干旱和遮荫对马尾松幼苗生长和光合特性的影响

为探究马尾松对干旱和遮荫胁迫的生理响应规律和适应机制,以2年生马尾松幼苗为对象,设置对照(CK)、模拟干旱(DR)、遮荫(LL)以及干旱与遮荫的交互处理(DRLL)4种环境,研究干旱和遮荫对马尾松幼苗的生长和光合生理特性的影响。结果表明:(1)在干旱、遮荫和二者的交互处理下,马尾松幼苗的基径和株高增长量均显著减小,且二者的交互处理加重了干旱和遮荫单一处理下的减小趋势,二者交互作用的影响符合"相互作用理论"。(2)在干旱处理下,针叶长度和比叶面积减小,净光合速率、蒸腾速率、气孔导度和细胞间隙CO_2浓度显著降低,水分利用效率显著增加,光合色素含量基本不变。(3)在遮荫处理下,针叶长度和比叶面积增大,净光合速率、蒸腾速率、气孔导度显著降低,光合色素含量显著增加,水分利用效率和细胞间隙CO_2浓度基本未发生改变。(4)二者的交互处理下,针叶长度、比叶面积减小,净光合速率、蒸腾速率和气孔导度显著降低,且降低程度大于干旱单一处理,光合色素含量显著增加,但其增加程度小于遮荫单一处理。说明干旱和遮荫均能抑制马尾松植株的生长,但其光合生理特性在干旱和遮荫胁迫下分别表现出不同的响应特征。在干旱处理下,通过牺牲针叶长度和比叶面积、调节气孔导度达到保水目的来适应干旱环境;在遮荫处理下,通过增大针叶长度、比叶面积和光合色素含量来响应遮荫环境。在二者的交互处理下,干旱胁迫导致马尾松针叶长度、比叶面积和气孔导度的减小趋势不仅未因遮荫环境而得到缓解,而且还削弱了对光合色素的合成能力,因此,二者的交互作用会进一步加重对马尾松生长的抑制。

Effects of drought and shading on growth and photosynthetic characteristics of Pinus massoniana seedlings

To explore the physiological response and adaptation mechanism of Pinus massoniana to drought and shading stress, we investigated the effects of growth and photosynthetic physiological characteristics in control (CK), drought (DR), shading (LL), and the interaction of drought and shading (DRLL) environments on 2-year-old P. massoniana seedlings. The result showed that: (1) under drought, shading and their interaction treatment, the increment of the basal diameter and height of P. massoniana seedlings significantly reduced, and their interaction aggravated the respective negative effect of drought and shading alone. The influence of the interaction conforms to the "Interaction theory". (2) Under drought treatment, the length of needles and specific leaf area decreased. The net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), and intercellular CO₂ concentration (C_i) significantly decreased. The water use efficiency (WUE) significantly increased. However, there was no effect on photosynthetic pigment content. (3) Under shading treatment, the length of needles and specific leaf area increased. The P_n, T_r, and G_s significantly decreased. The photosynthetic pigment content significantly increased, while the WUE and C_i had no variation. (4) Under the interaction of drought and shading treatment, the length of needles and specific leaf area decreased. The P_n, T_r, and G_s significantly decreased and the decreasing degree was higher than drought alone. The photosynthetic pigment content significantly increased and the increasing degree was less than that in shading alone. We found that both drought and shading inhibited the growth of P. massoniana seedlings and their photosynthetic physiological characteristics showed different response mechanisms. The P. massoniana adapted to the drought environment by sacrificing the length of needles and specific leaf area and adjusting the stomatal conductance to achieve the purpose of water retention. By increasing the length of needles, specific leaf area and the photosynthetic pigment content, the P. massoniana adapted to the shading environment. While under the interaction between drought environment and shading environment, the shading environment not only relieved the decrease of needle length, specific leaf area, and stomatal conductance caused by drought-stress, but also weakened the ability to synthesize photosynthetic pigments. Furthermore, the drought combined with shading may generate greater risks on the growth of P. massoniana.