Biomassas radiculares e aéreas em comunidades de caatinga

Abstract

The root and aboveground biomass and the root: shoot ratio were estimated in three stages of native vegetation regeneration (18, 40 and> 60 years), in an area of litholic Neosol in semiarid, Paraíba state, and in open and dense vegetation physiognomies in four soil classes (Luvisol, litholic Neosol and quartzarenic Neosol and Planosol), in the semiarid of Pernambuco state. In Paraíba, twelve 3 m radius plots were installed at each regeneration stage, and in Pernambuco, three 5m radius plots were installed in each combination of vegetation x soil class. In each plot, all plants with stem diameter at 1.3 m above the soil level (DBH) ≥ 3 cm were measured and the DBH was used to estimate the aboveground biomass (kg) of plant using the equation: 0,173 DBH(cm) 2,295. The roots were collected in 0.7 × 0.7 × 1m trenches, in successive soil layers of 20 cm depth, separated in fine (≤ 5 mm) and thick roots (≥ 5 mm), dried and weighed. In Paraíba, the root biomass was significantly higher in the vegetation > 60 years regeneration (23 Mg ha-1) than in the younger regeneration stages (5 Mg ha-1 in the 40-year regeneration and 2 Mg ha-1 in the 18-year regeneration stages). The aboveground biomass was also higher in the > 60 years regeneration (60, 28 and 22 Mg ha-1, respectively). In all regeneration stages, most (> 79%) of the total root biomass was in the 20 cm layer of soil. In Pernambuco, the root (13.1 Mg ha-1) and aboveground (47.2 Mg ha-1) biomasses were significantly higher in the dense vegetation physiognomies than in the open vegetation physiognomies (5.75 Mg ha-1 and 16.5 Mg ha-1, respectively). In the two phytophysiognomies, in three of the soil classes most of the root biomass (>90%) were in the top 40 cm soil layers but in the N. quartzarênico the proportion in these layers were below 45%.The root: shoot ratio ranged from 23 to 39%, with the highest values in the > 60 years regeneration (38%) and in sandy soil (39%) area, where the roots reached their greatest depth. In the open physiognomy no thick root grew below 40 cm depth. Therefore, the biomass stocks tend to increase with the advance of the successional stage and the roots reach greater depths and larger root: shoot ratio in soils of sandy texture.