Leaf litter processing rates in four cave-stream ecosystems

Due to a lack of photoautotrophs, nearly all groundwater ecosystems are reliant on allochthonous inputs of organic matter to support biological productivity. Input and decomposition of organic matter therefore comprise a key energy pathway supporting these ecosystems. However, little is known about the factors influencing organic matter dynamics in groundwater systems. In this study, we examined variability in decomposition rates of corn (Zea mays, non-Bt) and red maple (Acer rubrum) litter among four separate cave-stream ecosystems in Alabama and Tennessee (USA). Maple litter decay rates were slower than those of corn, but were within the bounds of previously reported estimates, while estimates for corn were lower. Decomposition rates and standing crop organic matter varied significantly among the four caves, but standing crop was not a significant predictor of decay rates. Energy availability is thought to be a significant factor influencing the ecology and evolution of groundwater communities, but may not influence in situ litter processing rates in the four cave streams that we studied. Our results suggest that total detritivore biomass and activity in caves may scale with total energy input, while being under the strong control of physical and chemical factors such as temperature and nutrient availability.