Tracing the fate of Mg and Ca originating from liming in Beech forest ecosystems of Northern France over 40 years : ecosystem nutrient budgets and 26Mg/24Mg and 87Sr/86Sr natural isotope ratio variations
Résumé
Most forest ecosystems grow on acid and nutrient poor
soils. In many cases, the chemical fertility of forest soils is
slowly degrading due to increasing external pressures (e.g.
decreasing atmospheric inputs, increasing biomass expor-
tations) and is a growing concern in the international forest
community. Forest liming with a carbonate product is a
solution to restore soil fertility and acidity, globally improve
the ecosystem functioning and compensate for nutrient losses
caused by biomass harvest and exportation. However, the
effects of liming on ecosystem processes and the
biogeochemical cycling of nutrients in forest ecosystems are
little known.
In this study we studied over 40 years the fate of
magnesium and calcium originating from the dissolution of
liming products in the soils and trees of five beech plots
located in Northern France from ecosystem Mg and Ca
budgets combined with the natural variations of magnesium
and strontium isotopes (26Mg/24Mg and 87Sr/86Sr).
Compared to the control plots, soil exchangeable pools of
Mg and Ca in the 0-40cm layer increased during the first
decade after liming but differences were no longer observable
in soil pools after 20 to 30 years. However, the effect of
liming on tree nutrition and growth was still observed after 40
years, most probably because the biological cycling of these
elements was more dynamic in the limed plots. Liming effects
varied between sites depending on the liming product and
amount, and the initial chemical fertility level of the soil. The
natural variations of Mg and Sr isotopic ratios are an
interesting tool which enables to trace the incorporation over
time of Mg and Ca liming products into their biogeochemical
cycle in forest ecosystems and better understand the changes
(biogeochemical processes and cycling) induced by liming
operations