玉米叶片水分利用效率的保守性

水分利用效率是植物个体或生态系统水分利用过程的重要特征参数,可表征不同时空尺度的植物碳-水耦合关系,对植物适应气候变化研究具有重要意义。以玉米为例,利用中国气象局固城农业气象野外科学试验基地2013—2014年玉米不同灌溉方案模拟试验资料,对不同叶位叶片的水分利用效率特征及其影响因素进行分析。结果表明:植株顶部第1片叶片水分利用效率在拔节期和乳熟期呈现明显的峰值,反映出明显的周期变化规律及其与叶片生理生态特征的紧密相关。在相同环境条件下,不同叶位叶片的水分利用效率不存在显著性差异,即玉米叶片水分利用效率具有空间稳定性与叶龄保守性。同时,研究指出叶片光合速率和蒸腾速率在叶位之间的协调变化是导致空间稳定性和叶龄保守性的主要原因。研究结果可为植物水分关系研究提供参考,也可为水分利用效率的尺度化研究提供依据。

Water conservation in terms of leaf water use efficiency of maize (Zea mays L.)

Water use efficiency (WUE), which is the ratio of CO₂ assimilation to water loss, has been recognized as an important parameter in water use of plant individuals or ecosystems. As a classic index of carbon-water coupling at various temporal and spatial scales, from leaves to ecosystems, it is useful to determine the adaptation of plants to climate change. The North China Plain is the main maize (Zea mays L.) production region in China, where water is the key resource for optimum crop production. Leaf water use efficiency is defined as the ratio of P_n to T_r, which is mostly affected by biological and environmental factors. Although many findings about leaf water use efficiency have been published previously, limited attention has been focused on the water use efficiency relationship between leaves from the same individual plant under water stress during the whole growth period. Therefore, to understand changes of water use efficiency among different leaf positions at the leaf scale and investigate the main factors controlling leaf water use efficiency under water stress, an experiment with different water treatments (only one time irrigation, water controlled at seven and three leaf stages in 2013 and 2014, respectively) for maize was designed and conducted at the Gucheng Agro-meteorological Field Scientific Experiment Base, China Meteorological Administration (115°40''E, 39°08''N) in northern China. The amount of water irrigated in the experiment was in accordance with the total average precipitation during late July and July during 1980-2010 separately in 2013 and 2014. The results showed that there was an obvious pattern for the first opened leaf''s water use efficiency during progressive water stress, as it had two peaks at the jolting and milking stage. Then, leaf water use efficiency in the later growth stage was higher than that in the earlier stage; moderate water deficit improves water use efficiency, but the quantitative relationship between soil water availability and plant water use efficiency needs further investigation. Moreover, leaf water use efficiency was closely connected to its physiological and ecological characteristics, such as leaf water content and specific leaf area. Furthermore, leaf water use efficiency among different leaf positions along the maize plant showed little variation under nearly identical environments, such as soil water content and atmospheric conditions, which means leaf water use efficiency had spatial stability or conservation regardless of leaf ages to some degree. Meanwhile, the results also showed the coordinative changes between the photosynthetic and transpiration rates had mostly contributed to the leaf water use efficiency stability at different leaf positions. The findings provide information for plant-water relationship research and facilitate a mechanistic understanding of the carbon-water relationships at a leaf scale under water stress conditions, and lay a foundation for and up-scaled study of water use efficiency.