Dehesas are Mediterranean agro-sylvo-pastoral
systems sensitive to climate change. Extreme climate conditions forecasted
for Mediterranean areas may change soil C turnover, which is of relevance
for soil biogeochemistry modeling. The effect of climate change on
soil organic matter (SOM) is investigated in a field experiment mimicking
environmental conditions of global change scenarios (soil temperature
increase, +2–3 °C, W; rainfall exclusion, 30%, D; a combination
of both, W+D). Pyrolysis-compound-specific isotope
analysis (Py-CSIA) is used for C and H isotope characterization of
SOM compounds and to forecast trends exerted by the induced climate
shift. After 2.5 years, significant δ13C and δ2H isotopic enrichments were detected. Observed short- and
mid-chain n-alkane δ13C shifts point
to an increased microbial SOM reworking in the W treatment; a 2H enrichment of up to 40‰ of lignin methoxyphenols
was found when combining W+D treatments under the tree canopy, probably
related to H fractionation due to increased soil water evapotranspiration.
Our findings indicate that the effect of the tree canopy drives SOM
dynamics in dehesas and that, in the short term,
foreseen climate change scenarios will exert changes in the SOM dynamics
comprising the biogeochemical C and H cycles.