increasing supplied nitrogen strongly increased Co2 assimilation (A),Photosynthetic nitrogen use efficiency(PNUE),and respiration for P.arundinacea but had only a small effect on these a parameters for C.stricta. relative to growth at 15mM nitrogen,growth at 0.15 mM for young leaves decreased carboxylation capacity and efficiency and the capacity for electron transport for P.arundinacea and a larger,stouter Carex species,Carex lacustris,by 53 to 70% but only 20 to 24% for C.stricta.