No abstract

The contribution of soil respiration to the photosynthesis of the shade flora in the Amazon forest was evaluated by measuring the δC values of leaves collected at different levels in two forest communities. Canopy leaves have an average δC of-30.5‰ in the podsol forest and-28.7‰ in the laterite forest. Leaves from plants in the lower forest strata have a significantly lower value of-35.2‰ in the podsol forest and-34.3‰ in the laterite forest.

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No abstract

Species of the 'bana' vegetation in the Amazonas region of equatorial South America have scleromorphic leaves. This leaf type, which characterizes the vegetation of Mediterranean climates, among others, has apparently evolved in this community in response to the oligotrophic soils and widely fluctuating water table.Anatomically, the leaves have several features commonly found in xeromorphic plants, including greater leaf and cuticle thickness, pubescent leaves and sunken stomata, and a high incidence of sclerenchyma.Concentrations of K and P decrease with leaf age, while N remains nearly constant and Ca increases. Concentrations of N and P are lower than in other sclerophyllous species, but the amount of these nutrients recovered before leaf shedding are similar. The correlation between P and N as expressed per unit dry weight is high (r=0.87; p<0.01) as is the relation between leaf specific area (area/dry wt.) and N (r-0.83; p<0.01) and P (r= 0.82; p<0.01).Soils of this region are very acidic (extreme lowest value pH 3.6) and have high levels of exchangeable Al and Mn. Among the 'bana' plant species are some which accumulate high levels of Mn (>300 ppm) and Al (>1000 ppm).