控水与补水条件下连续热浪对闽楠光合特性和生长速率的影响

Influences of multiple successive heat waves combined with water control and supplement on photosynthetic characteristics and growth rate of Phoebe bournei seedlings

全球变暖背景下,亚热带地区极端气候热浪事件发生频率持续增加。高频热浪及其伴随的高温和干旱复合胁迫将严重影响植物的光合特性,抑制植物的生长,甚至造成死亡。然而,目前亚热带树木光合特性及生长对高频热浪及复合胁迫的响应仍不明确。以亚热带阔叶树种闽楠苗木为研究对象进行了热浪模拟实验,关注了补水和控水处理不同水分环境下连续热浪对闽楠光合特性及生长速率的影响。结果表明,补水处理下闽楠净光合速率(Pn)在单次热浪影响下显著下降了34%,同时水分利用效率显著(WUE)下降,但蒸腾速率(Tr)、气孔导度(Gs)和叶片水汽压亏缺(Leaf_(vpd))显著上升(P<0.05)。表明水分充沛的高温环境中闽楠可通过增加蒸腾耗水加速水分蒸散来调节叶片的温度,增强植株光合特性对热浪的抗性。而控水处理下单次热浪处理组Tr和Gs未显著上升,以及Tr与Leaf_(vpd)在干湿环境下线性拟合的不同斜率,说明水分胁迫会降低叶片降温的效率,加剧热浪对闽楠光合特性的影响。水分和高温的复合胁迫还延长了闽楠光合特性在热浪后的恢复过程,高温胁迫下闽楠Pn在15 d后恢复至未干扰水平,但复合胁迫组未能恢复。此外,连续发生的热浪存在累加效应,表现为降低闽楠对热浪的抗性,其中闽楠Tr、Gs和WUE在连续热浪处理组变化显著(P<0.05)。但连续发生的热浪事件不会显著影响闽楠光合特性在热浪后的恢复过程,且会增加闽楠的高度,补水处理下连续热浪处理组闽楠苗高相对生长率显著高于其它处理组,但地径相对增长率未见显著差异。该研究结果表明,热浪阶段的水分供给可以增强亚热带树种闽楠的热浪抗性,并加速恢复,但控水处理的干环境下闽楠热浪抗性下降,若该环境下连续热浪事件发生可能增加闽楠苗木死亡的概率。因此,植物对气候变化响应的研究应该增强对复合胁迫或极端气候模式变化的关注。

Under the background of global warming,the frequency of extreme climatic heat wave events continues to increase in subtropical region.The high frequency heat wave events severely reduced plants photosynthetic properties,especially when the combined thermal and drought stresses occurred,it will inhibit plant growth,and further lead to plant mortality.However,the response of subtropical tree species photosynthetic characteristics and growth to high-frequency heat waves and their complex stresses is still unclear.In this study,we created a heat wave simulation experiment on subtropical tree species,Phoebe bournei,focusing on the influences of heat waves on the photosynthetic characteristics and growth rates with or without water supplement during heat waves.The results showed that the single heat wave event in wet environment with water supply can resulted in 34%decrease in net photosynthetic rate(Pn)and also decrease in water use efficiency(WUE),but transpiration rate(Tr),stomatal conductance(Gs)and leaf vapor pressure deficit(Leaf_(vpd))showed significant increase(P<0.05).This indicates that the Phoebe bournei in sufficient water environment can regulate leaf temperature via accelerating the water evapotranspiration consumption under high temperature stress,which could enhance the resistance of plant photosynthetic characteristics to heat waves.However,there was no significant increase in Tr and Gs in the single heat wave treatment group in drought habitat without water supplement,as well as the different slopes of the linear fit between Tr and Leaf_(vpd)in dry and wet environments.It suggests that without water supply,heat waves can cause drought stress,reduce the efficiency of leaf cooling,and exacerbate the effect of heat wave on photosynthetic characteristics of Phoebe bournei.The combined drought and high temperature stress also prolonged the recovery process of Phoebe bournei photosynthetic characteristics after heat wave,while Pn recovered to the undisturbed level at 15 days later after heat wave influences,but failed to recover in the combined stress group.In addition,there was a cumulative effect when successive heat wave occurred,which showed a reduction of Phoebe bournei resistance to heat waves,evidenced by the significant variation(P<0.05)of Tr,Gs and WUE during multiple successive heat wave events.But the multiple successive heat wave events did not significantly influence the recovery process of photosynthetic characteristics after heat wave,even caused an increasing of plant height.Under the wet environment with water supply,the Phoebe bournei seeding height relative growth rate of cumulative effect of continuous heat wave was significantly higher than other treatments,but no significant difference was observed in the relative growth rate of ground diameter.Our results indicate that the subtropical tree species,Phoebe bournei,has a strong heat wave resistance in wet environment,but such resistance will largely reduce in dry environment,and the successive heat wave events may also increase the probability of seedling mortality in dry environment.Therefore,studies of plant response to climate change should pay more attention on compound environment stresses or changes in extreme climate patterns.