Ana Dolores Santiago de Freitas

Caracterização de rizóbios isolados de Jacatupé cultivado emsolo salino do Estado de Pernambuco, Brasil

Investigation on microbiological biodiversity in the saline soils involves searching for tolerant genotypes to this type of emvironmental stress. Genotypic data associated to morphologic, physiological and biochemical characteristics of bacteria provide important information regarding its identification and clusters. The objective of this work was to characterize indigenous rhizobial strains of saline soils in the Wasteland and Hinterland of Pernambuco State, using yam bean (Pachyrhizus erosus L. Urban) as plant-tramp. Assays had been performed in YMA media and the observed cultivation characteristics of twenty-four isolates had been: change of pH, time of growth, transparency, form, edge, production of exopolysaccharides of the colonies and resistance to salinity. DNA amplification by the PCR technique of the repetitive sequence BOX indicated a high level of genetic and fenotipic diversity between the thirteen indigenous isolates. Comparing cultivation and genetic characteristics of these isolates with nineteen reference strains, indicated that isolates NFB746 and NFB747 had presented high similarity between then and also with the Rhizobium sp. NGR234 (BR2406) and Mesorhizobium ciceri USDA3383 (BR521).The isolated NFB742 possibly belongs to of the same species of the M. ciceri BR521. In relation to the isolated NFB741, the similarity with the Rhizobium tropici IIA CFN299T (BR10016) and Sinorhizobium terangue USDA4894 (BR527) was of 87%. All others isolates had clustered in comparative independent groups when comared to reference lineages. These results are important for diagnosis of new species of native rhizobia in areas where the use of FBN can improve and rehabilitate saline soil using the rizobia-leguminous interaction.

Nitrogen isotopic patterns in tropical forests along a rainfall gradient in Northeast Brazil

Background and aimsThe interpretation of ecosystem nitrogen isotopic patterns is subject to controversies since there are few surveys of signals along climate gradients within the same region. We determined the effects of a rainfall gradient, under high temperatures, on the soil and plant δ15N signals in Northeast Brazil.MethodsNitrogen, carbon and δ15N signals were determined from coastal perennial to subhumid and semiarid deciduous forests to savanna – deciduous forest transition.ResultsSoil C and N concentrations were linearly related and both related quadratically with mean annual rainfall while δ15N concentrations decreased with higher rainfall (16 to 4‰). Plant δ15N was 1–3‰ lower than soil δ15N (Δδ15N) in all areas. Only in the deciduous forests, leaves of target species had significantly lower 15 N signals than those of non-fixing species, allowing estimation of fixation.ConclusionsIn the perennial forests the low signals indicated that the 15 N natural abundance method was not suitable to estimate fixation, while in the savanna – deciduous forest transition, high signals indicated that the legume species were not fixing. The smaller Δδ15N than those reported in cooler areas and the absence of rainfall effect indicates that, when high, temperature overrides the rainfall effect.

Nodulação e fixação de nitrogênio por forrageiras da caatinga cultivadas em solos do semiárido paraibano

A fixacao biologica de nitrogenio foi avaliada em jureminha (Desmanthus pernambucanus), orelha-de-onca (Macroptilium martii) e feijao-de-rolinha (Macroptilium lathyroides) cultivados em solos do semiarido da Paraiba, em vasos sem e com esterco bovino. Foram determinados o numero e a biomassa de nodulos, os teores e as proporcoes de nitrogenio (N) fixado (percentual de nitrogenio da planta derivado do ar-%Ndda), pelo metodo da abundância natural, utilizando-se o capim-buffel como planta controle. As leguminosas tiveram nodulacao abundante, nos tres solos e na ausencia ou presenca de esterco, salvo quando cultivadas em Neossolo Fluvico sem adubacao. A adubacao com esterco aumentou o numero e a biomassa de nodulos. A fixacao biologica de nitrogenio foi alta nas tres especies, nos tres solos: na maioria das plantas, os valores superaram 50%, chegando a 85%. Esses dados permitem estimar a capacidade de fixacao das especies no campo em 10 a 30 kg ha-1 de N, considerando as densidades de plantio e produtividade usuais. As menores %Ndda e quantidades fixadas foram encontradas nas plantas cultivadas em Neossolo Regolitico e aumentaram com a adicao de esterco. Entre as especies testadas, a fixacao biologica de nitrogenio foi menos importante para D. pernambucanus. Nenhum dos parâmetros de nodulacao avaliados (numero, biomassa e biomassa/nodulo) explicou as proporcoes nem as quantidades de nitrogenio fixadas pelas plantas.

15 N natural abundance of non-fixing woody species in the Brazilian dry forest (caatinga)

Foliar δ15N values are useful to calculate N2 fixation and N losses from ecosystems. However, a definite pattern among vegetation types is not recognised and few data are available for semi-arid areas. We sampled four sites in the Brazilian caatinga, along a water availability gradient. Sites with lower annual rainfall (700 mm) but more uniform distribution (six months) had δ15N values of 9.4 and 10.1 ‰, among the highest already reported, and significantly greater than those (6.5 and 6.3 ‰) of sites with higher rainfall (800 mm) but less uniform distribution (three months). There were no significant differences at each site among species or between non-fixing legume and non-legume species, in spite of the higher N content of the first group. Therefore, they constitute ideal reference plants in estimations of legume N2 fixation. The higher values could result from higher losses of 15N depleted gases or lower losses of enriched 15N material.

Efeito da fertilização com fósforo, potássio e magnésio em jacatupé infectado com rizóbio em um Latossolo álico

In order to evaluate the effects of phosphorus, potassium and magnesium application on the nutrient absorption and yield of yam bean (Pachyrhizus erosus (L.) Urban), in a Yellow Latosol of the Zona da Mata of Pernambuco State, Brazil, an experiment was carried out using the strain of Bradyrhizobium sp. NFB 450, isolated from yam bean and selected for efficient N2 fixation in previous experiments. Potassium and magnesium were applied in the proportion of 2:1 (K2O:MgO) in increasing levels (0:0, 40:20, 60:30 and 80:40 kg ha-1 of K2O and MgO, respectively), and crescent levels of phosphorus (0, 20, 40, 60 and 80 kg ha-1 of P2O5) were added in the form of triple superphosphate. Maximum dry matter production, total N and total P accumulated were obtained when applying 64 kg ha-1 of P2O5. A significant effect of K2O:MgO levels was observed in relation to the treatment without K and Mg application; nevertheless, higher levels of K2O:MgO decreased dry matter and total N, and increased total P accumulation. Yam bean responded to low levels of P, K and Mg fertilizer, and showed ability in N2 fixation, with great potential for biomass production.

Interações entre fungos micorrízicos arbusculares, rizóbio e actinomicetos na rizosfera de soja

Actinomycete isolates and arbuscular mycorrhizal fungi were evaluated in vivo using jointly inoculation systems with soybean plants inoculated with rhizobia, with the aim to observe microbial interactions. The study was carried out at the National Center of Agrobiologic Research (Embrapa CNPAB). Soil of the Itaguai series (medium texture) was used as substrate mixed with river sand in proportion 1:1 (v:v), adding actinomycete isolates (ACT 78 and ACT 370), rhizobia strains (Bradyrhizobium elkanii - BR 29 and Bradyrhizobium japonicum - BR 33), and arbuscular mycorrhizal fungi (Gigaspora margarita and Glomus clarum). The results revealed the effect of the arbuscular mycorrhizal fungi addition with significant and expressive influence on growth parameters, nodulation and density of actinomycete isolates on the soybean rhizosphere which showed greater values compared with fungi uninoculated plants. Synergistic and antagonistic effects were observed between the arbuscular mycorrhizal fungi with actinomycetes isolates and rhizobia strains.

Rock biofertilizer and earthworm compost on sugarcane performance and soil attributes in two consecutive years

The deployment of soluble fertilizers has been one of the most commonly applied agricultural practices in the bid to increase crop yield. However, the production of soluble fertilizers has a considerable economic cost and consumes a substantial amount of energy. In general, soil organic matter provides the nutrients needed for plant growth in organic agriculture. However, these nutrients are not sufficient if the best yield is to be obtained. The aim of our field experiment was to evaluate the effectiveness of phosphate and potassic sources (rocks, bio-fertilizers and soluble fertilizers) based on several sugarcane characteristics and soil attributes. Our experiment was conducted over two consecutive years, and we assessed the effect of using sugarcane filter mud cake (SFMC). In addition, we mixed the phosphate and potassic sources with earthworm compost enriched in N by inoculation with diazotrophic bacteria (OM) and applied at 50, 100 and 150 % of the recommended dosage rate (RDR). The PK biofertilizer with OM enriched in N positively affected sugarcane height, yield, and industrial characteristics. The application of SFMC greatly increased available P and K in the soil and plant characteristics with residual effect in the two consecutive harvests. We conclude that the biofertilizer has the potential to increase sugarcane characteristics and may represent an alternative to soluble fertilizers.

Phenotypic, genetic and symbiotic characterization of Erythrina velutina rhizobia from Caatinga dry forest.

Erythrina velutina (“mulungu”) is a legume tree from Caatinga that associates with rhizobia but the diversity and symbiotic ability of “mulungu” rhizobia are poorly understood. The aim of this study was to characterize “mulungu” rhizobia from Caatinga. Bacteria were obteined from Serra Talhada and Caruaru in Caatinga under natural regeneration. The bacteria were evaluated to the amplification of nifH and nodC and to metabolic characteristics. Ten selected bacteria identified by 16S rRNA sequences. They were tested in vitro to NaCl and temperature tolerance, auxin production and calcium phosphate solubilization. The symbiotic ability were assessed in an greenhouse experiment. A total of 32 bacteria were obtained and 17 amplified both symbiotic genes. The bacteria showed a high variable metabolic profile. Bradyrhizobium (6), Rhizobium (3) and Paraburkholderia (1) were identified, differing from their geographic origin. The isolates grew up to 45 °C to 0.51 mol L−1 of NaCl. Bacteria which produced more auxin in the medium with l-tryptophan and two Rhizobium and one Bradyrhizobium were phosphate solubilizers. All bacteria nodulated and ESA 90 (Rhizobium sp.) plus ESA 96 (Paraburkholderia sp.) were more efficient symbiotically. Diverse and efficient rhizobia inhabit the soils of Caatinga dry forests, with the bacterial differentiation by the sampling sites.

Symbiotic efficiency of native rhizobia in legume tree Leucaena leucocephala derived from several soil classes of Brazilian Northeast region

The effective symbiotic activity of rhizobia can contribute increment of biological nitrogen fixation (BNF), which is of great importance in low technology regions. This study aimed to evaluate the symbiotic efficiency of native rhizobia from Brazilian Northeast soils for selection of the most efficient and competitive strains for Leucaena leucocephala plant. The greenhouse test was conducted in factorial scheme (7x3), with seven fertilization treatments and three soil classes (Luvisol, Ultisol and Oxisol). The fertilization treatments were: (a) four native rhizobia isolates, obtained from nodules of L. leucocephala grown in Brazilian semiarid soils; (b) recommended strain (SEMIA 6069); (c) control without rhizobia inoculation and without N fertilization; (d) control without rhizobia, but with N fertilization (100 mg kg -1 ). The plants were harvested at 90 days and the following characteristics were determined: plant height, diameter, shoots dry matter, roots dry matter and nodules dry matter, number of nodules, nitrogen concentration and accumulation in shoots, and efficiency of nitrogen fixation. The isolates 36F and 45G are very promising on Biologic Nitrogen Fixation (BNF). They showed high symbiotic efficiency (higher than 90%). These selected strains provided the best characteristics such as plant height (57 and 52 cm), diameter (4.03 and 4.02 mm), dry matter of shoot (3.2 and 3.6 g plant -1 ) and nitrogen accumulation in shoots (60 and 65 mg plant-1).

Sustainable Agricultural Uses in the Caatinga

The productive use of the Caatinga vegetation, as native pasture, fallow in itinerant agriculture, and firewood production, has been the main reason why it still covers 40% of its original 1 million km2. Producers could not find systems composed solely of planted species that were more profitable over long periods and large areas because of the low plant biomass production capacity due to low water availability. In the last decades, low productivity and high production costs, mainly labor, has rendered agriculture increasingly less competitive in relation to other Brazilian regions. Therefore, the area dedicated to agriculture has been decreasing and crops such as perennial cotton and sisal have almost disappeared. Since it has been predicted that plant-growing conditions will tend to become even harsher, with lower rainfall and higher potential evapotranspiration, a reversal of this trend is unlikely and corn and beans, the major crops, will be planted less. Conversely, livestock production may increase with the planting of African grasses. The balance of agriculture abandonment and pasture planting will determine how much Caatinga will be preserved. Firewood production may increase, mainly around large consumption centers, but the overall stock is enough to meet the demand. Efforts should be directed to improve productivity and land conditions in the portions that will be maintained under use. The current trends indicate that the area under native vegetation will not decrease from its present situation.