Biogeochemical cycling in terrestrial ecosystems of the Caatinga Biome

Geotechnologies on the phosphorus stocks determination in tropical soils: General impacts on society

Phosphorus (P) is a critical nutrient for primary production in terrestrial and aquatic ecosystems. As P mineral reserves are finite and non-renewable, there is an increasing discussion on its sustainable utilization to safeguard food security for future generations. Understanding the spatial distribution of soil P is central in advancing effective phosphorus management and fostering sustainable agricultural practices. This study aims to digitally map the stocks of available P (AP) and total P (TP) in Brazil at a fine resolution (30 m). Using the Random Forest machine learning algorithm and a database of topsoil (0-20 cm) with 28,572 samples for AP and 3154 for TP, we predicted P stocks based on environmental covariates related to soil formation processes. By dividing Brazil into two sub-regions, representing areas with native coverage and anthropogenic ones, we built independent predictive models for each sub-region. Our results show that Brazil has a TP stock of 531 Tg and an AP stock of 17.4 Tg. The largest soil TP stocks are in the Atlantic Forest biome (73.8 g.m2), likely due to higher organic carbon stocks in this biome. The largest AP stocks were in the Caatinga biome (2.51 g.m2) because of younger soils with low P adsorption capacity. We also found that fertilizer use significantly increased AP stocks in agricultural areas compared to native ones. Our results indicated that AP stocks strongly influenced Brazil's agricultural production, with a correlation coefficient ranging from 0.20 for coffee crops to 0.46 for soybean. The maps generated in this study are expected to contribute to the sustainable use of P in agriculture and environmental systems.

Biomass and carbon balance in a dry tropical forest area in northeast Brazil

Forest ecosystems play an important role in mitigating the concentration increase of carbon dioxide (CO2) in the atmosphere through carbon sequestration by plants and its storage in biomass and soil. The objective was to determine the aerial biomass carbon stock in a dry tropical forest in Brazil. It was developed between 2012 to 2015, in an area with an advanced regeneration stage (50 years) in the semi-arid region of Pernambuco and it was used 40 permanent plots (400 m²) distant 80 m apart, with 50 m from the border, totaling 1.6 ha of the area to sample the shrubby-arboreal component, where all individuals with circumference at breast height (1.30 m of the soil) equal or greater than 6 cm were identified, measured and labeled in 2012 and remeasured in 2015. It was calculated the biomass and carbon stocks through developed equations available in the literature. The results showed that the total biomass and carbon stock in the first year was 27.97 e 12.92 Mg.ha-1 while in 2015 it was 18.49 and 8.39 Mg.ha-1 respectively. The results showed a biomass and carbon stock reduction of more than 30% in the period evaluated, even this, the area manages to present values within the expected pattern for the region, assuring the importance of sustainable forest management of these native/natural vegetation areas.

Slash and burn management and permanent or rotation agroforestry systems: A comparative study for C sequestration by century model simulation

Understanding the effects of agroforestry systems (AFs) on soil organic carbon (SOC) requires long-term experiments, but scenarios simulations can anticipate the potential of these systems to sequester or lose carbon (C). This study aimed to simulate the SOC dynamics in slash and burn management (BURN) and AFs using the Century model. Data from a long-term experiment implemented in the Brazilian semiarid region were used to simulate SOC dynamics under BURN and AFs situations, and the natural vegetation (NV) "Caatinga" as a reference. BURN scenarios considered different fallow periods (0, 7, 15, 30, 50 and 100 years) among cultivation of the same area. The two types of AFs (agrosilvopastoral-AGP and silvopastoral-SILV) were simulated in two contrasting conditions: (i) each one of the AFs and also NV area were permanently conducted with no rotation among these areas; and (ii) the two AFs and NV rotated among them every 7 years. The correlation coefficients (r), coefficients of determination (CD) and coefficients of residual mass (CRM) showed adequate performance, meaning that the Century model is able to reproduce the SOC stocks in the slash and burn management and AFs situations. The equilibrium points of NV SOC stocks stabilized around 30.3 Mg ha^-1, as similar to the measured average of 28.4 Mg ha^-1 at field conditions. The adoption of BURN without a fallow period (0 years) resulted in a reduction of 50% of SOC, approximately 20 Mg ha^-1, after the first 10 years. Permanent (p) and rotating (r) AFs management systems recovered (in 10 years) fast to the original SOC stocks, resulting in higher SOC stocks than NV SOC at equilibrium. The fallow period of 50 years is necessary to recovery SOC stocks in the Caatinga biome. The simulation shows that the AFs systems increase more SOC stocks than observed in natural vegetation in long-term.

Vegetation cover and seasonality as indicators for selection of forage resources by local agro-pastoralists in the Brazilian semiarid region

Local knowledge and uses of forage resources are highly dynamic, and can be mediated by multiple factors, such as seasonality, floristic diversity and the morphophysiological characteristics of plants. We investigate how seasonality and vegetation cover mediate the use of forage resources. The study was carried out with agro-pastoralists from two areas of Brazilian semiarid region. To select the areas, we used the normalized difference vegetation index. We selected one area with low vegetation cover (Area I) and another with high vegetation cover (Area II). Respondents were selected using the snowball technique. Using semi-structured interviews, we collect the information about forage use in the dry and rainy seasons, preferences of ruminants and specific characteristics of plant species. A total of 57 informants were interviewed in the two areas. We used the Chi-square test to assess differences in the richness of species cited between areas, seasons (dry/rainy), origins (exotic/native) and strate (herbaceous/woody). Our results revealed that agro-pastoralists living in the area with the highest vegetation cover (Area II) cited a greater number of species. We found that the use and selection of species is guided by a series of functional characters, related to palatability and nutritional value, which change between seasons. These results highlight the vast knowledge of ecological characteristics of species and diet of ruminants acquired by agro-pastoralists during field experience, with seasonality defining the use of species. Different from what we expected, the richness of exotic species mentioned did not differ between areas. This diversity of information contributes to a better understanding of the use of forage resources and indicates the importance of including local experiences as strategies to ensure proper use and provide insights for the conservation of local resources.

Influence of parent material on soil chemical characteristics in a semi-arid tropical region of Northeast Brazil

Soil parental material is one of the main factors that influence pedogenesis. Several studies evaluated the relationship between the parent material and soil chemistry, but few studies have assessed such a relationship in semi-arid tropical regions. This investigation was carried out to assess the effect of different parent materials on the chemical composition and available concentrations of macronutrients and micronutrients, including potentially toxic elements (Cd, Cr, Ni, and Pb) in soils in a semi-arid tropical setting. The chemical composition of the soils inherited the geochemical signature of their parent materials. Quartz sandstones, augen gneisses, and peraluminous granites exhibited the lowest reservoirs of plant nutrients and formed sandy, acid, and infertile soils. On the other hand, alkaline soils and soils with high concentrations of nutrients formed on ultramafic rocks (harzburgite), marble, and anorthosite. The pH, clay content, and CEC were the main attributes of the soils governing the availability of macro and micronutrients. The low soil organic carbon contents did not influence the availability of the nutrients. The parent material also influenced the soil texture. Parent materials that are richer in silica formed more sandy soils. The availability of Cd, Cr, and Pb in soils was low; however, the elevated Ni concentrations of soils derived from ultramafic rocks may pose risks to the environment and human health. Cluster and discriminant analyses were used to discriminate the natural fertility of soils. These results are useful for the agro-pedological zoning of the Brazilian semi-arid tropical region and for land use planning.

Soil predictors are crucial for modelling vegetation distribution and its responses to climate change

Bioclimatic envelope models have been extensively used to predict the vegetation dynamics in response to climate changes. However, they are prone to the uncertainties arising from General Circulation Models (GCMs), classification algorithms and predictors, with low-resolution results and little detail at the regional level. Novel research has focused on the improvement of these models through a combination of climate and soil predictors to enhance ecological consistency. In this framework, we aimed to apply a joint edaphoclimatic envelope to predict the current and future vegetation distribution in the semiarid region of Brazil, which encompasses several classes of vegetation in response to the significant environmental heterogeneity. We employed a variety of machine learning algorithms and GCMs under RCP 4.5 and 8.5 scenarios of Coupled Model Intercomparison Project Phase 5 (CMIP5), in 1 km resolution. The combination of climate and soil predictors resulted in higher detail at landscape-scale and better distinction of vegetations with overlapping climatic niches. In forecasts, soil predictors imposed a buffer effect on vegetation dynamics as they reduced shifts driven solely by climatic drift. Our results with the edaphoclimatic approach pointed to an expansion of the dry Caatinga vegetation, ranging from an average of 16% to 24% on RCP 4.5 and RCP8.5 scenarios, respectively. The shift in environmental suitability from forest to open and dry vegetation implies a major loss to biodiversity, as well as compromising the provision of ecosystem services important for maintaining the economy and livelihoods of the world's largest semiarid population. Predicting the most susceptible regions to future climate change is the first step in developing strategies to mitigate impacts in these areas.

Optimizing multifunctional agroecosystems in irrigated dryland agriculture to restore soil carbon - Experiments and modelling

Irrigated dryland agroecosystems could become more sustainable if crop and soil management enhanced soil organic carbon (SOC). We hypothesized that combining high inputs from cover crops with no-tillage will increase long-term SOC stocks. Caatinga shrublands had been cleared in 1972 for arable crops and palm plantations before implementing field experiments on Mango and Melon systems (established in 2009 and 2012, respectively). Each of the two experiments were managed with no-till (NT) or conventional till (CT), and three types of cover cropping, either a plant mixture of 75% (PM1) or 25% (PM2) legumes, or spontaneous vegetation (SV). The RothC model was used with a daily timestep to simulate the soil moisture dynamics and C turnover for this dry climate. Carbon inputs were between 2.62 and 5.82 Mg C ha^-1 year^-1 and increased the depleted SOC stocks by 0.08 to 0.56 Mg C ha^-1 year^-1. Scenarios of continuous biomass inputs of ca. 5 Mg C ha^-1 year^-1 for 60 years are likely to increase SOC stocks in the mango NT beyond the original Caatinga SOC by between 19.2 and 20.5 Mg C ha^-1. Under CT similar inputs would increase SOC stocks only marginally above depletion (2.75 to 2.47 Mg C ha^-1). Under melon, annual carbon inputs are slightly greater (up to 5.5 Mg C ha^-1 year^-1) and SOC stocks would increase on average by another 8% to 22.3 to 20.6 Mg C ha^-1 under NT and by 8 Mg C ha^-1 under CT. These long-term simulations show that combining NT with high quality cover crops (PM1, PM2) would exceed SOC stocks of the initial Caatinga within 20 and 25 years under irrigated melon and mango cultivation, respectively. These results present a solution to reverse prior loss of SOC by replacing CT dryland agriculture with irrigated NT plus high input cover crops agroecosystems.

Seasonal variation in net ecosystem CO2 exchange of a Brazilian seasonally dry tropical forest

Forest ecosystems sequester large amounts of atmospheric CO₂, and the contribution from seasonally dry tropical forests is not negligible. Thus, the objective of this study was to quantify and evaluate the seasonal and annual patterns of CO₂ exchanges in the Caatinga biome, as well as to evaluate the ecosystem condition as carbon sink or source during years. In addition, we analyzed the climatic factors that control the seasonal variability of gross primary production (GPP), ecosystem respiration (R_eco) and net ecosystem CO₂ exchange (NEE). Results showed that the dynamics of the components of the CO₂ fluxes varied depending on the magnitude and distribution of rainfall and, as a consequence, on the variability of the vegetation state. Annual cumulative NEE was significantly higher (p < 0.01) in 2014 (−169.0 g C m⁻²) when compared to 2015 (−145.0 g C m⁻²) and annual NEP/GPP ratio was 0.41 in 2014 and 0.43 in 2015. Global radiation, air and soil temperature were the main factors associated with the diurnal variability of carbon fluxes. Even during the dry season, the NEE was at equilibrium and the Caatinga acted as an atmospheric carbon sink during the years 2014 and 2015.

A close look at above ground biomass of a large and heterogeneous Seasonally Dry Tropical Forest - Caatinga in North East of Brazil

This work is focused on characterizing and understanding the aboveground biomass of Caatinga in a semiarid region in northeastern Brazil. The quantification of Caatinga biomass is limited by the small number of field plots, which are inadequate for addressing the biome's extreme heterogeneity. Satellite-derived biomass products can address spatial and temporal changes but they have not been validated for seasonally dry tropical forests. Here we combine a compilation of published field phytosociological observations with a new 30m spatial resolution satellite biomass product. Both data were significantly correlated, satellite estimates consistently captured the wide variability of the biomass across the different physiognomies (2-272 Mg/ha). Based on the satellite product we show that in year 2000 about 50 percent of the region had very low biomass (<2 Mg/ha) and that the majority of the biomass (86%) is concentrated in only 27% of the area. Our work confirm other estimates of biomass 39 Mg/ha (9-61 Mg/ha) and carbon 0.79 PgC. The satellite products together with ground based estimates has the potential to improve forest management in Caatinga and other seasonally dry tropical forests through improved approximation of spatial variability, how they relate to climate, and support numerical modeling experiments in semiarid regions.

Spatial-temporal variation in litterfall in seasonally dry tropical forests in Northeastern Brazil

The production of litterfall is essential for nutrient cycling in terrestrial ecosystems. From November 2009 to October 2011, analyzed the monthly litterfall production in two areas of Caatinga, a type of Seasonally Dry Tropical Forest located in the Cariri Paraibano, in the semiarid region of the Paraíba, Northeastern Brazil. One of the areas, Private Natural Heritage Reserve (RPPN) Fazenda Almas, is legally protected, and the other, Fazenda Moreiras, does not. The aims were to evaluate the effects of precipitation, evapotranspiration and vegetation structure on the temporal and spatial dynamics of litterfall production. Eight sampling points were randomly chosen at each site, and two 1 m2 collectors were installed 50 m apart from each other. The collected material was sorted, dried and weighed. Additionally, the characteristics (density, species richness, height and mean basal area) of the tree-shrub stratum in plots with a 10 m radius surrounding each collector. Total litterfall production was 4,500 kg ha-1 yr-1 for Fazenda Almas and 3,300 kg ha-1 yr-1 for Fazenda Moreiras; these values were within the expected range for Seasonally Dry Tropical Forests. The inter- and intra-annual variation in litterfall production was positively correlated with precipitation and evapotranspiration rates, and four months after the highest precipitation rates, there was a marked decrease in litterfall occurred during the dry season. Furthermore, the contributions of the material fractions were distinct with the leaf fraction representing for more than 60% of the litterfall, and the vegetation structure explained 75% of the variation in litterfall production. Therefore, climatic factors and vegetation structure affect the temporal and spatial dynamics of litterfall production and consequently influence nutrient dynamics in the semiarid region of Brazil.

Effects of seasonality, trophic state and landscape properties on CO2 saturation in low-latitude lakes and reservoirs

The role of tropical lakes and reservoirs in the global carbon cycle has received increasing attention in the past decade, but our understanding of its variability is still limited. The metabolism of tropical systems may differ profoundly from temperate systems due to the higher temperatures and wider variations in precipitation. Here, we investigated the spatial and temporal patterns of the variability in the partial pressure of carbon dioxide (pCO₂) and its drivers in a set of 102 low-latitude lakes and reservoirs that encompass wide gradients of precipitation, productivity and landscape properties (lake area, perimeter-to-area ratio, catchment size, catchment area-to-lake area ratio, and types of catchment land use). We used multiple regressions and structural equation modeling (SEM) to determine the direct and indirect effects of the main in-lake variables and landscape properties on the water pCO₂ variance. We found that these systems were mostly supersaturated with CO₂ (92% spatially and 72% seasonally) regardless of their trophic status and landscape properties. The pCO₂ values (9-40,020 μatm) were within the range found in tropical ecosystems, and higher (p < 0.005) than pCO₂ values recorded from high-latitude ecosystems. Water volume had a negative effect on the trophic state (r = -0.63), which mediated a positive indirect effect on pCO₂ (r = 0.4), representing an important negative feedback in the context of climate change-driven reduction in precipitation. Our results demonstrated that precipitation drives the pCO₂ seasonal variability, with significantly higher pCO₂ during the rainy season (F = 16.67; p < 0.001), due to two potential main mechanisms: (1) phytoplankton dilution and (2) increasing inputs of terrestrial CO₂ from the catchment. We conclude that at low latitudes, precipitation is a major climatic driver of pCO₂ variability by influencing volume variations and linking lentic ecosystems to their catchments.

Land Use and Seasonal Effects on the Soil Microbiome of a Brazilian Dry Forest

Drylands occupy approximately 41% of the Earth's terrestrial surface. Climate change and land use practices are expected to affect biogeochemical cycling by the soil microbiome in these ecosystems. Understanding how soil microbial community might respond to these drivers is extremely important to mitigate the processes of land degradation and desertification. The Caatinga, an exclusively Brazilian biome composed of an extensive seasonal tropical dry forest, is exposed to variable spatiotemporal rainfall patterns as well as strong human-driven pressures. Herein, an integrated analysis of shotgun metagenomics approach coupled to meteorological data was employed to unravel the impact of seasonality and land use change on soil microbiome from preserved and agriculture-affected experimental fields in Caatinga drylands. Multivariate analysis suggested that microbial communities of preserved soils under seasonal changes were shaped primarily by water deficit, with a strong increase of Actinobacteria and Proteobacteria members in the dry and rainy seasons, respectively. In contrast, nutrient availability notably played a critical role in driving the microbial community in agriculture-affected soils. The strong enrichment of bacterial genera belonging to the poorly-known phylum Acidobacteria ('Candidatus Solibacter' and 'Candidatus Koribacter') in soils from dry season affected by ferti-irrigation practices presupposes a contrasting copiotrophic lifestyle and ecological role in mitigating the impact of chemical fertilization. Functional analyses identify overrepresented genes related to osmotic stress response (synthesis of osmoprotectant compounds, accumulation of potassium ions) and preferential carbon and nitrogen utilization when comparing the microbiome of preserved soils under seasonal changes, reflecting differences in the genetic potential for nutrient cycling and C acquisition in the environment. However, the prevalence of nitrosative stress and denitrification functions in irrigation/fertilization-affected soils of the dry season clearly suggest that nutrient input and disruption of natural water regime may impact biogeochemical cycles linked to the microbial processes, with potential impacts on the ecosystem functionality. These findings help to better understand how natural seasonality and agricultural management differentially affect soil microbial ecology from dry forests, providing support for the development of more sustainable land management in dryland ecosystems.

Land cover changes and greenhouse gas emissions in two different soil covers in the Brazilian Caatinga

The Caatinga biome covers an area of 844,453km(2) and has enormous endemic biodiversity, with unique characteristics that make it an exclusive Brazilian biome. It falls within the earth's tropical zone and is one of the several important ecoregions of Brazil. This biome undergoes natural lengthy periods of drought that cause losses in crop and livestock productivity, having a severe impact on the population. Due to the vulnerability of this ecosystem to climate change, livestock has emerged as the main livelihood of the rural population, being the precursor of the replacement of native vegetation by grazing areas. This study aimed to measure GHG emissions from two different soil covers: native forest (Caatinga) and pasture in the municipality of São João, Pernambuco State, in the years 2013 and 2014. GHG measurements were taken by using static chamber techniques in both soil covers. According to a previous search, so far, this is the first study measuring GHG emissions using the static chamber in the Caatinga biome. N2O emissions ranged from -1.0 to 4.2mgm(-2)d(-1) and -1.22 to 3.4mgm(-2)d(-1) in the pasture and Caatinga, respectively, and they did not significantly differ from each other. Emissions were significantly higher during dry seasons. Carbon dioxide ranged from -1.1 to 14.1 and 1.2 to 15.8gm(-2)d(-1) in the pasture and Caatinga, respectively. CO2 emissions were higher in the Caatinga in 2013, and they were significantly influenced by soil temperature, showing an inverse relation. Methane emission ranged from 6.6 to 6.8 and -6.0 to 4.8mgm(-2)d(-1) in the pasture and Caatinga, respectively, and was significantly higher only in the Caatinga in the rainy season of 2014. Soil gas fluxes seemed to be influenced by climatic and edaphic conditions as well as by soil cover in the Caatinga biome.

Nutrient load concept-reservoir vs. bay impacts: a case study from a semi-arid watershed

Large flow-through reservoirs and lakes possess environmental gradients and monitoring programs are mostly adapted for cost and time effectiveness. Bay areas are often more isolated from the main water body and are likely to have unobserved different environmental processes and impacts. This study was performed at the Itaparica Reservoir, São Francisco River, located in semi-arid Northeast Brazil, with dendritic form. Water residence time in the Icó-Mandantes Bay was estimated by hydrodynamic flow and transport simulations. The P-chlorophyll a relationship was used to develop the P use efficiency coefficient for critical P load estimation of 25 μg P L^-1. Phosphorus sources and input rates into a bay and the respective reservoir were calculated and compared regarding their different origins for the period after flooding (1988) and for 2013. After impoundment, the P load highly exceeded the carrying capacity because of leaching and mineralization processes. In 2013, P inputs were still above this threshold, whereas inflow and sub-basin P export during the rainy season were crucial. But eutrophication processes have increased in the bay relative to the main water body. Hence, water in hydraulic isolated parts is prone to eutrophication processes, thus, bays have to be specially considered in water resource management.

High Primary Production Contrasts with Intense Carbon Emission in a Eutrophic Tropical Reservoir

Recent studies from temperate lakes indicate that eutrophic systems tend to emit less carbon dioxide (CO₂) and bury more organic carbon (OC) than oligotrophic ones, rendering them CO₂ sinks in some cases. However, the scarcity of data from tropical systems is critical for a complete understanding of the interplay between eutrophication and aquatic carbon (C) fluxes in warm waters. We test the hypothesis that a warm eutrophic system is a source of both CO₂ and CH₄ to the atmosphere, and that atmospheric emissions are larger than the burial of OC in sediments. This hypothesis was based on the following assumptions: (i) OC mineralization rates are high in warm water systems, so that water column CO₂ production overrides the high C uptake by primary producers, and (ii) increasing trophic status creates favorable conditions for CH₄ production. We measured water-air and sediment-water CO₂ fluxes, CH₄ diffusion, ebullition and oxidation, net ecosystem production (NEP) and sediment OC burial during the dry season in a eutrophic reservoir in the semiarid northeastern Brazil. The reservoir was stratified during daytime and mixed during nighttime. In spite of the high rates of primary production (4858 ± 934 mg C m^-2 d^-1), net heterotrophy was prevalent due to high ecosystem respiration (5209 ± 992 mg C m^-2 d^-1). Consequently, the reservoir was a source of atmospheric CO₂ (518 ± 182 mg C m^-2 d^-1). In addition, the reservoir was a source of ebullitive (17 ± 10 mg C m^-2 d^-1) and diffusive CH₄ (11 ± 6 mg C m^-2 d^-1). OC sedimentation was high (1162 mg C m^-2 d^-1), but our results suggest that the majority of it is mineralized to CO₂ (722 ± 182 mg C m^-2 d^-1) rather than buried as OC (440 mg C m^-2 d^-1). Although temporally resolved data would render our findings more conclusive, our results suggest that despite being a primary production and OC burial hotspot, the tropical eutrophic system studied here was a stronger CO₂ and CH₄ source than a C sink, mainly because of high rates of OC mineralization in the water column and sediments.

The influence of microhabitat on the population dynamics of four herbaceous species in a semiarid area of northeastern Brazil

Variation in annual rainfall is considered the most important factor influencing population dynamics in dry environments. However, different factors may control population dynamics in different microhabitats. This study recognizes that microhabitat variation may attenuate the influence of climatic seasonality on the population dynamics of herbaceous species in dry forest (Caatinga) areas of Brazil. We evaluated the influence of three microhabitats (flat, rocky and riparian) on the population dynamics of four herbaceous species (Delilia biflora, Commelina obliqua, Phaseolus peduncularis and Euphorbia heterophylla) in a Caatinga (dry forest) fragment at the Experimental Station of the Agronomic Research Institute of Pernambuco in Brazil, over a period of three years. D. biflora, C. obliqua and P. peduncularis were found in all microhabitats, but they were present at low densities in the riparian microhabitat. There was no record of E. heterophylla in the riparian microhabitat. Population size, mortality rates and natality rates varied over time in each microhabitat. This study indicates that different establishment conditions influenced the population size and occurrence of the four species, and it confirms that microhabitat can attenuate the effect of drought stress on mortality during the dry season, but the strength of this attenuator role may vary with time and species.

Microbial Community Profile and Water Quality in a Protected Area of the Caatinga Biome

The Caatinga is a semi-arid biome in northeast Brazil. The Paraguaçú River is located in the Caatinga biome, and part of its course is protected by the National Park of Chapada Diamantina (PNCD). In this study we evaluated the effect of PNCD protection on the water quality and microbial community diversity of this river by analyzing water samples obtained from points located inside and outside the PNCD in both wet and dry seasons. Results of water quality analysis showed higher levels of silicate, ammonia, particulate organic carbon, and nitrite in samples from the unprotected area compared with those from protected areas. Pyrosequencing of the 16S rRNA genes revealed that Burkholderiales was abundant in samples from all three sites during both seasons and was represented primarily by the genus Polynucleobacter and members of the Comamonadaceae family (e.g., genus Limnohabitans). During the dry season, the unprotected area showed a higher abundance of Flavobacterium sp. and Arthrobacter sp., which are frequently associated with the presence and/or degradation of arsenic and pesticide compounds. In addition, genes that appear to be related to agricultural impacts on the environment, as well as those involved in arsenic and cadmium resistance, copper homeostasis, and propanediol utilization, were detected in the unprotected areas by metagenomic sequencing. Although PNCD protection improves water quality, agricultural activities around the park may affect water quality within the park and may account for the presence of bacteria capable of pesticide degradation and assimilation, evidencing possible anthropogenic impacts on the Caatinga.

Land use intensification effects in soil arthropod community of an entisol in Pernambuco State, Brazil

The interactions between soil invertebrates and land use and management are fundamental for soil quality assessment but remain largely unaddressed. The aim of this study was to evaluate the changes in soil arthropod community of an entisol brought about by different land use systems under semiarid climate in Pernambuco State, Brazil. The soil invertebrate community was sampled using pitfall traps from areas with eight vegetation types by the end of the austral winter. The land uses studied were native thorn forest plus seven agricultural fields planted with elephant grass, apple guava, passion fruit, carrot, maize, tomato, and green pepper. Native vegetation was considered as a reference, whereas the agricultural fields showed a range of soil use intensities. The abundance of organisms, the total and average richness, Shannon's diversity index, and the Pielou uniformity index were determined, and all of these were affected by several crop and soil management practices such as residue cover, weed control, and pesticide application. Our study found differences in community assemblages and composition under different land use systems, but no single taxa could be used as indicator of soil use intensity.

Taxonomic and functional profiles of soil samples from Atlantic forest and Caatinga biomes in northeastern Brazil

Although microorganisms play crucial roles in ecosystems, metagenomic analyses of soil samples are quite scarce, especially in the Southern Hemisphere. In this work, the microbial diversity of soil samples from an Atlantic Forest and Caatinga was analyzed using a metagenomic approach. Proteobacteria and Actinobacteria were the dominant phyla in both samples. Among which, a significant proportion of stress-resistant bacteria associated to organic matter degradation was found. Sequences related to metabolism of amino acids, nitrogen, and DNA and stress resistance were more frequent in Caatinga soil, while the forest sample showed the highest occurrence of hits annotated in phosphorous metabolism, defense mechanisms, and aromatic compound degradation subsystems. The principal component analysis (PCA) showed that our samples are close to the desert metagenomes in relation to taxonomy, but are more similar to rhizosphere microbiota in relation to the functional profiles. The data indicate that soil characteristics affect the taxonomic and functional distribution; these characteristics include low nutrient content, high drainage (both are sandy soils), vegetation, and exposure to stress. In both samples, a rapid turnover of organic matter with low greenhouse gas emission was suggested by the functional profiles obtained, reinforcing the importance of preserving natural areas.