Since the 1970s, southwestern Georgia has seen significant decreases in annual stream flows and changes in seasonal rainfall patterns (i.e., slightly wetter winters and drier springs) that have implications for leaf breakdown processes in wetlands. In four separate study years (1999–2002), we examined leaf breakdown processes in two types of forested wetlands, floodplain and depressional. Using a reciprocal transfer design, litter bags containing black gum (Nyssa sylvatica biflora) and water tupelo (Nyssa aquatica) were placed in three wetlands of each type. We predicted open wetlands (floodplain) would have faster breakdown rates than isolated wetlands (depressional), and water tupelo leaves acquired from high-nutrient wetlands (floodplain) would be less refractory and decompose faster than black gum leaves obtained from low-nutrient wetlands (depressional). There was no consistent pattern of one wetland type having faster breakdown rates than the other. Breakdown of water tupelo (k = −0.57 to −1.77 yr−1) was faster than black gum (k = −0.53 to −1.31 yr−1) in three out of eight instances (i.e., same wetland type and year); otherwise, no difference was detected between species. Results from the drier years (1999, 2000, and 2001) suggest that litter species was more important than wetland type in determining P levels in litter and in some instances N concentrations, but in the wetter year (2002) N and P patterns in litter differed by wetland type. This multiyear study allowed us to conclude that in drought years, moisture levels primarily influenced breakdown of organic matter, but in years with prolonged flooding, faster breakdown rates occurred in the wetland type and litter species with the higher nutrient levels. A 1.4 to 3-fold difference in breakdown rates among study years (for the same wetland type and litter) suggest that caution should be used in making conclusions based on a single decomposition study.
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Vol. 27 • No. 2