Peculiar growth dynamics of the surfgrass <Emphasis Type="Italic">Phyllospadix japonicus</Emphasis> on the southeastern coast of Korea |
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Authors: | Jung-Im Park Kun-Seop Lee |
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Institution: | (1) Department of Biological Sciences, Pusan National University, Pusan, 609-735, Korea; |
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Abstract: | The surfgrass Phyllospadix japonicus is endemic to exposed shores of the northeastern Pacific Ocean. Unlike the majority of seagrasses, P. japonicus grows on rocky substrata. The specific physical features of the habitat are likely related to the peculiar ecological characteristics
of P. japonicus. However, few studies have been conducted thus far on the growth dynamics of Phyllospadix spp., largely due to the turbulent water conditions in its habitat. P. japonicus is a dominant seagrass species, and it plays critical ecological roles on the eastern coast of Korea. Here, we examined its
growth dynamics for the first time on the Korean coast. We measured shoot density, biomass, leaf production, phenology, morphology,
tissue nutrient content, as well as environmental factors including underwater photon flux density (PFD), water temperature
and water column nutrient concentrations from March 2003 to December 2005. Shoot density, biomass, leaf productivity and morphological
characteristics exhibited significant seasonal variations; maximum values of these variables occurred in winter and early
spring, and the minima were recorded in late summer and early fall. PFD and water temperature were, respectively, positively
and negatively correlated with leaf production. Nutrient availability fluctuated substantially, but there was no evidence
of distinct seasonal variation, nor was it correlated with leaf production. Leaf chlorophyll concentrations were correlated
strongly with leaf production, whereas tissue nutrient contents were unrelated to leaf production. Maximum potential seed
production ranged from 1,200 seeds m−2 in 2004 to 3,445 seeds m−2 in 2003; however, seedlings were rarely detected through the observation period. Thus, P. japonicus meadows at the study site appeared to persist through vegetative propagation. Leaf C content varied bimodally, with peaks
in spring and fall. Leaf N content was minimal during months in which leaf productivity was lowest. These patterns in tissue
nutrient content are clearly different from those of the majority of soft-substratum seagrasses and appear to relate to the
reduced physiological tolerance of high temperature in P. japonicus compared to other temperate seagrasses. |
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