The role of fungi and invertebrates in litter decomposition in mitigated and reference wetlands

Wetland plant litter decomposition influences many wetland processes and is itself driven by a complex web of interacting parameters. Invertebrates and fungi make up one portion of that web by processing organic material; however, their role is poorly understood. To explore invertebrate and fungal influence on plant litter decomposition rate, we measured the decomposition of litter in three mitigated (created wetlands) and three reference wetlands in the Mid-Atlantic Highlands of West Virginia, USA. Litter decomposition rates and most invertebrate metrics were not statistically different between mitigated and reference wetlands; only oligochaetes (worms) and the functional feeding group (FFG) collector/gatherers had numbers that were statistically higher in mitigated wetlands. Invertebrate metrics were able to explain 25% (FFG) to 31% (taxonomic groups) of variance during the first phase of decomposition (<224 days) and 15% (FFG) to 21% (taxonomic groups) during the second phase (≥224 days). Shredders, collector/gatherers, and omnivores were more strongly associated with early phases of decomposition, while oligochaetes and omnivores were most strongly associated with trends in decomposition during the later phase. Fungal biomass, as measured by ergosterol concentration, was similar between mitigated and reference wetlands and was significantly higher in the first phase of litter decomposition than the second phase, but was not statistically correlated with litter decomposition rate. Decomposition influences many aspects of wetland function, making the variables that determine decomposition rates important for assessing and mitigating for lost wetland function.