Vegetation influence on organic matter source of black soils from high altitude rocky complexes traced by 13C and 15N isotopic techniques

The organic soil layer (0–35 cm) of seventeen sites under high altitude rocky complexes (HARC) was sampled in eastern Brazil to evaluate the relationship of vegetation type and carbon and nitrogen isotopic composition of bulk soil and humic acid (HA). The δ13C and δ15N values obtained for bulk soil and for AH (extracted with NaOH 0.1 mol L− 1) were not statistically different (p < 0.05). Also, the high C to N ratio, and lower E4/E6 and TGI corroborate with the hypothesis that bulk soil organic matter (SOM) and HA have similar characteristics and high recalcitrance. The majority of sites in the HARC presented a soil organic matter originated from C3-vegetation and demonstrated an intense N cycling based on the δ15N data. Even though charcoal could be suggested as a component of soil genesis for most of the HARC sites, the raised data was not consistent to consider fire a key process for soil organic matter existence in these areas.