Plant carbohydrate limitation on nitrate reduction in wetland microcosms.

Although nitrate limitation in most natural wetlands results in pseudo-first-order reductions, large site-to-site variations in apparent denitrification rates cannot be easily explained by water quality (e.g., pH, Temp, DOC) or plant productivity. Our microcosm results show increasing nitrate removal efficiencies at higher ratios of total applied plant carbon to nitrate reduced, suggesting that denitrification rates may be limited by the rates of supply of both electron donor or acceptor, described by an applied carbon to nitrate (C(App): N(Red)) ratio. However, the observed first-order rate constants varied more strongly (r2 = 0.77, p <0.0001) with the acid-soluble carbohydrates to nitrate (CH2O(App): N(Red)) ratio than the total C(App): N(Red) ratio. Although observed rate constants for bulrush (Scirpus sp.) were significantly lower (0.01