蓄水后洪水胁迫对三峡库区消落带狗牙根幼苗生长的影响

Influence of flooding stress on the growth of Cynodon dactylon seedlings in a water-level-fluctuating zone after impoundment of the Three Gorges reservoir

为了进一步评估蓄水期后三峡库区消落带狗牙根的水淹耐受能力,于蓄水期后引种库区消落带狗牙根植株,模拟洪水发生时水下无光、淹水逆境,探讨洪水复合胁迫持续时间对其后期生长恢复的影响。结果表明:洪水胁迫显著抑制狗牙根分株的生长发育,随着胁迫时间的延长其分株数、分株茎长、分株总茎长、分株茎宽、分株叶片数、分株总叶片数均显著低于对照,仅短期(20d)胁迫促进了分株叶片的伸长;短期(20d)胁迫促进了分枝数、分枝直径和分枝茎节长的生长,分别比对照增加20.0%(P<0.05)、15.0%(P<0.05)、18.2%(P<0.05),但是随着洪水胁迫时间的延长,狗牙根的分枝数、分枝长、总分枝长、分枝直径、分枝茎节长、分枝茎节数、分枝总茎节数均呈降低趋势;随着洪水胁迫时间的延长植株叶片光合作用能力也呈降低趋势,原初光化学效率、实际光化学效率、电子传递速率、光化学淬灭系数显著低于对照,而非光化学淬灭系数则相反,表明能量更多的以热的形式被耗散掉,参与CO2固定的电子数显著减少,光合产物显著降低。因此,三峡库区消落带狗牙根幼苗对洪水复合胁迫的耐受能力较强,胁迫时间≥40d后其耐受能力呈显著降低趋势,会导致库区消落带(特别是低水位消落带)狗牙根种群衰退演替加快。

In order to further evaluate flooding tolerance ability of Cynodon dactylon, C. dactylon seedlings were transplanted from a water-level-fluctuating zone(WLFZ) after impoundment of the Three Gorges reservoir, and they were submerged again in the simulated flood environment. Then, it was discussed that the influence of compound stress duration on their late growth recovery. The results showed that flooding stress significantly inhibited the growth and development of ramets. Ramets number, stem length, total stem length, stem width, leaf number and total leaves number of the ramets were significantly lower than the control with the increasing of flooding time. Only the short-term(20 d) stress promoted leaf elongation of the ramets. The short-term(20 d) stress promoted the growth of branch number, branch diameter and branch internodes length to grow, which respectively increased 20.0%(P < 0.05), 15.0%(P < 0.05) and 18.2%(P < 0.05) compared with the control. However, as the extension of stress time, branch number, branch length, total branches length, branch diameter, node length, node number and total nodes number of C. dactylon’s branches showed a reducing trend. With the prolongation of flooding time, the photosynthesis ability of C. dactylon also showed a decreasing trend. Primary photochemical efficiency, actual photochemical efficiency, electron transfer rate and photochemical quenching coefficient of their leaves were significantly lower than the control. And non-photochemical quenching coefficient showed an opposite result. It suggested that more light energy, absorbed by leaves, was dissipated in the form of heat. Simultaneously, the number of electrons involved in CO2 fixation was significantly reduced so that photosynthetic product significantly decreased. Therefore, C. dactylon seedlings have relatively strong tolerance ability to the short-term flooding stress. However, the tolerance ability will decrease significantly with the increasing of stress time(≥ 40 d), which will accelerate population decline of C. dactylon in the WLFZ(especially the low WLFZ) of the Three Gorges reservoir.