Land‐use change (LUC) can impact soil quality. In semi‐arid areas of Brazil, impacts of LUC need to be understood for better soil management. This study evaluated the impact of LUC on soil organic ...carbon (SOC), nitrogen (N), and phosphorus (P) distributions through the soil profile and stocks of a Haplic‐Cambisol in the Brazilian Semi‐arid region. Three land‐use systems (LUS) were investigated: agricultural management (30 years), regeneration under controlled grazing (25 years) after 5 years arable management, and native dry forest. Soil contents of P, total C, total N, and N fractions were used to calculate stocks and their stoichiometric ratios for layers 0–5, 5–10, 10–20, and 20–40 cm. Data from these LUS were compared using Kruskal–Wallis non‐parametric tests. Changes to soil microbial biomass reflected the substantially reduced SOC concentration and stock in managed soils compared with that of the natural dry forest area. Total N stock was not affected by LUC, although increases in nitrate and ammonium offset a significantly reduced organic N fraction in the agricultural area. The largest P stock was found in agricultural land, followed by the grazed fallow regeneration site. LUC significantly influenced the stoichiometric ratio of C, N, and P, with the change from Caatinga to agriculture affecting the equilibrium between organic residues’ input and mineralization. LUC resulted in significant changes to C, N, and P stocks, which did not recover to the original values, even after 25 years of regeneration under controlled grazing.
Semiarid regions are apparently low biodiversity environments; however, these environments may host a phylogenetically diverse microbial community associated with plants. Their microbial inhabitants ...are often recruited to withstand stressful settings and improve plant growth under harsh conditions. Thus, plant-associated microorganisms isolated from semiarid and seasonally dry environments will be detailed in the present review, focusing on plant growth promotion potential and the microbial ability to alleviate plant abiotic stress. Initially, we explored the role of microbes from dry environments around the world, and then, we focused on seasonally dry Brazilian biomes, the Caatinga and the Cerrado. Cultivable bacteria from semiarid and seasonally dry environments have demonstrated great plant growth promotion traits such as plant hormone production, mobilization of insoluble nutrients, and mechanisms related to plant abiotic stress alleviation. Several of these isolates were able to improve plant growth under stressful conditions commonly present in typical semiarid regions, such as high salinity and drought. Additionally, we highlight the potential of plants highly adapted to seasonal climates from the Caatinga and Cerrado biomes as a suitable pool of microbial inoculants to maintain plant growth under abiotic stress conditions. In general, we point out the potential for the exploitation of new microbial inoculants from plants growing in dry environments to ensure a sustainable increase in agricultural productivity in a future climate change scenario.
To evaluate the interaction between foliar application of salicylic acid and
Bradyrhizobium
inoculation on the morphophysiology of cowpea under water stress conditions, four genotypes (BRS Rouxinol, ...BRS Marataoã, BRS Aracê and BR 17 Gurguéia) were subjected to five combinations of water availability: 100% replacement of crop evapotranspiration (control); 50% replacement of crop evapotranspiration (water stress); water stress + salicylic acid; water stress +
Bradyrhizobium
inoculation; and water stress + salicylic acid +
Bradyrhizobium
inoculation. The experiment was set up in a 4 × 5 factorial randomized block design, with four replicates and four plants per plot. Water stress negatively affected the leaf water potential, growth, proline contents and antioxidant activity of the cowpea genotypes, and BRS Marataoã was the most sensitive. Under water stress conditions,
Bradyrhizobium
inoculation was efficient for BRS Rouxinol, but was only efficient for BRS Marataoã, BRS Aracê and BR 17 Gurguéia when associated with foliar application of salicylic acid, maintaining their values of leaf water potential, growth, proline content and activities of superoxide dismutase, ascorbate peroxidase, and catalase similar to those of the control treatment.
The soil environment adjacent to plant roots, termed the rhizosphere, is home to a wide variety of microorganisms that can significantly affect the physiology of nearby plants. Microbes in the ...rhizosphere can provide nutrients, secrete signaling compounds, and inhibit pathogens. These processes could be manipulated with synthetic biology to enhance the agricultural performance of crops grown for food, energy, or environmental remediation, if methods can be implemented in these nonmodel microbes. A common first step for domesticating nonmodel organisms is the development of a set of genetic engineering tools, termed a synthetic biology toolbox. A toolbox comprises transformation protocols, replicating vectors, genome engineering (e.g., CRISPR/Cas9), constitutive and inducible promoter systems, and other gene expression control elements. This work validated synthetic biology toolboxes in three nitrogen-fixing soil bacteria: Azotobacter vinelandii, Stutzerimonas stutzeri (Pseudomonas stutzeri), and a new isolate of Klebsiella variicola. All three organisms were amenable to transformation and reporter protein expression, with several functional inducible systems available for each organism. S. stutzeri and K. variicola showed more reliable plasmid-based expression, resulting in successful Cas9 recombineering to create scarless deletions and insertions. Using these tools, we generated mutants with inducible nitrogenase activity and introduced heterologous genes to produce resorcinol products with relevant biological activity in the rhizosphere.
Endophytic bacteria play a crucial role in plant development and adaptation, and the knowledge of how endophytic bacteria assemblage is influenced by cultivation site and plant genotype is an ...important step to achieve microbiome manipulation. This work aimed to study the roots and stems of endophytic bacteriome of four maize genotypes cultivated in two regions of the semi-arid region of Pernambuco - Brazil. Our hypothesis is that the endophytic community assemblage will be influenced by plant genotypes and cultivation region. Metabarcoding sequencing data revealed significant differences in alfa diversity in function of both factors, genotypes, and maize organs. Beta diversity analysis showed that the bacterial communities differ mainly in function of the plant organ. The most abundant genera found in the samples were
Leifsonia
,
Bacillus
,
Klebsiella
,
Streptomyces
, and
Bradyrhizobium
. To understand ecological interactions within each compartment, we constructed co-occurrence network for each organ. This analysis revealed important differences in network structure and complexity and suggested that
Leifsonia
(the main genera found) had distinct ecological roles depending on the plant organ. Our data showed that root endophytic maize bacteria would be influenced by cultivation site, but not by genotype. We believe that, collectively, our data not only characterize the bacteriome associated with this plant and how different factors shape it, but also increase the knowledge to select potential bacteria for bioinoculant production.
Objetivo: Este estudo teve como objetivo determinar o perfil enzimático para xilanase, amilase, celulase e pectinase em áreas com diferentes níveis de desertificação, a fim de investigar como esse ...processo influencia a variação enzimática de actinobactérias. Método: Amostras de solo foram coletadas de áreas suscetíveis à desertificação com diferentes níveis de cobertura vegetal no semiárido brasileiro. As atividades enzimáticas de 46 cepas de actinobactérias isoladas dessas áreas foram avaliadas utilizando meios de cultura específicos. Os índices enzimáticos foram calculados e correlacionados com as propriedades físico-químicas do solo. Resultados: Houve diferença significativa na atividade enzimática de acordo com o gradiente de desertificação. A xilanase exibiu o maior índice enzimático, seguida pela pectinase, amilase e celulase. A área aberta apresentou melhor desempenho para degradação de xilana, indicando que a falta de cobertura vegetal e a baixa disponibilidade de nutrientes influenciaram esta atividade enzimática. Conclusão: As cepas de actinobactérias têm potencial para produzir enzimas funcionais através de um gradiente de desertificação. A xilanase foi a mais frequente, sugerindo adaptação das actinobactérias à degradação de polissacarídeos vegetais complexos em solos desprovidos de nutrientes.
Aims
To evaluate the occurrence, the characterization and identity of nodulating bacteria in symbiosis with
Mimosa
spp. in the ultramafic massif of Barro Alto, Goiás state, Brazil.
Methods
Nodules ...from field grown
M. somnians
and
M. claussenii
were sampled for bacteria isolation and
in situ
detection using microscopy. Isolates were characterized for their nodulation capacity on
M. pudica
and common bean, and their tolerance to Ni in culture medium. Bacteria were also partially identified by their 16S rRNA gene sequences. In addition,
recA
,
gyrB
,
nodC
and
nifH
genes from five representative isolates were sequenced for phylogenetic studies
.
Results
In situ
detection indicated the exclusive presence of
Paraburkholderia
sp. within the nodules. This identification was confirmed for most of the isolates by the analysis of their 16S rRNA gene sequences. All isolates identified as
Paraburkholderia
sp. were able to effectively nodulate
M. pudica
, but those tested in common bean produced ineffective nodules. Inoculation tests showed that these bacteria improved
M. pudica
growth in the absence of nitrogen. None of the isolates showed Ni tolerance. The concatenated 16S rRNA,
recA
and
gyrB
, and the
nodC
and
nifH
genes sequences demonstrated that the five selected isolates were closely related to
P. atlantica
.
Conclusions
This is the first report of
Paraburkholderia
present in nodules from
Mimosa
plants naturally growing in ultramafic soils. These results suggest that this symbiosis may be a factor to be considered as part of programs to restore ultramafic soils in Barro Alto areas degraded by mining activity.
To isolate and characterize non-rhizobial nodule-associated bacteria (NAB) from cowpea root-nodules regarding their performance of plant-growth-promoting mechanisms and their ability to enhance ...cowpea growth and symbiosis when co-inoculated with bradyrhizobia.
Sixteen NAB were isolated, identified, and in vitro evaluated for plant growth promotion traits. The ability to promote cowpea growth was analyzed when co-inoculated with Bradyrhizobium pachyrhizi BR 3262 in sterile and non-sterile substrates. The 16S rRNA gene sequences analysis revealed that NAB belonged to the genera Chryseobacterium (4), Bacillus (3), Microbacterium (3), Agrobacterium (1), Escherichia (1), Delftia (1), Pelomonas (1), Sphingomonas (1), and Staphylococcus (1). All strains produced different amounts of auxin siderophores and formed biofilms. Twelve out of the 16 strains carried the nifH, a gene associated with nitrogen fixation. Co-inoculation of NAB (ESA 424 and ESA 29) with Bradyrhizobium pachyrhizi BR 3262 significantly promoted cowpea growth, especially after simultaneous inoculation with the three strains.
NAB are efficient cowpea growth promoters and can improve the efficiency of the symbiosis between cowpea and the N2-fixing microsymbiont B. pachyrhizi BR 3262, mainly under a specific triple microbial association.
The objective of this work was to assess the efficiency of the inoculation of a diazotrophic bacterial consortium by the drip irrigation system into sugarcane (Saccharum spp.), in the Brazilian ...semiarid region. The evaluated treatments were: standard inoculation by submersion; one or two inoculations by drip irrigation; nitrogen (urea) applied by fertigation; and negative controls, without inoculation or nitrogen fertilization. Leaf gas exchanges and plant growth and yield were assessed. Inoculation by irrigation is efficient for all variables, and double inoculation by the drip irrigation system stands out, increasing stem yield in 16% when compared with the negative control, without differing from the treatment with nitrogen fertilizer.
Resumo: O objetivo deste trabalho foi avaliar a eficiência da inoculação de um consórcio de bactérias diazotróficas por meio do sistema de irrigação por gotejamento em cana-de-açúcar (Saccharum spp.), em região semiárida brasileira. Os tratamentos avaliados foram: inoculação padrão por submersão; uma ou duas inoculações por irrigação por gotejamento; ureia aplicada por fertirrigação; e controles negativos, sem inoculação ou fertilização com nitrogênio. Avaliaram-se as trocas gasosas foliares e o crescimento e a produtividade das plantas. A inoculação por irrigação é eficiente para todas as variáveis, com destaque para a dupla inoculação pelo sistema de irrigação por gotejamento, que aumentou a produtividade de colmos em 16% quando comparado ao controle negativo, não tendo diferido do tratamento nitrogenado com ureia.
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