Root respiratory quotient and nitrate uptake in hydroponically grown non-mycorrhizal and mycorrhizal wheat

Oxygen and CO2 fluxes were measured in hydroponically grown mycorrhizal and non-mycorrhizal Triticum aestivum L. cv. Hano roots. The NO3- uptake of th e plants was used to estimate the amount of root respiration attributable t o ion uptake. Plants were grown at 4 mM N and 10 mu M P, where a total and viable mycorrhizal root colonisation of 48% and 18%, respectively, by Glomu s mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) was observed. The O -2 consumption and NO3- uptake rates were similar and the CO2 release was h igher in mycorrhizal than in nonmycorrhizal wheat. This resulted in a signi ficantly higher respiratory quotient (RQ, mol CO2 mol(-1) O-2) in mycorrhiz al (1.27 +/- 0.13) than in non-mycorrhizal (0.79 +/- 0.05) wheat. As the bi omass and N and P concentrations in mycorrhizal and non-mycorrhizal wheat w ere the same, the higher RQ resulted from the mycorrhizal colonisation and not differences in nutrition per se.