Dangremond Emily M, Feller Ilka C, Sousa Wayne P
Department of Integrative Biology, University of California, 3040 VLSB MC 3140, Berkeley, CA, 94720-3140, USA.
Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, MD, 21037, USA.
Oecologia. 2015 Dec;179(4):1187-98. doi: 10.1007/s00442-015-3408-1. Epub 2015 Aug 13.
Although mangroves possess a variety of morphological and physiological adaptations for life in a stressful habitat, interspecific differences in survival and growth under different environmental conditions can shape their local and geographic distributions. Soil salinity and light are known to affect mangrove performance, often in an interactive fashion. It has also been hypothesized that mangroves are intrinsically shade intolerant due to the high physiological cost of coping with saline flooded soils. To evaluate the relationship between stress tolerance and species distributions, we compared responses of seedlings of three widespread mangrove species and one narrow endemic mangrove species in a factorial array of light levels and soil salinities in an outdoor laboratory experiment. The more narrowly distributed species was expected to exhibit a lower tolerance of potentially stressful conditions. Two of the widespread species, Avicennia germinans and Lumnitzera racemosa, survived and grew well at low-medium salinity, regardless of light level, but performed poorly at high salinity, particularly under high light. The third widespread species, Rhizophora mangle, responded less to variation in light and salinity. However, at high salinity, its relative growth rate was low at every light level and none of these plants flushed leaves. As predicted, the rare species, Pelliciera rhizophorae, was the most sensitive to environmental stressors, suffering especially high mortality and reduced growth and quantum yield under the combined conditions of high light and medium-high salinity. That it only thrives under shaded conditions represents an important exception to the prevailing belief that halophytes are intrinsically constrained to be shade intolerant.
尽管红树林具有多种形态和生理适应性以在压力较大的栖息地生存，但不同环境条件下种间在存活和生长方面的差异会影响它们在当地和地理上的分布。已知土壤盐分和光照会影响红树林的表现，且通常以相互作用的方式。也有人提出，由于应对盐碱水淹土壤的生理成本较高，红树林本质上不耐荫。为了评估耐胁迫能力与物种分布之间的关系，我们在室外实验室实验中，以光照水平和土壤盐分的析因组合，比较了三种广布红树林物种和一种狭域特有红树林物种的幼苗的反应。预计分布较窄的物种对潜在胁迫条件的耐受性较低。两种广布物种，即白骨壤和总状卤蕨，在中低盐度下无论光照水平如何都能存活并良好生长，但在高盐度下表现不佳，尤其是在强光下。第三种广布物种，红树，对光照和盐分变化的反应较小。然而，在高盐度下，其在每个光照水平下的相对生长率都很低，且这些植株均未长出新叶。正如预测的那样，稀有物种，红茄苳，对环境胁迫最为敏感，在强光和中高盐度的组合条件下死亡率极高，生长和量子产率降低。它仅在遮荫条件下茁壮成长，这是一个重要的例外，打破了盐生植物本质上不耐荫的普遍观念。
