A. Pornon et B. Doche, NITROGEN MINERALIZATION AND NITRIFICATION IN DIFFERENT COLONIZING STAGES OF SUB-ALPINE RHODODENDRON-FERRUGINEUM L HEATHLANDS, Comptes rendus de l'Academie des sciences. Serie 3, Sciences de la vie, 318(8), 1995, pp. 887-895
Potential nitrogen mineralization and nitrification was measured in so
ils from 3 different colonizing stages (meadow open heathland, closed
heathland) of Rhododendron ferrugineum subalpine heathlands. This stud
y was conducted on 2 sites: the Collet-d'Allevard (CA; altitude = 1 65
0 m) and the Cote des Salieres (CS; altitude = 1 860 m). The CA popula
tions have a greater productivity and a faster dynamics than the CS po
pulations. If annual soil nitrogen production investigated in soil inc
ubation war no more than 1.5 g.m(-2) (15 kg.ha(-1)) in all situations,
the peak of mineralization did not. occur at the same time and the N-
NO3-/N-NH4+ ratio was dependent on the sites. At the CS, the greatest
concentrations of soil mineral nitrogen happened 1 month later than th
ey happened at the CA. Moreover the N-NO3-/N-NH4+ ratio from CS was ne
ar 1 while from CA it was near 0. However, closed heathlands of the 2
sites behaved differently because there was no mineralization at CS an
d nitrification occurred at CA during august period. This allows us to
hypothesize about the relationships between available soil nitrogen,
the biological and ecological performances of the Rhododendron populat
ions.