canopy in N2-fixing and non-N2-fixing woody species
复制标题
叶子脱落增加了固氮和非固氮木本植物冠层的光合速率
DOI：
10.1093/treephys/tpy104
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发表时间：
2018
期刊：
影响因子：
4
通讯作者：
Shimpei Oikawa
中科院分区：
文献类型：
--
作者：
Tomoki Tanaka;Chiharu Kurokawa;Shimpei Oikawa
长期以来，人们一直假设叶片脱落的时间对植物适应性至关重要，但很少有实验证据支持这一假设。根据最优理论，当老叶的日光合作用与叶片氮的比值（N-利用效率ε）（以新叶ε的分数表示）低于叶片在脱落前吸收的氮的分数（RN）时，尽管凋落物损失了一些氮(N)，但老叶的脱落增加了冠层光合作用。盆栽试验结果表明，这一现象在缺氮植株上成立，而在富氮植株上不成立；然而，盆栽的使用施加了各种物理、化学和生物限制，这些限制可能会改变实验结果。在这里，我们进行了为期3年的野外调查，在一个凉爽的温带落叶林中，以确定是否有桤木（alnus siboldianamatsum）。（n2固定）和carpinus tschonoskiiMaxim。（非固氮植物）的叶片脱落以增加冠层光合作用，符合上述准则。这些物种通常是同缘生长的，分别被选为富氮和缺氮植物的代表。总体而言，日光合作用随叶龄的增加而减少，同时叶氮变化较小，导致ε降低。在这两个物种中，脱落时叶片ε与新叶ε的比值在所有年份几乎相等，这表明脱落老叶是为了增加冠层光合作用。我们的结果，连同之前的野外调查结果，表明叶片脱落的时间可以通过在广泛的物种群体中最大化冠层光合作用的N使用来解释。
It has long been hypothesized that timing of leaf shedding is critical for plant fitness but there is little experimental evidence to support the hypothesis. According to an optimality theory, shedding of old leaves increases canopy photosynthesis despite some nitrogen (N) being lost as litterfall, when the ratio of daily photosynthesis to leaf N (N-use efficiency, ε) in old leaves, expressed as a fraction of ε in new leaves, becomes lower than the fraction of leaf N that is resorbed before shedding (RN). This was shown to be true for N-poor plants but not for N-rich plants in a pot experiment; however, the use of planting pots imposes a variety of physical, chemical and biological constraints that could change the experimental results. Here we conducted a 3-year field survey in a cool temperate deciduous forest to examine whetherAlnus sieboldianaMatsum. (N2-fixing) andCarpinus tschonoskiiMaxim. (non-N2-fixing) shed their leaves to increase canopy photosynthesis in accord with the above criterion. These species often grow sympatrically and were chosen as representatives of N-rich and N-poor plants, respectively. Overall, daily photosynthesis decreased with leaf age, accompanied by small changes in leaf N, resulting in a decrease in ε. In both species, ε of leaves at shedding expressed as a fraction of ε in new leaves was nearly equal toRNin all years, implying that the old leaves were shed to increase canopy photosynthesis. Our results, together with those of previous field surveys, suggested that the timing of leaf shedding is explained by N use in maximizing canopy photosynthesis across broad groups of species.