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

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.