Morphological and physiological adaptations underpin drought resilience in contrasting populations of annual ryegrass (Lolium rigidum)

This study investigated the biological responses of its two contrasting populations under five moisture regimes ranging from 100% to 12.5% of soil water holding capacity (WHC) in a glasshouse. Moderate moisture limitation (50–75% WHC) enhanced vegetative growth, particularly in the resistant population, where leaf number and tillering increased by up to 132% and 153%, respectively, compared with saturated conditions (100% WHC).

Severe drought (12.5–25% WHC) reduced plant height by 35–38% and caused up to 64% and 90% reductions in shoot and root fresh weights, respectively. Root length increased by 20% under moderate moisture limitation but declined under severe stress. The resistant population exhibited greater phenological plasticity, reflected by stronger shifts in flowering timing under moisture stress (35% earlier), and maintained higher (6%) relative water content than the susceptible population.