Decomposition rates in black mangrove (Avicennia germinans) sediment determined using the Tea Bag Index (TBI) method
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Abstract
A fundamental problem in comparing decomposition rates among ecosystems is that different kinds of plant litter (e.g., leaves vs wood) and the litter produced by each species decompose at different rates, depending on temperature, moisture, and soil type. The Tea Bag Index (TBI) is a simplified litter bag experiment that uses green tea and rooibos tea as standard substrates. This allows standardization of methods and calculations for determining and comparing decomposition rates across ecosystems. In this study, the suitability of green and rooibos tea as substrates for standardized methods was evaluated and, the TBI method was used to determine decomposition rates of black mangrove (Avicennia germinans), as well as the effects of tidal inundation and sediment type on those decomposition rates. To determine decomposition rates in the black mangrove habitat, bags filled with tea or native litter were buried and left out for 90 days in the spring and summer, were collected and processed. Decomposition rates were calculated using TBI constants and experimental tea constants found from chemical analysis of tea sourced for the experiment. In a lab experiment, tea bags were incubated for a maximum of 90 days and loss of mass was determined at regular intervals to construct standard decomposition curves for each plant material type. Overall, tidal inundation had the greatest effect on decomposition rates in this study. Decomposition rates measured in the intertidal and subtidal zones were significantly greater than in the supratidal zone regardless of plant material type; mangrove material generally decomposed at a slightly, but significantly (p < 0.05) faster rate than the teas. Sediment type did not affect decomposition rates and decomposition rates were faster in summer. While more study is needed, the results of this study support the use of the TBI standardized method for determining decomposition rates that can be compared within/among ecosystems.