Carbon exchange between the atmosphere and subtropical forested cypress and pine wetlands

[摘要] Carbon dioxide exchange between the atmosphere and forested subtropicalwetlands is largely unknown. Here we report a first step in characterizingthis atmospheric–ecosystem carbon (C) exchange, for cypress strands and pineforests in the Greater Everglades of Florida as measured with eddycovariance methods at three locations (Cypress Swamp, Dwarf Cypress and PineUpland) for 2 years. Links between water and C cycles are also examined atthese three sites, as are methane emission measured only at the Dwarf Cypresssite. Each forested wetland showed net C uptake from the atmosphere bothmonthly and annually, as indicated by the net ecosystem exchange (NEE) of carbondioxide (CO₂). For this study, NEE is the difference betweenphotosynthesis and respiration, with negative values representing uptakefrom the atmosphere that is retained in the ecosystem or transportedlaterally via overland flow (unmeasured for this study). Atmospheric C uptake (NEE) was greatest at the Cypress Swampp (−900 to −1000 g C m² yr⁻¹), moderate at the PineUpland (−650 to −700 g C m² yr⁻¹) and least at the Dwarf Cypress(−400 to −450 g C m² yr⁻¹). Changes in NEE were clearly a functionof seasonality in solar insolation, air temperature and flooding, whichsuppressed heterotrophic soil respiration. We also note that changes in thesatellite-derived enhanced vegetation index (EVI) served as a usefulsurrogate for changes in NEE at these forested wetland sites.

[学科分类] 地球化学与岩石