江苏滨海湿地芦苇和互花米草光合特性对模拟增温的响应

滨海湿地生态系统具有较高的初级生产力，是地球生态系统主要的碳库之一。然而，气候变暖和外来物种入侵通过改变植物光合特征性能使这一碳库的稳定性存在诸多的不确定性。利用在江苏盐城芦苇湿地和互花米草湿地建设的两个增温观测站，采用便携式光合荧光测量系统研究了本土植物芦苇（Phragmites australis）和入侵物种互花米草（Spartina alterniflora）光合特性对模拟增温的响应特征和机制。光合作用日调查变化曲线显示，增温使芦苇的净光合速率（P_n）、气孔导度（G_s）、蒸腾速率（T_r）和水分利用效率（WUE）都发生了显著的下降，但互花米草的各同名参数却表现出相反的变化特征，表明增温使互花米草的生理机能增强，促进了光合作用；根据P_n和胞间CO₂浓度（C_i）的变化趋势推断互花米草和芦苇光合速率变化均为非气孔限制因素驱动。利用直角双曲线修正模型拟合的光响应曲线结果显示，芦苇增温组的光响应曲线位于对照组下方，互花米草增温组的光响应曲线位于对照组上方；增温降低了所研究植物的光补偿点（LCP），表明增温可提高两种植物利用弱光的能力；增温增加了互花米草光补偿点（LCP）和光饱和点（LSP）间值域范围，从而揭示了增温可有效提高互花米草利用光合有效辐射的能力；增温降低了芦苇的暗呼吸速率（R_d），芦苇受到增温的胁迫，在减缓新陈代谢的同时也减弱了光合作用，而互花米草表现出相反特征。由此推测增温条件下入侵植物互花米草同化大气CO₂的能力（即碳汇能力）优于本土植物芦苇，这也是互花米草成为入侵物种的主要原因之一。

Responses of photosynthetic characteristics of Phragmites australis and Spartina alterniflora to the simulated warming in Jiangsu coastal wetlands

Coastal wetland ecosystem has high primary productivity and is one of the main carbon pools of the earth''s ecosystems. However, climate warming and the exotic plant invasion will change the photosynthetic characteristics of plants, resulting in many uncertainties in the stability of carbon pool in coastal wetlands. In this study, we examined the potential effects of climate warming on photosynthetic characteristics of a native (Phragmites australis) and an exotic (Spartina alterniflora) species in Yancheng coastal wetland, Jiangsu Province. The in-sute simulated warming experiments were conducted using passive warming manipulation methodologies. Six open-top chambers (OTCs) and six control chambers were built in the early 2018 in P. australis and S. alterniflora wetlands, respectively. Photosynthetic indices of two species were determined using a portable photosynthetic fluorescence measurement system. The diurnal variation of photosynthesis indicated that, the simulated warming significantly decreased the leaf net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r) and water use efficiency (WUE) of P. alternate, while simulated warming increased these parameters of S. alterniflora in a certain extent. The physiological function of S. alterniflora was enhanced by simulated warming, resulting in the promoted level of photosynthesis. According to the trends of P_n and intercellular CO₂ concentration (C_i), it concluded that the photosynthetic rates of both S. alterniflora and P. australis were driven by non-stomatal limiting factors such as biochemistry or soil nutrients. The modified rectangular hyperbolic model was used to fit the light response curves of two species. The light response curve of P. australis under warming condition jumped down comparing to the controlling condition, while the curve of S. alterniflora under warming condition moved up comparing to the controlling condition. Warming improved the ability of these two species to utilize weak light by reducing the light compensation point (LCP). The simulated warming increased the range of difference between LCP and light saturation point (LSP) of S. alterniflora, thus effectively improving its ability to use photosynthetically active radiation. Warming reduced the dark respiration rate (R_d) of P. australis. Under the stress of elevated temperature, metabolism of P. australis slowed down and the rates of photosynthesis reduced, while S. alterniflora showed the opposite characteristics. Our results suggest that, under warming conditions, the exotic S. alterniflora has a better ability to assimilate atmospheric CO₂ (i.e. carbon sink capacity) than the native P. australis, which is also one of the main reasons that why S. alterniflora has become an invasive species.