Physiological Responses to N-NO<sub>3</sub> and N-NH<sub>4</sub> of Triazine Resistant and Susceptible Plants of Horseweed (Erigeron canadensis L.)

Abstract

Triazine resistant and susceptible biotypes of horseweed (<i>Erigeron canadensis</i> L.) were grown under controlled conditions in nutrient solution with NH<sub>4</sub> or NO<sub>3</sub> ions as nitrogen source. Indicators such as: dry matter, CO<sub>2</sub> assimilation, chloroplasts activity, dark respiration and the content of K, Ca, Mg in the above ground parts displayed lower levels when plants were fed with NH<sub>4</sub> than with NO ions. Reduction of these indicators was stronger for the triazine susceptible plants which grew better than their resistant counterparts when fed with N-NO<sub>3</sub>. The triazine resistant plants grown with N-NH<sub>4</sub> contained more protein-N and K than the susceptible ones. Chloroplasts of the resistant plants were also less sensitive to NH<sub>4</sub>CL treatment. It is concluded that the resistant plants appear to be more tolerant to NH<sub>4</sub> ions as compared with their susceptible counterparts. For this reason application of ammonium forms of nitrogen fertilization in horticultural practice could favour spreading of triazine resistant horseweed.