Magnesium supplementation alleviates drought damage during vegetative stage of soybean plants

Abstract

Our working hypothesis was that magnesium (Mg) supplementation modulates plant performance under low water availability and improves drought tolerance in soybean genotypes. Plants of Bônus 8579, M8808 and TMG1180 genotypes were grown under field conditions and subjected to three water stress treatments (control, moderate and severe stress) and three Mg levels [0.9 (low), 1.3 (adequate) and 1.7 cmolc dm-³ (supplementation)]. After 28 days of drought imposition, the growth parameters, osmotic potential, relative water content, leaf succulence, Mg content and photosynthetic pigments were assessed. In general, drought drastically decreased the growth in all genotypes, and the reductions were intensified from moderate to severe stress. Under adequate Mg supply, TMG1180 was the most drought-tolerant genotype among the soybean plants, but Mg supplementation did not improve its tolerance. Conversely, although the M8808 genotype displayed inexpressive responses to drought under adequate Mg, the Mg-supplemented plants were found to have surprisingly better growth performance under stress compared to Bônus 8579 and TMG1180, irrespective of drought regime. The improved growth of high Mg-treated M8808-stressed plants correlated with low osmotic potential and increased relative water content, as well as shoot Mg accumulation, resulting in increased photosynthetic pigments and culminating in the highest drought tolerance. The results clearly indicate that Mg supplementation is a potential tool for alleviating water stress in M8808 soybean plants. Our findings suggest that the enhanced Mg-induced plant acclimation resulted from increased water content in plant tissues and strategic regulation of Mg content and photosynthetic pigments.

Fig 1. Results of drought treatments comparison within Mg levels and soybean genotypes.

Clustering analysis of growth and physiological and biochemical indexes relative to changes due to drought treatments in Bônus 8579 (a), M8808 IPRO (b) and TMG 1180 (c) soybean genotypes. The assays were performed in plants 28 days after grown under adequate (Mg) and (High Mg) supplementation magnesium regimes, and subjected to three drought treatments (control, moderate drought—MD and severe drought—SD). Each row represents an individual assay. In all cases, blue color indicates an increase, and red indicates a decrease in the analyzed indexes, taking control plants as reference. Gray indicates no change. Number inside the box and different red and blue intensities express the extent of the change according to fold increase/decrease related to reference. For absolute values and statistical details, see Tables 1–3.

Fig 2. Results of Mg treatments comparison within drought levels and soybean genotypes.

Clustering analysis of growth and physiological and biochemical indexes relative to changes due magnesium (Mg) treatments in Bônus 8579 (a), M8808 IPRO (b) and TMG 1180 (c) soybean genotypes. The analyzes were carried out in plants after 28 days grown well irrigated (control) and subjected to moderate and severe drought. Each row represents an individual assay. For all cases, the color intensity refers to changes due to Mg supplementation within the soybean genotype and drought treatment. Blue color indicates an increase, and red indicates a decrease in analyzed indexes, taking data from the Mg-grown plants as reference. Number inside the box and different red and blue intensities express the extent of the change according to fold increase/decrease related to reference. For absolute values and statistical details, see Tables 1–3.

Fig 3. Results of soybean genotypes comparison within Mg and drought treatments.

Clustering analysis of growth and physiological and biochemical indexes relative to changes due to soybean genotypes. The data were analyzed in plants grown well irrigated (control, a) and under moderate (b) and severe (c) drought, in different magnesium regimes (adequate and supplementation Mg). Each row represents an individual assay. For all cases, the color intensity refers to changes due to the soybean genotype (Bônus 8579, M8808 IPRO and TMG 1180) within the Mg dose and drought treatment. Blue color indicates an increase, and red indicates a decrease in analyzed indexes, taking data from the Bônus 8579 genotype as reference plants. Number inside the box and different red and blue intensities express the extent of the change according to fold increase/decrease related to reference. For absolute values and statistical details, see Tables 1–3.

Fig 4. Principal component analysis (PCA).

Scatter plots of the studied variables for Bônus 8579, M8808 IPRO and TMG 1180 soybean genotypes subjected to drought and Mg supply treatments. The percent variance for each PC is specified on axes X and Y. PCA shows the loading plot of variables: plant height (PH), stem diameter (SD), number of leaves (NL), leaf area (LA), shoot fresh mass (SFM), shoot dry mass (SDM), relative tolerance to drought (tolerance), osmotic potential (Ψs), relative water content (RWC), leaf succulence (LS), chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll total (Chl total), carotenoids (Car), Chl a/Chl b ratio and Car/Chl total ratio.