云南干热河谷水库气候效应对车桑子幼苗生长发育的影响及其作用机制

干热河谷地区水电站建设对当地植被的潜在影响是一个值得关注的生态学问题。车桑子是当地植被灌木层的主要成分,开展水库气候效应对车桑子生长、发育影响的研究具有现实价值。以车桑子的实生幼苗为材料,将土壤含水量控制为13%、7%和1.5%,空气湿度控制为50%、65%和75%,从幼苗生长、构件发育、根系发育、生物量分配等方面研究了降水减少和大气湿度增加的气候效应对车桑子的影响,通过叶绿素含量、Fv/Fm、丙二醛(MDA)含量和叶片可溶性糖含量等指标,从光合系统特性、膜质过氧化和渗透调节3个方面研究了车桑子的受损与适应机制。结果表明,土壤干旱能够抑制车桑子幼苗高生长和根系发育的各项指标,并促进生物量向根系分配;当大气湿度增加时,幼苗高生长和根长虽呈增加趋势,但生物量积累、根系发育指标及RMR却具有单峰效应,显示空气湿度过高时对其生长发育具有抑制作用。综合而言,由于大气湿度增加能够部分补偿土壤的干旱效应,干热河谷区水库建设的气候效应不会对车桑子幼苗的生长和发育产生重要影响。结果还表明,土壤干旱和大气湿度变化对叶绿素含量无影响,土壤水分胁迫和空气湿度下降导致Fv/Fm显著下降,说明光合电子传递链受损是车桑子光合抑制的主要原因;土壤水分胁迫导致MDA含量升高,说明细胞膜质过氧化是车桑子幼苗受损的重要机制;而土壤干旱导致叶片可溶性糖含量升高,说明车桑子幼苗具有较好的渗透调节机制。研究结果对评估干热河谷区水电站建设对植被的影响具有参考价值。

Climatic effects of the artificial reservoir of China's dry-hot valleys on the growth and physiological traits of Dodonaea viscosa seedlings

The climatic impacts of the construction of water power stations in the dry-hot valleys in China, including local increases in air moisture and decreased precipitation, negatively affect native vegetation, and thus are a significant ecological problem. Dodonaea viscosa, an indigenous shrub of dry-hot valleys, was used to evaluate the effects of these climatic changes. In this paper, a growth chamber experiment was conducted to quantify the growth and development responses of D. viscosa seedlings to different soil water and air humidity conditions, and further to explore how soil drought and air humidity damage this species. D. viscosa seedlings were subjected to three water (13.0%, 7.0%, and 1.5%, water capacity) and three air humidity (RH 75%, 65%, and 50%) regimes, arranged in a completely random design. Then, seedling growth, root development, and biomass allocation were measured to evaluate climatic effects on seedling growth, and leaf chlorophyll, Fv/Fm, and MDA were measured to detect sites damaged by soil drought and increased air humidity; finally, leaf soluble sugar was measured to determine whether the seedlings respond to soil drought and air humidity through osmoregulation. Our results suggestted that soil drought dramatically decreased the height, leaf number, branch number, and biomass of seedlings. However, these characteristics increased with air humidity from 50% RH to 65% RH, then deceased when the humidity rose to 75% RH. In addition, soil drought decreased root length, root surface area, root projected area, root tips, and root volume, but increased the seedlings'' RMRs (root mass ratio); in contrast, higher air humidity increased root length and decreased RMR, but maximized root surface area, root projected area, root tips, and root volume at the moderate RH 65% level. We also found that soil drought and air humidity had no effect on chlorophyll, but influenced Fv/Fm significantly, which indicates that its photosynthetic electron transport chain was damaged; furthermore, MDA increased under soil drought stress, which suggests that membrane peroxidation occurs under such conditions, but there was no significant MDA increase when air humidity increased from 50% RH to 70% RH. Soil drought also increased leaf sugar levels, suggesting that D. viscosa responds to soil water stress through osmoregulation. Thus, we conclude that increased air humidity can alleviate the effects of soil drought on the seedling growth of D. viscosa, which implies that the construction of water power stations in the dry-hot valleys of China would not have a significant negative impact the population dynamics of D. viscosa. Our results would be useful in evaluating the impacts of water power station construction on vegetation dynamics in dry-hot valleys in China.