Tropical Rainforest Soils Research Articles

The status of soil phosphate fractions and the ability of fungi to dissolve hardly soluble phosphates

Brazilian soils predominantly consist of iron and aluminum oxides and have a low phosphorus content. The present study was carried out in order to assess the status of phosphate fractions in pasture, forest and agricultural soils and the ability of soil fungi to solubilize iron and aluminum phosphates. The abundance of P fractions in the soils studied occurred in the following order: Fe–P > reductant-soluble Fe–P > occluded Fe–P > occluded Al–P > Al–P > Ca–P. Of the 481 fungi isolated, 33 showed the ability to solubilize the inorganic phosphates in culture. Of these, 14 were considered to be high or very high solubilizers based on a solubilization capacity >1000 μg PO 4 3− ml −1. Isolate F 111 was the only one that dissolved all the insoluble phosphates used. Nine isolates solubilized both Al–P and Ca–P, and four other isolates only solubilized Ca–P. The highest number of isolates with high solubilization capacity were detected in pasture soil, followed by tropical rain forest and forest patch soils. Pasture soil presented both the largest contents of insoluble phosphates and the largest number of fungal isolates with phosphate-solubilizing ability. The range and size of P fractions influenced the number of fungi and their ability to solubilize hardly soluble phosphates.

Using glomalin as an indicator for arbuscular mycorrhizal hyphal growth: an example from a tropical rain forest soil

Using glomalin as an indicator for arbuscular mycorrhizal hyphal growth: an example from a tropical rain forest soil

Using glomalin as an indicator for arbuscular mycorrhizal hyphal growth: an example from a tropical rain forest soil

Glomalin concentrations of extra-radical arbuscular mycorrhizal (AM) hyphae were estimated by deploying hyphal in-growth cores containing glomalin-free sand in field soils in a tropical forest and in pot cultures. In field soils, glomalin was 0.044±0.013 μg m −1 hyphae. In pot cultures glomalin concentrations were lower (range 0.0068–0.036 μg m −1), and varied significantly among species. Using this technique, preliminary estimates of extraradical AM hyphal production on Inceptisols were 1.91 Mg ha −1yr −1 and on Oxisol were 1.47 Mg ha −1 yr −1, but they could range between 0.9–5.7 Mg ha −1 yr −1. These rates of hyphal production are approximately 10% (range 5–33%) of estimated above ground primary production of the forest.

Bioremediation of a crude oil polluted tropical rain forest soil

A combination of options including Biostimulation with agricultural fertilizers, Bioaugumentation and physical processes were evaluated in-situ in the clean-up of crude oil polluted tropical rain forest soil for a period of nine weeks. Soil physicochemical parameters such as moisture (19% to 13%), pH (6.34 to 4.5) and organic carbon (85% to 1.5%) dropped during the remediation treatment. Total Nitrogen increased (0.021% to 0.081%) with increase in period of remediation. There was an increase in the total heterotrophic bacterial (THB) and hydrocarbon utilizing bacterial (HUB) counts in all the remediation options throughout the period. The control site O (no treatment employed) revealed no significant hydrocarbon loss (2%) within the study period. The hydrocarbon losses (73% to 88 %) experienced in five other options were significantly different from the control. Option A (a combination of Biostimulation and Bioaugumentation with indigenous HUB, hot water washing and tilling) recorded a hydrocarbon loss of 83%. Option B (a combination of mixing uncontaminated soil from a different location with polluted soil, tilling and Bioaugumentation with indigenous hydrocarbon utilizing bacteria) produced the lowest level of hydrocarbon loss (73%). Option C (a combination of Biostimulation, Bioaugumentation with indigenous HUB) recorded the highest level of hydrocarbon loss (88%). Option D (a combination of Bioaugumentation with genetically engineered strains of hydrocarbon utilizing Pseudomonas, Biostimulation and tilling) produced a hydrocarbon loss of 82%. Option D1 (a combination of Biostimulation with tilling) produced a hydrocarbon loss of 86%. These results suggest that Biostimulation with tilling (nutrient enhanced in-situ bioremediation) and or the combination ofBiostimulation and Bioaugumentation with indigenous hydrocarbon utilizers would be effective in the remediation of crude oil polluted tropical soils. Key Words: Bioremediation, Bioaugumentation, Biostimulation, Hydrocarbon, Fertilizer [Global Jnl Environ Sci Vol.2(1) 2003: 29-40]

Two new species of Neosartorya from Amazonian soil, Brazil

Neosartorya indohii and N. tsurutae, two new Neosartorya species isolated from tropical rainforest soil in the Amazonian area, Brazil, are described and illustrated. Neosartorya indohii is characterized by its spreading growth on Czapek's and malt extract agars, light yellow cleistothecia, broadly lenticular ascospores with two conspicuously serrate-incised equatorial crests and tuberculate convex surfaces, and globose to subglobose conidia with a smooth wall. Neosartorya tsurutae is characterized by its spreading growth on Czapek's and malt extract agars, white cleistothecia, broadly lenticular ascospores with four equatorial crests and rugulose-ruminate convex surfaces, and ovoid to broadly ellipsoidal conidia with a smooth wall.

Metabolic cold adaptation in arthropods: a smaller‐scale perspective

Metabolic cold adaptation in arthropods: a smaller‐scale perspective

Trampling resistance of tropical rainforest soils and vegetation in the wet tropics of north east Australia

Controlled trampling was conducted to investigate the trampling resistance of contrasting high fertility basaltic and low fertility rhyolitic soils and their associated highland tropical rainforest vegetation in north east Australia's Wet Tropics. Although this approach has been taken in numerous studies of trampling in a variety of ecosystem types (temperate and subtropical forest, alpine shrubland, coral reef and seagrass beds), the experimental method does not appear to have been previously applied in a tropical rainforest context. Ground vegetation cover and soil penetration resistance demonstrated variable responses to trampling. Trampling, most noticeably after 200 and 500 passes reduced organic litter cover. Bulk density increased with trampling intensity, particularly on basalt soils as rhyolite soils appeared somewhat resistant to the impacts of trampling. The permeability of the basalt and rhyolite soils decreased markedly with increased trampling intensity, even after only 75 passes. These findings suggest physical and hydrological changes may occur rapidly in tropical rainforest soils following low levels of trampling, particularly on basalt soils.

Seasonal variability of N2O emissions and CH4 uptake by tropical rainforest soils of Queensland, Australia

Over 1 year we followed the seasonal variations of N2O and CH4 fluxes at a tropical rain forest site in Australia. In addition, meteorological parameters, litter fall and decomposition, plant species composition, and concentrations of NH4+/NO3− in the soil and N2O and CH4 in the soil atmosphere were measured. N2O emissions showed a pronounced seasonal pattern with highest rates in the wet season (108.6 μg N m−2 h−1) and significantly lower rates during dry season (mostly <10 μg N2O‐N m−2 h−1). N2O emissions were positively correlated to N2O‐concentrations in the soil profile and to moisture, but not to concentrations of NH4+ and NO3−. The annual emission of N2O (N = 6015) was 0.97 kg N ha−1 yr−1, and, thus, approximately 7 times lower than a previous estimate for the year 2000. The marked differences in N2O emissions between different years indicate that the interannual variability of N2O emissions from rain forest soils cannot be neglected. With regard to CH4 the soil functioned throughout the entire year as a significant sink. Rates of CH4 uptake during the dry period (35–68 μg CH4 m−2 h−1) were higher as compared to the wet period (4–45 μg CH4 m−2 h−1). A close linear correlation between soil moisture and magnitude of CH4 uptake was found. The calculated annual CH4 uptake (N = 6090) is 3.2 kg CH4 ha−1 yr−1. This implies that tropical rain forest soils function as significant sinks for atmospheric CH4 on a global scale.

Nitrification activity in tropical rain forest soils of the Coastal Lowlands and Atherton Tablelands, Queensland, Australia

AbstractIntact soil cores from a montane tropical rain forest site in the Atherton Tablelands (Kauri Creek) and from a lowland tropical rain forest site in the Coastal Lowlands (Bellenden Ker), Queensland, Australia were investigated during different hygric seasons for the magnitude of gross nitrification rates using the Barometric Process Separation technique (BaPS). Pronounced seasonal variations of gross nitrification rates were found at both sites with highest values during the transition period between dry and wet season (montane site: 24.0 mg N (kg SDW)—1 d—1; lowland site: 13.1 mg N (kg SDW)—1 d—1) and significantly lower rates of gross nitrification during the dry and wet season. Rates of gross nitrification were always higher at the montane site than at the lowland site, but the opposite was found for N2O emissions. The results indicated that the high losses of N2O at the lowland tropical rain forest site may be contributed largely by high denitrification activity due to its wetter and warmer climate as compared to the dryer and colder climate at the montane tropical rain forest site. This conclusion was supported by analysis of cell numbers of microbes involved in N‐cycling. Higher numbers of denitrifiers were present at the lowland site, whereas higher numbers of nitrifiers were found at the montane site.

Phosphorus Limitation of Microbial Processes in Moist Tropical Forests: Evidence from Short-term Laboratory Incubations and Field Studies

Although there is a widespread belief that phosphorus (P) limits basic ecosystem processes in moist tropical forests, direct tests of this supposition are rare. At the same time, it is generally believed that P does not limit soil microorganism respiration or growth in terrestrial ecosystems. We used natural gradients in P fertility created by soils of varying age underlying tropical rain forests in southwestern Costa Rica, combined with direct manipulations of carbon (C) and P supply, to test the effects of P availability on the decomposition of multiple forms of C, including dissolved organic carbon (DOC) and soil organic carbon (SOC). Results from a combination of laboratory and field experiments suggest that C decomposition in old, highly weathered oxisol soils is strongly constrained by P availability. In addition, P additions to these soils (no C added) also revealed that microbial utilization of at least labile fractions of SOC was also P limited. To our knowledge, this is the first direct evidence of P limitation of microbial processes in tropical rain forest soil. We suggest that P limitation of microbial decomposition may have profound implications for C cycling in moist tropical forests, including their potential response to increasing atmospheric carbon dioxide. Furthermore, this site is still relatively rich in P when compared to many other tropical forests on old soils; thus, we believe that P limitation of soil microorganisms throughout the humid tropics is a possibility.

Terrestrial vertebrates promote arbuscular mycorrhizal fungal diversity and inoculum potential in a rain forest soil

We examined whether terrestrial vertebrates affected the arbuscular mycorrhizal fungal spore communities and mycorrhizal inoculum potential (MIP) of a tropical rain forest soil by comparing plots where terrestrial vertebrates had been excluded for 3 years to adjacent control plots. We extracted spores from soil using sucrose density gradient centrifugation and assayed MIP by growing seedlings of maize (Zea mays) and a rain forest tree (Flindersia brayleana) in intact soil cores from exclosure and control plots. Control plots had significantly higher spore abundance, species richness and diversity than exclosures. Spore community composition also differed significantly between exclosure and control plots. Seedlings of both plant species grown in control cores had significantly higher arbuscular‐mycorrhizal colonization than those grown in exclosure cores. This study suggests that loss of vertebrates could alter rates of mycorrhizal colonization with consequences for community and ecosystem properties.

Geographic and vertical patterns of stable carbon isotopes in tropical rain forest soils of Costa Rica

Understanding the natural variability in the stable carbon isotope composition of vegetation and soils can aid studies of soil carbon dynamics, and is a prerequisite for using 13C as a natural tracer when vegetation communities change from one photosynthetic pathway to another (e.g. C4 pasture grasses replacing C3 forests). To examine the geographic and vertical patterns of δ 13C under mature rain forest vegetation, we measured the isotopic composition of leaf litter, roots, and mineral soil profiles in 35 plots located in a 140,000-ha study region in northeastern Costa Rica. We hypothesized that soil carbon isotopic composition would be closely coupled to the signature of detrital inputs (the average δ 13C of forest floor and fine-root biomass) and that the increase in δ 13C with depth would be related to abiotic variables that influence soil carbon turnover rates. The correlations between surface soil isotopic composition (0–10 cm) and biophysical factors varied across the landscape. In multiple regression analyses, combinations of soil particle-size distribution and soil C/N ratio explained between 60% and 82% of the variation in surface soil isotopic composition for different regions in the landscape, but the isotopic composition of litter and roots did not explain any additional variation. The isotopic composition of litter, roots, and surface soils (0–20 cm) was fairly similar over large, regional gradients of elevation and edaphic properties (the range of variation was 2.6‰), but diverged considerably at depths below 20 cm (up to 5.8‰ differences). These large regional differences in the isotopic composition of soil C at depth are attributed to variation in soil carbon turnover rates across the landscape.

Temperature and Moisture Effects on Nitrification Rates in Tropical Rain-Forest Soils

Intact soil cores from three tropical rainforest sites on the Atherton Tablelands, Australia, were sampled at different hygric seasons to determine the effects of soil temperature and soil moisture on gross nitrification using the barometric process separation technique (BaPS). Parameterization experiments revealed that gross nitrification was positively correlated to increases in soil temperature, but negatively correlated to increased rates of water-filled pore space (WFPS) because of simulated rainfall. Pronounced seasonal variations of gross nitrification rates were observed at all three sites with lowest values during the dry season (1.9–9.7 mg NH+4-N m−2 h−1) and highest values during the transition period between dry to wet season (14.8–27.6 mg NH+4-N m−2 h−1). Highest nitrification activities were found for two sites characterized by a narrow C/N ratio and a high total C content in the mineral soil, whereas the site with a wider C/N ratio and lower C content in the soil showed significantly lower nitrification rates. Gross nitrification was positively correlated to in situ N2O-emission rates indicating that nitrification is a key regulating process of N2O-production and emission in these tropical soils.

Radioactive contamination of tropical rainforest soils in Southern Costa Rica

Radionuclide content in soils from four locations in a tropical rainforest near Golfito in Southern Costa Rica was investigated. For comparison, two nearby locations in open grassland were also studied. From each site 5 soil cores down to a depth of 15 cm were taken. The median contamination with 137 Cs was 584 Bq m −2 (reference date 1 January 1996) and the coefficient of variation (CV) was 50%. This contamination can be attributed to global fallout from atmospheric nuclear weapon tests between 1945 and 1980. The mean contamination is slightly lower than the value expected for the latitude (8°42′: 700 Bq m −2), which may be explained by migration of radiocaesium to subsoil below 15 cm or by uptake into the living biomass. Out of the total variability of 50%, around 20% can be attributed to the sampling and measuring process uncertainties, thus leaving a 45% contribution of spatial variability. A significant difference between forest and meadow sites could be detected: the meadow sites showed lower radiocaesium soil inventories (median: 291 Bq m −2) than the forest sites (643 Bq m −2). This may be explained by the agricultural activities carried out on meadow sites which lead to an increased redistribution of caesium in the soil profile and therefore a larger fraction of the total 137 Cs lying below 15 cm. Another reason for higher contamination levels under forest can be attributed to the high interception potential of dense tree canopies for dry deposition. Extrapolating the 137 Cs concentration below the sampling horizon, i.e. accounting for the cut-off of the profiles by the sampling technique, results in an estimated mean of 710 Bq m −2 for the forest sites, which is very close to the expected figure. The mainly mineral part of the forest soil profiles was analysed for the 137 Cs transport parameters, apparent convection velocity ( v=0.14±0.09 cm a −1) and apparent diffusion constant ( D=0.79±0.49 cm 2 a −1). The maximum concentration can be found at 5.3±2.9 cm depth, the half-value depth being 7.4±1.3 cm. The mean 40 K activity concentration was 175 Bq kg −1 dry matter (CV=69%) and 226 Ra and 228 Ra concentrations of 9.90 Bq kg −1 (CV=23%) and 7.93 Bq kg −1 (CV=20%) have been found, respectively.

N2O emission from tropical forest soils of Australia

Three different tropical rain forest sites (Kauri Creek, Lake Eacham, and Massey Creek) on the Atherton Tablelands, Queensland, Australia, were investigated for the magnitude of N2O emission from soils during different seasons, that is, wet season, dry season, and transition periods. Highest mean N2O emission rates were observed for soils derived from granite at the Kauri Creek site with 74.5±25.2 μg N2O‐N m−2 h−1, whereas for soils derived from Metamorphics (Lake Eacham site) mean N2O emission rates were much lower (13.1±1.1 μg N2O‐N m−2 h−1). For the Massey Creek site, with soils derived from Rhyolite, a mean annual N2O emission rate of 46. ±1.1 μg N2O‐N m−2 h−1 was calculated. The mean annual N2O emission rate calculated for all three sites over the entire observation period was 39.0 μg N2O‐N m−2 h−1 and thus at the high end of reports from tropical rain forest soils. N2O emission rates showed at all sites pronounced temporal as well as spatial variability. The magnitude of N2O emissions was strongly linked to rainfall events; that is, N2O emissions strongly increased approximately 6–8 hours after precipitation. Correlation analysis confirmed the strong dependency of N2O emissions on changes in soil moisture, whereas changes in soil temperature did not mediate considerable changes in N2O fluxes. Spatial variability of N2O fluxes on a site scale could be explained best by differences in water‐filled pore space, CO2 emission, and C/N ratio of the soil. On the basis of all published N2O flux rates from tropical rain forest soils we recalculated the contribution of such forests to the global atmospheric N2O budget and come up with a figure of 3.55 Tg N2O‐N yr−1, which is approximately 50% higher than reported by others.

Isotopic variability of N2O emissions from tropical forest soils

We report measurements of the 15N and 18O signature of N2O emitted from tropical rain forest soils at the La Selva Biological station in Costa Rica and in the Fazenda Vitoria in the State of Pará, Brazil. The δ15N values ranged from −34 to 2‰ with respect to atmospheric N2, while δ18O values had a smaller range, from −4 to 18‰ with respect to atmospheric O2. We attribute these large variations to differences in microbial production, consumption, and transport of N2O. In general the δ15N of N2O emissions from an Oxisol soil in Brazil were consistently enriched by ∼20‰ in 15N compared to those from Ultisol and Inceptisol soils in Costa Rica. Denitrification is the most likely source of N2O in both locations during the rainy season, and the 15N of nitrate was similar in both locations. We attribute the overall variability in emitted 15N to differences in the ratio of N2O:N2 escaping from the soil to the atmosphere, with a larger fraction of the N2O reduced to N2 at the Brazilian sites. We found light δ15N‐N2O values associated with high N2O emissions in a fertilized agricultural site in Costa Rica and in a “hot spot” of high emissions in the forest site in Brazil. This result suggests that the increase of substrate availability might increase the fractionation associated with N2O production. Overall, the Brazilian Oxisol soils had the most enriched δ15N‐N2O emissions yet measured from soils. If these are more representative of tropical soil emissions than the Costa Rica emissions, then the globally averaged δ15N‐N2O tropical rain forest soil source is more enriched than previously estimated. The large variations in isotopic signature for N2O emissions demonstrate the potential utility of stable isotopes as tools for understanding the processes of N2O production and consumption in soils.

Microcalorimetric study of some Amazonian soils

Microcalorimetric method was applied to study some Amazonian soils in order to establish the way by which the microbial soil activity is affected by the actual deforestation and burning suffered by the Amazonian rain forest. Different soil samples were collected in the Amazonian State of Brazil. Places with autochthonal vegetation and places that which had been deforested or burnt were elected due to its use in agriculture and cattle raising in an attempt to explore the difference in microbial growth behaviour. An LKB 2277 heat-flow microcalorimeter was used for all measurements at 298.15±0.02 K. The microcalorimetric data are presented together with some other measurements such as the physicochemical parameters and the number of microorganisms in soil samples. Power–time curves recorded from soil samples amended with the same quantity of glucose showed significant differences among soils used in the study. Results obtained were systematically studied in a more quantitative way and the values of the microbial growth rate constant, μ, total thermal effect, Q T , and duration of the peak-time, PT, were calculated from power–time curves. The collected data showed again important differences in the microbial activity among the soil samples suggesting that the native microbial activity of soils in tropical rain forests are dramatically affected by the deforestation and burning.

Les symbioses mycorhiziennes des arbres de la forêt tropicale humide de Guyane française

Roots of 75 tree species, belonging to 28 families, were sampled on different types of soil in the forest of French Guiana. Both seedlings and mature trees of each species were studied. The roots were first observed for ectomycorrhizas, then thinned and stained to observe and quantify endomycorrhizal associations. Ectomycorrhizas were found only on two genera: Coccoloba (Polygonaceae) and Neea (Nyctaginaceae). All the species studied had zygomycetous endomycorrhizas with hyphal coils and vesicles. It is remarkable that some families (Caesalpiniaceae, Myrtaceae, Tiliaceae, Euphorbiaceae, Lauraceae), considered as frequently ectomycorrhizal in other regions of the world, were not so in our sample. In addition, the results contradict the theory that ectomycorrhizal species are dominant in the poorest soils in tropical rainforests (tropical podzols). Key words: tropical rainforest, symbioses, mycorrhizas, French Guiana.

Chronic effects of oil spill on soil properties and microflora of a rainforest ecosystem in Nigeria

Soil and microbiological properties of a tropical rain forest soil were evaluated 17 years after oil spillage to access the chronic effects of, and interrelationship between population of petroleum hydrocarbon utilizing and nitrifying microorganisms. The spatial distribution of petroleum hydrocarbons (oil), the nutrient status and the abundance of heterotrophic microbes along soil transect lines in the contaminated zones served as the index for corroborating the results. The pH status of soil in the contaminated (Heavy impact — HI, and moderate inpact — MI) zones varied from acidic, that is 4.0 to near neutral PH, that is 6.0. The C content of soils decreased from 3.6% at the HI zones to 2.84% at the MI zones. Total N in the HI and MI zones differed by a factor of 0.10%. Available P was higher at the MI than HI zone, while CEC decreased from a combined mean of 6.48 at the HI zones to 4.46 at the MI zones. Although residual oil content was higher in the HI zones than MI zone, the soil nutrient status within these two zones did not vary significantly (P=0.05). However, soil microbes responded differently. For instance, petroleum hydrocarbon utilizers correlated positively with the distribution of oil in the environment. But, not the nitrifying microorganisms. Aerobic nitrifiers were abundant at the HI than MI zones, while anaerobic nitrifiers were higher at the MI than HI zones. With the presence of petroleum hydrocarbon utilizers anf nitrifying microbes. It is possible to enhance the degradation of oil in the 17 yr old spillage by adopting bioremediation.

Controls on nitric oxide emissions from tropical pasture and rain forest soils

In field studies, forest soils in the Atlantic Lowlands of Costa Rica emitted greater amounts of nitric oxide (NO) than soils from pastures that had been actively grazed for over 20 years following their conversion from forest. We measured NO production from intact soil cores from these land uses. Laboratory tests using ammonium(NH 4 + ), nitrate (NO 3 − ), nitrite (NO 2 − ), water, and acetylene (C2H2) additions demonstrate a response consistent with field studies.Forest soil cores produced more NO than pasture cores regardless of treatment. In forest soil the response toNH 4 + solution was significantly greater than response to water or an ambient moisture control. Addition of 10 kPa C2H2 caused a marked decrease in NO production in forest soil cores. These responses suggest a nitrification-linked control over NO production. Large and rapid responses toNO 2 − additions suggest that chemical decomposition of this ion may contribute to NO production. Pasture soil cores did not show a significant response to any of the treatments including NO 2 − . Low porosity in the pasture soils may restrict emission of NO produced therein.