Soil biological studies in contrasting types of vegetation in central Amazonian rain forests

Studies were carried out in a lowland evergreen rain forest (LERF), on an ultisol, in the 'Reserva da Campina', 45 km north of Manaus, and in two facies of the highly distinct formation called heath forest, on spodosols. The spodosols had a layer of mor humus of thickness varying from nil in some parts in the smaller facies of heath forest (SHF) to 35 cm in the taller facies (THF). The overall aim was to investigate the forest soil biota and its role in nutrient turnover by comparing the SHF, THF and LERF. Microbial biomass, soil respiration and nitrogen transformation rates were measured in the three forest types in both wet and dry seasons. Field and laboratory fertilization experiments were made to investigate potential limiting nutrients for microorganisms and plants. The role of fine roots in decomposition and litter animal colonization was assessed in litter bag studies. SHF soils have a small microbial population with no net nitrification in any season. THF soils showed a variable microbial population adapted to high acidity, which immobilises nitrogen during the wet season, but which allows a net release during the dry season. LERF showed the most diverse population which causes mineralization and nitrification in both seasons. A bioassay with nutrient addition showed that the low pH, and nitrogen and sulphur supply were likely to be limiting nitrogen dynamics in all forest types, but especially in THF and LERF. The ingrowth bags showed that despite the lower values of fine root growth in the SHF (particularly when the white sand of the spodosol was used as the substrate), the roots showed in all plots an increased production with added calcium as carbonate or sulphate. In the decomposition bioassay to evaluate the role of roots in the nutrient turnover it was shown that in all forest types there was no effect of roots on the mass loss of Clitoria leaves but there was a significant effect on concentrations of some nutrients. In general, roots contributed to the accumulation of aluminium and iron and to a faster release and uptake of calcium, magnesium and zinc. A survey of the mycorrhizal associations in all forest types showed that both VAM and ECM fungi with some unknown VAM fungal species are common. VAM and ECM adaptation to low pH and high phenolic compounds in the soils may be important in the maintenance of these ecosystems

Ecological studies in contrasting forest types in central Amazonia

Most of the Amazonia is covered by the lowland evergreen rain forest (LERF) formation. A small proportion of the region (5-6% in total) is covered by heath forest, which is particularly common in the Rio Negro basin on Spodosols - white sand soils with a layer of mor humus. The smaller facies of heath forest (SHF) is called 'Camping' in Brazil and often lacks the mor humus; the taller facies (TBF) is called 'Campinarana'. The present study was made in central Amazonia, on a gradient from SHF through THF to well developed LERF. Soil, vegetation, and nutrient dynamics were studied in three 50 m x 50m plots in each type of forest. Litterfall was measured during one year and litter standing crop was measured three times a year. Three decomposition experiments, using bagged leaf litter, were made using leaves of two common species from the heath forests and one from the LERF. Fertiliser addition experiments in the field and in the laboratory were carried out to determine the potential nutrient limitations for plants in the three forest types. Annual litterfall was highest in the dry season and was 3.8 t ha-1 yr-1 in the SHF, 6.3 t ha-1 yr-1 in the THF and 7.8 t ha-1 yr-1 in the LERF. The rates of weight loss of the enclosed leaf litter were most rapid in the LERF and slowest in the SHF. The leaves of the LERF species Clitoria racemosa decomposed faster than those of the heath forest species. Fine roots penetrating litter-bags differed significantly among forest types and leaf species, and increased the decay rates. There were no significant differences in decomposition rates between the wet and dry season experiments. Significant differences in the release of chemical elements were observed: higher immobilization of iron and aluminium in the LERF; higher potassium and copper release in THF; and lower calcium, but higher boron release rates in SHF. Significantly higher immobilization of iron and aluminium (mainly in LERF) was found in bags penetrated by fine roots, while release of magnesium, calcium, manganese and zinc was significantly increased by fine roots, particularly in the TI-IF. Leaf mass loss and nutrient release were mostly controlled by abiotic factors in the SHF, but organisms were more active in the THF and LERF. Diplopoda were the dominant decomposers, particularly in the THF. Fertiliser addition showed an overall positive effect of liming, especially in heath forest soils. Nitrogen and phosphorus additions did not induce higher biomass production, while calcium chloride addition invariably induced a high mortality. 11÷ ion toxicity, together with a higher concentration of soil phenolics are suggested as causes of the poor growth in the heath forests, but in the SHF, where it lacks mor humus, limitation by nutrients, especially basic cations, may occur

Microbial respiration and biomass in tropical forest soil and litter.

doi nefunkčníLaminated glass units exhibit complex response as a result of different mechanical behavior and properties of glass and polymer foil. We aim to develop a finite element model for elastic laminated glass plates based on the refined plate theory by Mau. For a geometrically nonlinear description of the behavior of units, each layer behaves according to the ReissnerMindlin kinematics, complemented with membrane effects and the von K´arm´an assumptions. Nodal Lagrange multipliers enforce the compatibility of independent layers in this approach. We have derived the discretized model by the energy-minimization arguments, assuming that the unknown fields are approximated by bi-linear functions at the element level, and solved the resulting system by the Newton method with consistent linearization. We have demonstrated through verification and validation examples that the proposed formulation is reliable and accurately reproduces the behavior of laminated glass units. This study represents a first step to the development of a comprehensive, mechanics-based model for laminated glass systems that is suitable for implementation in common engineering finite element solvers.Web of Science1261181115

Soil CO2_2 efflux in Central Amazonia: Environmental and methodological effects

Soil respiration plays a significant role in the carbon cycle of Amazonian rainforests. Measurements of soil respiration have only been carried out in few places in the Amazon. This study investigated the effects of the method of ring insertion in the soil as well as of rainfall and spatial distribution on C