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Thermal sensitivity in ectothermic organisms is often contingent upon environmental factors. Nutrient availability in particular is believed to influence the physiological responses of primary producers to global warming and is thus relevant to consider when forecasting the structure and functioning of future marine ecosystems. This study measured the effect of nutrient enrichment on the thermal sensitivity of 4 genera of Galápagos seaweeds (Ulva,Caulerpa,Padina, andOchtodes), estimated as the thermal optimum (Topt), performance maximum (Pmax), activation energy, and deactivation energy. These parameters were quantified by modeling thermal performance curves for net photosynthesis under ambient and nutrient-enriched conditions. Our findings revealed variation inToptamong genera, ranging from 27.6° to 36.0°C. Nutrient additions enhancedToptby ~2°C for 2 (PadinaandCaulerpa) of the 4 taxa and also significantly increasedPmaxinPadina, suggesting the ability for warming-induced ocean stratification and associated effects (i.e. decreasing nutrient availability) to reduce the capacities of these populations to maintain and support new growth. No significant differences inToptorPmaxwere observed for eitherUlvaorOchtodeswith enrichment. Ambient net photosynthesis and respiration rates were also compared across genera;Pmaxrates for net photosynthesis were consistently higher than those for respiration (i.e. until just beyondTopt); however, photosyntheticToptvalues were lower. Thus, this study suggests that further warming could reduce overall net primary productivity, with potentially far-reaching implications for marine food webs.
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Similar temperature responses suggest future climate warming will not alter partitioning between denitrification and anammox in temperate marine sediments
Abstract Removal of biologically available nitrogen (N) by the microbially mediated processes denitrification and anaerobic ammonium oxidation (anammox) affects ecosystem N availability. Although few studies have examined temperature responses of denitrification and anammox, previous work suggests that denitrification could become more important than anammox in response to climate warming. To test this hypothesis, we determined whether temperature responses of denitrification and anammox differed in shelf and estuarine sediments from coastal Rhode Island over a seasonal cycle. The influence of temperature and organic C availability was further assessed in a 12‐week laboratory microcosm experiment. Temperature responses, as characterized by thermal optima (Topt) and apparent activation energy (Ea), were determined by measuring potential rates of denitrification and anammox at 31 discrete temperatures ranging from 3 to 59 °C. With a few exceptions,ToptandEaof denitrification and anammox did not differ in Rhode Island sediments over the seasonal cycle. In microcosm sediments,Ea was somewhat lower for anammox compared to denitrification across all treatments. However,Topt did not differ between processes, and neither Ea nor Topt changed with warming or carbon addition. Thus, the two processes behaved similarly in terms of temperature responses, and these responses were not influenced by warming. This led us to reject the hypothesis that anammox is more cold‐adapted than denitrification in our study system. Overall, our study suggests that temperature responses of both processes can be accurately modeled for temperate regions in the future using a single set of parameters, which are likely not to change over the next century as a result of predicted climate warming. We further conclude that climate warming will not directly alter the partitioning of N flow through anammox and denitrification.
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- PAR ID:
- 10243930
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 23
- Issue:
- 1
- ISSN:
- 1354-1013
- Page Range / eLocation ID:
- p. 331-340
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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