Semi-arid Region Of Northeast Brazil Research Articles

Purple Sulfur Bacteria Dominate Microbial Community in Brazilian Limestone Cave.

The mineralogical composition of caves makes the environment ideal for inhabitation by microbes. However, the bacterial diversity in the cave ecosystem remains largely unexplored. In this paper, we described the bacterial community in an oxic chamber of the Sopradeira cave, an iron-rich limestone cave, in the semiarid region of Northeast Brazil. The microbial population in the cave samples was studied by 16S rDNA next-generation sequencing. A type of purple sulfur bacteria (PSB), Chromatiales, was found to be the most abundant in the sediment (57%), gravel-like (73%), and rock samples (96%). The predominant PSB detected were Ectothiorhodospiraceae, Chromatiaceae, and Woeseiaceae. We identified the PSB in a permanently aphotic zone, with no sulfur detected by energy-dispersive X-ray (EDX) spectroscopy. The absence of light prompted us to investigate for possible nitrogen fixing (nifH) and ammonia oxidizing (amoA) genes in the microbial samples. The nifH gene was found to be present in higher copy numbers than the bacterial-amoA and archaeal-amoA genes, and archaeal-amoA dominated the ammonia-oxidizing community. Although PSB dominated the bacterial community in the samples and may be related to both nitrogen-fixing and ammonia oxidizing bacteria, nitrogen-fixing associated gene was the most detected in those samples, especially in the rock. The present work demonstrates that this cave is an interesting hotspot for the study of ammonia-oxidizing archaea and aphotic PSB.

Photosynthetic pigments and photochemical efficiency of precocious dwarf cashew (<i>Anacardium occidentale</i> L.) under salt stress and potassium fertilization

Cashew cultivation is an activity of great socioeconomic relevance, especially for agriculture in the semi-arid region of Northeast Brazil, standing out as an option to generate jobs and income. Thus, the present study aimed to evaluate the photosynthetic pigments and photochemical efficiency of precocious dwarf cashew under salt stress and potassium fertilization. The study was conducted using a Regolithic Neosol with sandy loam texture, adopting a randomized block design in 5×2 factorial arrangement, which corresponded to five levels of electrical conductivity of irrigation water—ECw (0.4; 1.2; 2.0; 2.8 and 3.6 dS m-1) associated with two doses of potassium fertilization—KD (100 and 150% of recommendation), with three replicates and two plants per plot. Increasing water salinity inhibited chlorophyll synthesis and decreased electron transport rate and quantum yield of non-regulated energy dissipation in precocious dwarf cashew, at 50 days after sowing. There was significant interaction for chlorophyll a and b contents and the effects of salt stress were intensified by potassium doses on the chlorophyll b content of precocious dwarf cashew. Potassium doses of 100 and 150% of recommendation (150 and 225 mg K2O kg-1 of soil) do not mitigate the effect of salt stress on photosynthetic pigment synthesis and photochemical efficiency of cashew plants in the rootstock formation phase.

Extreme drought events and the sustainability of fish farming in net cages in reservoirs of the semi-arid northeastern region in Brazil

Abstract Reservoirs play important roles in local socioeconomic development and are particularly relevant in developing countries. The rearing of Nile tilapia (Oreochromis niloticus) in cages is one of the fastest growing activities carried out in reservoirs since it is a strategy to sustain the growing demand for food fish. Most reservoirs are in eutrophic or hypereutrophic conditions in the semi-arid northeast region of Brazil and thus, the expansion of aquaculture endangers the ecological functions of the reservoirs by increasing the eutrophication potential. On the other hand, aquaculture contributes to economic development by generating jobs and income for the population and being an important alternative in the production sector for riverine populations. In this context, we present in this article our opinion about the sustainability of fish farming activities in net cages in reservoirs of the Brazilian semiarid, especially when subjected to extreme drought events.

Drought monitoring in the Brazilian Semiarid region.

Drought is a natural and recurrent phenomenon. It is considered 'a natural disaster' whenever it occurs in an intensive manner in highly populated regions, resulting in significant damage (material and human) and loss (socioeconomic). This paper presents the efforts developed to monitor the impact of drought in the semiarid region of Northeast Brazil. In this scope, information from different sources is compiled to support the evaluation and identification of impacted municipalities, with the main objective of supporting emergency actions to mitigate their impact. In the semiarid region of Brazil there are frequent occurrences of dry periods during the rainy season, which, depending on the intensity and duration, can cause significant damage to family-farmed crops, with a farming system characterized by low productivity indices. However, rain-fed agriculture has great economic expression and high social importance due to the region is densely occupied, and contributes to the establishment of communities in the countryside. Specifically, in the present study, the methodology adopted to monitor the impact of agricultural droughts, including an analysis of the hydrological year 2015-2016, is presented, considering different water stress indicators for the identification of the affected municipalities and assessment of the methods and tools developed.

Anti-ophidian activity of Bredemeyera floribunda Willd. (Polygalaceae) root extract on the local effects induced by Bothrops jararacussu venom.

Bredemeyera floribunda roots are popularly used to treat snakebites in the semiarid region of Northeast Brazil, and previous studies indicate the anti-ophidian actions of triterpenoid saponins found in its roots. To assess B. floribunda root extract (BFRE) activity against the effects of Bothrops jararacussu venom (BjuV), antiphospholipasic, antiproteolytic, antihemorrhagic, antinecrotic, and anti-edematogenic activities were investigated in mice. Phytochemical analysis revealed the presence of saponins, flavonoids, and sugars, with rutin and saccharose being the major constituents of BFRE. Acute toxicity was determined and BFRE was nontoxic to mice. Phospholipase A2 and proteolytic activities induced by BjuV were inhibited in vitro by BFRE at all concentrations tested herein. BFRE (150 mg/kg) inhibited paw edema induced by BjuV (50 µg/animal), reducing total edema calculated by area under the curve, but carrageenan-induced paw edema was unchanged. Hemorrhagic and necrotizing actions of BjuV (50 µg/animal) were considerably decreased by BFRE treatment. Thus, BFRE blocked the toxic actions of B. jararacussu venom despite having no anti-inflammatory activity, which points to a direct inhibition of venom’s toxins, as demonstrated in the in vitro assays. The larger amounts of rutin found in BFRE may play a role in this inhibition, since 3′,4′-OH flavonoids are known inhibitors of phospholipases A2.

Physiological alterations and production of guava under water salinity and nitrogen fertilizer application

Adequate management of saline water irrigation and nitrogen (N) fertilizer application in agriculture can contribute substantially to expanding guava cultivation in the semi-arid region of Northeast Brazil. This study aimed to evaluate gas exchange and production of ‘Paluma’ guava cultivated with different levels of water salinity and N. The experiment was carried out in drainage lysimeters under field conditions in an experimental area of the Federal University of Campina Grande (UFCG), Campus of Pombal, PB, Brazil. The experimental design was randomized blocks, in a 5 × 4 factorial scheme, with five levels of water salinity – ECw (0.3, 1.1, 1.9, 2.7 and 3.5 dS m-1) and four doses of N (70, 100, 130 and 160% of the recommendation) with three replicates. The dose relative to 100% corresponded to 541.1 mg of N dm-3 of soil. The following production components were evaluated: number of fruits, mean fruit weight, polar and equatorial diameter of fruits, and polar diameter/equatorial diameter ratio. In addition, the following physiological variables were evaluated at 180 days after fruit pruning: stomatal conductance, CO2 assimilation rate, internal CO2 concentration and transpiration rate. CO2 assimilation and transpiration rate were used to calculate instantaneous water use efficiency. The interaction between water salinity and N doses did not cause significant effects on any variable studied. Irrigation water salinity above 0.3 dS m-1 hampered gas exchange at 180 days after fruit pruning and negatively affected production components.

Detection of anti-Toxoplasma gondii antibodies in small wild mammals from preserved and non-preserved areas in the Caatinga biome, a semi-arid region of Northeast Brazil.

This study was conducted to determine the seroprevalence of anti-Toxoplasma gondii antibodies in 152 free-living small wild mammals from distinct regions in the Caatinga biome, a semi-arid region in the Northeast of Brazil: the National Park of Serra das Confusões (NPSC), which is a preserved area in the state of Piauí, and the municipalities of Petrolina and Lagoa Grande, two non-preserved areas in the state of Pernambuco. Using the modified agglutination test (MAT), we found that 5.3% (4/75) and 3.3% (2/60) of small wild mammals were positive for IgG anti-T. gondii antibodies in the NPSC and Petrolina, respectively. All mammals from Lagoa Grande (0/17) tested negative on the MAT. Indirect infection of T. gondii was determined by MAT in Galea spixii, Monodelphis domestica and Thrichomys laurentius (from NPSC) and in Didelphis albiventris (from Petrolina). Seropositive animals were observed in both preserved and non-preserved areas within the Caatinga biome. Low seroprevalences observed can be related to the extreme temperature and humidity in this particular biome.

Morphophysiology of ‘Faga 11’ Cashew Rootstock Under Saline Water Irrigation and Exogenous Proline Application

Due to the reduced availability of good-quality water in the semi-arid region of Northeast Brazil, the utilization of saline waters in irrigation became an alternative for the expansion of agriculture in this region. Thus, it is necessary to develop techniques which can make viable the use of these waters in agriculture. Given the above, this study aimed to evaluate the morphophysiology of ‘FAGA 11’ cashew rootstock subjected to different levels of irrigation water salinity and exogenous proline application through the leaves. The experiment was carried out in a greenhouse of the Federal University of Campina Grande, at the Center of Sciences and Agri-Food Technology, Campus of Pombal, PB, Brazil, in a randomized block design, in 5 × 4 factorial scheme, with three replicates and two plants per plot. Treatments consisted of different levels of irrigation water electrical conductivity—ECw (0.3; 1.0; 1.7; 2.4 and 3.1 dS m-1) combined with proline concentrations applied through the leaves—PC (0; 4; 8 and 12 mM). Irrigations with water up to ECw of 1.37 dS m-1 may be used as it causes an acceptable 10% reduction in the variables of morphology of cashew FAGA 11 seedlings. The proline concentrations tested, with the exception of the Dickson’s quality index of seedlings, did not attenuate the deleterious effects of irrigation water salinity on the cashew FAGA 11 rootstock seedlings.

Use of local ecological knowledge as phenology indicator in native food species in the semiarid region of Northeast Brazil

Phenological studies that aggregate local ecological knowledge on the expression of phenophases may be useful in the elaboration of management strategies of species that are important to a given local system. In this study, we seek to answer the following questions: 1) How do the different phenophases of two important native food species are expressed in the three phytophysiognomies of the Cerrado (Brazilian savannah) where they are collected? 2) How does rainfall influence the expression of the phenophases of these species on the evaluated phytophysiognomies? 3) Does the local ecological knowledge of the residents of the Araripe National Forest (hereafter FLONA) on the phenophases of native species of high importance correspond to what occurs in the three phytophysiognomies of the Cerrado? The phenological monitoring was executed monthly from January 2012 to December 2013. In order to retrieve the local knowledge about phenophases, key informants from three communities located around the FLONA were selected. Rainfall is a limiting factor for the expression of the reproductive phenophases of Caryocar coriaceum, differently from what occurs for the vegetative phases and for Hancornia speciosa. There were no significant differences between the local knowledge of communities that collect resources in the forest and most of the data collected in the phenological evaluation. In addition, there was no difference in the expression of the phenophases among the three phytophysiognomies, also corroborating with the local ecological knowledge. As for the community that collects in agroforestry yards, there were significant differences between knowledge and expression of phenophases. Thus, the use of local ecological knowledge of people who collect resources in the forest has proved to be reliable and may be promising mainly in rapid diagnoses of biodiversity.

Assessment of SM2RAIN-Derived and State-of-the-Art Satellite Rainfall Products over Northeastern Brazil

Microwave-based satellite rainfall products offer an opportunity to assess rainfall-related events for regions where rain-gauge stations are sparse, such as in Northeast Brazil (NEB). Accurate measurement of rainfall is vital for water resource managers in this semiarid region. In this work, the SM2RAIN-CCI rainfall data obtained from the inversion of the microwave-based satellite soil moisture (SM) observations derived from the European Space Agency (ESA) Climate Change Initiative (CCI), and ones from three state-of-the-art rainfall products (Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS), Climate Prediction Center Morphing Technique (CMORPH), and Multi-SourceWeighted-Ensemble Precipitation (MSWEP)) were evaluated against in situ rainfall observations under different bioclimatic conditions at the NEB (e.g., AMZ, Amazônia; CER, Cerrado; MAT, Mata Atlântica; and CAAT, Caatinga). Comparisons were made at daily, 5-day, and 0.25° scales, during the time-span of 1998 to 2015. It was found that 5-day SM2RAIN-CCI has a reasonably good performance in terms of the correlation coefficient over the CER biome (R median: 0.75). In terms of the root mean square error (RMSE), it exhibits better performance in the CAAT biome (RMSE median: 12.57 mm). In terms of bias (B), the MSWEP, SM2RAIN-CCI, and CHIRPS datasets show the best performance in MAT (B median: −8.50%), AMZ (B median: −0.65%), and CER (B median: 0.30%), respectively. Conversely, CMORPH poorly represents the rainfall variability in all biomes, particularly in the MAT biome (R median: 0.43; B median: −67.50%). In terms of detection of rainfall events, all products show good performance (Probability of detection (POD) median > 0.90). The performance of SM2RAIN-CCI suggests that the SM2RAIN algorithm fails to estimate the amount of rainfall under very dry or very wet conditions. Overall, results highlight the feasibility of SM2RAIN-CCI in those poorly gauged regions in the semiarid region of NEB.

EMERGENCE, GROWTH, AND PRODUCTION OF COLORED COTTON SUBJECTED TO SALT STRESS AND ORGANIC FERTILIZATION

ABSTRACT The semi-arid region of Northeast Brazil is vulnerable to problems of water scarcity and salinity, resulting in low-quality irrigation water and the need to adopt cultivation strategies that make the production system viable. Given the above, this study aimed to evaluate emergence, growth, and production of colored cotton subjected to increasing levels of irrigation water salinity and organic matter doses. The experiment was carried out in a eutrophic Regolithic Neosol with a sandy loam texture in a greenhouse in the municipality of Campina Grande - PB, Brazil. A randomized block design was used in a 4 x 4 factorial scheme with three replicates, and the treatments corresponded to four levels of electrical conductivity of water - ECw (1.7, 3.4, 5.1, and 6.8 dS m-1) and four doses of organic matter - OM (0, 2.5, 3.5, and 4.5% based on soil volume). Increasing irrigation water salinity with ECw values above 1.7 dS m-1 reduced emergence, growth, and production of colored cotton, and the cotton seed weight was the variable most affected by salinity. Organic matter addition led to increased cotton growth and production, especially in terms of seed weight. Increasing doses of organic matter attenuated the effect of irrigation water salinity on the number of bolls in ‘BRS Jady’ cotton.

Use of MSI/Sentinel-2 and airborne LiDAR data for mapping vegetation and studying the relationships with soil attributes in the Brazilian semi-arid region

The Caatinga is an important ecosystem in the semi-arid region of northeast Brazil and a natural laboratory for the study of plant adaptation to seasonal water stress or prolonged droughts. The soil water availability for plants depends on plant root depth and soil properties. Here, we combined for the first time the remote sensing classification of Caatinga physiognomies with soil information derived from geostatistical analysis to relate vegetation distribution with physico-chemical attributes of soils. We evaluated the potential of multi-temporal data acquired by the MultiSpectral Instrument (MSI)/Sentinel-2 for Random Forest (RF) classification of seven physiognomies. In addition, we analyzed the contribution of airborne LiDAR metrics to improve classification accuracy compared to six vegetation indices (VIs) and 10 reflectance bands from the MSI instrument. Using a detailed soil survey, the spatial distribution of the vegetation physiognomies mapped by RF was associated with the variability of 20 physico-chemical attributes of 75 soil profiles submitted to principal components analysis (PCA) and ordinary kriging. The results showed gains in overall classification accuracy with use of the multi-temporal data over the mono-temporal observations. Gains in classification of arboreous Caatinga were also observed after the insertion of LiDAR metrics in the analysis, especially the percentage of vegetation cover with height greater than 5 m, the terrain elevation and the standard deviation of vegetation height. Overall, the most important metrics for classification were the VIs, especially the Enhanced Vegetation Index (EVI), Normalized Difference Infrared Index (NDII-1), Optimized Soil-Adjusted Vegetation Index (OSAVI) and the Normalized Difference Vegetation Index (NDVI). The most important MSI/Sentinel-2 bands were positioned in the red-edge spectral interval. From PCA, soil attributes responsible for most of the data variance were related to soil fertility, soil depth and rock fragments in the surface horizon. The amounts of gravels and pebbles were factors of physiognomic variability with shrub and sub-shrub Caatinga occurring preferentially over shallow and stony soils. By contrast, arboreous Caatinga occurred over soils with total profile depth greater than 1 m. Finally, areas of sub-shrub Caatinga had greater values of cation exchange capacity (CEC) and water retention at field capacity than areas of arboreous Caatinga. The differences were statistically significant at 95% confidence level, as indicated by Mann-Whitney U tests.

Can Bradyrhizobium strains inoculation reduce water deficit effects on peanuts?

Drought is one of the environmental factors that most affects peanut cultivation in semi-arid regions, resulting in economic losses to growers. However, growthpromoting bacteria are able to reduce water deficit damage in some plant species. In this context, this study aimed to evaluate the interaction of Bradyrhizobium strains reducing water stress effects on peanut genotypes by antioxidantenzymes activities, leaf gas exchangesand vegetative growth, as well as to determine the taxonomic positioning of strain ESA 123.The 16S rRNA gene of ESA 123 was amplified by PCR and sequenced by dideoxy Sanger sequencing method. An experiment was performed in greenhouse with three peanut genotypes (BRS Havana, CNPA 76 AM and 2012-4), two Bradyrhizobium strains (SEMIA 6144 and ESA 123), a mineral source of N and an absolute control (without N) under two water regimes (with and without irrigation). Seeds of peanut were sown and the plants were grown until 30days after emergence. On the 20th day, the water deficit plants group had their irrigation suspended for 10days. At in silico analyzes, ESA 123 presented 98.97% similarity with the type strain of B. kavangense. Leaf gas exchange was affected by water deficit; as well as alteration of antioxidant activities and reduction of vegetative growth variables. However, some plants inoculated with SEMIA 6144 and ESA 123 strains presented lower reductions and increment of some evaluated variables, mainly the ones inoculated with the ESA 123 strain, Bradyrhizobium sp. from the semi-arid region of Northeast Brazil. Thisdata suggests beneficial effects of the peanut-Bradyrhizobiuminteraction in a water stress condition, specially with the ESA 123 strain.

Effects of saline water and potassium fertilization on photosynthetic pigments, growth and production of West Indian Cherry

Due to the scarcity of water in the semi-arid region of Northeast Brazil, in both quantitative and qualitative terms, the use of saline water in agriculture should be considered as one alternative for irrigated agriculture. This study therefore aimed to evaluate the photosynthetic pigments, growth and production of West Indian Cherry as a function of irrigation using waters with different salinity levels and potassium (K) fertilization, after grafting. The study was carried out in drainage lysimeters under greenhouse conditions, in a eutrophic Regolithic Neosol with sandy loam texture, in the municipality of Campina Grande, PB. The experiment was set in a randomized block design, to test two levels of irrigation water electrical conductivity - ECw (0.8 and 3.8 dS m-1) and four K2O doses - KD (50, 75, 100 and 125% of recommendation), with three replicates. The dose relative to 100% corresponded to 79.2 mg K2O kg-1 of soil. Irrigation with high salinity water stimulated the biosynthesis of chlorophyll b and carotenoids, while the chlorophyll a content and the growth of the cherry were reduced markedly in the post-grafting phase. The harmful effects of salinity on the total number of fruit and fresh mass of West Indian Cherry fruit were minimized with potassium fertilization.

Low back pain among adolescents in the semiarid region: results of a population census in the city of Caracol, State of Piauí, Brazil

The scope of this article is to assess low back pain prevalence and associated factors in the last 12 months among adolescents in a city in the south of the State of Piauí. It was a cross-sectional study which included 1,112 adolescents aged 13-19 in the city of Caracol, Piauí. Demographic, socio-economic, nutritional, behavioral and comorbidty characteristics were investigated. The outcome was the occurrence of low back pain (LBP) in the last 12 months. The outcome prevalence was calculated in accordance with independent variables. The proportion of individuals with chronic LBP was calculated among adolescents with LBP in the last 12 months. Crude and adjusted Poisson regression was used to estimate the prevalence ratio in the analysis of associated factors. The prevalence of LBP in the last 12 months was 32.9%. According to the adjusted analysis, being female (PR = 1.75; 95%CI:1.45-2.10), being aged 18-19 (PR = 1.27; 95%CI:1.01-1.62), having higher income (PR = 1.33; 95%CI:1.06-1.67), having a job (PR 1.25 95%CI:1.02-1.53) and having minor psychiatric disorders (PR 1.51 95%CI: 1.25-1.82) were associated with LBP in the last 12 months. This study found a high prevalence of LBP among adolescents in a poor city in the semiarid region of Northeast Brazil.

Lactic Acid Bacteria as Biological Control of Staphylococcus aureus in Coalho Goat Cheese.

SUMMARYThe aim of this study is to investigate the bacterial population in coalho goat cheese produced in the semi-arid northeast region of Brazil, to analyse the antibiotic resistance profiles of the identified pathogenic bacteria, to detect the staphylococcal enterotoxin genes and to evaluate the addition of autochthonous lactic acid bacteria (LAB) with technofunctional properties for the control of Staphylococcus aureus growth. In the analysed samples, strains of Escherichia coli (N=11), Salmonella spp. (N=18), Listeria spp. (N=6) and S. aureus (N=9) were classified as multidrug resistant (MDR). The most commonly isolated pathogen from the studied coalho goat cheese was S. aureus. Its isolates were positive for the genes encoding enterotoxins A (sea), B (seb), C (sec) and D (sed). The autochthonous LAB with the potential to inhibit S. aureus were identified as Enterococcus faecium. These strains were selected for in vitro tests of protective, safety, technological and functional properties. In the coalho goat cheese food matrix, these selected autochthonous LAB were able to reduce the enterotoxigenic MDR S. aureus load by approx. 3 log units.

Cyanobacterial blooms in freshwaters bodies in a semiarid region, northeastern Brazil: A review

Harmful cyanobacterial blooms have caused several problems in freshwater environments due to their prolific growth and the harmful cyanotoxins produced by some species. The occurrence of these organisms has increased in recent decades due to climate change and eutrophication, although most studies are from temperate regions in the Northern hemisphere. This review presents data about cyanobacteria occurrence, dominance, and toxicity events in freshwater bodies in a semiarid region of Northeast Brazil, in the tropical Southern hemisphere. We performed a literature survey of cyanobacteria publications from 1930 to 2016. We made a list of all the dominant species registered in each state, noted their distribution and occurrence of dominance events involving one or more species, and the registered records of toxic blooms, including information about the toxins involved and the range of values. We selected 102 publications that described cyanobacteria occurrence from states in Northeast Brazil; these publications included relevant contributions regarding cyanobacteria distribution, richness, density, and biomass. Forty-nine dominant species were recorded, with the most representation found in the state of Pernambuco (30 spp.). The genera with the highest occurrences were Microcystis, Cylindrospermopsis, Planktothrix, Dolichospermum (=Anabaena), and Geitlerinema, especially the species Cylindrospermopsis raciborskii, Microcystis aeruginosa, and Planktothrix agardhii. Episodes of toxic blooms were observed in four states. Microcystins, cylindrospermopsin, saxitoxins, and anatoxin-a(S) were found to be associated with these blooms. In Northeast Brazil, harmful cyanobacterial blooms are common in urban and public reservoirs. However, in recent years, cyanobacterial blooms in this region have been more intense and perennial, with high biomass occurring throughout the year.

Three new species of Graphidaceae (lichenized Ascomycota) from the semi-arid region of northeast Brazil

Three new lichenized fungal species in the family Graphidaceae are described from Northeast Brazil. Graphis alba has lirellae with a conspicuous white cover, eventually becoming striate, small, (sub-)muriform ascospores, and stictic acid. Halegrapha redonographoides features somewhat pseudostromatic ascomata with immersed lirellae, a completely carbonized excipulum, and small, submuriform ascospores, in combination with a norstictic acid chemistry. Thelotrema pachysporoides has an ecorticate, white thallus and produces brown, 7–13-septate, 25–35 × 7–10 µm large ascospores. The new species were found in an isolated remnant of Caatinga vegetation, at Fazenda Santa Maria da Lage, Poço Verde, Sergipe state, with additional material of one of the species also detected in the state of Tocantins.

Impact of Soil Moisture on Crop Yields over Brazilian Semiarid

The objective of this work was to investigate the relationship between soil water content and rainfall with rice, beans, cassava and corn yields of in the semiarid region of Northeast Brazil. Precipitation and modeled soil water content were compared to yields recorded at the county levels in this region. The results were also integrated over the area of the nine States that lie within the officially recognized region of semiarid climate in Brazil. The influence of water balance components was quantified by calculating their correlation coefficient with yields of the different crop species over the municipalities of the region. It was found that rainfall had higher correlation to crop yields over most of the region, while soil water content had lower values of correlation. This result is consistent with the fact that average root depth is 40 cm, lower than the layer of soil used in the model used to estimate soil water content (100 cm). Plants respond better to the precipitation in the top layers of soil, while the water storage in the deep layer of soil might be important only in other temporal and spatial scales of the hydrological cycle. It is concluded that the average crop yield is directly associated with practices that increase soil moisture at the depth of the root system in order to reduce the effects caused by drought.

Recovery of carbon stocks in deforested caatinga dry forest soils requires at least 60 years

Abstract Caatinga forests occupy an area of around one million km2 in the semiarid region of northeast Brazil. These landscapes are undergoing rapid change because of accelerated deforestation for cultivation and firewood. The capacity of Caatinga forests to regenerate after clearing determines the magnitude of the carbon (C) sink in the soil, and thus is fundamental information for developing management policies for long-term sustainability. The objective of this study was to investigate C stocks and microbial activity in soils of dry Caatinga forests that had undergone harvesting at different times in the past. Soils were collected from three depths (0–5, 5–10, and 10–20 cm) within seven sites representing a sequence of years since cutting: 0.5, 6, 9, 12, 25, 50, and undisturbed (at least 80 years since cutting). Samples from each depth interval were analyzed for total C concentration and stock, humic substances, labile-C, and microbial biomass C. In addition, indicators of microbiological activity, such as basal respiration, microbial quotient, and metabolic quotient, were determined for the two shallow layers. The results showed that C stocks and microbiological activity were strongly influenced by forest cutting times, and reflect significant C losses associated with this type of management. They also suggest that reaccumulation of C following disturbance is slow. Those areas in which the vegetation has remained undisturbed for longer periods have larger C stocks, indicating that long-term maintenance of vegetation increases C storage in soils. For example, 20 years after cutting the C concentrations in soil and humic fractions had recovered to only about 32% of the presumed maximum found for the 80-year site. The average time for C in soil and humic fractions to return to their initial values at these sites is estimated to be approximately 65 years. Even achieving 50% recovery would require at least 33 years between cutting campaigns. Our findings show that in the context of mitigating climate change on a global scale, forest management entities should restrict cutting intervals in semiarid regions such as the Caatinga to longer than 30 years, to allow these soils to rebuild significant C stocks.