Litter decomposition promotes differential feedbacks in an oligotrophic southern Everglades wetland

Abstract

The differential accumulation or loss of carbon and nutrients during decomposition can promote differentiation of wetland ecosystems, and contribute to landscape-scale heterogeneity. Tree islands are important ecosystems because they increase ecological heterogeneity in the Everglades landscape and in many tropical landscapes. Only slight differences in elevation due to peat accumulation allow the differentiation of these systems from the adjacent marsh. Hydrologic restoration of the Everglades landscape is currently underway, and increased nutrient supply that could occur with reintroduction of freshwater flow may alter these differentiation processes. In this study, we established a landscape-scale, ecosystem-level experiment to examine litter decomposition responses to increased freshwater flow in nine tree islands and adjacent marsh sites in the southern Everglades. We utilized a standard litterbag technique to quantify changes in mass loss, decay rates, and phosphorus (P), nitrogen (N) and carbon (C) dynamics of a common litter type, cocoplum (Chrysobalanus icaco L.) leaf litter over 64 weeks. Average C. icaco leaf degradation rates in tree islands were among the lowest reported for wetland ecosystems (0.23 ± 0.03 yr -1 ). We found lower mass loss and decay rates but higher absolute mass C, N, and P in tree islands as compared to marsh ecosystems after 64 weeks. With increased freshwater flow, we found generally greater mass loss and significantly higher P concentrations in decomposing leaf litter of tree island and marsh sites. Overall, litter accumulated N and P when decomposing in tree islands, and released P when decomposing in the marsh. However, under conditions of increased freshwater flow, tree islands accumulated more P while the marsh accumulated P rather than mineralizing P. In tree islands, water level explained significant variation in P concentration and N:P molar ratio in leaf tissue. Absolute P mass increased strongly with total P load in tree islands (r 2 = 0.81). In the marsh, we found strong, positive relationships with flow rate. Simultaneous C and P accumulation in tree island and mineralization in adjacent marsh ecosystems via leaf litter decomposition promotes landscape differentiation in this oligotrophic Everglades wetland. However, results of this study suggest that variation in flow rates, water levels and TP loads can shift differential P accumulation and loss leading to unidirectional processes among heterogeneous wetland ecosystems. Under sustained high P loading that could occur with increased freshwater flow, tree islands may shift to litter mineralization, further degrading landscape heterogeneity in this system, and signaling an altered ecosystem state.

Analysis of Plant Species Community within Upland Wetlands at Mt. Ilgwang

“…Ilkwang revealed a broad gradient in N:P supply ratios but highly constrained producer stoichiometry. The differential accumulation or loss of carbon and nutrients during decomposition can promote differentiation of wetland ecosystems, and contribute to landscape-scale heterogeneity (Troxler and Childers, 2009 Busan City has a plan to construct a mountain trail near the studied regions.…”

Recent and Historic Drivers of Landscape Change in the Everglades Ridge, Slough, and Tree Island Mosaic

“…In interior portions of the Everglades that receive minimal canal water, P enrichment may result from degradation of tree islands (Wetzel et al, 2009), which accumulate P in soil and litter Troxler and Childers, 2009). Significant gradients in vegetation community composition occur with proximity to tree islands, which Givnish et al (2008) attributed to a subtle P gradient.…”

Soil Building Processes in Reconstructed Tree Islands in The Everglades, Florida

“…Phosphorus loading increased through the wet season while N loading decreased in tree islands located in the southern Everglades . Troxler and Childers (2009) found that more mass was lost in decomposition experiments with litter in Everglades tree islands under flowing conditions compared to islands with non-flowing conditions. Hydrologic variations affect nutrient concentrations in tree islands soils.…”

“…Troxler et al (2005) found high nutrient use efficiency on highly organic seasonally flooded tree islands, and immobilization of N and P taking place on tree islands. Surface water on tree islands contains two times greater total nitrogen (TN) and total organic carbon (TOC) concentrations than marsh sites (Troxler and Childers, 2009). Litter decomposition experiments on nine tree islands in the southern Everglades indicate that N and P increase while C decreases as the litter decomposition process takes place (Troxler and Childers, 2009).…”

“…Surface water on tree islands contains two times greater total nitrogen (TN) and total organic carbon (TOC) concentrations than marsh sites (Troxler and Childers, 2009). Litter decomposition experiments on nine tree islands in the southern Everglades indicate that N and P increase while C decreases as the litter decomposition process takes place (Troxler and Childers, 2009). A steep gradient exist in soil total phosphorus (TP) concentration from the most flood prone to the least likely to be flooded on tree islands soils, with higher values at the less flooded section (Fig.…”