Xueying Zhao

Fodder soybean (Glycine max L.) with high protein and yield is a popular forage grass in northeast China. Seasonal drought inhibits its growth and development during seedling stage. The objective of this study was to observe morpho-physiological changes in fodder soybean seedlings under melatonin (MT) treatments and identify appropriate concentration to alleviate the drought damage. Two varieties commonly used in northeast China were treated with 0, 50, 100, and 150 μM melatonin at soil water content of 30%. The results indicated that applying melatonin enhanced height, biomass and altered root morphology of fodder soybean seedlings under water-deficient conditions. The treatments with melatonin at different concentrations significantly reduced the contents of H₂O₂, O₂⁻ and MDA, while boosting the capacity of the antioxidant defense system and the content of osmotic adjustment substances. Meanwhile, increases in light energy capture and transmission efficiency were observed. Furthermore, treatment with melatonin regulated the expression levels of genes associated with photosynthesis and the antioxidant defense system. Notably, 100 μM melatonin treatment produced the most favorable effect in all treatments under drought conditions. These research results provide new information for enhancing the drought tolerance of fodder soybean using chemical measures.

The fodder soybean (Glycine max) is an excellent leguminous forage with a high protein content and hay yield, cultivated comprehensively in alpine regions, but seasonal drought in northern regions severely impacts the growth of seedlings. Melatonin (MT) and strigolactone (SL) are critical in relieving the restraint of plant growth in water-deficient environments, but the mechanisms of MT- and SL-mediated drought resistance in fodder soybean needs to be explored. This study mainly investigated the potential morphophysiological mechanism of MT and SL treatments in protecting fodder soybean from drought stress. The fodder soybean ‘Gongnong 535’ was treated with 100 µM MT or 1 µM SL under normal, moderate, and severe water deficit conditions. The results showed that MT and SL treatments enhanced the plant growth parameters and stomatal aperture under drought stress. Moreover, the observed reductions in superoxide ion (O₂^.-), malondialdehyde (MDA), and relative electrical conductivity (REC), along with enhancements in the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as higher levels of ascorbate (AsA), glutathione (GSH), soluble sugar (SS), soluble protein (SP), and free proline (Pro), indicated that MT and SL application effectively alleviated the oxidative damage and prevented the cell membrane disruption caused by drought stress. Additionally, MT and SL treatments improved photosynthesis and growth in fodder soybean seedlings under water stress by adjusting chlorophyll pigments, gas exchange indexes, and chlorophyll fluorescence parameters, as well as endogenous hormone levels. Simultaneously, MT and SL influenced the expression of genes associated with photosynthesis and antioxidant defenses, as well as phytohormone concentrations. Notably, the protective effect of the SL treatment was superior to that of MT in water-deficient conditions. This study contributes to further understanding the defensive mechanism of MT and SL against drought stress.

White clover (Trifolium repens L.) is one of the legume herbages with high feed quality, but it is sensitive to water deficiency. The objectives of this study were to compare morpho-physiological responses to drought stress and post-drought recovery in four-leafed white clover cultivars. Under well-watered conditions, drought stress (3 d, 6 d, 9 d and 12 d), and rehydration, the relative water content (RWC), membrane lipid permeability, osmoregulatory substances, photosynthetic characteristics and stomatal features of Chinese native Longping No.1 (LP, small-leafed) and three introduced cultivars, namely Pudi (PD, small-leafed), Rivendel (RD, medium-leafed) and Koala (KL, large-leafed), were evaluated. Results showed that small-leafed white clover maintained higher RWC and better membrane stability and osmotic regulation with increased drought intensities, compared to the medium-leafed and large-leafed cultivars. Following rewatering, small-leafed white clover recovered more rapidly with all of the parameters than the other cultivars. The increase of drought stress intensity led to the decline of net photosynthetic rate (Pn), transpiration rate (Tr) and stomatal conductance (Cs). However, the decreased range of Pn, Tr and Cs in the small-leafed white clover was significantly smaller than that in the medium-leafed and large-leafed white clovers. Meanwhile, the small-leafed white clover showed a smaller size and higher density of stoma either under normal or drought conditions than the intermediate- and large-leafed cultivars. Taken together, the results indicated that the adaptability of small-leafed white clover to drought stresses and post-drought recovery was better than that of medium-leafed and large-leafed white clovers. The study will provide better insights into the mechanism of drought response and recovery potential in different white clover cultivars.

Understanding the differences in cool-season turfgrass responses to shade is critical for future turfgrass management and breeding for improved shade tolerance. The purpose of this study was to evaluate the shade-tolerance mechanisms of two cool-season turfgrass species in terms of turf performance, growth, and physiological characteristics. Two turfgrass species, namely, ’SupraNova’ (Poa. supina Schrad.) and ‘Lark’ (Lolium perenne L.), were subjected to 0 (CK, unshaded), 35% (LS), 70% (MS), and 92% (HS) shade, respectively. Compared with ‘Lark’, ‘SupraNova’ showed better turf quality (TQ) and turf color intensity (TCI) under shade. The total length and surface area of the roots of ‘Lark’ gradually decreased as the shade increased, while those of ‘SupraNova’ increased and then decreased with increasing shade. The chlorophyll fluorescence photochemical quenching coefficient (qP), electron transport rate (ETR), and maximum quantum yield of primary photosystem II (PSII) photochemistry (Fv/Fm) decreased significantly under HS; however, these decreases were more significant in ‘Lark’ than in ‘SupraNova’. The leaf reflectance of the two turfgrasses under shade was lower than that under CK, but the leaf reflectance of ‘Lark’ was higher than that of ‘SupraNova’ in the visible light band. The normalized difference vegetation index (NDVI) of the two grasses first decreased and then increased. The NDVI of ‘Lark’ under shade was slightly higher than that under CK. ‘SupraNova’ showed strong tolerance on the basis of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), superoxide anion (O₂·⁻), and ascorbic acid (AsA) contents and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity. The MDA, H₂O₂, O₂·⁻, and AsA contents and SOD, POD, and CAT activity (which represent indicators) changed the most under MS. Taken together, the results indicated that the adaptability of ‘SupraNova’ to shade was better than that of ‘Lark’.