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Canopy carbon and water exchanges on forest sites with contrasting soil water availability

Denis Loustau, Marion Devaux, Jean-Marc J.-M. Bonnefond, Eric Lamaud,

Alexandre Bosc

To cite this version: Canopy carbon and water exchanges on forest sites with contrasting soil water availability.

In w ater limited environments, the predictability of the annual soil w ater regime varies geographically, from sites w ith a periodic seasonal rainfall pattern to sites w ith erratic and therefore much less predictable w ater availability. In order to investigate the contrasting adaptative pattern of trees in such environments, w e compared pine stands grow ing on either shallow sandy soils, limited to the top 0.6 m w ith a high w ater table (W), to sites with deeper soils where roots reach a depth of 3 m below the soil surface (D). The tree sap flow, cambial grow th and carbon stable isotopes composition of cellulose from thin tree rings fractions were determined over several consecutive years. In addition, w ater and carbon exchanges were monitored for 11 consecutive years on the W site. The carbon stable isotope composition of the thin tree ring fractions w as linked to the canopy-atmosphere CO2 flux using a simple model. The data shows that trees grow ing on the W site exhibit a faster growth and higher production, but experienced more severe drought than trees grow ing in the D site. Although the mean ring values of 13C was seasonally or annually similar among sites, the intra-ring profile w as much more amplified during dry years and this seems to be more pronounced on the W site. From these data, we hypothesize that pine stands grow ing on the W site may be more affected by the regional climate changes expected in this area.

Key Words

Water availability, maritime pine, w ater use efficiency, Tree-ring, carbon isotope ratio, climate.