前期水淹对牛鞭草后期干旱胁迫光合生理响应的影响

水淹和干旱是限制植物生长的两种主要环境因子。三峡库区消落带由于其特殊的地形条件和人工水文节律,呈现以年度为周期的“水淹-落干”交替变化的水文变动特征,在消落带生长的植物因此受到水淹和干旱交替胁迫的双重影响。为了探究库区蓄水对消落带植被干旱耐受性的影响,以当年生牛鞭草扦插苗为试验对象,设置对照组(CK)、表土水淹组(SF)、全淹组(TF)、对照-干旱组(CD)、表土水淹-干旱组(SFD)、全淹-干旱组(TFD)6个处理组,研究不同水分处理对牛鞭草光合特性的影响。结果表明:(1)水淹和干旱胁迫均对牛鞭草光合特性造成显著影响;(2)水淹胁迫阶段,与CK组相比,牛鞭草SF和TF组净光合速率、气孔限制值和水分利用效率显著下降,胞间CO_2浓度显著上升;(3)干旱胁迫阶段,牛鞭草CD和SFD组净光合速率、气孔导度、胞间CO_2浓度和蒸腾速率等光合参数显著低于CK组,TFD组净光合速率、气孔导度、胞间CO_2浓度和蒸腾速率等指标与CK组无显著差异;(4)复水阶段,各处理组净光合速率、气孔导度、胞间CO_2浓度和蒸腾速率等指标均与CK组无显著差异。研究表明,前期水淹并未增加牛鞭草对后期干旱胁迫的敏感性,牛鞭草对水淹和干旱胁迫均具有较好的耐受性,有助于牛鞭草对库区消落带生境变化的适应性。

Effects of flooding on the photosynthetic response of Hemarthria altissima to drought

In the hydro-fluctuation belt of the Three Gorges Reservoir Area (TGRA), plants are subjected to a long period of flooding which can affect their growth and survival. In additional, when the flooding recedes, plants may experience drought stress that can also affect their growth and photosynthesis. Thus, screening for suitable species that can survive these fluctuating conditions is necessary for the successful restoration of vegetation to the hydro-fluctuation belt of the TGRA. Hemarthria altissima, a plant commonly found in the TGRA, may be one such suitable plant in the remediation process of the hydro-fluctuation belt. H. altissima has a high survival rate and is well adapted to flooding; however, the response of these plants to drought following flooding and the physiological mechanisms behind this response are unknown. In order to characterize these mechanisms, we studied leaf gas exchange, stomatal limitation (L_s), and water use efficiency (WUE) in H. altissima under different water regimes in the hydro-fluctuation belt of the TGRA. We applied the following six water regimes:control (CK, soil water content 60%-63% of soil water field capacity), soil surface flooding (SF, with water level 5 cm above the soil surface), total flooding (TF, with water level 1 m above the soil surface), control-drought (CD, control group followed by drought treatment), soil surface flooding-drought (SFD, soil surface flooding followed by drought) and total flooding-drought (TFD, total flooding followed by drought). Net photosynthetic rate (P_n), transpiration rate (T_r), L_s, and WUE of H. altissima in the SF and TF groups were significantly lower than that in the control group, whereas the intercellular CO₂ concentration (C_i) in SF and TF were significantly higher than in the control group after the end of flooding stress, which indicated that the decrease in P_n may be attributed to non-stomatal limitation. Under drought stress, P_n, G_s, and T_r in groups CD and SFD were significantly lower than in the control group, whereas in TFD, they showed no significant differences to the control after the end of drought stress. In contrast to the SF and TF groups, C_i in the CD, SFD, and TFD groups was slightly lower than that in the control group. However, L_s in the CD, SFD, and TFD groups increased under drought stress, indicating that stomatal limitation could be the main cause of the decline of P_n. WUE in the CD, SFD, and TFD groups was significantly higher than in the control group, indicating H. altissima coped with water stress by increasing WUE. By the end of the recovery period, the P_n, G_s, C_i, T_r, L_s, and WUE of the SF, TF, CD, SFD, and TFD groups showed no significant difference to those of the control, indicating that H. altissima can adapt to flooding followed by drought stress. Previous flooding did not affect the subsequent sensitivity of H. altissima to drought. This characteristic of H. altissima is beneficial to its potential survival when transplanted to the hydro-fluctuation belt of the TGRA.