Effect of short-term experimental warming on photosynthetic characteristics of Phragmites australis in a coastal wetland in the Yellow River Delta, China
黄河三角洲滨海湿地地下水位浅,淡咸水交互作用明显,其土壤水盐状况成为影响该地区生态系统关键过程的主要因子。另外,随着气候变暖,黄河三角洲在过去50年(19612010年)进入显著升温阶段,温度升高直接或间接影响着植物的光合作用和光响应特征,从而影响黄河三角洲滨海湿地的演变。采用红外辐射加热器模拟增温,分析了增温对黄河三角洲滨海湿地生长季(2015年5月初一2015年10月底)芦苇光响应特征的影响。根据土壤含水量波动情况生长季可分为3个时期,即干旱期、淹水期和湿润期。结果表明,干旱期,10 cm 土壤温度升高3.3℃,土壤水分含量升高了9.4%, 土壤盐分含量升高了16.7%;盐分增加使芦苇叶片在强光下发生光抑制,并且显著降低最大光合速率(Pnmax)、暗呼吸速率(Rd)、光补偿点(LCP)和光饱和点(LSP)。淹水期,增温对10 cm 土壤温度、湿度和盐分均无显著影响,过饱和的水分状况限制叶片光合速率,使得Pnmax达到最低。湿润期,10 cm 土壤温度显著升高3.0℃,土壤含水量升高了2.9%,土壤盐分无显著差异;这一阶段,温度升高促进中强光下芦苇叶片的光合速率;同时叶片pnmax、Rd和LSP分别增加27.7%、14.9%和23.3%。从整个生长季来看,增温使土壤温度显著升高2.9℃,土壤盐分含量升高7.0%,而对光合参数无显著影响。由此可见,在滨海湿地生态系统中,增温对光合作用的影响受土壤水盐状况的控制。
英文摘要:
The coastal wetland in the Yellow River Delta has a shallow underground water level and is affected by both fresh and salt water. As a result,the conditions of the soil water and the presence of salt become the main factors affecting the key processes of the ecosystem. In addition, owing to global warming the average near-surface air temperature of the Yellow River Delta has risen significantly in the last 50 years (1961-2010). Warming can affect plant photosynthesis and photosynthetic characteristics both directly and indirectly,which affects the evolution of the coastal wetlands in the Yellow River Delta. A manipulative warming experiment was conducted in a coastal wetland of the Yellow River Delta using infrared heaters. The light response curve of Phragmites australis was measured during the growing season. During each light response curve measurement, soil environmental parameters were measured simultaneously, including soil temperature, moisture, and salinity. Based on soil moisture conditions, the entire growing season could be divided into three periods, the drought period, flooding period, and wet period. The results obtained were (1) During the drought period, soil temperature was significantly increased by warming by approximately 3.3 ℃, soil moisture increased by 9.4%, and soil salt content increased by 16.7% compared to the control. Similarly, photosynthesis of P. australis was suspended under intensive irradiation due to increased salt concentration. Meanwhile, warming significantly decreased the maximum net photosynthetic rate (Pnmax), dark respiration rate (Rd),light compensation point (LCP),and light saturation point (LSP). (2) During the flooding period, no significant differences in soil temperature, moisture, and salt content under warming were discovered. However, photosynthesis of P. australis was suspended due to the saturated soil water content. (3) During the wet period, warming increased the soil temperature at 10 cm depth by 3.0 ℃ and increased the soil moisture by 2.9%; however, had no effect on soil salt content compared to the control. Meanwhile, warming increased the photosynthetic rate under middle and high light conditions and increased Pnmax, Rd, and LSP significantly by 27.7%, 14.9%,and 23.3%, respectively. (4) During the entire growing season, soil temperature at 10 cm depth was significantly increased by warming by 2.9 ℃ and soil salt content was increased by 7.0% compared to the control. However, no significant effect on light responsive parameters occurred under warming conditions. Therefore,the effect of warming on photosynthesis is obviously controlled by the conditions of the soil water and concentration of salt in the wetland ecosystem.