Marcos Valério Garcia

Structure and function of soil fauna communities in Amazonian anthropogenic and natural ecosystems

The soil biological conditions of two 5-year-old polyculture tree plantations in Amazonia were studied comparatively to a 13-year-old secondary forest and a nearby undisturbed primary forest. The polycultures had been planted to regenerate the soil degraded by land preparation and a former rubber tree monoculture. Abundance and biomass of functional groups of soil meso- and macrofauna were measured at three-months-intervals over 2 years and litterbag experiments with fauna exclusion were carried out. This paper concentrates on the description of the structure of the soil fauna communities, forming the background for an evaluation of the decomposition processes in polyculture plantations. Decomposition rates were strongly determined by the macrofauna particularly in primary forest, where large earthworms, termites and ants dominated the soil fauna. In the plantations, where litter originated predominantly from the non-planted, adventitious vegetation, an abundant decomposer fauna was found, in which however other groups or species dominated. Although decomposition rates in the plantations were about 60 % lower and soil biological variables like organic matter-, nitrogen-content and water holding capacity were slightly lower than in the primary forest, conditions seem favourable for a manipulation of the soil fauna by management of secondary vegetation and litter quantities.

Litter fall, litter stocks and decomposition rates in rainforest and agroforestry sites in central Amazonia

The sustainability of agroforestry systems in Amazonia was assessed from their litter dynamics and decomposition. Litter fall and litter stocks were determined from July 1997 to March 1999 in four sites in central Amazonia: a primary rainforest, a 13-year-old secondary forest, and two sites of a polyculture forestry system which consisted of four planted tree species of commercial use amidst upcoming secondary growth. The average annual litter fall in the undisturbed primary rainforest (FLO) was 8.4 t ha−1 year−1, which is within the range of litter fall in other rainforests in the region. It was similar in one of the two polyculture sites (8.3 t ha−1 year−1), but lower in the secondary forest and in the second polyculture site. In the litter fall in secondary forest and agroforestry sites, the leaf portion was higher (76–82% of total litter fall) than in FLO, due to reduced fine matter and wood fall. Leaf litter fall variability was much lower in the plantation sites than in the forests, which is explained by the much more homogeneous stand structure of the plantations. The quality of the produced litter, measured as C/N ratio, differed significantly between the primary forest site and one polyculture and the secondary forest site. The cumulative input of nitrogen through litter fall was 144 kg ha−1 year−1 in FLO, and 91–112 kg ha−1 year−1 in the polycultures and the secondary forest. Litter fall was not correlated with soil parameters, but had a significant linear regression with canopy closure. For the primary rainforest, litter fall was also (inversely) correlated with monthly rainfall. Litter fall was higher in the first year (1997–1998; an El Niño period) than in 1998–1999. Litter stocks on the forest floor were highest in the secondary forest (24.7 t ha−1), and much lower in the polyculture sites (15.1–16.2 t ha−1) and the primary forest (12.0 t ha−1). There were no differences in the relative N content (C/N ratio) of the litter stocks between the sites, but the larger stocks led to higher absolute N contents in the litter layer in the secondary forest. From the monthly values of litter stocks (S) and litter fall (P), the decomposition coefficient ke=P/S was calculated, which was, on average, highest for the primary forest (0.059), followed by the polyculture systems (0.040–0.042), and by the secondary forest (0.024). Thus, due to low decomposition rates, the secondary forest site showed large litter accumulations in spite of a relatively low litter fall. In contrast, the primary forest showed high litter fall but low stocks, due to high decomposition rates. The decomposition coefficients of the polyculture systems ranged between the primary and the secondary forest. The reduced decomposition rates in the man-managed agroecosystems indicate quantitative and/or qualitative changes in the decomposer communities of these systems that lead to a higher build-up of litter stocks on the forest floor. However, the decomposer systems in the polyculture sites still were more functional than in the site of non-managed secondary growth. Thus, from a soil biological viewpoint, ecologically sustainable low-input agroforestry in Amazonia will benefit from the application of these polyculture systems.

Polycyclic aromatic hydrocarbon (PAH) patterns in climatically different ecological zones of Brazil

Abstract Understanding the global distribution of PAHs requires knowledge of their sources. The objective of our work was to test the hypothesis that termites and woody plants are sources of naphthalene (NAPH), phenanthrene (PHEN), and perylene (PERY) for soils of different tropical climates. We determined the concentrations of 20 PAHs in soil, wood, and different compartments of termite nests (central part, inner wall, outer wall) in the Amazon (Terra firme, Varzea, and Igapo), Pantanal, Cerrado, Mata Atlântica, and Caatinga regions. The sum of 20 PAH concentrations was low in all soils (4.8–347 μg kg −1 , n =47) and much higher in many of the wood (47–3894, n =31) and termite nest samples (29–4208, n =121). In general, NAPH, PHEN, or PERY were most abundant. In the Amazon region, wood samples contained up to 3785 and termite nest samples up to 3645 μg kg −1 of NAPH. In all regions, most termite nests contained higher PERY concentrations (up to 1109 μg kg −1 ) than wood or soil, indicating that PERY was produced or accumulated in these nests. In many termite nests, the central part had larger NAPH and PERY concentrations than the wall, indicating that these compounds may have been produced within the nests. With few exceptions, NAPH dominated the PAH pattern in the Amazon and west Cerrado regions, PHEN in the Mata Atlântica and Caatinga regions, and PERY in the Pantanal and central Cerrado regions. Our results suggest that there are large unknown sources of NAPH, PHEN, and PERY in the tropical environment. It is likely that part of these sources is biological. The release of NAPH and PHEN from these sources seems to depend on climatic factors.

Biological Sources of Polycyclic Aromatic Hydrocarbons (PAHs) in the Amazonian Rain Forest

Hazardous polycyclic aromatic hydrocarbons (PAHs) widely occur in the environment and are believed to be mainly anthropogenic. Here we present strong indications for large biological sources of the PAHs naphthalene, perylene, and possibly also phenanthrene in the Amazonian basin. Termite nests, plant wood, and soils were sampled. Naphthalene is detected in plant wood and is accumulated in the nests of termites from the genus Nasutitermes. Perylene is found in all studied termite nests including six different genera. Phenanthrene occurs at substantial concentrations in wood, soil, and termite nests. Biologische Quellen von polyzyklischen aromatischen Kohlenwasserstoffen (PAK) im Regenwald des Amazonasbeckens Gesundheitsschadliche PAK sind in der Umwelt weit verbreitet. Es wird angenommen, dass sie uberwiegend aus anthropogenen Quellen stammen. In dieser Arbeit weisen wir bedeutende biologische Quellen von Naphthalin und Perylen und moglicherweise auch von Phenanthren im Amazonasbecken nach. Termitenbauten, Holz von Pflanzen und Boden wurden beprobt. Naphthalin ist in erhohten Gehalten im Holz zu finden und ist in den Bauten der Termitengattung Nasutitermes akkumuliert, Perylen ist in allen untersuchten Proben von Nestern sechs unterschiedlicher Termitengattungen nachzuweisen. Phenanthren kommt in nennenswerten Gehalten in Holz, Boden und Termitennestern vor.

Microclimate in agroforestry systems in central Amazonia: does canopy closure matter to soil organisms?

Microclimate was recorded and soil organisms were collected 1997-1999 in ecosystem stands of contrasting structure in central Amazonia (a primary forest, a 12-year secondary forest, two different agroforestry systems, a rubber tree (Hevea brasiliensis) plantation, and a peach palm (Bactris gasipaes) monoculture with a densely closed canopy). The aim was to look at the effects of canopy closure on microclimate and soil organisms. Monthly maxima temperature, average air and soil temperatures, and saturation deficit were highest in September 1997, and total annual rainfall in 1997 was 12-28% lower than in the other study years. The monthly average litter temperatures were consistently 2-4 °C higher in the plantation sites than in the rainforest and the secondary forest, and temperatures on single days (not the monthly averages) in the plantations were up to 10 °C higher than in the primary forest. The highest average litter and soil temperatures and the highest temperature maxima were recorded in the agroforestry plantations. Canopy closure strongly determined the litter temperatures in the sites. Soil macrofauna biomass was also strongly correlated to canopy closure (linear regression, P = 0.05). We conclude that a well developed canopy effectively protects the soil macrofauna from high temperature variation and drought stress. Therefore, optimizing these agroforestry systems for canopy closure may contribute to a better management of the beneficial soil decomposer community.

Litter decomposition, microbial biomass and activity of soil organisms in three agroforestry sites in central Amazonia

Soil organisms play a central role in the decomposition of organic matter. The activity of soil organisms was comparatively examined in three experimental sites in central Amazonia (Brazil): a peach palm monoculture (Bactris gasipaes) a, rubber tree plantation (Hevea sp.), and an agroforestry system (four tree species planted in rows, the space between covered by upcoming secondary vegetation). The overall decomposition rates in the systems and the role of different groups of soil organisms (macrofauna, mesofauna, microflora) were studied with leaf litter (Vismia guianensis) enclosed in litter bags. Microbial respiration and biomass (SIR method) in litter and soil were measured (IRGA). Microbial respiration in all sites decreased in the gradient litter > topsoil (0–5 cm) > soil at 5–15 cm. The highest decomposition rate was always observed in the litter bags of coarse mesh size, pointing to the crucial role of the macrofauna in maintaining a high decomposition rate of the organic material in all systems. The Hevea (k = 3.4) and the Bactris plantation (k=3.1) both showed the highest decomposition rates, followed by the polyculture system (k=1.9). The Bactris plantation also had the highest level of microbial respiration and biomass in litter and soil. We discuss these findings in the light of data on rainfall, pH and canopy closure. They suggest that microclimate is a more important factor than biomass in determining litter decomposition rates and activity of soil organisms at these sites.

Feeding activities of soil organisms at four different forest sites in Central Amazonia using the bait lamina method

A recently developed technique in soil ecology is the use of the bait lamina method, for assessing the feeding activity of soil animals in situ. Here the bait lamina method (slightly adapted to tropical conditions) was used for the comparison of four closely situated sites (a primary rain forest, a secondary rain forest and two mixed- species tree plantations) in the Brazilian Amazon (project SHIFT ENV-52). The total feeding activity (portion of empty apertures in a set of laminae) and the vertical distribution of the feeding activity were evaluated for differences between the sites. The feeding activities in the primary and secondary forest were at the same level and significantly lower than in the two plantations. Feeding activity in subplots where surface litter has been experimentally removed was significantly lower than in the controls with the litter layer intact, at all four sites. The abundance of soil macrofauna or Enchytraeidae was not correlated with the results of the bait lamina tests, while the abundance of mesofauna (probably mainly Oribatida) was consistent with the pattern of feeding activity. The feeding activities as determined with bait laminae did not correlate with the decomposition activities determined with litterbags. Due to the easy applicability in combination with its feasibility for statistical evaluation and its consistent responses to site differences in experimental treatments we consider the bait lamina method to be a promising approach for the biological assessment of tropical soils.

Chemical identification of Tagetes minuta Linnaeus (Asteraceae) essential oil and its acaricidal effect on ticks

The control of tick species that affect animal production is vital for the economic welfare of the cattle industry. This study focused on testing the acaricidal activity of the essential oil from the leaves and stems of Tagetes minuta against several Brazilian tick species, including Rhipicephalus (Boophilus) microplus, Rhipicephalus sanguineus, Amblyomma cajennense and Argas miniatus. The chemical composition of the essential oil was determined by chromatography and spectroscopy analyses, which revealed the presence of monoterpenes. The adult immersion test (AIT) and the larval packet test (LPT) were used to evaluate the efficacy of T. minuta essential oil in tick management at concentrations of 2.5, 5, 10, 20 and 40%. The results demonstrated that the T. minuta essential oil had over 95% efficacy against four species of ticks at a concentration of 20%. These results suggest that the essential oil of T. minuta could be used as an environmentally friendly acaricide.

Effects of Charcoal as Slow Release Nutrient Carrier on N-P-K Dynamics and Soil Microbial Population: Pot Experiments with Ferralsol Substrate

Giardina et al. (2000) reported that 300 million people annually practice shifting agriculture, affecting 400 million hectares of the planet’s 1,500 million ha of arable land. The sustainability of shifting cultivation and slash-and-burn continues to be a topic of discussion. Kleinman et al. (1995) characterized sound slash-and-burn agriculture as an ecologically sustainable agroecosystem because crop yields can be maintained without inputs of non-renewable fossil energy resources for fertilizers, pesticides, and irrigation. According to Woods and McCann (1999) shifting cultivation can be an environmentally friendly analogue to the natural processes of disturbance and regen-erative succession in tropical forests. They suggest that the Amerindian population made long lasting improvements to notoriously infertile tropical soils by long-term mulching, frequent burning, and the application of charcoal and ash which increased soil pH and thereby suppressed Al activity favourable for specific microorganisms responsible for the darkening of these soils, called

The effects of the insecticide lambda-Cyhalothrin on the earthworm Eisenia fetida under experimental conditions of tropical and temperate regions

Plant Protection Products can affect soil organisms and thus might have negative impacts on soil functions. Little research has been performed on their impact on tropical soils. Therefore, the effects of the insecticide lambda-Cyhalothrin on earthworms were evaluated in acute and chronic laboratory tests modified for tropical conditions, i.e. at selected temperatures (20 and 28°C) and with two strains (temperate and tropical) of the compost worm Eisenia fetida. The insecticide was spiked in two natural soils, in OECD artificial soil and a newly developed tropical artificial soil. The effects of lambda-Cyhalothrin did rarely vary in the same soil at tropical (LC50: 68.5-229 mg a.i./kg dry weight (DW); EC50: 54.2-60.2 mg a.i./kg DW) and temperate (LC50: 99.8-140 mg a.i./kg DW; EC50: 37.4-44.5 mg a.i./kg DW) temperatures. In tests with tropical soils and high temperature, effect values differed by up to a factor of ten.