Rethinking economic theories of plant water use
Rethinking economic theories of plant water use
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DOI：
10.1007/s12038-023-00350-6
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发表时间：
2023-06
影响因子：
2.9
通讯作者：
A. Roddy
中科院分区：
文献类型：
--
作者：
A. Roddy
植物生态生理学的一个中心假设是碳是植物适应性的主要货币。为此，植物被认为最大化碳增益，而任何偏离最大碳增益的情况都归因于资源限制（如温度、干旱）、生物物理限制（如细胞大小的生物物理限制）或植物生活史的变化，这些变化可能优先考虑未来的碳增益而不是当前的碳增益（即，对碳应用经济贴现率）。与生活在水中相比，生活在陆地上更容易获得二氧化碳：二氧化碳在空气中的扩散速度大约是在水中的1万倍。然而，由于这些二氧化碳必须扩散到光合代谢发生的叶肉细胞的水环境中（th<s:1> - rancourt et al. 2021），陆地生活方式中更大的二氧化碳供应也有代价：光合作用固定的每一个二氧化碳分子通过蒸腾作用损失大约200-400个水分子（Nobel et al. 2005）。因此，水被认为是一种宝贵的资源，必须加以保护，不能浪费。因此，植物生态生理学的大部分领域都假定碳是水交易的中心货币。我们对水和碳的概念框架是基于新古典经济理论的。传统的想法认为，通过消耗水分来进行光合作用，那么固定碳可以分配给个体适应性的三个组成部分：生长、繁殖和生存（Violle et al. 2007）。然而，在最近的一篇综述中，Blonder等人（2023）认为，这种框架忽略了水的重要用途，这些用途可能与碳没有直接联系，当然也不会与短期碳收益有关。Blonder等人（2023）指出了水本身的各种功能，而不是它对碳的交换速率。将水的使用提升到与碳分配同等重要的水平，可能会揭示出关键的植物生态策略和行为，否则这些策略和行为可能很容易被忽视。虽然碳对植物的功能无疑是重要的，但它能成为生态生理学家经常假设的适应性指标吗？大多数生态生理学家都同意，所有资源分配的最终目标是整合终身生殖健康。虽然通常认为支持更多碳吸收的短期蒸腾作用允许对生殖进行更大的投资，但水的消耗直接和独立于碳来支持生殖功能。例如，水对于建造廉价但具有吸引力和生物力学健壮的花朵至关重要（Olson和Pittermann 2019； Roddy等人2019,2023），以及吸引和奖励传粉者（De la Barrera和Nobel 2004； von Arx等人2012；Dahake等人2022）。水可能优先流向生殖器官而不是营养器官，特别是在缺水的情况下（Harrison Day et al. 2022; Sinha et al. 2022）。除了繁殖之外，水被用于促进个体碳增加以外的其他手段，并且可能由于不可避免的权衡或其他植物功能或限制的限制而在无意中损失。作为潜热损失的主要来源，蒸发水对于将植物叶片和生殖器官维持在安全操作温度下至关重要（Patino and Grace 2002; Borges et al. 2016; Roddy 2019; Kullberg et al. 2023）。这种影响可能超出单个叶片水平，包括整个冠层，因为阳光叶片的过度蒸腾可能为遮荫叶片提供更冷、更暗的小气候，使它们能够以更低的水成本进行光合作用，更接近其最佳光照（Blonder et al. 2023）。但Blonder等人（2023）超越了……
A central assumption in plant ecophysiology is that carbon is the primary currency for plant fitness. To this end, plants are thought to maximize carbon gain and any deviations from maximum carbon gain are ascribed to resource limitations (eg, temperature, drought), biophysical limitations (eg, biophysical limits on cell size), or variation in plant life history that may prioritize future carbon gain over current carbon gain (ie, applying an economic discount rate to carbon). Compared to living in water, living on land made accessing CO2 substantially easier: CO2 diffuses approximately 10,000 times faster in air than in water. However, because this CO2 must diffuse into the aqueous environment of the living mesophyll cells where photosynthetic metabolism occurs (Théroux-Rancourt et al. 2021), the greater CO2 supply of the terrestrial lifestyle also comes with a cost: losing approximately 200–400 molecules of water by transpiration for every molecule of CO2 fixed by photosynthesis (Nobel et al. 2005). Water, therefore, is considered a valuable resource to be conserved and not wasted. As such, much of the field of plant ecophysiology posits carbon as the central currency for which water is traded. Our conceptual framing of water and carbon is based in Neoclassical economic theory. By expending water to enable photosynthesis, the traditional thinking goes, then the fixed carbon can be allocated to the three components of individual fitness: growth, reproduction, and survival (Violle et al. 2007). However, in a recent review, Blonder et al.(2023) argue that this framing ignores important uses of water that may not be directly linked to carbon and certainly not to short-term carbon gain. Blonder et al.(2023) point out various functions of water itself, separate from its exchange rate for carbon. Elevating water use to be on par in importance with carbon allocation may illuminate critical plant ecological strategies and behaviors that may otherwise be easy to ignore. While carbon is undoubtedly important to plant function, can it be the metric of fitness so often assumed by ecophysiologists? Most ecophysiologists would agree that the ultimate goal of all resource allocation is integrated lifetime reproductive fitness. While it is typically assumed that short-term transpiration to support more carbon uptake allows for greater investment in reproduction, water is expended to support reproductive functions directly and independently of carbon. For example, water is critical for building flowers that are cheap but nonetheless attractive and biomechanically robust (Olson and Pittermann 2019; Roddy et al. 2019, 2023) and for attracting and rewarding pollinators (De la Barrera and Nobel 2004; von Arx et al. 2012; Dahake et al. 2022). Water may be preferentially directed towards reproductive organs over vegetative organs, particularly under conditions of water scarcity (Harrison Day et al. 2022; Sinha et al. 2022).Beyond reproduction, water is used for means other than promoting individual carbon gain and may be lost inadvertently because of either unavoidable trade-offs or constraints due to other plant functions or limitations. As a major source of latent heat loss, transpired water can be critical to maintaining plant leaves and reproductive organs within safe operating temperatures (Patino and Grace 2002; Borges et al. 2016; Roddy 2019; Kullberg et al. 2023). This effect may extend beyond the individual leaf level to include the whole canopy, as excessive transpiration by sun leaves may provide a cooler, darker microclimate for shade leaves so that they may photosynthesize closer to their light optimum at lower water cost (Blonder et al. 2023). But Blonder et al.(2023) move beyond the …