Comparison of biomass production and decomposition between Phragmites australis (common reed) and Spartina patens (salt hay grass) in brackish tidal marshes of New Jersey, USA

The recent expansion of Phragmites australis (common reed) from the marsh-u pland interface into high marsh zones provides an opportunity to assess the impact of individual plant species on biomass production and decomposition in salt marshes. Seasonal harvests of aboveground and belowground biomass demonstrate that annual production of P. australis is approximately three t imes greater for aboveground biomass, two times greater for belowground bio mass, and 30% lower in root: shoot ratio than neighboring populations of S. patens. Whole-plant litter (stems and leaves) also decomposes at a much sl ower annual rate for P. australis (k = 0.25) than S patens litter (k = 0.57 ). By crossing litter type with site of litter decomposition, I found these plant species to influence decay rates through litter type and not through their effects on marsh surface conditions (e.g., temperature, sedimentatio n rates). Based on these calculations, annual rates of carbon accumulation in the peat of high marshes are likely to increase 5-fold once P. australis becomes established due to its greater rates of biomass production and res idence time in infrequently flooded brackish marshes.