气候变化对海藻龙须菜生长与光合作用耐热特性的影响

Effect of climate change on the growth and photosynthetic thermal tolerance in the marine macroalga Gracilaria lemaneiformis

为探讨大气CO2升高和温室效应对龙须菜生长及生理生化特性的影响,在4种条件下培养龙须菜:1)对照组(390μL/L CO2+20℃),2)CO2升高组(700μL/L CO2+20℃),3)温度升高组(390μL/L CO2+24℃),4)温室效应组(700μL/L CO2+24℃),测定藻体生长和生化组分以及高温胁迫下的最大光化学量子产量(Fv/Fm)和光能利用效率(α)、光合速率(Pn)和呼吸速率(Rd)。结果表明,CO2升高、温度升高以及温室效应均促进龙须菜的生长,温室效应下的促进作用更明显。温室效应使龙须菜具较高的Pn和Rd以及较低的可溶性蛋白(SP)和可溶性碳水化合物(SC)含量。高浓度CO2对叶绿素(Chl a)和类胡萝卜素(Car)含量没有显著影响,而高温使其上升;藻红蛋白(PE)和藻蓝蛋白(PC)含量不受CO2浓度和温度的影响。龙须菜Fv/Fm、α、Pn和Rd值,在32℃处理3 h后略有上升,在36℃处理3 h后下降,而在40℃处理20 min后降到极低水平。正常温度(20℃)生长的龙须菜最高耐受温度在32—36℃之间,而较高温(24℃)生长的龙须菜在36—40℃之间;生长温度对光合作用和呼吸作用耐热性能的影响比CO2浓度的影响更大;而温室效应生长条件下的龙须菜光合作用表现出更突出的耐热性能。

It was predicted that the atmospheric CO2 concentrations in the end of this century would be twice as much as the present level, and as a consequence of this the mean global temperature would elevate 4-5 ℃. At present, there are many researches on seaweeds in response to elevated atmospheric CO2 concentrations or temperature alone. However, the investigations concerning the impacts of combined effects of elevated atmospheric CO2 concentrations and temperature on seaweeds is very limited. The marine red macroalga Gracilaria lemaneiformis has been cultivated on large scales in both the southern and the northern parts of China. It is essential to evaluate how the climate change （such as the elevated atmospheric CO2 concentrations and global warming） affect this economically important species. In this study, G. lemaneiformis was cultured under the following four different conditions： 1） ambient control （390 μL/L CO2 ＋ 20 ℃）; 2） elevated CO2 （700 μL/L CO2 ＋ 20 ℃）; 3） elevated temperature （390 μL/L CO2 ＋ 24 ℃）; and 4） greenhouse effect （700 μL/L CO2 ＋ 24 ℃）. After cultured for 10 d, the growth and biochemical compositions were examined. At the same time, the changes of maximum photochemical quantum yield （Fv/Fm）, light use efficiencies （α）, net photosynthetic rate （Pn） and dark respiratory rate （Rd） under high-temperature stresses （32 ℃, 36 ℃ and 40 ℃） were explored. The results showed that elevated CO2, elevated temperature, or greenhouse effect all enhanced the growth of G. lemaneiformis, with the highest relative growth rate occurring under the culture treatment with greenhouse effect. The growth condition treated with greenhouse effect increased the rates of Pn and Rd in situ, but decreased the contents of solution protein （SP） and soluble carbohydrate （SC） in algal thalli. Elevated CO2 in culture increased the rate of Pn in situ, but the growth condition treated with elevated temperature had hardly affected the Pn in situ. Both chlorophyll a （Chl a） and carotenoid （Car） were increased with elevated temperature in culture, but their contents were unaltered with high CO2. Elevated CO2 or elevated temperature alone had no significant effects on the contents of phycoerythrin （PE） and phycocyanin （PC） of the algal thalli. The changes of Fv/Fm and α of the algal thalli under high-temperature stresses displayed the same tendency, i.e： their values all increased slightly under 32 ℃-stress, but decreased under 36 ℃-stress, and declined fiercely under 40 ℃-stress. In the course of 6 h of 32 ℃-stress, the rates of Pn in elevated temperature-grown algae and greenhouse effect-grown algae were much higher than those in the algae grown under control condition. In the course of 6 h of 36 ℃-stress, the rates of Pn in greenhouse effect-grown algae displayed the highest levels relative to the algae grown with other three treatments. It was shown that the high-temperature tolerance limit of photosynthesis in 20 ℃ grown algae was between 32 ℃ and 36 ℃, while that of 24 ℃-grown algae was between 36 ℃ and 40 ℃. Taken together, our results suggested that growth of G. lemaneiformis would benefit from elevated CO2 and/or elevated temperature. Moreover, the greenhouse effect （combined with elevated CO2 and elevated temperature） would improve the photosynthetic thermal tolerance to high temperature for G. lemaneiformis.