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Adaptations to nitrogen form: comparing inorganic nitrogen and amino acid availability and uptake by four temperate forest plants

Metcalfe, R. J., J. Nault and B. J. Hawkins. 2011. Canadian Journal of Forest Research

Abstract

There are few examinations of the relative availability and plant uptake of inorganic N and amino acid N in temperate forest regions. We determined the availability of amino acid N and inorganic N in soils under two shrub species (Vaccinium ovalifolium Sm. versus Rubus spectabilis Pursh) on three sites near Jordan River, British Columbia, over a growing season. We compared biomass production of the two shrubs and two conifers (Picea sitchensis (Bong.) Carr. and Pseudotsuga menziesii (Mirb.) Franco var. menziesii) when given inorganic N (20:80 or 80:20 NH4+NO3-) or organic N (glycine and glutamic acid) and assessed short-term uptake (24 h) of 15N-labelled NH4+ , NO3-, glycine, or glutamic acid by the four species. Water-extracted soil concentrations of NH4+ were up to 1.5 times greater than NO3- averaged across sites. Concentrations of amino acid N and inorganic N were similar on soils under Rubus, but the amino acid N to inorganic N ratio was up to 2.4:1 in soils under Vaccinium. Soils dominated by Rubus had up to twice the NO3--N and two thirds the amino acid N concentrations of soils dominated by Vaccinium, averaged across sites and Rubus had relatively high short-term 15NO3- uptake. The dry biomass of conifers was approximately four times greater when supplied mainly with NH4+ compared with NO3-, but biomass of the two shrub species was similar in both inorganic N treatments. All plants had comparable rates of short-term 15N uptake from amino acids and inorganic N, suggesting that amino acids could contribute to the N nutrition of these temperate species; however, dry biomass of all four species grown with amino acids was less than one half that of plants grown with inorganic N.