半红树植物黄槿的气体交换特性

Gas exchange characteristics in the mangrove associate Hibiscus tiliaceus

关键词:  黄槿, 半红树, 气体交换, 生境适应性

Key words:  Hibiscus tiliaceus, mangrove associate, gas exchange, habitat adaptation

摘要:

半红树植物是一类既可在海岸潮间带又可在陆地生长和繁殖的海陆两栖植物。夏季强光和高温是海岸带生境突出的特点,半红树植物如何在这样的自然生境中生存和繁衍是值得探讨的问题。该研究以具有较高应用价值的锦葵科(Malvaceae)木槿属(Hibiscus)的常绿半红树植物黄槿(H. tiliaceus)作为研究对象,采用LI-6400便携式光合测定系统(Li-Cor Inc., USA)对南亚热带气候条件下的广东省珠海淇澳岛红树林自然保护区自然生长的黄槿在夏季高温季节的叶片气体交换特性进行测定,探讨了其在自然生境下的光合行为和相关的形态解剖特征,揭示其生境适应性的光合生理生态机制。结果表明:(1)黄槿净光合速率、气孔导度、胞间二氧化碳浓度和蒸腾速率的日变化均表现为单峰型曲线,中午未出现明显光抑制现象。(2)黄槿较高的净光合速率与其较高的气孔导度相关,而后者则可能与其较大的气孔密度和具有表皮毛等叶片解剖结构特征有关。(3)黄槿光饱和点、光补偿点、最大净光合速率和日均净光合速率均符合阳生植物特征,因而是一种阳生性树种。以上结果说明黄槿在自然环境中具有的快速生长特性可能与其较强和较稳定的光合能力有关,该研究结果为深入揭示黄槿以及其他半红树植物适应海岸带高温强光生境的生理生态机制提供了基础数据,为黄槿的合理栽培及造林实践提供了理论参考。

Abstract:

Mangrove associates are a category of plants that can grow and reproduce on both intertidal coastal zones and land. As subtropical coastal zones are characterized by high sun light and temperature, how mangrove associates adapt to such an environment is an important issue. Some researches show that mangrove associates are similar to land plant as well as thalassophyte in certain morphological structures and biochemical characteristics. However, there are few studies focusing on plant physiological characteristics of mangrove associates, especially in leaf gas exchange characteristics. Hibiscus tiliaceus(Malvaceae)is a pantropical mangrove associate that usually occurs in coastal zones. It is widely used for the conservation of sea banks, architecture and medicine. In order to disentangle the photosynthetic physiological mechanims underlying its habitat adaptation to high light and temperature under south subtropical climate, leaf gas exchange characteristics of H. tiliaceus were measured using LI-6400 portable photosynthesis system(Li-Cor Inc, USA)at Mangrove Natural Reserve of Qi'ao Island of Zhuhai City, Guangdong Province during July and August of 2013. The nature reserve(22°23'40″ N, 113°36'40″ E)is characterized by a typical south subtropical monsoon climate. The diurnal changes in photosynthetic rate(Pn), stomatal conductance(Gs), intercellular CO₂ concentration(Ci)and transpiration rate(E)in H. tiliaceus all exhibited a mono-peak modal, and the peak value of Pn occurring at noon was around 26.8 μmol CO₂·m^-2·s^-1 without obvious photoinhibition during the daytime. The high photosynthetic rate in H. tiliaceus was associated with high stomatal conductance, which was probably related to anatomical features of leaves, such as high stomatal density and dense trichomes in the lower leaf epidermis. Analysis of light response curves revealed that its light saturation point was 800 μmol photons·m^-2 ·s^-1 and its light compensation point was 26 μmol photons·m^-2 ·s^-1. The net photosynthesis at saturating irradiances was high at 27.8 μmol CO₂·m^-2·s^-1. These photosynthesis parameters, along with high daily mean photosynthetic rate(19.6 μmol CO₂·m^-2 ·s^-1)in H. tiliaceus suggested that this mangrove associate was characterized as a typical sun plant species. The results showed that the fast growth of H. tiliaceus might be attributed to its high and stable photosynthetic capacity, thus providing basic data for further revealing the eco-physiological mechanism underlying habitat adaptation of H. tiliaceus and other mangrove associates to coastal environment with high temperature and high light in summer. These results can also provide theoretical supports for its planting and reforestation practices.