不同植物叶片水分利用效率对光和CO2的响应与模拟

植物叶片水分利用效率的高低取决于气孔控制的光合作用和蒸腾作用两个相互耦合的过程,模拟水分利用效率对环境变化的响应特征和机制是理解生态系统碳循环和水循环及其耦合关系的基础.研究通过人工控制光强和CO2浓度,对叶片水分利用效率进行了研究.提出了植物水分利用效率在光强和CO2浓度共同作用下的估算模型.数据分析表明,该模型在包括C3和C4植物、草本和木本植物在内的9种植物上能很好地模拟水分利用效率对光强和CO2浓度共同作用的响应.该模型可以用于估算CO2浓度升高条件下光合速率的提高和蒸腾速率的降低对水分利用效率提高的贡献量.CO2浓度变化条件下,水分利用效率在不同植物之间有巨大差异,研究区域尺度植物的水分利用效率时至少需要将植物区分为C4植物和C3植物,其中C3植物区分为草本和木本植物3种生态功能型才能较为准确地估算植物的整体水分利用效率.应用本研究提出的水分利用效率估算模型和植物水分利用效率生态功能型分类标准,可以为建立以植物的水分利用效率为基本参数的陆地生态系统水循环模型和陆地生态系统生产力模型提供重要依据.

Responses of water use efficiency of 9 plant species to light and CO2 and their modeling

Photosynthesis coupled with transpiration determines water use efficiency (WUE) at leaf level, and the responses of WUE controlled by gas exchanges through stomata to environment are the basis of carbon and water cycles in the ecosystem. In this paper, by using Li-6400 Portable Photosynthesis System (LI-COR), WUE at leaf level was analyzed under controlled photosynthetic photons flux density (PPFD) and CO₂ concentration conditions across 9 plant species including maize (Zea mays), sorghum (Sorghum vulgare), millet (Setaria italica), soybean (Glycine max), peanut (Arachis phyogaea), sweet potato (Ipomoea batatas), rice (Oryza sativa), Masson pine (Pinus massoniana) and Schima superba. We had developed a new model to estimate the water use efficiency in response to the combined effects of light and CO₂ concentration. Our measured data validated that this model could simulate the changes of water use efficiency very well under combined effect of light and CO₂ concentration. It could be used to estimate contribution of photosynthesis increase and transpiration decline on water use efficiency with the rising of CO₂ concentration. Great differences in water use efficiency occurred in these different plant species under various CO₂ concentration levels. Based on water use efficiency at regional scale, we concluded that plants should be separated into C₃ plants and C₄ plants, and furthermore, C₃ plants should be separated into herbaceous plants and woody plants. Our separation criteria would do a great favor in modeling the evapotranspiration of terrestrial ecosystem with carbon and water balance.