Soil diffusive fluxes constitute the bottleneck to tree nitrogen nutrition in a Scots pine forest

• In nutrient poor environments, plant nitrogen (N) acquisition is governed by soil diffusive fluxes and root uptake capacities. However, the relationship between these two processes is not well understood. We explored a way of comparing the processes, enabling identification of the limiting factor for tree N acquisition.The study comprised N-fertilized and N-limited Scots pine stands, and measurements of uptake capacities of detached tree roots and of induced soil diffusive fluxes (through in-situ microdialysis) done at the onset and the end of the growing season.Soil N fluxes were higher at the onset than at the end of the growing season and amino acids comprised a larger fraction of N than inorganic N. N fertilization reduced root uptake capacities of NH4 (+), glycine and NO3 (-) but not of arginine. For all N compounds except NO3 (-), diffusive fluxes were significantly lower than root N uptake capacities.Our results suggest that soil N supply in both, N-fertilized and N-limited forest stands, is dominated by amino acids, thus being the major component of plant-available N. Uptake of N appears more constrained by the diffusive fluxes of N compounds rather than root uptake capacity, except for NO3 (-).

Ämnesord

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Skogsvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Forest Science (hsv//eng)

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