Allochthonous carbon delivery from the invasive grass (Phalaris arundiancea L.) to a lotic ecosystem

Abstract

Reed canarygrass (RCG; Phalaris arundiancea L.;) invades wetlands throughout the United States of America, including floodplain forests (FPF) found along the upper Mississippi River (UMR). This study was done to determine how this invasive grass alters the allochthonous material delivered to UMR. A plant litter mass loss study was done to determine the decomposition rate or RCG litter compared to river birch (RB; Betula nigra L); silver maple (SM; Acer saccharinum L.); swamp white oak (SWO; Quercus bicolor Willd.) leaf litter. Screen mesh (inhibit macroinvertebrate activity) and hardware mesh (to allow macroinvertebrate activity) litter packs filled with plant litter from RCG and FPF leaf litter, submerged in a stream and withdrawn nine different days to determine loss of mass. Macroinvertebrates from litter packs were identified, counted and dried to a constant weight. In well water without and with microbial activity, the concentration (mg/L) of dissolved organic carbon (DOC) leached from RCG litter and native FPF leaf litter was compared over time. With microbial activity in well water the decomposition of DOC leached from RCG and native FPF leaf litter was also compared over time. Silver maple leaf litter decomposed at a significantly faster rate than RCG, SWO and RB litter (P < 0.001). Macroinvertebrate shredder activity was observed on FPF leaf litter one week prior to RCG litter, and peaked by week 17 compared to week 7 on RCG. Macroinvertebrate biomass and abundance were not significantly different between litter types. With microbial activity DOC (mg/L) leached from SM litter was significantly higher than DOC (mg/L) leached from RCG litter over time (P < 0.05). Overall decomposition rate, and rate of the labile portion of DOC leached from RCG litter was significantly higher that DOC leached from native FPF leaf litter (P < 0.0001) and (P < 0.0001), respectively. These results suggest that RCG litter is of lower quality that FPF leaf litter, which could alter allochthonous carbon made available to secondary consumers in the UMRS.