Organic matter decomposition is a fundamental process of nutrient cycling in ecosystems. Subtropical wetlands are one of the most biologically productive ecosystems and representative of detritus-based systems where dead organic matter is the major nutrient source. Plant litter decomposition has been thoroughly studied in terrestrial or aquatic ecosystems, but rarely studied in the transitional systems, such as temporary freshwater marshes with seasonally fluctuating water levels. We aim to fill this gap and answer how land-use and management practices affect litter decomposition in subtropical wetlands, and what underlying abiotic factors control this process. We used the Tea Bag Index (TBI) in 40 seasonal wetlands from an ongoing long-term whole-ecosystem experiment with a 2x2x2 factorial design to manipulate land-use intensity (high- vs. low-intensity), presence/absence of cattle grazing and fire disturbance on Buck Island Ranch in central Florida. Tea bags with standardized litter quality allowed us to focus on the external drivers and compare the decomposition process across ecosystems. Tea bags were deployed aboveground at three sites along a hydrological gradient (edge, middle, and center) within each wetland. The experiments were conducted during the dry-cool season (January 2019-March 2019) and dry-warm season (March 2019-June 2019) to examine the seasonal dynamics in decomposition.
Results/Conclusions
Across two seasons, land-use and management practices affected tea decomposition in subtropical wetlands. High-intensity land-use decreased tea recalcitrant fractions by 36% (p=0.008), prescribed fire in previous years increased recalcitrant fractions by 42% (p=0.002), and presence of cattle grazing reduced decomposition rates by 23% (p=0.077). Interactive effects between or among land-use and management practices existed on tea recalcitrant fractions. In wetlands under high-intensity land-use, fire resulted in higher recalcitrant fractions without cattle grazing, but tea was less stable with cattle grazing. In wetlands under low-intensity land-use, cattle grazing reduced tea recalcitrant fractions, regardless of fire treatments. Effects of land-use and management practices on decomposition changed across time. For instance, fire only increased recalcitrant fractions in dry-cool season but had no significant effects in dry-warm season. There was also a temporal pattern of decomposition rates where tea decomposed significantly faster during the dry-cool season (k=0.0253±0.0072) than dry-warm season (k=0.0151±0.0052), and a spatial variation in the stabilization of tea that recalcitrant fractions were lower where tea bags were closer to wetlands center. The effects of land-use and management practices on decomposition processes along seasonal and hydrological variability highlighted their significance to productivity, nutrient cycling, and carbon sequestration in seasonal wetlands.