Márcia do Vale Barreto Figueiredo

Microbiological process in agroforestry systems. A review

Soils around the world are degraded due to inappropriate management practices. There is thus the necessity to find more conservationist agricultural systems. Agroforestry system is an alternative system that helps prevent land degradation while allowing continuing use of land to produce crops and livestock on a sustainable basis. Agroforestry system is a form of sustainable land use that combines trees and shrubs with crops and livestock in ways that increase and diversify farm and forest production while also conserving natural resources. This system enhances organic carbon accumulation in soils by the inclusion of cover crops and permanent vegetation, which is expected to increase the soil microbial biomass. The use of microorganisms aims at improving nutrient availability for plants. Currently, there is an emerging demand to decrease the dependence on chemical fertilizers and achieve sustainable agriculture and agroforestry. Arbuscular mycorrhizal fungi, plant growth-promoting rhizobacteria, and the association of rhizobia with leguminous plants are mutualistic symbioses of high economic importance for increasing agricultural production. The biological nitrogen fixation (BNF) process is an economically attractive and ecologically sound method to reduce external nitrogen input and improve the quality and quantity of internal resources. BNF by associative diazotrophic bacteria is a spontaneous process where soil nitrogen is limited and adequate carbon sources are available. However, the ability of these bacteria to contribute to increased crop yields is only partly a result of BNF. The successful use of legumes is dependent upon appropriate attention to the formation of effective symbioses with root nodule bacteria. An essential component for increasing the use of legumes is the integration of plant breeding and cultivar development, with appropriate research leading to the selection of elite strains of root nodule bacteria. An expansion of the utility of inoculants is also necessary to develop a broad conceptual framework and methodology that is supported by scientific arguments; it is destined to impact assessment of the use of new biological products in agriculture.

Fungos micorrízicos arbusculares em áreas de plantio de leucena e sábia no estado de Pernambuco

RESUMO n A ocorrŒncia de fungos micorrIzicos arbusculares (FMAs) foi investigada em AEreas cultivadas com leucena (Leucaena leucocephala L.) e sabiAE (Mimosa caesalpiniaefolia Benth), no Estado de Pernambuco. Amostras de solo foram coletadas em cinco estaAies experimentais da Empresa Pernambucana de Pesquisa AgropecuAEria (IPA), nas cidades de Arcoverde, com plantio de leucena (AL) e sabiAE (AS); Caruaru, com plantio de leucena (CL); e ItambO (IS), Sao Bento do Una (SBS) e Serra Talhada (STS), com plantio de sabiAE. O nœmero de esporos variou de 69 (STS) a 437/50 g de solo (CL) e a colonizaAao micorrIzica, de 11 (CL) a 64% (IS). Nas AEreas com plantio de leucena, a colonizaAao foi inferior a 15%, enquanto naquelas com cultivo de sAEbia houve variaAao de 36 a 64%. Foram observadas 24 espOcies de FMAs, pertencentes aos gŒneros: Acaulospora (6), Archaeospora (1), Entrophospora (1), Gigaspora (3), Glomus (6), Paraglomus (1) e Scutellospora (6). As AEreas CL e STS foram as que apresentaram maior nœmero de espOcies (14). Acaulospora scrobiculata, Archaeospora leptoticha e Glomus etunicatum foram encontradas em todas as AEreas. ABSTRACT n The occurrence of arbuscular mycorrhizal fungi (AMF) in plantations of Leucaena leucocephala L. (leucaena) and Mimosa caesalpiniaefolia Benth (sabia) in the State of Pernambuco was investigated. Soil samples were collected in five research centers of the Agricultural Research Institute of Pernambuco (IPA), in the cities of Arcoverde n plantation of leucaena (AL) and sabiAE (AS); Caruaru (CL) n leucaena plantation; ItambO (IS), Sao Bento do Una (SBS) and Serra Talhada (STS) n plantation of sabiAE. Mycorrhizal spores were extracted from soil, with the highest number (437/50g of soil) being found in the CL region and the lowest (69/50g of soil) in the STS region. The mycorrhizal colonization ranged from 11% (CL) to 64% (IS). The colonization was inferior to 15% in areas of leucaena plantation, however, in areas of sabiAE, it ranged from 36% to 64%. Twenty-four AMF species were identified in the genus: Acaulospora (6), Archaeospora (1), Entrophospora (1), Gigaspora (3), Glomus (6), Paraglomus (1) and Scutellospora (6). The highest species number was recorded in the CL and STS regions (14). Acaulospora scrobiculata, Archaeospora leptoticha and Glomus etunicatum were found in all regions.

Interrelationship of Bradyrhizobium sp. and plant growth-promoting bacteria in cowpea: Survival and symbiotic performance

The objective of this study was to evaluate the survival of cowpea during bacterial colonization and evaluate the interrelationship of the Bradyrhizobium sp. and plant growth-promoting bacteria (PGPB) as a potential method for optimizing symbiotic performance and cowpea development. Two experiments using the model legume cowpea cv. “IPA 206” were conducted. In the first experiment, cowpea seeds were disinfected, germinated and transferred to sterilized Gibson tubes containing a nitrogen-free nutritive solution. The experimental design was randomized blocks with 24 treatments [Bradyrhizobium sp. (BR 3267); 22 PGPB; absolute control (AC)] with three replicates. In the second experiment, seeds were disinfected, inoculated according to their specific treatment and grown in Leonard jars containing washed and autoclaved sand. The experimental design was randomized blocks with 24 treatments [BR 3267; 22 BR 3267 + PGPB; AC] with three replicates. Scanning electron microscopy demonstrated satisfactory colonization of the roots of inoculated plants. Additionally, synergism between BR 3267 and PGPB in cowpeas was observed, particularly in the BR 3267 + Paenibacillus graminis (MC 04.21) and BR 3267 + P. durus (C 04.50), which showed greater symbiotic performance and promotion of cowpea development.

WATER STRESS RESPONSE ON THE ENZYMATIC ACTIVITY IN COWPEA NODULES

A greenhouse experiment was carried out aiming to study the effect of water stress on metabolic activity of cowpea nodules at different plant development stages. Cowpea plants were grown in pots with yellow latosol soil under three different matric potentials treatments: -7.0 (control-S1), -70.0 (S2) and <-85.0 KPa (S3). The experimental design was randomized blocks with sub-divided plots, each plot containing a different degree of water stress, divided in sub-plots for the four different developmental stages: E1 (0-15), E2 (15-30), E3 (20-35) and E4 (30-45) days after emmergence. Water stress treatments were applied by monitoring soil water potential using a set of porous cups. The effect of water stress was most harmful to cowpea when it was applied at E2 than at other symbiotic process stages. Shoot/root ratio decreased from 2.61 to 2.14 when matric potential treatment was <-85.0 and -70.0 KPa respectively. There was a reduction in the glutamine synthetase activity and phosphoenolpyruvate carboxilase activity with increased stress, while glutamine synthase activity was the enzyme most sensitive to water stress. Glutamate dehydrogenase activity increased in more negative matric potential, indicating that this enzyme is sufficiently activitye under water stress.

Hospedeiros e ciclos sucessivos de multiplicação afetam a detecção de fungos micorrízicos arbusculares em áreas impactadas por mineração gesseira

RESUMO ‐ O objetivo deste trabalho foi verificar a influencia de diferentes plantas hospedeiras e de ciclos de multiplicacao em potes de cultura sobre a deteccao e avaliacao da diversidade de fungos micorrizicos arbusculares (FMA) no semiarido, em areas de caatinga preservadas e impactadas por mineracao de gesso no semiarido (Araripina, PE). Foram selecionadas quatro areas de coleta: AN - caatinga nativa preservada, AM - arredores da mina, AR-rejeito e AI - interface entre o deposito de rejeito e uma area de caatinga degradada pela mineracao, todas com solo do tipo Latossolo Amarelo, variando de franco-arenoso a argiloso, com pH de 5,7 a 7,5; 8 a 161 mg.dm -3 P e 0,23 a 79,8 mg.dm -3 Fe. Amostras foram retiradas desses solos para exame imediato e preparo de culturas-armadilha para FMA, utilizando-se como plantas hospedeiras amendoim ( Arachis hypogaea L.) e sorgo granifero (Sorghum bicolor (L.) Moench) cultivar IPA-7301011. Logo apos a coleta e depois de cada ciclo de multiplicacao na cultura-armadilha (tres ciclos de tres meses cada), foram avaliados em amostras de raizes e de solo rizosferico: colonizacao radicular, numero de esporos, diversidade e similaridade de especies de FMAs entre as areas. As plantas de amendoim apresentaram valores mais altos de colonizacao radicular (76,5 a 99,5%) que as de sorgo (21% a 73%). Maior producao de esporos ocorreu no 2o e no 3o ciclo de culturasarmadilha. Foram identificadas 25 especies de FMAs nas areas estudadas, onde se destacaram Glomus intraradices Schenck & Smith, Glomus mosseae Gerdemann & Trappe e Paraglomus occultum Morton & Redecker, pela alta densidade de esporos produzidos. As areas apresentaram indice de similaridade de especies de FMAs variando de 40 a 67%, com os maiores indices entre as areas impactadas.

Estoque de serapilheira e fertilidade do solo em pastagem degradada de Brachiaria decumbens após implantação de leguminosas arbustivas e arbóreas forrageiras

Pastures are the fodder supply of Brazilian livestock, and are exhaustively degraded by nitrogen (N) deficiency. Intercropping with legumes, aside from nitrogen fixation, may have secondary effects on soil fertility, such as acidification or nutrient movement from deeper to the surface soil layers. This study evaluated the soil litter stock and fertility of degraded Brachiaria decumbens pastures after planting leguminous shrubs and forage trees. For this purpose, we sampled (March 2010) degraded Brachiaria decumbens pasture planted in July 2008 in an intercropping experiment with sabia (Mimosa caesalpiniaefolia), leucaena (Leucaena leucocephala), mororo (Bauhinia cheilantha) and gliricidia (Gliricidia sepium), as well as N-fertilized and unfertilized brachiaria. Soil and litter was sampled (layers 0-10, 10-20 and 20-40 cm) in three transects, at alternating points covered by grasses and by legumes, totaling seven composite samples per plot to determine soil pH, P, K , Ca, Mg, and Al and calculate sum of bases, effective cation exchange capacity and aluminum saturation. Litter was visually separated in legumes, grasses and unidentified material to quantify dry matter, organic matter, N, P, C, acid-detergent fiber, and lignin. The use of legumes increased the levels of total N in litter and reduced the C: N ratios, especially of gliricidia and sabia, although the lignin levels in the latter were high. There was a significant effect of legume soil cover, with no differences between them, on pH and K (layer 0-10 cm) and on pH, K and Al (layer 10-20 cm).

Characterisation and identification of arbuscular mycorrhizal fungi species by PCR/RFLP analysis of the rDNA internal transcribed spacer (ITS)

The polymerase chain reaction coupled with restriction fragment length polymorphism analysis (PCR/RFLP) was applied to distinguish arbuscular mycorrhizal fungi (AMF) species from an impacted semiarid soil. The ITS1-5.8S-ITS2 region was amplified with the primers ITS1 and ITS4 and the products of amplification were digested with the restriction enzymes HinfI, MboI and AluI. The obtained banding pattern, except for the AluI, allowed the distinction at the molecular level of the AMF species:Paraglomus occultum, Glomus mosseae, Glomus intraradices andGlomus etunicatum. The results showed that this technique has a potential to be used as a marker to differentiate AMF species with high phylogenetic affinity.

Water deficit stress effects on N2 fixation in cowpea inoculated with different Bradyrhizobium strains

The objectives of this experiment were to select strains of Bradyrhizobium sp. resistant to water stress, envisaging an increase in N2 fixation in cowpea (Vigna unguiculata [L.] Walp.), and to verify the plants adaptive physiological responses to water stress. The experiment was carried out in greenhouse conditions using random complete blocks subdivided into plots adjusted to soil water potential levels of −6.0, −75.0, and −85.0 kPa, and subplots containing strains of Bradyrhizobium sp. (SEMIA 6145, 6086, 6002 and NFB 700), with four blocks. The soil was a Yellow Latosol with pH 6.3. The crop used was cowpea cv. IPA 204. Stress was applied continuously beginning 15 d after planting, by the control of water potential through a porous cup. Various parameters were evaluated every 7 days, until final harvest at 45 d. There was significant interaction between Bradyrhizobium strains and water stress. At the more negative ψm, plants inoculated with the SEMIA 6145 had higher LHb concentration, ureide-N, ψw and ...

Distinct bacterial communities across a gradient of vegetation from a preserved Brazilian Cerrado

The Cerrado biome in the Sete Cidades National Park, an Ecological Reserve in Northeastern Brazil, has conserved its native biodiversity and presents a variety of plants found in other savannas in Brazil. Despite this finding the soil microbial diversity and community structure are poorly understood. Therefore, we described soil bacterial diversity and distribution along a savanna vegetation gradient taking into account the prevailing environmental factors. The bacterial composition was retrieved by sequencing a fragment of the 16S ribosomal RNA gene. The bacterial operational taxonomic units (OTUs) were assigned to 37 different phyla, 96 classes, and 83 genera. At the phylum level, a core comprised by Proteobacteria, Acidobacteria, Actinobacteria, Firmicutes, Verrucomicrobia and Planctomycetes, was detected in all areas of Cerrado. ‘Cerrado stricto sensu’ and ‘Cerradao’ share more similarities between edaphic properties and vegetation and also present more similar bacterial communities, while ‘Floresta decidual’ and ‘Campo graminoide’ show the largest environmental differences and also more distinct bacterial communities. Proteobacteria (26%), Acidobacteria (21%) and Actinobacteria (21%) were the most abundant phyla within the four areas. All the samples present similar bacteria richness (alpha diversity) and the observed differences among them (beta diversity) were more related to the abundance of specific taxon OTUs compared to their presence or absence. Total organic C, N and P are the main abiotic factors structuring the bacterial communities. In summary, our findings show the bacterial community structure was clearly different across the Cerrado gradient, but that these environments share a bacterial phylum-core comprising Proteobacteria, Acidobacteria, Actinobacteria, Verrucomicrobia and Planctomycetes with other Brazilian savannas.

Plant Growth-Promoting Rhizobacteria: Key Mechanisms of Action

Plant growth-promoting rhizobacteria (PGPR) have gained worldwide importance and acceptance for their agricultural benefits through the application of combinations of different mechanisms of action, which allows increases in crop yield. This is due to the emerging demand for reduced dependence on synthetic chemical products and to the growing necessity of sustainable agriculture within a holistic vision of development and environmental protection. The use of selected plant-beneficial rhizobacteria may represent an important biotechnological approach to alleviate the negative effects of stress and to optimize nutrient cycling in different crops. Recent progress in our understanding of their action mechanisms, diversity, colonization ability, formulation, and application should facilitate their development as reliable components in the management of sustainable agricultural systems. In addition, numerous studies indicate increased crop performance with the use of these microorganisms. In this chapter, an understanding of the direct and indirect mechanisms of action of PGPR and their various benefits to plants are summarized and discussed.