Abstract
BackgroundAlfalfa is a high-quality forage cultivated widely in northern China. Recently, the failure of alfalfa plants to survive the winter has caused substantial economic losses. Water management has attracted considerable attention as a method for the potential improvement of winter survival. The aim of this study was to determine whether and how changes in the water regime affect the freezing tolerance of alfalfa.ResultsThe alfalfa variety WL353LH was cultivated under water regimes of 80 and 25% of water-holding capacity, and all the plants were subjected to low temperatures at 4/0 °C (light/dark) and then − 2/− 6 °C (light/dark). The semi-lethal temperatures were lower for water-stressed than well-watered alfalfa. The pool sizes of total soluble sugars, total amino acids, and proline changed substantially under water-deficit and low-temperature conditions. Metabolomics analyses revealed 72 subclasses of differential metabolites, among which lipid and lipid-like molecules (e.g., fatty acids, unsaturated fatty acids, and glycerophospholipids) and amino acids, peptides, and analogues (e.g., proline betaine) were upregulated under water-deficit conditions. Some carbohydrates (e.g., D-maltose and raffinose) and flavonoids were also upregulated at low temperatures. Finally, Kyoto Encyclopedia of Genes and Genomes analyses revealed 18 significantly enriched pathways involved in the biosynthesis and metabolism of carbohydrates, unsaturated fatty acids, amino acids, and glycerophospholipids.ConclusionsWater deficit significantly enhanced the alfalfa’ freezing tolerance, and this was correlated with increased soluble sugar, amino acid, and lipid and lipid-like molecule contents. These substances are involved in osmotic regulation, cryoprotection, and the synthesis, fluidity, and stability of the cellular membrane. Our study provides a reference for improving alfalfa’ winter survival through water management.
Highlights
Alfalfa is a high-quality forage cultivated widely in northern China
In phase 2, the remaining 36 pipes were divided into two groups, the moisture content in the mixed soil of one group was controlled to 25% water-holding capacity (WD) and that of the other group was maintained at 80% water-holding capacity (WW)
Dry weights of aboveground and belowground parts To evaluate the effects of alfalfa growth on its freezing tolerance, the dry weights of aboveground and belowground parts were determined (Fig. 2)
Summary
Alfalfa is a high-quality forage cultivated widely in northern China. The failure of alfalfa plants to survive the winter has caused substantial economic losses. Alfalfa (Medicago sativa L.) is a high-quality forage that is widely cultivated in northern China where there is little snow but severe cold in winter. The extreme cold has caused the failure of alfalfa to survive the winter, which is an obstacle to its regeneration and production and leads to serious economic losses. Alfalfa accumulates compatible soluble sugars and low-molecularweight nitrogenous compounds in response to freezing, and there are changes in the cell membrane composition [4, 5] that contribute to improved freezing tolerance [6].
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