Nitrogen distribution and leaf area indices in relation to photosynthetic nitrogen use efficiency in savanna grasses
Nitrogen distribution and leaf area indices in relation to photosynthetic nitrogen use efficiency in savanna grasses
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DOI：
10.1023/a:1009727822617
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发表时间：
1998-09-01
期刊：
影响因子：
1.7
通讯作者：
Medina, E
中科院分区：
文献类型：
--
作者：
Anten, NPR;Werger, MJA;Medina, E
对委内瑞拉中部热带稀树草原的C-4草、C-4草（Paspalum fasciculatum）和两种C-3草（Leersia hexandra和Hymenachne amplexicaulis）的自然林分进行了叶片光合特性、单位叶面积氮含量（n(L)）和单位叶面积产量（n(L)）分布模式的测量。还计算了冠层光合作用的日速率（P-cD）以及在给定冠层总氮量（即冠层- pnue）下，单位n(L)下P-cD最大的最佳叶面积产量。洪泛稀树草原C-3和C-4种的单位n(L)光合作用的光饱和速率（即叶片- pnue）和冠层- pnue相似，这与以往的研究结果形成了强烈对比。特别是骆家辉，也有柳杉和花楸的叶片和冠层光合效率，其计算值明显高于具有相同光合途径（即C-3或C-4）的大多数其他物种。与以往的研究相比，林分间冠层光梯度的差异只能部分解释N分布的差异。实测叶面积指数较大，平均n(L)值小于计算最优值。然而，最优氮肥产量和实际平均氮肥产量之间存在很强的线性相关性，这表明尽管该模型高估了平均氮肥产量，但它确实很好地预测了单位氮肥叶面积产量的差异——逆平均氮肥产量。这一结果强烈表明，单位叶片氮的叶面积产量随叶片氮素利用率的增加而增加，随光消光系数的增加而减少。来自季节性热带稀树草原的草种具有极高的叶片光合效率，因此每单位n(L)产生大量的最佳叶面积。这有助于解释为什么这些物种的林分可能具有高叶面积指数和高光合生产力，尽管它们生长的养分利用率非常低。
Leaf photosynthetic characteristics, distribution patterns of nitrogen content per unit leaf area (n(L)) and leaf area production per unit n(L) were measured in natural stands of a C-4 grass (Hyparrhenia rufa) from the seasonal savannas and of a C-4 grass (Paspalum fasciculatum) and two C-3 grasses (Leersia hexandra and Hymenachne amplexicaulis) from the flooded savannas in central Venezuela. Daily rates of canopy photosynthesis (P-cD) as well as the optimal leaf area production per unit n(L) at which P-cD for a given total amount of nitrogen in the canopy (i.e., canopy-PNUE) is maximized were also calculated. The C-3 and C-4 species from the flooded savannas had similar light saturated rates of photosynthesis per unit n(L) (i.e. leaf-PNUE) and similar canopy-PNUEs which was in strong contrast with previous studies. Especially H. rufa but also L. hexandra and H. amplexicaulis had leaf- and canopy-PNUEs which were considerably higher than the values calculated for most other species with the same photosynthetic pathway (i.e., C-3 or C-4). In contrast to previous studies, differences in the light gradient in the canopy between stands only partially explained differences in N distribution. Measured leaf area indices were greater and the average n(L) values were consequently smaller than the calculated optima. There was, however, a very strong linear correlation between the optimal and actual average nL indicating that even though the model overestimated average n(L), it did predict the differences in leaf area production per unit nitrogen - the inverse average n(L) - very well. This result strongly indicates that leaf area production per unit of leaf nitrogen increases with leaf-PNUE and decreases with the extinction coefficient for light. Grass species from seasonal savannas have extremely high leaf-PNUEs and thus optimally produce large amounts of leaf area per unit n(L). This helps explain how stands of these species may have high leaf area indices and achieve high photosynthetic productivity despite the very low nutrient availability at which they grow.