干旱对夏玉米苗期叶片权衡生长的影响

叶片是植物对干旱响应最敏感的器官之一,叶片性状变化及其权衡关系能够反映植物对资源的利用策略以及对干旱的适应对策。基于2014年6个初始土壤水分梯度的夏玉米持续干旱模拟试验研究表明,随着干旱的发展,夏玉米各叶片性状均会受到影响,但不同干旱程度的影响不一致。基于水分胁迫系数及干旱持续时间提出了干旱程度的定量表达,随着干旱的发生发展,干旱程度在0—1之间变化。当干旱程度小于0.21时,夏玉米叶片性状不会受到显著影响;0.21—0.76时,叶片性状大小受到影响,但变化趋势不会发生改变;0.76—0.91时,新叶形成补偿不了老叶脱落,有效叶片数、叶干重、绿叶面积和叶含水量等性状提前出现下降趋势;大于0.91时,叶片生长几乎停滞。夏玉米叶片性状在干旱条件下的适应性生长本质上体现了其在快速生长与维持生存之间的权衡,但不同干旱程度下,夏玉米叶片性状生长的权衡策略不同:未发生干旱时,夏玉米倾向于维持较高的代谢活性,一旦干旱程度大于0,夏玉米就会降低叶片代谢活性;当干旱程度小于0.48时,夏玉米倾向于通过迅速增加叶面积来吸收较多的能量,以获得较大的生长速率,为生殖器官的生长及产量形成储备能量;当干旱程度大于0.48时,夏玉米会减小单叶面积以减少水分散失,倾向于资源贮存以提高其生存能力。

Effects of drought on the trade-off growth of leaf traits of summer maize in the seedling stage

Changes in leaf traits and their trade-offs are reflections of how plants use resources, as well as their adaption strategies to environmental changes. Drought is acknowledged as one of the greatest threats to the growth and development of plants worldwide, and leaves are one of the most drought-sensitive parts of a plant. At present, the effects of drought on leaf traits have been widely studied; however, the trade-off growth between different leaf traits during the progress of drought is less studied, which limits the understanding of plant adaptation strategies in the arid environment. Maize is one of the leading crops in the world, although it is also the most susceptible to drought. Understanding how leaf traits of maize change during the progress of drought and their trade-off growth would help promote the understanding of the adaptation strategies of maize plants to drought and contribute to the development of targeted drought-resistant and drought-relief measures. Therefore, based on the consecutive drought simulation experiment having six primary soil water levels for maize that was conducted in 2014, we investigated changes in five key leaf traits of maize. These were green leaf area, leaf dry mass, specific leaf weight, leaf water content, and effective leaf number, as well as the trade-off growth between the green leaf area and effective leaf number, green leaf area and specific leaf weight, leaf dry mass and leaf water content, respectively. In addition, we developed an indicator to quantitatively evaluate the degree of drought, which consisted of available soil water content, readily available soil water content, and drought duration time, and comprehensively involved factors that were related to the intensity and progress of the water deficit, such as soil texture, meteorological environment, and plant water requirement, among others. Based on this indicator, we quantitatively characterized these leaf trait changes and their trade-off strategies under different drought degrees. The results showed that every leaf trait was affected by drought, however, the extent to which they were affected was related to the degree of drought. The leaf traits were not significantly affected when the degree of drought was below 0.21, and their quantities were affected, although their tendencies were not when the degree of drought was 0.21-0.76. When the degree of drought increased to 0.76-0.91, the effective leaf number, dry mass of leaf, green leaf area, and leaf water content decreased prematurely because the growth of new leaves failed to compensate for the losses caused by senescence of old leaves. When the degree of drought exceeded 0.91, stagnation in leaf growth occurred, and leaf traits barely changed. The adaptive growth of leaves under drought embodied the trade-off between rapid growth and survival, which varied with the degree of drought. Maize maintained high metabolic activity of its leaves until the degree of drought was greater than 0. When the degree of drought was below 0.48, maize tended to grow rapidly by investing more resources into leaf expansion so that more energy could be absorbed. When the degree of drought exceeded 0.48, maize conserved its resources for survival by maintaining relatively lower metabolic activity and smaller leaf size to minimize water loss.