Root uptake of inorganic and organic N chemical forms in two coexisting Mediterranean forest trees

Abstract

Background and aims Plants differ in their ability to usedifferent nitrogen (N) chemical forms, these differencescan be related to their ecology and drive communitystructure. The capacity to uptake intact organic N hasbeen observed in plants of several ecosystems. However,soil organic N uptake by Mediterranean plants is unknowndespite organic N being abundant inMediterranean ecosystems. We compare the uptake ofdifferent N forms in two widespread coexistingMediterranean forest trees with contrasting ecophysiologicalcharacteristics: Quercus ilex and Pinus halepensis.Methods To estimate root uptake rate of eachN form weused equimolar solutions (1 mM N) of 15NO3-, 15NH4+ and 15N-13C glycine.Results NH4+ and glycine were taken up at a similarrate, but faster than NO3− in both species. Intact duallabeled glycine was found in both species, demonstratingthat both species can absorb intact organic N. Conclusions: Despite their ecological differences, both species had similar preference for N forms suggesting no niche complementarity for N uptake. The higher preference for NH4 + and glycine over NO3 - possibly reflects adaptation to the differing proportions of N forms in Mediterranean soils.