Evolution of C4 plants: a new hypothesis for an interaction of CO2 and water relations mediated by plant hydraulics
Evolution of C4 plants: a new hypothesis for an interaction of CO2 and water relations mediated by plant hydraulics
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DOI：
10.1098/rstb.2011.0261
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发表时间：
2012-02-19
影响因子：
6.3
通讯作者：
Sack, Lawren
中科院分区：
文献类型：
--
作者：
Osborne, Colin P.;Sack, Lawren
作为一种碳浓缩机制，碳-4光合作用已经进化了60多次，以增强祖先的碳-3光合作用途径。在大气CO2耗竭、强光和高温条件下，C-4型植物的光合速率和光合效率高于C-3型植物，说明这些因素是重要的选择因子。这一假设与禾草的比较分析是一致的，禾草表明了从荫蔽森林到开放栖息地的反复进化转变。然而，这种环境转变也强烈影响植物与水的关系。我们推测，低CO2、高光照和高温度条件下对水分运输的过度需求选择了C-4光合作用，这不仅是为了提高光合作用的效率和速率，也是一种节水机制。我们的建议得到了文献和生理模型的支持。C-4途径允许在低气孔导度下的高光合速率，即使在低大气CO2条件下。蒸腾作用的减少保护了液压系统，使气孔保持开放，在干燥的大气和土壤条件下，光合作用可以持续更长时间。因此，C-4光合作用的进化同时改善了植物碳和水的关系，随着大气CO2的下降和生态对水的需求的增加，赋予了强烈的好处。
C-4 photosynthesis has evolved more than 60 times as a carbon-concentrating mechanism to augment the ancestral C-3 photosynthetic pathway. The rate and the efficiency of photosynthesis are greater in the C-4 than C-3 type under atmospheric CO2 depletion, high light and temperature, suggesting these factors as important selective agents. This hypothesis is consistent with comparative analyses of grasses, which indicate repeated evolutionary transitions from shaded forest to open habitats. However, such environmental transitions also impact strongly on plant-water relations. We hypothesize that excessive demand for water transport associated with low CO2, high light and temperature would have selected for C-4 photosynthesis not only to increase the efficiency and rate of photosynthesis, but also as a water-conserving mechanism. Our proposal is supported by evidence from the literature and physiological models. The C-4 pathway allows high rates of photosynthesis at low stomatal conductance, even given low atmospheric CO2. The resultant decrease in transpiration protects the hydraulic system, allowing stomata to remain open and photosynthesis to be sustained for longer under drying atmospheric and soil conditions. The evolution of C-4 photosynthesis therefore simultaneously improved plant carbon and water relations, conferring strong benefits as atmospheric CO2 declined and ecological demand for water rose.