The effects of plant genes on in stream nitrification rates

Nitrification, the conversion of ammonia to nitrate, is an essential process in aquatic food webs. Previous work has shown an inverse relationship between dissolved organic carbon and nitrification rates. Tannic acids, a ubiquitous organic carbon, vary both interspecifically and intraspecificlly in cottonwoods (Populus).  Common garden experiments reveal a strong genetic component to tannic acid concentrations in cottonwood leaves. We tested how cottonwood leaf quality affected nitrification in stream sediment from an Arizona stream, hypothesizing that DOC derived from leaves with higher tannic acid concentrations would have a greater inhibitory effect on nitrification. Dissolved organic carbon leachate (n=4) from three distinct genotypes (P. angustifolia, high tannin; P. angustifolia, low tannin; P. fremontii, low tannin) were incubated in 110 ml of stream sediment and stream water. Nitrification was assessed using nitrapyrin inhibition.  These results link the genetics of a riparian foundation species with freshwater biogeochemical processes.