Growth responses of spring barley to varying levels of drought priming

Drought-associated environmental changes pose a significant threat to global agricultural sustainability. While barley's response to single drought events is well-documented, its adaptations to recurrent drought-rehydration cycles during the vegetative stages remain unexplored.

Barely plants were subjected to five glasshouse watering regimes and harvested at six sampling times (S1-S6): full irrigation (FI, 85% soil water-holding capacity, SWHC), and four drought treatments varying in severity (mild 65% vs. severe 45% SWHC) and pattern (intermittent ID1/ID2 with rehydration vs. persistent PD1/PD2 without).

Persistent drought (PD1, PD2) consistently reduced interval-specific water-use efficiency (WUEn) across all stages, while intermittent drought (ID2) enhanced WUEn during tillering. Stomatal conductance (g_s ) was lowest in PD treatments, with PD1 exhibiting minimum values at seedling (S1) and jointing (S5), indicating severe transpiration limitation. ID2 maintained higher g_s than ID1 during seedling and tillering stages (S2, S3). However, cumulative severe stress ultimately impaired stomatal regulation in ID2, leading to ID1's superiority by the jointing stage (S5-S6). Multivariate analysis identified stress severity as the primary initial driver of physiological disruption, revealing a fundamental shift to a biochemical stress-acclimation strategy in later stages.

The findings delineate a dynamic recovery response under intermittent drought from a conservative, high-cost strategy under persistent drought. They suggest that applying more severe cyclic drought early (ID2, S1-S4) followed by milder cyclic stress later (ID1, S5-S6) optimizes stomatal function and productivity, enhancing resource-use efficiency under water limitation.