Nodulacao, trocas gasosas e producao do amendoim cultivado com Bradyrhizobium em solos com texturas diferentes/Nodulation, gas exchanges and production of peanut cultivated with Bradyrhizobium in soils with different textures.
Nitrogen fertilization from biological source is an uncommon practice for peanut growers due to the limited results, mainly in environments with water restriction. In this study, the response of a commercial Bradyrhizobium was evaluated on the nodulation and production of peanuts grown in sandy and medium textured soils. Two experiments using different soils were carried out in the field during the dry season, in Campina Grande, Paraiba State, Brazil. Three peanut genotypes were submitted to the following treatments: 1-no nitrogen fertilization (control), 2- chemical fertilization (ammonium sulfate) and 3- inoculation with Bradyrhizobium [commercial strain BR 1405 (SEMIA 6144)]. A completely randomized 3x3 factorial design was adopted with five repetitions for both experiments. The evaluates variables were: height of the main stem, number of nodes/plant, root length, root dry weight, weight of pods/plant and number of pods/plant. In addition, gas exchanges were estimated using IRGA apparatus. Both genotypes (BRS Havana and L7 Bege) were benefited in relation to production due to an inoculation with SEMIA 6144. No physiological response was verified in genotypes or N-treatments to gas exchange, excepting for the Ci/Ca ratio in the medium textured soil experiment. BRS Havana showed low Ci/Ca ratio in Bradyrhizobium treatment, indicating that SEMIA 6144 improved the plants photosynthetic efficiency.
Keywords: Arachis hypogaea, biological nitrogen fixation, soil fertilization, gas exchange.
A adubacao nitrogenada por fonte biologica e uma pratica raramente adotada por agricultores de amendoim, devido a limitacoes de informacoes, principalmente em ambientes com restricao hidrica. Neste trabalho, a resposta de um inoculante comercial de Bradyrhizobium foi avaliada sobre a nodulacao e producao de amendoim cultivado em solos arenoso e de textura media. Dois experimentos foram conduzidos em campo durante a estacao seca, em Campina Grande, PB, com cada tipo de solo citado. O delineamento adotado foi o inteiramente casualizado com fatorial 3 x 3 e cinco repeticoes. Tres genotipos de amendoim foram submetidos aos seguintes tratamentos: 1-sem adubacao nitrogenada (controle), 2-fertilizacao quimica (sulfato de amonio) e 3- fertilizacao biologica [estirpe comercial BR 1405 (SEMIA 6144)-Bradyrhizobium]. As variaveis avaliadas foram: altura da haste principal, numero de nodulos/planta, comprimento da raiz, peso seco da raiz, peso das vagens/planta e numero de vagens/planta alem das trocas gasosas que foram estimadas com o auxilio do equipamento IRGA. Dois genotipos (BRS Havana e L7 Bege) foram beneficiados na producao devido a inoculacao com a estirpe SEMIA 6144. Nenhuma resposta fisiologica foi verificada nos genotipos ou nos tratamentos com N para trocas gasosas, com excecao da relacao Ci/Ca, no experimento em solo de textura media. A BRS Havana apresentou baixa relacao Ci/Ca no tratamento com Bradyrhizobium, indicando que SEMIA 6144 melhorou a eficiencia fotossintetica das plantas.
Palavras-chave: Arachis hypogaea, fixacao biologica de nitrogenio, fertilizacao do solo, trocas gasosas.
Biological nitrogen fixation (BNF) is a natural process that occurs mainly through symbiotic association in legumes species by rhizobial bacteria that convert elemental nitrogen into ammonia. In nature, only a few microorganisms are able to reduce [N.sub.2] through the nitrogenase complex. Such interaction with plants account for 65% of the current nitrogen used in agriculture (Jones et al., 2007, Swain & Abhijita, 2013).
Several bacteria have been used as inoculants to improve the crops fertilization, providing an effective establishment of the nitrogen-fixing symbiosis. In addition to the nitrogen fixation, those bacteria are able to produce several molecules that promote plant growth and grain yield (Hayat et al., 2008). The advantage of this process is the total use of the fixed nitrogen by plants (Epstein & Bloom, 2006, Swain & Abhijita, 2013).
BNF varies with soil fertility and temperature, genotypes and Rhizobium strains (Santos et al., 2005; Borges et al., 2007). High soil temperatures in tropical and subtropical climates are a major problem for BNF because it can affect [N.sub.2] fixation. Critical temperatures for [N.sub.2] fixation are around 35[degrees]C - 40[degrees]C (Nehra et al., 2007, Yadav & Nehra, 2013).
Peanut (Arachis hypogaea L.) is nodulated by an array of rhizobial species. The route that rhizobia fixes nitrogen is brief: rhizobia initiates the infection at the axils of emerging lateral roots and proliferates in intercellular spaces before entering in cortical cells. Then, rhizobia spreads further through the root cortex via an intercellular matrix and are eventually released into plant cells (Angelini et al., 2011, Lyra et al., 2013, Ahemad & Kibret, 2014). Among the bacteria that can nodulate peanut, several are very efficient and the prospection of bacterial isolates to this crop revealed some promising bacteria as new inoculants (Lyra et al., 2013, Torres-Junior et al., 2014).
Siddique & Bal (1991) reported that peanut is privileged by BNF, since plants are able to maintain nitrogen fixation even with poor supply of photosynthates. This ability is due to the presence of lipid bodies near the periobacteroid membrane. However, since Arachis presents hypogeal fruits, soil sandy texture is more appropriate for the management, although it affects the strains efficiency due to low fertility and water retention (Bolonhezi et al., 2013).
Montans et al. (2008) evaluated the nodulation of peanut, using sandy and clay soils, both without previous cropping and observed that in clay soil plants had high number of nodules with improved strain and no effect in competition was verified between inoculant and native strains.
Despite to evidence of BNF benefits to crops management, there is limited information about the interactions between Bradyrhizobium genotypes and isolates, especially in semiarid regions, where soil and weather conditions may reduce the isolates efficiency. The present study aimed to provide further information about BNF in peanuts focused in different genotypes and soil textures. Nodulation and pod production were estimated based on chemical fertilization and inoculation of a commercial Bradyrhizobium sp. strain.
Material and methods
The experiments were carried out at Campina Grande, Paraiba State, Brazil (07[degrees]13'S; 35[degrees]53'W), during the 2013 dry season (sept/dec), using three upright genotypes, represented by commercial cultivars (BR 1 and BRS Havana), developed to semiarid environment by the Brazilian Agricultural Research Corporation (Embrapa), and a top line (BRS L7 Bege), generated by crossing with African and Brazilian germplasm (Santos et al., 2013). The assays were set up with two different soil samples. The first experiment was installed with a sample of a loamy-sandy Fluvic soil [Neossolo Fluvico] (pH: 5.2, [Ca.sup.+2]: 1.8 mmolc [dm.sup.-3], [K.sup.+]: 4.3 mmolc [dm.sup.-3], P: 2.1 mg [dm.sup.-3] and organic matter: 4.7 g [kg.sup.-1] of soil). This soil presented 777, 170 and 53 g.[kg.sup.-1] of sand, silt and clay, respectively. The second experiment was installed using as substrate a sample of a medium-textured Red-Yellow Ultisol (Argissolo Vermelho-Amarelo) (pH: 5.4, [Ca.sup.+2]: 5.4 mmolc [dm.sup.-3], [K.sup.+]: 1.8 mmolc [dm.sup.-3], P: 4.9 mg [dm.sup.-3] and organic matter 14.9 g [kg.sup.-1] of soil). The granulometric analysis presented amounts of 791, 91 and 118 g.[kg.sup.-1] of sand, silt and clay, respectively. The soils were classified according to Embrapa (2013). Both soils were previously limed and fertilized based on peanut crop demands for the Brazilian Northeast region (Embrapa, 2013).
The average data of temperature and air relative humidity during the experiment were 23[degrees]C and 78%, respectively. The total rainfall in the period was 101 mm. This data were obtained from the INMET-National Institute of Meteorology, collected in the main climatological station of Campina Grande, Paraiba State, Brazil.
Three seeds of three upright genotypes were sowed in pots with capacity of 15 L of soil and filled with the soil samples cited above. The experiments had a completely randomized 3x3 factorial design, with five repetitions. The following treatments were adopted: 1- crop without N fertilization (control); 2- crop with chemical N fertilization (ammonium sulfate, 0.25 g [plant.sup.-1], equivalent to 40 kg [ha.sup.-1] of N), in a single application at sowing, and 3- Inoculation of Bradyrhizobium SEMIA 6144, (1 mL at [10.sup.9] cells [mL.sup.-1] per seed), applying directly to the seeds at sowing.
Bacterial strain and growth conditions
The commercial Bradyrhizobium strain SEMIA 6144 recommended to inoculant production in peanut was used (MAPA, 2011) and grown in liquid YEM medium (Vincent, 1970) for 4-7 days at 28[degrees]C up to the late exponential growth phase with about [10.sup.9] cells [mL.sup.-1].
IRGA (Infra-Red Gas Analyzer, LI-6400, LI-COR, USA) was used in order to estimate the physiological traits. Leaf gas exchanges of C[O.sub.2], [H.sub.2]O vapor, net C[O.sub.2] assimilation, stomatal conductance, transpiration and intercellular C[O.sub.2] concentration/ambient C[O.sub.2] concentration (Ci/Ca) were estimated from 30% of the plants, for each treatment. The measurements were collected from fully expanded leaves of 70 d-plants, from 9:00 am to 11:00 am. Each variable had three repetitions.
Plants were harvested after 90 days and were naturally dried in the field during 5 days. The following characteristics were evaluated: main stem height, number of nodes/plant, root length, root dry weight, weight of pods/plant and number of pods/plant.
Statistical analyses were performed using the SAS program, version 9.1.3 (SAS/STAT, 2005). Data were submitted to analysis of variance and means were compared by Tukey's test (p <0.05).
Results and discussion
Nodulation and agronomical traits
The genotypes showed limited responses to N-treatments for most of the evaluated variables, except for NN and PW, that increased in sandy soil (Table 1). Both BR 1 and L7 Bege did not depend on N-source to improve the nodulation, although L7 Bege showed increasing of 31% and 50% in pod weight, to Ammonium sulfate and Bradyrhizobium treatments, respectively, when compared to control. However, the cv. BRS Havana resulted in a better response to Bradyrhizobium treatment, showing an increase of 39% to NN and 48% to PW, when compared to control.
For N-treatments in medium textured soil, statistical differences were verified for all evaluated characteristics, except for RL (Tables 2 and 3). However, between genotypes the statistic differences were observed only for MSH and NN. The cv. BRS Havana was broadly benefited by the Bradyrhizobium treatment, presenting an increase of 29% for MSH and 28% for NN, comparing to control. The opposite response was verified for BR 1 and L7 Bege that showed, respectively, 10% and 42% of reduction in NN in plants treated with N, suggesting that both genotypes were more responsive to native strains, which are widely distributed throughout soil profiles, while improved isolates remains at the first layers (Santos et al., 2005, Bogino et al., 2008, Lopez-Garcia et al., 2009). For these genotypes it can be a benefit, since root set is located at the first 30 cm of the soil depth (Nogueira et al., 2013). Despite for nodulation results, the root weight and pod production were improved by N-treatments for all peanut genotypes, especially BRS Havana fertilized with Bradyrhizobium.
Santos et al. (2007) reported that peanut has broad capacity of nodulation with native strains presented in sandy and clay loam soils in the semiarid environment. However, this ability is genotype-dependent because the climate may affect directly the non-native rhizobia and restrict the survival and efficiency of the root set in nodulating plants. Studies of interactions between legumes and rhizobia in semiarid environment demonstrated that native strains were more able to fix [N.sub.2] in conditions that would not be supported by exotic species (Taurian et al., 2006, Ibanez et al., 2008, Ruiz-Diez et al., 2012).
Although there is an availability of exotic species with high efficiency in nitrogen fixation for several legume species, selection of native strains provides perspectives to broad the exploration of new isolates adapted to dry environments, favoring low responsive cultivars to commercial isolates. Nevertheless, it is worth pointing that the soil properties, involving fertility, texture and depth contribute to response of isolates x genotypes. The agronomic responses observed in the present study in medium textured soil were associated to texture, that favored the nutrients retention and soil moisture, and the high organic matter content in the Ultisol. In sandy soils, the leaching of fertilizers due to its texture and the low organic matter content possibly limited the SEMIA 6144 activity.
No statistical differences were verified according to genotypes and treatments on the physiological traits, excepting for Ci/Ca ratio in the medium-textured soil treatment (Table 4).
The lowest Ci/Ca value was observed for BRS Havana in Bradyrhizobium treatment, indicating that the inoculation with SEMIA 6144 contributed to an improvement of the plants photosynthetic efficiency. The cv. BR 1 showed intermediate behavior between BRS Havana and L7 Bege in treatments with ammonium sulfate and Bradyrhizobium.
The Ci/Ca ratio is a trait that is directly involved in plant photosynthetic activity. The value can be changed due to variations in the rates of net assimilation and stomatal conductance. Reduced stomatal conductance restricts the C[O.sub.2] entrance in intercellular areas, which tends to be consumed by the photosynthetic assimilation. Thus, the lower the Ci/Ca ratio, the higher the photosynthesis efficiency. In some crops, it may lead to a production increase (Kaschuk et al., 2012).
In literature, some authors reported that the photosynthesis of rhizobial plants increased regardless the lower leaf N concentration in N-fertilized plants. Kaschuk et al. (2012) compared the photosynthetic capacity of soybean inoculated with two different B. japonicum strains, and observed that nodulated plants had 14-31% higher rates of photosynthesis and accumulated less starch in the leaves than N-fertilized plants. According to the authors, rhizobial symbiosis stimulated photosynthesis due to the removal of photosynthates sink limitation by the nodule activity. Oliveira et al. (2012) also observed the same results to cowpea, where plants inoculated with a commercial rhizobia strain showed more efficiency on gas exchanges than the control plants. Also, in the present study, peanut presented a better gas exchange behavior when inoculated with SEMIA 6144.
The inoculation of Bradyrhizobium sp. SEMIA 6144 in peanut plants grown in medium textured and sandy soils benefited the nodulation, pod production and gas exchanges of BRS Havana cultivar. For other cultivars, it is necessary to incorporate the BNF in breeding programs in order to identify responsive isolates that can increase plant development.
To REPENSA (National Network for Research on Agricultural Biodiversity and Sustainability - MCT/ CNPq/ MEC/ CAPES/ CT AGRO/ CT IDRO/ FAPS/ EMBRAPA), for the financial support and to CAPES, for the grants.
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Emanuelle Barros Sobral de Melo (1), Liziane Maria de Lima (2), Paulo Ivan Fernandes-Junior (2), Saulo de Tarso Aidar (3), Maria Aline Oliveira Freire (2), Rosa Maria Mendes Freire (2), Roseane Cavalcanti dos Santos (2,*)
(1) State University of Paraiba, Campina Grande, PB, Brazil (2) Brazilian Agricultural Research Corporation - Embrapa Algodao, Campina Grande, PB, Brazil (3) Brazilian Agricultural Research Corporation - Embrapa Semi-arido, Petrolina, PE, Brazil (*) Corresponding author, e-mail: email@example.com
Table 1. Agronomical variables for peanut genotypes grown in sandy soil. Main stem height (MSH), root length (RL), root weight (RW), number of nodules (NN), number of pods (NP) and pod weight (PW) Genotypes MSH RL RW NN NP (cm) (cm) (g) C AS BR C BR 1 13.2 17 1.3ab 60Aa 18Cb 31Bb 7.0ab 3.5Aa BRS Havana 12.9 18 1.3ab 23Bb 15Cb 32Ab 8.9a 3.0Bb L7 Bege 13.3 20 1.5a 63Aa 51Ba 49Ba 9.0a 3.2Bab Mean 13.1 18 1.4 49 28 37 8.6 3.2 CV (%) 12.6 13.8 18.2 26.8 22.9 Genotypes PW (g) AS BR BR 1 3.4Ab 3.5Ab BRS Havana 3.0Bc 3.8Ab L7 Bege 4.2AB 4.8Aa Mean 3.5 4.0 CV (%) 14.7 Means followed by the same letter are not statistically different according to Tukey's test at 5% of probability. Capital letters should be compared between treatments (N-sources) and lowercase letters between genotypes. C: control (no nitrogen), AS: Ammonium sulfate, BR: Bradyrhizobium. Table 2. Agronomic characteristics for peanut genotypes grown in medium textured soil. Main stem height (MSH), root length (RL) and root weight (RW) Genotypes MSH (cm) RL RW (g) C AS BR (cm) C AS BR BR 1 26Aab 29Aab 26Ab 63 5.8B 6.5A 6.0AB BRS Havana 28Ba 34Aa 36Aa 69 5.9B 6.3A 6.4A L 7 Bege 26Bab 34Aa 31Aab 68 5.7B 6.2A 6.5A Mean 27 32 31 67 5.8 6.3 6.3 CV (%) 15.8 11.9 25.1 Means followed by the same letter are not statistically different according to Tukey's test at 5% of probability. Capital letters should be compared between treatments (N-sources) and lowercase letters between genotypes.. C: control (no nitrogen), AS: Ammonium sulfate, BR: Bradyrhizobium Table 3. Agronomic characteristics for peanut genotypes grown in medium textured soil. Number of nodules (NN), number of pods (NP) and pod weight (PW). Genotypes NN NP PW (g) C AS BR C AS BR C AS BR BR 1 180Ac 166Bc 159Bc 24B 32A 34A 10.3B 24.8A 26.8A BRS Havana 215Cb 258Ba 275Aa 22C 29B 33A 10.1C 22.7B 26.6A L 7 Bege 389Aa 229Bb 225Bab 25C 31AB 35A 10.5B 24.7A 27.6A Mean 261 218 220 24 31 34 10.3 24.1 27 CV (%) 23.6 21.3 29.2 Means followed by the same letter are not statistically different according to Tukey's test at 5% of probability. Capital letters should be compared between treatments (N-sources) and lowercase letters between genotypes.C: control (no nitrogen), AS: Ammonium sulfate, BR: Bradyrhizobium Table 4. Estimated Ci/Ca ratio for peanut genotypes grown in medium textured soil experiment. Genotyps C AS BR BR 1 0.64Aa 0.58Bab 0.58Bab BRS Havana 0.61Aa 0.56Bb 0.53BCb L7 Bege 0.63Aa 0.61Aa 0.62Aa Mean 0.63 0.58 0.58 Means followed by the same letter are not statistically different according to Tukey's test at 5% of probability. Capital letters should be compared between treatments (N-sources) and lowercase letters between genotypes. C: control (no nitrogen), AS: Ammonium sulfate, BR: Bradyrhizobium sp. CV = 3.91%
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|Author:||Melo, Emanuelle Barros Sobral de; Lima, Liziane Maria de; Fernandes-Junior, Paulo Ivan; Aidar, Saulo|
|Date:||Apr 1, 2016|
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