Enzymatic stoichiometry in tropical soil under pure and mixed plantations of eucalyptus with N2-fixing trees

Soil enzymes play a fundamental role in nutrient cycling in forest systems. The stoichiometry of C, N, and P­acquiring enzymes has been used to indicate nutrient limitation in the soil. However, the enzymatic stoichiometry remains poorly understood in pure and mixed eucalypt plantations. Thus, this study aims to assess the activity of enzymes in the soil to address the hypothesis that the introduction of N2-fixing trees could influence the enzymatic stoichiometry on C, N, and P cycling. The activity of ß-glucosidase (BG), urease (U), and acid phosphatase (AP) was assessed in soil (0-20 cm depth) of pure Eucalyptus grandis without (E) and with N fertilization (E+N), and a mixed system with E. grandis and Acacia mangium (E+A), and a pure A. mangium (A) plantation at 27 and 39 months after planting. The activities of BG/U, BG/AP, and U/AP were used to calculate the enzyme C/N, C/P, and N/P ratios, respectively. Rates of N­acquiring enzymes were higher in E and E+N, while soil microorganisms invested in P­acquiring enzymes in A and E+A. The vector length and angle demonstrated that C demand by microorganisms does not change in relation to N and P, regardless of the treatment. However, N demand decreased in relation to P in A and E+A (mainly at 27 months). Our results suggest that enzymes activity in pure eucalypt systems is limited for their soil-litter nutrient contents. At the same time while acacia and mixed plantation seem to invest in P­acquiring enzymes to improve biological N2 fixation promoted by diazotrophic bacteria associated to acacia.

Soil-sediment linkage and trace element contamination in forested/deforested areas of the Itacaiúnas River Watershed, Brazil: To what extent land-use change plays a role?

Trace elements (TE) contamination in forested areas of the Itacaiúnas River Watershed (IRW), Brazilian Amazon, arouses growing interest owing to the rapid deforestation and mining activities. In this study, soils (surface, SS; bottom, BS) and stream sediments (SD) from forested/deforested areas of IRW were analyzed with the aim of (1) evaluating the major sources of TE (mainly As, Ba, Cd, Cu, Co, Cr, Hg, Mo, Mn, Ni, Pb, V, and Zn), and (2) examining the soil-sediment TE link related to land-use change and/or geologic factors. Compositional data analysis (CoDA) was used to eliminate data closure issues and the centred log-ratio (clr) transformation yielded better results in Principal Component Analysis (PCA). The TE distribution pattern was significantly different (p < 0.05) between forested and deforested areas, but in both areas the TE distribution pattern is significantly correlated between SS, BS, and SD, indicating a strong lithogenic control. PCA (clr-transformed) identified the major geochemical bedrock signature as Fe-Ti-V-Cu-Cr-Ni, which is nearly similar in soil and sediments. The more accentuated enrichment and the maximum number of anomalies of these elements were found in the Carajás Basin and are highly coincident with mineral deposits/local lithologies without clear indication of anthropogenic contamination from point sources. Besides geogenic factors, deforestation is also affecting TE distribution in the basin. In deforested areas, Mn was significantly enriched in the surface horizon. Furthermore, linear regression analysis shows stronger TE relationships between soils and sediments in deforested areas than in forested ones, reflecting higher erosion in the former. This could be the reason for the relatively higher enrichment of TE (e.g., Fe, Mn, Cu, Cr, Ni) in deforested sediments. The TE contamination using regional background values provides more accurate results than worldwide reference values. Thus, the former should be considered for a more realistic environmental risk assessment in IRW and other forest ecosystems in the Brazilian Amazon.

Oxidizable organic carbon fractions in soils under leguminous nitrogen-fixing trees in a degraded pasture / Frações oxidáveis do carbono em solos sob leguminosas florestais fixadoras de nitrogênio em pastagens degradadas

The chemical fractionation of C by an increasing oxidation gradient, has shown to be a fast and promising methodology to detect changes in C lability. The objectives of the present study presents were: to evaluate the level of lability of soil organic C after conversion of degraded pasture into leguminous trees; evaluate the influence of soil depth on the lability of soil organic C. The experimental area consisted of pure plantations of Acacia auriculiformis, Mimosa caesalpiniifolia and Inga sp., a pasture and a secondary forest. The oxidizable organic carbon was determined by wet oxidation and allowed separation of four fractions according to the lability level (labile, moderately labile, moderately recalcitrant, recalcitrant). Labile fraction was the predominant fraction in all vegetation covers and depths. The conversion of degraded pasture into forest legume plantations and the soil depth promoted changes in the chemical composition of C. The continuous deposition of vegetable residues 13 years of leguminous trees favored the distribution of labile and moderately labile fractions along the soil profile and the recalcitrant fraction in the topsoil. The reference covers contributed to the recalcitrant fraction in the soil below 20 cm depth.

O fracionamento químico de carbono (C) por um gradiente crescente de oxidação, tem se mostrado uma metodologia rápida e promissora para detectar alterações na labilidade de C. Os objetivos do presente estudo foram: avaliar o nível de labilidade do C orgânico do solo após a conversão de pastagens degradadas em leguminosas; avaliar a influência da profundidade do solo na labilidade do C orgânico do solo. A área experimental consistiu em plantios puros de Acacia auriculiformis, Mimosa caesalpiniifolia e Inga sp., uma pastagem e uma mata secundária. O carbono orgânico oxidável foi determinado por oxidação úmida e permitiu a separação de quatro frações de acordo com o nível de labilidade (lábil, moderadamente lábil, moderadamente recalcitrante, recalcitrante). A fração lábil foi a fração predominante em todas as coberturas vegetais e profundidades. A conversão de pastagens degradadas em leguminosas florestais e a profundidade do solo promoveram mudanças na composição química do C. A deposição contínua de resíduos vegetais por 13 anos de leguminosas favoreceu a distribuição das frações lábil e moderadamente lábil ao longo do perfil do solo e da fração recalcitrante na camada superficial do solo. As coberturas de referência contribuíram para a fração recalcitrante no solo abaixo de 20 cm de profundidade.

Five new species of dictyostelid social amoebae (Amoebozoa) from Thailand.

BACKGROUND: Dictyostelid cellular slime molds (dictyostelids) are common inhabitants of the soil and leaf litter layer of fields and forests, along with animal dung, where they feed mostly on bacteria. However, reports on the species diversity of dictyostelids in South Asia, particularly Thailand, are limited. The research reported in this paper was carried out to increase our knowledge of the species diversity of this group of organisms in northern Thailand. RESULTS: Forty soil samples were collected at four localities in northern Thailand to assess the species richness of dictyostelids. These samples yielded five dictyostelid isolates that were not morphologically consistent with any described species. Based on molecular signatures, all five of these isolates were assigned to the family Cavenderiaceae, genus Cavenderia. All five share a number of morphological similarities with other known species from this family. The new taxa differ from previously described species primarily in the size and complexity of their fruiting bodies (sorocarps). This paper describes these new species (Cavenderia aureostabilis, C. bhumiboliana, C. protodigitata, C. pseudoaureostipes, and C. subdiscoidea) based on a combination of morphological characteristics and their phylogenetic positions. CONCLUSIONS: At least 15 taxa of dictyostelids were obtained from the four localities in northern Thailand, which indicates the high level of species diversity in this region. Five species were found to be new to science. These belong to the family Cavenderiaceae, genus Cavenderia, and were described based on both morphology and phylogeny.

Mercury critical concentrations to Enchytraeus crypticus (Annelida: Oligochaeta) under normal and extreme conditions of moisture in tropical soils - Reproduction and survival.

Soil provides many ecosystem services that are essential to maintain its quality and healthy development of the flora, fauna and human well-being. Environmental mercury levels may harm the survival and diversity of the soil fauna. In this respect, efforts have been made to establish limit values of mercury (Hg) in soils to terrestrial fauna. Soil organisms such as earthworms and enchytraeids have intimate contact with trace metals in soil by their oral and dermal routes, reflecting the potentially adverse effects of this contaminant. The main goal of this study was to obtain Hg critical concentrations under normal and extreme conditions of moisture in tropical soils to Enchytraeus crypticus to order to assess if climate change may potentiate their acute and chronic toxicity effects. Tropical soils were sampled from of two Forest Conservation Units of the Rio de Janeiro State - Brazil, which has been contaminated by Hg atmospheric depositions. Worms were exposed to three moisture conditions, at 20%, 50% and 80% of water holding capacity, respectively, and in combination with different Hg (HgCl2) concentrations spiked in three types of tropical soil (two natural soils and one artificial soil). The tested concentrations ranged from 0 to 512mg Hg kg-1 dry weight. Results indicate that the Hg toxicity is higher under increased conditions of moisture, significantly affecting survival and reproduction rate.

Assessment of Indexes for Heavy Metal Contamination in Remote Areas: A Case Study in a Pyrenean Forest, Navarra, Spain.

The objective of the present work was to verify and compare the performance of different geochemical indices employed to identify the anthropogenic origin of selected heavy metals and other trace elements in soils. To that end, two background values, the upper continental crust and the metal content in the bed rock, were used and obtained from a forested basin of the western Pyrenees. The enrichment factor (EF), geo-accumulation index (Igeo), and contamination factor (Cif) were finally evaluated for their ability to determine anthropogenic contamination: Results indicate that an in-depth knowledge of the bed rock geochemistry and the geological background content is essential to distinguish between the natural variability of soils and any anthropogenic contribution of heavy metals. Although both EF and Cif show a similar ability to detect soil contamination, the latter is proposed as a more appropriate and sensitive marker given its ability for finding episodically elevated contamination levels.

Ecology of Nitrogen Fixing, Nitrifying, and Denitrifying Microorganisms in Tropical Forest Soils.

Soil microorganisms play important roles in nitrogen cycling within forest ecosystems. Current research has revealed that a wider variety of microorganisms, with unexpected diversity in their functions and phylogenies, are involved in the nitrogen cycle than previously thought, including nitrogen-fixing bacteria, ammonia-oxidizing bacteria and archaea, heterotrophic nitrifying microorganisms, and anammox bacteria, as well as denitrifying bacteria, archaea, and fungi. However, the vast majority of this research has been focused in temperate regions, and relatively little is known regarding the ecology of nitrogen-cycling microorganisms within tropical and subtropical ecosystems. Tropical forests are characterized by relatively high precipitation, low annual temperature fluctuation, high heterogeneity in plant diversity, large amounts of plant litter, and unique soil chemistry. For these reasons, regulation of the nitrogen cycle in tropical forests may be very different from that of temperate ecosystems. This is of great importance because of growing concerns regarding the effect of land use change and chronic-elevated nitrogen deposition on nitrogen-cycling processes in tropical forests. In the context of global change, it is crucial to understand how environmental factors and land use changes in tropical ecosystems influence the composition, abundance and activity of key players in the nitrogen cycle. In this review, we synthesize the limited currently available information regarding the microbial communities involved in nitrogen fixation, nitrification and denitrification, to provide deeper insight into the mechanisms regulating nitrogen cycling in tropical forest ecosystems. We also highlight the large gaps in our understanding of microbially mediated nitrogen processes in tropical forest soils and identify important areas for future research.

Diversity of Arbuscular Mycorrhizal Fungi in a Brazilian Atlantic Forest Toposequence.

The diversity of arbuscular mycorrhizal fungi (AMF) was studied in the Atlantic Forest in Serra do Mar Park (SE Brazil), based on seven host plants in relationship to their soil environment, altitude and seasonality. The studied plots along an elevation gradient are located at 80, 600, and 1,000 m. Soil samples (0-20 cm) were collected in four seasons from SE Brazilian winter 2012 to autumn 2013. AMF spores in rhizosperic soils were morphologically classified and chemical, physical and microbiological soil caracteristics were determined. AMF diversity in roots was evaluated using the NS31/AM1 primer pair, with subsequent cloning and sequencing. In the rhizosphere, 58 AMF species were identified. The genera Acaulospora and Glomus were predominant. However, in the roots, only 14 AMF sequencing groups were found and all had high similarity to Glomeraceae. AMF species identities varied between altitudes and seasons. There were species that contributed the most to this variation. Some soil characteristics (pH, organic matter, microbial activity and microbial biomass carbon) showed a strong relationship with the occurrence of certain species. The highest AMF species diversity, based on Shannon's diversity index, was found for the highest altitude. Seasonality did not affect the diversity. Our results show a high AMF diversity, higher than commonly found in the Atlantic Forest. The AMF detected in roots were not identical to those detected in rhizosperic soil and differences in AMF communities were found in different altitudes even in geographically close-lying sites.

The history of soil use by forests in the region of campos de Lages, Santa Catarina, Brazil / A trajetória do uso do solo por florestas na região dos campos de Lages

The history of soil use by forests during XX century in Campos de Lages region, Santa Catarina state, Brazil was studied. The changes in the soil use and its relations to sociotechnical contexts have been approached, along with how these relations have affected the meaning and the value of forest soils in the Regions history. To understand the relations among soils, forests and society, a conceptual arrangement was used based on Actor-network Theory (ANT). Since the early XIX Century, when the Region insertion in Minas Gerais network through the tropeirismo occurred, cattle creation has been the typical scenario of the native landscape use. In 1940´s, changes on sociotechniques initiated the cycle of the pine, with intense Araucaria angustifolia wood exploitation. At the end of XX Century, the soil forest vocation was modified by forestry. However, existing controversies about the reforestations might change the meaning of the soil used by forests, creating a new confl ict. The study concludes that the forest use was more diverse. The forest soil had assumed distinct meanings for different actors in the course of time, although keeping the same sociallogic of land use.

Estudou-se a história do uso do solo por florestas durante o século XX na região dos Campos de Lages, em Santa Catarina, Brasil. Abordaram-se as mudanças no uso do solo e suas relações com contextos sóciotécnicos, e como estas relações afetaram o significado e o valor dos solos florestais ao longo da história da região. Para compreender as relações entre solos, florestas e sociedade, foi adotado um arranjo conceitual com base na Teoria do Ator-rede (ANT - Actor-network Theory). Trabalhou-se com a hipótese de que a história florestal da Região está relacionada com a dinâmica da ocupação do território e a percepção do valor dos solos ocupados por florestas, mudando esta de acordo com o contexto e as redes socioeconômicas na qual estava inserido o território, mantendo, no entanto uma sociológica similar. Desde a inserção da região na rede das Minas Gerais através do tropeirismo, no início do século XIX, a pecuária tem sido o retrato do uso de uma paisagem campestre nativa, até que, a partir da década de 40, mudanças sociotécnicas dessem início ao ciclo do pinho, com intensa exploração da madeira da Araucaria angustifolia. No final do século XX a silvicultura altera a vocação florestal do solo, mas controvérsias existentes sobre os reflorestamentos ressignificam o solo utilizado por florestas, instaurando um novo conflito socioambiental. Em todo o período, os solos florestais a

The history of soil use by forests in the region of campos de Lages, Santa Catarina, Brazil / A trajetória do uso do solo por florestas na região dos campos de Lages

The history of soil use by forests during XX century in Campos de Lages region, Santa Catarina state, Brazil was studied. The changes in the soil use and its relations to sociotechnical contexts have been approached, along with how these relations have affected the meaning and the value of forest soils in the Regions history. To understand the relations among soils, forests and society, a conceptual arrangement was used based on Actor-network Theory (ANT). Since the early XIX Century, when the Region insertion in Minas Gerais network through the tropeirismo occurred, cattle creation has been the typical scenario of the native landscape use. In 1940´s, changes on sociotechniques initiated the cycle of the pine, with intense Araucaria angustifolia wood exploitation. At the end of XX Century, the soil forest vocation was modified by forestry. However, existing controversies about the reforestations might change the meaning of the soil used by forests, creating a new confl ict. The study concludes that the forest use was more diverse. The forest soil had assumed distinct meanings for different actors in the course of time, although keeping the same sociallogic of land use.

Estudou-se a história do uso do solo por florestas durante o século XX na região dos Campos de Lages, em Santa Catarina, Brasil. Abordaram-se as mudanças no uso do solo e suas relações com contextos sóciotécnicos, e como estas relações afetaram o significado e o valor dos solos florestais ao longo da história da região. Para compreender as relações entre solos, florestas e sociedade, foi adotado um arranjo conceitual com base na Teoria do Ator-rede (ANT - Actor-network Theory). Trabalhou-se com a hipótese de que a história florestal da Região está relacionada com a dinâmica da ocupação do território e a percepção do valor dos solos ocupados por florestas, mudando esta de acordo com o contexto e as redes socioeconômicas na qual estava inserido o território, mantendo, no entanto uma sociológica similar. Desde a inserção da região na rede das Minas Gerais através do tropeirismo, no início do século XIX, a pecuária tem sido o retrato do uso de uma paisagem campestre nativa, até que, a partir da década de 40, mudanças sociotécnicas dessem início ao ciclo do pinho, com intensa exploração da madeira da Araucaria angustifolia. No final do século XX a silvicultura altera a vocação florestal do solo, mas controvérsias existentes sobre os reflorestamentos ressignificam o solo utilizado por florestas, instaurando um novo conflito socioambiental. Em todo o período, os solos florestais a