Silicon application induces changes C:N:P stoichiometry and enhances stoichiometric homeostasis of sorghum and sunflower plants under salt stress.

Beneficial effects of silicon (Si) on growth have been observed in some plant species, reportedly due to stoichiometric changes of C, N, and P. However, little is known about the effects on the stoichiometric relationships between C, N, and P when silicon is supplied via different modes in sorghum and sunflower plants under salt stress conditions. Therefore, the current study was performed to investigate the impact of differing modes of Si supply on shoot biomass production and C:N:P stoichiometry in sorghum and sunflower plants under salt stress. Two experiments were performed in a glass greenhouse using the strong Si-accumulator plant sorghum, as well as the intermediate type Si-accumulator sunflower, both of which were grown in pots filled with washed sand. Plant species were cultivated for 30 days in the absence or presence of salt stress (0 or 100 mM) and supplemented with one of four Si treatments: control plants (without Si), 28.6 mmol Si L-1 via foliar application, 2.0 mmol Si L-1 via nutrient solution, and combined application of foliar and nutrient solution, each group with five replications. The results revealed that supplied Si modified the C, N, and P concentrations, thereby enhancing the C:N:P stoichiometry and shoot dry matter of sorghum and sunflower plants under salt stress. Both application of Si via nutrient solution, as well as combined application via foliar and nutrient solution, increased the C:N ratio in both plant species under salt stress, but in sorghum plants decreased the C:P and N:P ratios and increased the shoot biomass production by 39%, while in sunflower plants increased the C:P and N:P ratios and increased the shoot biomass production by 24%. Our findings suggest that salt stress alleviation by Si impacts C:N:P stoichiometric relationships in a variable manner depending on the ability of the species to accumulate Si, as well as the route of Si administration.

Different methods of silicon application attenuate salt stress in sorghum and sunflower by modifying the antioxidative defense mechanism.

Soil salinization is the most common abiotic stress limiting agricultural productivity worldwide. Recent research has suggested that the application of silicon (Si) has beneficial effects against salt stress in sorghum (Sorghum bicolor L. Moench) and sunflower (Helianthus annuus L.) by regulating the antioxidant system, mineral nutrients, and other important mechanisms. However, whether these effects can be achieved through foliar application of Si, or whether Si application affects Si-accumulating (e.g., sorghum), and intermediate-Si-accumulating (e.g., sunflower) plant species differently, remains unclear. This study investigated different methods of Si application in attenuating the detrimental effects of salt stress, based on the biological responses of two distinct species of Si accumulators, under greenhouse conditions. Two pot experiments were designed as a factorial (2 × 4), randomized complete blocks design (RCBD) with control and salt-stress groups (0 and 100 mmol.L-1 NaCl), and four Si-treatment groups: control (no Si), foliar application (28.6 mmol.L-1), root application (2 mmol.L-1), and combined foliar and root applications. Our results showed that the harmful effects of salt stress were attenuated by Si treatments in both plant species, which decreased Na+ uptake and lipid peroxidation, and increased Si and K+ uptake, relative leaf water content, antioxidant enzyme activities, leaf area, and shoot dry matter. These results were more prominent when Si was applied via nutrient solution in the sorghum plants, and the combined foliar and root applications of Si in sunflower plants. In addition, foliar application of Si alone is an efficient alternative in attenuating the effects of salinity in both plant species when Si is not available in the growth medium. These results suggest that the Si application method plays an important role in Na+ detoxification by modifying the antioxidative defense mechanism, which could actively mediate some important physiological and biochemical processes and helps to increase the shoot dry matter production in sorghum and sunflower plants under salt stress.

Resposta da alface à aplicação de biofertilizante sob dois níveis de irrigação / Response of the lettuce to the application of biofertilizer under two levels of irrigation

A utilização de biofertilizantes é interessante para a agricultura, pois além de ser uma alternativa econômica e ambiental favorável, aproveita resíduos orgânicos e reduz a aplicação de fertilizantes minerais. Objetivou-se com este trabalho, avaliar o efeito de doses de biofertilizante de origem bovina (efluente de biodigestor) aplicadas no solo e de dois níveis de irrigação na cultura da alface. O experimento foi conduzido em ambiente protegido, em vasos, aplicando-se ao solo diferentes doses de biofertilizante de origem bovina obtido de reator anaeróbio (10, 20, 40 e 60 m3 ha1 ) e adubação mineral como testemunha em dois níveis de irrigação calculados com base em 50 e 100% de evapotranspiração de referência. As plantas de alface foram analisadas em: altura, número de folhas, diâmetro de copa, massa de matéria fresca e massa de matéria seca da parte aérea. Os tratamentos com biofertilizante apresentam melhores resultados que a adubação mineral, e tem aumento com a elevação das doses de biofertilizante; a maior dose (60 m3 ha-1) apresentou os melhores resultados em todas as variáveis analisadas. Para a massa seca, a adubação mineral apresentou maiores valores. Os níveis de irrigação não influenciaram no crescimento das plantas.

The use of biofertilizers is interesting for agriculture as being an economical alternative as well as it is environmentally friendly by using organic waste and reducing the application of mineral fertilizers. The aim of this study was to evaluate the effect of biofertilizer doses of bovine origin (biodigester effluent) applied on the ground and two levels of irrigation on lettuce. The experiment was conducted under protection of a greenhouse in pots, applying to the soil different doses of biofertilizer of bovine origin obtained from anaerobic reactor (10, 20, 40 and 60 m3 ha-1) and mineral fertilizer as a witness in two irrigation levels calculated at 50 and 100% of reference evapotranspiration. The lettuce plants were analyzed in their: height, leaves number, crown diameter, fresh weight and dry weight of shoots. The biofertilizer treatments showed better results than the mineral fertilizer and has increased with increasing doses of biofertilizer, the highest dose (60 m3 ha-1) showed the best results in all variables. For dry, mineral fertilization showed higher values. The irrigation levels had no effect on plant growth.