Summary
Soil respiration measurements (Walter & Haber method) were taken in sand forest, campinarana and campina, in the INPA-SUFRAMA reserve and vicinities (02°38'S,60°01'W), near Manaus, Amazonas, Brazil. Carbon dioxide evolution from soil was measured during 7 periods (6 for campina) of 24 hours duration. Its conversion Into primary productivity has furnished mean values which have shown to be statistically different for each habitat, highly significant through the Willis rank-test. The mean values for soil respiration were 60.18, 52.85 and 44.99 mg CO2/m2.h, and the mean values for decomposition were 2.50, 2.20 and 1.87 tons org. mat./ha.year, respectively for sand forest, campinarana and campina. Considering aerial decomposition, the sand forest primary productivity was estimated at 5,0 tons org.mat./ha.year, the lowest figure reported to date for forests of this region. These results are probably due to the soil nutrient deficiency and to the low biomass of this kind of vegetation. Chemical analyses of leaves, litter and soil at different depths seem to indicate that nutrients may be deposited on and/or washed out of the phytomass by rain water; that they may accumulate in the litter layer; that they may then be transferred to biomass via microrhizae and predation in addition to the normal method of nutrient uptake by plants; and that there is a great loss of nutrients in the soil by water (and solutes) percolation. The accumulation of nutrients in the litter layer seems to be due to their complexation. chelation and insolubilization, processes in which microorganisms should have an Important role. Iron and aluminium should also be important in these processes, as well as for these microorganisms. The accumulation of nutrients in the litter layer seems also to be a direct result of the vegetation cover. An exception is iron, which has been shown to be indifferent to the vegetation cover. Except at 40 cm depth under campina all other soil samples have aluminium concentration considered to be toxic to most plants. The highest pH values were found for campina soil, and the lowest ones for campinarana soil. The different behaviour of the granulomerc fractions with increasing depths seems to indicate occurrence of different soil processes. The authors indicate complementary studies which might help in understanding these vegetation types: on annual soil respiration, on nutrient cycling, on aluminum and iron and their influence upon the vegetation and the decomposers, on the soil at different depths.