Ellison Aaron M, Farnsworth Elizabeth J
Department of Biological Sciences & Program in Environmental Studies, Mount Holyoke College, 50 College Street, South Hadley, MA 01075-6418, USA Fax: 413-538-2548; e-mail:
Department of Organismic and Evolutionary Biology, Harvard University Herbaria, 22 Divinity Avenue, Cambridge, MA 02138, USA, , , , , , US.
Oecologia. 1997 Nov;112(4):435-446. doi: 10.1007/s004420050330.
Tropical coastal forests - mangroves - will be one of the first ecosystems to be affected by altered sea levels accompanying global climate change. Responses of mangrove forests to changing sea levels depend on reactions of individual plants, yet such responses have not been addressed experimentally. We report data from a long-term greenhouse study that assessed physiological and individual growth responses of the dominant neotropical mangrove, Rhizophora mangle, to levels of inundation expected to occur in the Caribbean within 50-100 years. In this study, we grew potted plants in tanks with simulated semidiurnal (twice daily) high tides that approximated current conditions (MW plants), a 16-cm increase in sea level (LW plants), and a 16-cm decrease in sea level (HW plants). The experiment lasted 2½ years, beginning with mangrove seedlings and terminating after plants began to reproduce. Environmental (air temperature, relative humidity, photosynthetically active radiation) and edaphic conditions (pH, redox, soil sulfide) approximated field conditions in Belize, the source locale for the seedlings. HW plants were shorter and narrower, and produced fewer branches and leaves, responses correlated with the development of acid-sulfide soils in their pots. LW plants initially grew more rapidly than MW plants. However, the growth of LW plants slowed dramatically once they reached the sapling stage, and by the end of the experiment, MW plants were 10-20% larger in all measured growth parameters. Plants did not exhibit differences in allometric growth as a function of inundation. Anatomical characteristics of leaves did not differ among treatments. Both foliar C:N and root porosity decreased from LW through MW to HW. Relative to LW and HW plants, MW plants had 1-7% fewer stomata/mm, 6-21% greater maximum photosynthetic rates, 3-23% greater absolute relative growth rates (RGRs), and a 30% higher RGR for a given increase in net assimilation rate. Reduced growth of R. mangle under realistic conditions approximating future inundation depths likely will temper projected increased growth of this species under concomitant increases in the atmospheric concentration of CO.
热带沿海森林——红树林——将是首批受到全球气候变化导致海平面变化影响的生态系统之一。红树林对海平面变化的响应取决于个体植物的反应，但此类反应尚未通过实验得到研究。我们报告了一项长期温室研究的数据，该研究评估了新热带地区主要红树林物种红树对预计在未来50 - 100年内加勒比地区出现的淹没水平的生理和个体生长反应。在本研究中，我们将盆栽植物种植在水箱中，模拟半日（每天两次）高潮，分别模拟当前状况（MW组植物）、海平面上升16厘米（LW组植物）和海平面下降16厘米（HW组植物）。实验持续了两年半，从红树林幼苗开始，到植物开始繁殖后结束。环境条件（气温、相对湿度、光合有效辐射）和土壤条件（pH值、氧化还原电位、土壤硫化物）接近幼苗来源地伯利兹的野外条件。HW组植物更矮更窄，枝条和叶片更少，这些反应与花盆中酸性硫化物土壤的形成有关。LW组植物最初比MW组植物生长得更快。然而，LW组植物一旦达到幼树阶段，生长速度就会大幅放缓，到实验结束时，MW组植物在所有测量的生长参数上都比LW组大10 - 20%。植物并未表现出作为淹没函数的异速生长差异。不同处理之间叶片的解剖特征没有差异。从LW组到MW组再到HW组，叶片的碳氮比和根孔隙率均下降。相对于LW组和HW组植物，MW组植物每平方毫米的气孔少1 - 7%，最大光合速率高6 - 21%，绝对相对生长率（RGR）高3 - 23%，并且在净同化率给定增加的情况下，RGR高30%。在接近未来淹没深度的现实条件下，红树生长减缓可能会抑制该物种在大气中二氧化碳浓度增加时预计的生长增加。
