Effects of plant community and anthropogenic disturbance on decomposition in headwater wetlands

Background/Question/Methods

Riparian wetlands are well known for providing the important ecosystem service of carbon storage. Previous research has shown that changes in land-use regimes surrounding riparian wetlands can alter wetland plant community. Wetlands surrounded by agricultural land use (high disturbance) generally have an increased presence of invasive species and lower percent forest cover compared with wetlands surrounded primarily by forest (low disturbance). This shift could alter carbon storage by increasing or decreasing plant biomass or by affecting vegetation decomposition dynamics via changes in litter quality. To determine the effects of altered plant community on carbon storage, we studied plant decomposition and biomass in six headwater riparian wetlands in central Pennsylvania. The sites were split into three plant communities associated with different disturbance levels.  Of these sites two were dominated by Tsuga Canadensis (low disturbance), two were dominated by Fraxinus sp., Acer sp., and Carya sp (low or high disturbance), and two were dominated by Phalaris arundinacea and Rosa multiflora (high disturbance). We set up a yearlong decomposition experiment using in situ leaf, herbaceous, and control litter in each wetland. Leaf litter biomass, herbaceous litter biomass, and soil carbon were also measured to determine differences in these parameters between sites.

Results/Conclusions

Initial plant litter quality showed strong, significant relationships with percent mass remaining at the end of the yearlong experiment.  Wetlands dominated by Tsuga canadensis had greater percent mass remaining, percent C remaining, and overall soil percent C levels compared with wetlands dominated by Fraxinus sp., Acer sp., and Carya sp. , or wetlands dominated by Phalaris arundinacea and Rosa multiflora. Our results indicate that existing plant community and the litter quality thereof have great impact on C retention. This has important implications for improving wetland functional assessments of carbon storage, which often do not consider the composition of the plant community beyond tree density and litter layer depth.  Furthermore, our research supports a growing body of evidence showing that Tsuga canadensis dominated plant communities store more carbon that their deciduous counterparts, raising concerns for the continued loss of Tsuga canadensis plant communities through woolly adelgid infestations and logging.