THE ROLE OF NITROGEN NUTRITION IN HIGH‐TEMPERATURE TOLERANCE OF THE KELP, LAMINARIA SACCHARINA (CHROMOPHYTA)¹

Abstract

Mechanisms of high-temperature tolerance in the kelp Laminaria saccharina (L.) Lamour. were examined by comparing a heat-tolerant ecotype from Long Island Sound (US), New York, and a population from the Atlantic (ATL) coast of Maine. Greater heat tolerance was not attributable to greater thermal stability of the photosynthetic apparatus: LIS and ATL plants exhibited similar shortterm effects of high temperature on photosynthetic capacity (P,,J and quantum yield (estimated as the ratio of variable to maximum chlorophyll jluorescence, FJF,,,). A s LIS plants had consistently higher N and protein content than A T L plants, the interaction between nitrogen nutrition and high-temperature tolerance was examined. When grown under high N supply and optimal temperature (12" C), LIS plants had a higher density of photosystem 11 reaction centers (RCII), higher activity of two Calvin cyck enzymes (ribulose bisphosphate carboxylase oxjgenase [RUBISCO] and NADP-dependent glyceraldehyde-3=Phos-phate dehydrogenase [G3PDH]), and higher Pmx and F,J F, than A T L plants. Individual A T L plants, furthermore, exhibited close correlations of RCII density and enzyme activity with N and/or protein content. Variation in RCII density and enzyme activity, in turn, largely accounted for plant-to@ant d@erences in P,,,, and Fv/F,. Relationships among these parameters were generally weak or lacking among individual US plants grown under optimal conditions, apparently because luxury N consumption resulted in excess reserves of photosynthetic apparatus components. Exposure of N-repbte LIS and ATL plants to a superoptimal temperature (22" C) for 4 days caused a n increase in the minimum turnover time of the photosynthetic a p paratus (tau) and a decrease in P,,, but had no consistent effect on FJF,,,, RCII density, PSU size (chlorophyll a/RCII), or enzyme activities. When plants were su6jected to concurrent N limitation and heat stress, however, LIS and A T L populations exhibited quite dyferent responses. All photosynthetic parameters of N-limited ATL plants declined shaqly in response to high temperature, resulting in a negative rate of daily net Cfixation. In contrast, LIS plants showed a reduction in PSU size, but maintained other parameters, including daily C fixation, at levels similar to those of N-limited plants at optimal temperature. Overall, the ability of LIS plants to accumulate and maintain high N reserues appears to be critical for heat tolerance and, therefore, for survival during summer pm'ods of simultaneous low N supply and superoptimal temperature. A T L plants, which also experience low summer N supply but not superoptimal temperatures, do not accumulate large reserues of nitrogenous components and are unable I to tolerate the combined stress. Because low N supply often co-occurs with high temperatures in temperate marine systems, largescab declines in algal productivity, such as during El Niiio events, are probably due to the interactive effect of N limitation and heat stress. chlorophyll jluorescence; enzymes; heat stress;...

Deep-water kelp refugia as potential hotspots of tropical marine diversity and productivity

“…1a). Because kelp is more vulnerable to nutrient limitation than temperature stress (27,28), we used the depth of the seasonal thermocline to estimate the vertical extent of the mixed layer, and thus the zone within which deep-water nutrient replenishment occurs (Fig. 1b) (29).…”

Effects of concurrent low temperature and low nitrogen supply on polar and temperate seaweeds

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“…Mar Ecol Prog SE Activities of Calvin cycle enzymes in temperate algae are affected by nitrogen-availability, as weil as temperature (Wheeler & Weidner 1983, Gerard 1997. Although environmental conditions of arctic and antarctic marine waters are similar in terms of low temperature and low annual irradiance, they differ greatly in terms of nutrient concentrations.…”

The retreat of large brown seaweeds on the north coast of Spain: the case ofSaccorhiza polyschides

“…factors interact and contribute to the growth performance of a seaweed, since most studies focus on the effects of a single factor and the interactive effects of several factors are less well known. However, there is some evidence that an interaction between high temperatures and low availability of nitrate is responsible for a decline in the photosynthetic performance of Saccharina latissima (Gerard, 1997) and Ulva lactuca (Rivers & Peckol, 1995), as well as in the reproductive allocation and spore standing-stock in Macrocystis pyrifera (Reed et al, 1996) and in the distribution, abundance and size of Californian kelps (Dayton et al, 1999). Something similar could be affecting the growth of Saccorhiza polyschides but it is difficult to find a straightforward relationship between ecological responses and changes in the abiotic environment.…”