DISTRIBUTION OF SULFUR FORMS IN SOILS FROM BEECH AND SPRUCE FORESTS OF MONT-LOZERE (FRANCE)

From a quantitative inventory of sulphur forms and sulphur budget, the relation between the distribution of the various sulphur forms and th e sulphate fluxes in three soil profiles has been addressed. These pro files are located in two forested watersheds at Mont Lozere. One has b een sampled in a beech forest and the other two in a spruce forest and in a harvested plot of this spruce forest, respectively. The mean ann ual input-output budgets showed a sulphur immobilization in the soil c over of the three plots. In the preserved spruce forest plot, because of larger dry depositions, the sulphur immobilization is much greater than in other plots and occurs essentially in the B horizons. In the o ther two profiles, the dominant immobilization occurs in the parent ma terial. The total sulphur content is very high in the forest floor rea ching 2065 mug S g-1 in the litter of one of the soils under spruce. I n the organo-mineral horizons of soils under spruce, the total sulphur content decreases with depth and ranges from 310 to 520 mug S g-1 in the A horizons to 100-200 mug S g-1 in the parent material. In the pro file under beech, the total sulphur content is lower except in the par ent material. In all cases, the organic sulphur is the major part of s ulphur often representing more than 90% of total sulphur. In organo-mi neral soil horizons of the spruce forest, the part of the sulphate-est ers is more important than in the soil of the beech forest, probably r elated to the different nature of the microbial activity in the spruce forest. In contrast, the humification processes are more efficient in the soil under beech, which can be due to the greater input of organi c sulphur by litterfall. It appears that the dominant organic sulphur form varies as a function of microbial ecology and sulphate flux. The maximum of the inorganic sulphate is located at the base of the B hori zons in the soil of the spruce forest and in the parent material of th e soil under beech. In these horizons, the high content of inorganic s ulphate can be related to the higher amounts of amorphous Fe and Al ph ases.