Konrad W, Roth-Nebelsick A, Grein M
Institute for Geosciences, University of Tübingen, Sigwartstrasse 10, D-72076 Tübingen, Germany.
J Theor Biol. 2008 Aug 21;253(4):638-58. doi: 10.1016/j.jtbi.2008.03.032. Epub 2008 Apr 6.
Stomatal density tends to vary inversely with changes in atmospheric CO(2) concentration (C(a)). This phenomenon is of significance due to: (i) the current anthropogenic rise in C(a) and its impact on vegetation, and (ii) the potential applicability for reconstructing palaeoatmospheric C(a) by using fossil plant remains. It is generally assumed that the inverse change of stomatal density with C(a) represents an adaptation of epidermal gas conductance to varying C(a). Reconstruction of fossil C(a) by using stomatal density is usually based on empirical curves which are obtained by greenhouse experiments or the study of herbarium material. In this contribution, a model describing the stomatal density response to changes in C(a) is introduced. It is based on the diffusion of water vapour and CO(2), photosynthesis and an optimisation principle concerning gas exchange and water availability. The model considers both aspects of stomatal conductance: degree of stomatal aperture and stomatal density. It is shown that stomatal aperture and stomatal density response can be separated with stomatal aperture representing a short-term response and stomatal density a long-term response. The model also demonstrates how the stomatal density response to C(a) is modulated by environmental factors. This in turn implies that reliable reconstructions of ancient C(a) require additional information concerning temperature and humidity of the considered sites. Finally, a sensitivity analysis was carried out for the relationship between stomatal density and C(a) in order to identify critical parameters (= small parameter changes lead to significant changes of the results). Stomatal pore geometry (pore size and depth) represents a critical parameter. In palaeoclimatic studies, pore geometry should therefore also be considered.
气孔密度往往与大气中二氧化碳浓度（Ca）的变化呈负相关。由于以下两点，这一现象具有重要意义：（i）当前人为导致的Ca上升及其对植被的影响；（ii）利用化石植物残骸重建古大气Ca的潜在适用性。一般认为，气孔密度随Ca的反向变化代表了表皮气体传导对变化的Ca的一种适应。利用气孔密度重建化石Ca通常基于通过温室实验或对标本馆材料的研究获得的经验曲线。在本论文中，引入了一个描述气孔密度对Ca变化响应的模型。它基于水蒸气和二氧化碳的扩散、光合作用以及关于气体交换和水分可利用性的优化原则。该模型考虑了气孔导度的两个方面：气孔孔径程度和气孔密度。结果表明，气孔孔径和气孔密度响应可以分开，气孔孔径代表短期响应，气孔密度代表长期响应。该模型还展示了气孔密度对Ca的响应是如何受到环境因素调节的。这反过来意味着，对古代Ca的可靠重建需要有关所考虑地点温度和湿度的额外信息。最后，对气孔密度与Ca之间的关系进行了敏感性分析，以确定关键参数（即小的参数变化会导致结果的显著变化）。气孔孔几何形状（孔径和深度）是一个关键参数。因此，在古气候研究中也应考虑孔几何形状。
