Forest soil dynamics during stand development assessed by lysimeter and centrifuge solutions

Soil solution is the phase which is best able to characterize current soil mechanisms. However, there is great variation in residence time and chemistry. Fixed solutions collected in situ by porous-cup lysimeters (TL) or extracted by centrifugation (C) and the mobile phase collected by zero-tension lysimeters (ZTL), were investigated simultaneously in a chronosequence of Douglas-fir stands in order to characterize current soil dynamics in relation to stand development. These results were used to characterize the solution for plant nutrition and to calculate input-output budgets of the ecosystem. The results showed that the C-solution reflected the poles of nutrient production in soil both by mineralization of organic matter or by weathering of minerals: it is, therefore, the reference for investigating plant nutrition. The ZTL soil solution chemistry is the result of rainfall, tree crown interaction, mineralization in the forest floor and displacement of already existing products in the soil. It is the most interesting for characterizing drainage waters. The TL-solution, which is very often used in soil science, seems the most difficult to interpret as its chemistry reflects the resultant effect of production and uptake by vegetation. Stand development did not affect C-solution chemistry but strongly influenced the chemistry of ZTL-solution indicating the comparability of stands and the role of aerial processes in soil dynamics.