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 use different nitrogen (N) chemical forms, these differences can be related to their ecology and drive community structure. The capacity to uptake intact organic N has been observed in plants of several ecosystems. However, soil organic N uptake by Mediterranean plants is unknown despite organic N being abundant in Mediterranean ecosystems. We compare the uptake of different N forms in two widespread coexisting Mediterranean forest trees with contrasting ecophysiological characteristics: Quercus ilex and Pinus halepensis.

Methods To estimate root uptake rate of each N form we used equimolar solutions (1 mM N) of 15NO3 −, 15NH4 + and 15N-13C glycine.

Results NH4 + and glycine were taken up at a similar rate, but faster than NO3 − in both species. Intact dual labeled glycine was found in both species, demonstrating that both species can absorb intact organic N.

Conclusions Despite their ecological differences, both species had similar preference for N forms suggesting no fundamental 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.