Search

Enzymatic activity is a useful indicator for the evaluation of soil biological components. However, a detailed analysis of such indicators in Brazilian soils is lacking. In this study, the activity of soil enzymes was evaluated using data from 73 publications covering 57 locations across all six biomes and eight soil orders out of the 13 that occur in Brazil. The results indicated a wide variation of enzymatic activity in soils, where the means in μg p-nitrophenol g−1 soil h−1 were 569, 116, 112, and 80 for acid phosphatase, alkaline phosphatase, β-glucosidase, and arylsulfatase, respectively. Likewise, values of 148 μg reducing sugars g−1 soil day−1 for cellulase, 57 μg triphenyl tetrazolium formazan g−1 soil day−1 for dehydrogenase, and 38 μg N-NH 4 + g−1 soil h−1 for urease were recorded. Soil organic matter and microbial biomass were the best attributes correlated with enzymatic activity, followed by clay content and pH. A more detailed analysis of the acid phosphatase, arylsulfatase, and β-glucosidase activities showed that land-use effects were more pronounced in the Atlantic Forest and Cerrado than in the Caatinga biome. Soils under non-tillage and integrated crop-livestock systems showed higher enzymatic activity than soils under conventional tillage. Soils housing higher biodiversity and delivering higher crop yields also presented higher enzymatic activity, especially in terms of arylsulfatase and β-glucosidase. Enzymatic activity has been shown to be a versatile indicator of soil quality, as it can elucidate how to achieve high-quality standards in tropical and subtropical soils. [Display omitted] • This work has evaluated seven soil enzymes across Brazil. • Effects of land use on enzymatic activity depend on enzyme type and biome. • Conservation management systems favor soil enzymatic activity. • Edaphic attributes have contrasting impacts on enzymatic activity. • Enzymes are good indicators of soil quality in tropical and subtropical environments. [ABSTRACT FROM AUTHOR]

Land-use change has been identified, among global changes, as the main threat causing biodiversity loss, locally and regionally. This is especially true in Southern Brazil with the two main biomes (Pampa and Atlantic forest) facing high conversion rate into agricultural land to meet increasing demand for food and fuel. Within this region, we focused on epigeic biota across three land-use types (forest, grassland and Eucalyptus plantation). We used both a taxonomical and a trait-based approach to depict the changes of Epigeic Collembola assemblages across land-use types. Furthermore, we tested trait-convergence and trait-divergence across land-use types to infer how the environmental filtering and biotic interactions can affect assembly rules and collembolan community composition. Results differed according to the approach used (either taxonomical or trait-based). In general, diversity indices based on the taxonomical approach did not significantly differ between forest and grassland, whereas Eucalyptus plantation showed significantly lower values. Functional diversity was significantly higher in forest and similar between grassland and Eucalyptus plantation. Furthermore, we found both convergence and divergence of subsets of traits related to the land-use types. The trait-convergence tended to be higher in grassland sites and rather linked to sensorial traits (number of ocelli, antenna length, and trichobothria), drought tolerance traits (body size) and habitat preference traits (pigmentation level, furca development, scale, number of ocelli, antenna length, and body size). On the opposite, Trait-divergence was only linked to sensorial traits (antenna length and postantennal organ) and greatest in forest sites. Our findings showed that a trait-based approach associated with a taxonomic one provides a better understanding of the collembolan community structuring in response to biotic and abiotic changes across different land-use types. [ABSTRACT FROM AUTHOR]

In Central Brazil, over one million square kilometers of native savanna vegetation known as Cerrado have been cleared and converted to farmland over the past forty years. A factorial experiment was designed to assess the effects of land use, litter type, soil organisms and season on litter decay in the prevailing natural and agricultural systems ( i.e. Cerrado remnants, grasslands and soybean croplands) in Mato Grosso. Decay rates were estimated by using the litterbag method. Two different mesh sizes were used to evaluate the effects of soil macro- and mesofauna (coarse mesh; 5 mm) and of soil microorganisms (fine; 20 μm). The original litter found in each land use area (Cerrado leaf-litter, Brachiaria -grass or soybean residues) was used to estimate the decay of in situ litter; a standard substrate (maize litter) was employed to evaluate the effect of the environment. Finally, the experiment was carried out during a dry and a rainy season to differentiate the effect of the other factors from the seasonal effect. We found that: (1) the effects of land use and management practice were only significant in the dry season; (2) decomposability of litter was not predicted by the initial C:N ratio of the litter types; (3) soil fauna contributed to the litter breakdown with 13–57%; (4) decay rates were overall higher in the rainy season; (5) all evaluated factors (in following order: season > soil organisms > litter type > land use) and their interactions explained about 70% of the variance in the decay rates in the study area. Change in land use affected litter decay mainly through a shift in the litter quality; the introduced plant species produced highly decomposable litters. [ABSTRACT FROM AUTHOR]

The Amazon Rainforest plays major roles in global carbon and nitrogen cycling. Despite this region’s immense importance, deforestation and pasture creation are still occurring at alarming rates. In this study, we investigated the effects of land-use change on aerobic ammonia-oxidizers in primary rainforest, young and old pasture, and secondary forest in Rondônia, Brazil. Forest-to-pasture conversion decreased soil nitrate, phosphorus, and exchangeable acidity contents that recovered to pre-disturbance levels as pastures aged or were abandoned and formed secondary forest. The ammonia-oxidizing community, numerically dominated by thaumarchaea, shifted due to land-use change, both in terms of gene abundance and community structure. However, thaumarchaeal ammonia monooxygenase gene abundances did not correlate with any measured soil physicochemial parameters. Phylogenetic analyses showed that community structural changes in ammonia-oxidizing thaumarchaea are driven by a shift away from primary rainforest, old pasture, and secondary forest clusters to separate clusters for young pasture. Additionally, the nearly complete disappearance in young pasture, old pasture, and secondary forest sites of a thaumarchaeal genus, the Nitrosotalea , indicates that land-use change can have long lasting effects on large portions of the thaumarchaeal community. The results of this study can be used as a conceptual foundation for determining how ammonia-oxidizers become altered by land-use change in South American tropical forests. [ABSTRACT FROM AUTHOR]

The biodiversity in Amazon forest soils is continuously challenged by anthropogenic activities or disturbances, impacting the quantity and quality of its natural resources and a wide range of ecosystem services. Understanding microbial processes and response to various soil management practices provide valuable information to maintain sustainable ecological environments. We hypothesized that microbial assemblages (several not yet identified) and activities are continuously changing in forest ecosystems, mostly due to management selections. Therefore, our work's objective was to assess bacteria communities' changes via next-generation sequencing techniques and bridge knowledge gaps in our understanding of their responses to deforestations, intensive agriculture, and repeated forest burning activities in altered and native forest locations in the Northern Amazon Rainforest, Brazil. We evaluated soils during different climatic periods (dry and rainy) collected at selected sites for pasture, conventional agriculture, and forestry. Intensive conversion to pasture and conventional plantations seriously impacted the bacterial diversities and species richness. The forest area presented the greatest bacterial diversities and species richness, followed by the pasture areas, especially in the 0–5 cm soil layer. Conventional plantations showed the lowest diversities and species richness. There was no change in species richness between the dry and rainy periods; however, the wet period showed lesser species diversities. Based on the analyses, the bacterial communities comprised of the phyla: Acidobacteria , Firmicutes , Verrucomicrobia , Actinobacteria , Proteobacteria , Planctomycetes , and Cyanobacteria. Bacteria trends identified are being considered in future management decisions to preserve biodiversities and the region's forest ecosystems' functioning. Unlabelled Image • Conversion of native forest to agricultural affects the richness of the soils. • The use of fire reduces and selects the amount soil bacteria species. • The intensity of land use, soil revolving and burning leads to species extinction. • Pasture deactivation and infestation of spontaneous plants restore soil biodiversity. [ABSTRACT FROM AUTHOR]

Seasonally dry tropical forests are strongly impacted by human activities such as agriculture and ranching, as well as variations in climate conditions. Soil nematodes are sensitive to these changes, given that soil and climate characteristics influence their survival and occurrence. We analyzed the changes in the structure of nematode communities in three different types of land use (agricultural areas, secondary forest and natural forest) in the Caatinga, at Catimbau National Park, Pernambuco, northeastern Brazil. We recorded a total of 17,177 nematode individuals belonging to 104 genera. Nematode abundance and richness were highest in the secondary forest and lowest in the agricultural areas. The total abundance of bacterivores and omnivore-predators was affected by types of land use. Different soil properties as well as monthly mean rainfall and temperature were strongly related to the differences in taxonomic composition among the agricultural areas, secondary forest and natural forest, accounting for 65.42% of the total variation. In general, our results indicate that agricultural activities in the Caatinga negatively affect the nematode communities, and that soil characteristics and climate variables also strongly affect the structure and composition of these communities. • The agricultural activities negatively affect the nematode communities. • The secondary forest regenerating increases the nematode abundance. • Bacterivorous nematodes Acrobeles spp. dominated in various types of land use. • The nematode composition was related to soil properties and climate variables. • The nematode community can be used to assess soil health in Caatinga. [ABSTRACT FROM AUTHOR]