Sensitivity to Low-Temperature Events: Implications for CO2 Dynamics in Subtropical Coastal Ecosystems

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We analyzed the ecosystem effects of low-temperature events (<5 °C) over 4 years (2009–2012) in subtropical short and long hydroperiod freshwater marsh and mangrove forests within Everglades National Park. To evaluate changes in ecosystem productivity, we measured temporal patterns of CO2 and the normalized difference vegetation index over the study period. Both water levels and distance from the coast influenced the ecosystem response to low-temperature events. Photosynthetic capacity, or the maximum CO2 uptake rate, and sensitivity to low-temperature events were much higher in mangrove forest than in freshwater marsh ecosystems. During low-temperature events photosynthetic capacity was enhanced in freshwater marsh while it declined in mangrove forests, and respiration rates declined across Everglades ecosystems. While the long hydroperiod freshwater marsh gained 0.26 g CO2 m−2 during low-temperature events, the mangrove forest had the greatest C lost (7.11 g CO2 m−2 low-temperature event−1) followed by the short hydroperiod freshwater marsh (0.37 g CO2 m−2 low-temperature event−1). Results suggest that shifts in the frequency and intensity of weather anomalies with climate change can alter C assimilation rates in Everglades ecosystems through effects on the photosynthetic capacity of existing species, which might lead to changes in species composition and ecosystem productivity in the future.