Congreso celebrado del 16-19, julio, 2007, en Poitiers, Francia.Solid-state nuclear magnetic resonance (NMR) spectroscopy was applied to study the chemical
alteration of the stable soil organic matter (SOM) pool in various savanna soils from Southern Brazil after
ceasing annual burning. Irrespective of the time passed since the last fire, the topsoils showed the typical
pattern of humifying unburnt material, with considerable low contributions of pyrogenic organic matter
(PyOM), although stopping the fire decreased the organic-C content. The latter is most tentatively caused by
the reduced input of decaying roots of killed plants and lower biomass production due to the missing of the
liming effect of fire. Unexpected high aromaticity was detected for the SOM in the deeper soil (15-45 cm).
This is attributable to increasing accumulation of PyOM that had been transported through the soil column.
Our results clearly demonstrate that elucidating the impact of annual burning on the global C and N cycle,
one has to consider the fertilizing effect of fire as well as the fact that some black carbon (BC) can be
transported to deeper horizons. Here it may accumulate to important amounts that should not be neglected in
C budgeting studies.Peer reviewe
