Abstract
Drought is one of the major abiotic stresses affecting the morphological, physiological, and metabolic processes of plants, and hence their growth and production on a global scale. Lucerne (Medicago sativa L.) is one of the most popular pasture species in semi-arid regions and plays a critical role in sustaining agricultural systems in many areas of the world. In order to evaluate the effect of water deficits on the growth and biomass distribution in different tissues of lucerne, plant height, leaf dry weight, leaf number and area, root dry weight, taproot length and lateral root number, and stem dry weight were measured at four stages from the seedling to flowering stages under three water regimes: (i) adequate water supply (minimum soil water content 85% pot capacity (PC)), (ii) moderate water stress (65% PC), and (iii) severe water stress (45% PC), imposed under a rainout shelter. With limited water supply, plant height, leaf number, leaf area and dry weight, taproot length, and total biomass were reduced, while lateral root numbers increased. The number of smaller leaves and root dry weight increased under moderate water stress, whereas severe water stress reduced them. Leaf, stem, and total dry weight were all reduced by the water deficits, but leaf dry weight was reduced the most and root dry weight the least, so there was a redistribution of biomass towards the roots, increasing the root–shoot ratio. These results help us to understand the response of lucerce to water stress and assist in developing a foundation for the sustainable use of lucerne in semi-arid agricultural systems.
Highlights
Drought stress is one of the most important abiotic stresses on a global scale, causing major crop losses [1]
Height growth was not linear over this period, but plants grew at 7.8 ± 2.1 mm day−1 between seedling and branching, 6.9 ± 0.9 mm day−1 between branching and squaring, and 5.9 ± 0.5 mm day−1 between squaring and flowering
Water deficits are well known to reduce the growth of most crops and pastures [3,8,10,25,26]
Summary
Drought stress is one of the most important abiotic stresses on a global scale, causing major crop losses [1]. The tolerance of plants to drought stress is a complex phenomenon that involves specific morphological, physiological, biochemical, and metabolic adaptations that affect plant growth, development, and survival [3,4,5,6]. Plants respond to water deficits by strategies including drought escape, drought avoidance, and drought tolerance [7,8], but the adjustment of phenology to escape or avoid severe water shortage and the metering of water use to provide sufficient resources for the reproductive phase predominate in grain crops [9]. For perennial pasture species such as lucerne, the ability to use available water to maximize aboveground biomass, and survival of drought episodes, are more important than conserving water for the reproductive phase [10]. Nasreddine et al [11] reported that the growth patterns of different plant organs are affected
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