植物气孔导度的环境响应模拟及其尺度扩展

气孔导度是衡量植物和大气间水分、能量及CO2平衡和循环的重要指标,探讨气孔导度与环境因子的关系及其模拟,以及气孔导度在叶片、冠层及区域尺度间的尺度转换及累积效应,对更好地认识植被与大气间的水热运移过程,合理评价植被在陆面过程中的地位和作用都具有重要意义。从植物气孔导度与环境因子的关系、气孔导度模拟以及尺度扩展三个方面,对前人的研究成果进行了概括总结。从叶片和冠层两个尺度出发,归纳总结了前人对于不同植物气孔导度与环境因子关系的研究成果,发现由于不同植物的遗传特性、测定时的环境、时间尺度的不同,以及未考虑各个环境因子的相互作用对气孔导度的影响,由此得到的气孔导度与环境因子之间的关系也不尽一致。对各单一环境因子与气孔导度的关系,给出了生理学解释,从根本上说明了环境因子变化对气孔导度的影响,而研究环境因子对气孔导度的综合影响时,应对各环境因子进行系统控制与同步观测。模拟计算植物气孔导度的模型主要有Jarvis模型和BWB模型两类,这些模型的模拟能力随着研究对象、试验区域、环境条件的改变而存在一定的差异,在具体使用时应结合实际情况选择最优模型进行模拟。除上述常用模型外,还总结了其他学者分别从不同角度提出的新的模型,对现有气孔导度模型进行了全面的总结。从叶片-冠层、冠层-区域两个方面归纳总结了前人关于气孔导度尺度扩展的研究成果,发现叶片-冠层的尺度扩展研究较成熟而冠层-区域的尺度扩展在模拟精度的验证方面存在困难。针对以下几个方面提出了今后气孔导度的研究重点:(1)结合研究对象所在的区域及环境条件,选择最优模型进行模拟;(2)综合考虑环境因子之间的相互作用及其对气孔导度的累积影响;(3)BWB模型与光合模型的耦合;(4)提高大尺度范围内的气孔导度模拟精度。

Environmental response simulation and the up-scaling of plant stomatal conductance

Stomatal conductance is a key indicator of the balance and cycles of heat, H₂O, and CO₂ fluxes at the vegetation-atmosphere interface. Thus, it is essential to study the heat and H₂O transfer in the soil, vegetation, and atmosphere andevaluate the status and role of vegetation, by considering the relationships between stomatal conductance and environmental factors, and by modeling and extrapolating the cumulative effect of stomatal conductance at the leaf, canopy, and regional levels. This paper summarized three aspects of research in this area: (1) the relationships between stomatal conductance and environmental factors at the leaf and canopy levels, (2) the simulation of stomatal conductance, and (3) the up-scalingof stomatal conductance from the leaf to canopy level and from the canopy to regional level. The results showed that the relationships between stomatal conductance and environmental factors were not consistent, because hereditary characteristics, environmental conditions, and time-scales varied; in addition, the comprehensive effects of environmental factors were not considered. A hypothesis was made concerning the mechanism underlying the relationship between the environmental factors and stomatal conductance. Systematic control and simultaneous observation should receive more attention when studying these combined influences. At present, Jarvis and BWB are the most commonly used stomatal conductance models. The suitability of these two models differed among research goals, study sites, and environmental conditions, so model selection should be carried out on a case-by-case basis. This paper also summarized other models. The results of up-scaling stomatal conductance from the leaf to canopy level and from canopy to the regional level showed that while research on the former is well established, the latter is still difficult to validate. Finally, we recommend that future research should focus on the following: (1) choosing the best model to simulate stomatal conductance, based on the environmental conditions; (2) considering interactions between environmental factors, and take into consideration their combined influence on stomatal conductance; (3) studying the coupling between the BWB and photosynthetic models; and (4) improving simulation accuracy at large scales.