Intraspecific Variation for Leaf Physiological and Root Morphological Adaptation to Drought Stress in Alfalfa (Medicago sativa L.)

Abstract

Drought stress reduces crop biomass yield and the profitability of rainfed agricultural systems. Evaluation of populations or accessions adapted to diverse geographical and agro-climatic environments sheds light on beneficial plant responses to enhance and optimize yield in resource-limited environments. This study used the morphological and physiological characteristics of leaves and roots from two different alfalfa subspecies during progressive drought stress imposed on controlled and field conditions. Two different soils (Experiments 1 and 2) imposed water stress at different stress intensities and crop stages in the controlled environment. Algorithm-based image analysis of leaves and root systems revealed key morphological and physiological traits associated with biomass yield under stress. The Medicago sativa subspecies (ssp.) sativa population, PI478573, had smaller leaves and maintained higher chlorophyll content (CC), leaf water potential, and osmotic potential under water stress. In contrast, M. sativa ssp. varia, PI502521, had larger leaves, a robust root system, and more biomass yield. In the field study, an unmanned aerial vehicle survey revealed PI502521 to have a higher normalized difference vegetation index (vegetation cover and plant health characteristics) throughout the cropping season, whereas PI478573 values were low during the hot summer and yielded low biomass in both irrigated and rainfed treatments. RhizoVision Explorer image analysis of excavated roots revealed a smaller diameter and a narrow root angle as target traits to increase alfalfa biomass yield irrespective of water availability. Root architectural traits such as network area, solidity, volume, surface area, and maximum radius exhibited significant variation at the genotype level only under limited water availability. Different drought-adaptive strategies identified across subspecies populations will benefit the plant under varying levels of water limitation and facilitate the development of alfalfa cultivars suitable across a broad range of growing conditions. The alleles from both subspecies will enable the development of drought-tolerant alfalfa with enhanced productivity under limited water availability.

Effects of drought stress on water content and biomass distribution in summer maize(Zea mays L.)

“…Although the WCDR of root was the lowest among all component organs, it was higher than the CS at the same period under drought, while the WCDR of the fruit was lower than that of the CS at the same period. This also shows that, under drought, more water would be allocated to the root to improve the water absorption capacity, so as to provide enough water for the component organs above the ground, which is related to the physiological function of the root (Prince et al, 2022;Sandar et al, 2022). The summer maize fruit is the reproductive organ, and its physiological activity is the most vigorous component organ at this stage.…”

“…Crops adapt to drought through a series of physiological, morphological, and biochemical processes (Mahdid et al, 2011;Huseynova et al, 2016;Mubeen et al, 2021;Prince et al, 2022). Water is not only an important component of crops but also the raw material and medium of most life activities (Wei et al, 2016;David et al, 2018;Yang et al, 2022).…”

Root system architecture and anatomical traits variability of alfalfa at the seeding stage

“…Under drought stress, maize increased its rooting depth to enhance the absorption of water from deep soil to improve yield (Zhan et al 2015). Higher volume, width and number of roots were the key traits for alfalfa to uptake water e ciently under water limited condition (Prince et al 2022). Two alfalfa genotypes Arkaxiya and Longzhong showed increased speci c root length in response to P de ciency (Fan et al 2015).…”

“…Due to the opacity and complexity of root growth environment, the progress of root research is much slower than that of the aboveground traits. Few studies on roots morphology of alfalfa mainly used static and destructive sampling methods, which cannot achieve the observation of root dynamic growth and complete root system (He et al 2017;Prince et al 2022;Su et al 2022).…”

Adaptive pathway of summer maize under drought stress: Transformation of root morphology and water absorption law

“…Crop adaptability refers to its own survival ability to regrow in the changing environment. From the perspective of crop adaptation, many scholars analyze the adaptive changes of crops under drought stress from the morphology (Qi et al, 2012;Prince et al, 2022), physiology and biochemistry of crops (Annicchiarico et al, 2012;Hasanuzzaman et al, 2019). In drought stress, crops preferentially provide limited water to the root system, which is an important organ for crops to supplement nutrients and absorb water (Liu et al, 2021).…”