Restored prairie vegetation effects on the carbon cycle of a dewatered basin in Southwestern Wisconsin

Background/Question/Methods  

Ecological restoration of dewatered sediments following dam removal has become a growing trend in Wisconsin, but our understanding of how these restored plant assemblages affect carbon cycling is limited. For instance, because disturbed soils are prone to invasion by non-native species, many ecological restorations result in unexpected outcomes in terms of plant composition and the cycling of carbon. Typically, invasive species have tissue with lower carbon:nitrogen (C:N) ratios than native species and thus a faster rate of decomposition, which can alter soil carbon dynamics. The objective of this research is to compare the effects of proportional plantings of native prairie species relative to naturally invasive species on the carbon cycling in a novel environment: a recently dewatered basin following dam removal. We hypothesized that a greater native to invasive species ratio would have higher C:N ratio, leading to slower decomposition rate, and lower soil surface CO₂ flux. To test these hypotheses, we collected aboveground plant biomass, measured the decomposition rate of native and invasive litter, and quantified surface soil CO₂ fluxes.

Results/Conclusions  

Senesced tissue from mixed native species had a higher C:N ratio, 28:1, than tissue from mixed invasive species (22:1). The tissue from native species had a significant lower (P < 0.01) decomposition rate (k = 0.0022 day^-1) than the invasive species tissue (k = 0.003 day^-1). We also found a significant interaction between litter type and the location (i.e., under native or invasive species canopy) where the litter was located for decomposition (P < 0.01). During the 2009 growing season, the mean soil respiration rate over the entire basin was 4.72 µmol CO₂ m^-2 s^-1. Multiple linear regressions yielded a log-transformed soil CO₂ flux that was related with soil temperature and moisture, as both explained R² = 22% of the flux variation over the entire site. These abiotic factors appear to have a greater influence on soil respiration where there are higher proportions of native vegetation (R² = 38%) than plots supporting only invasive species (controls) (R²= 21%). Our results suggest that shifts in vegetation type combined within disturbed sediments may alter the cycling of carbon in restored prairie.