Drought response behavior of risk-taking and conserving spring barley cultivars

Breeding drought resilient crops requires understanding the mechanisms underlying plant physiological responses to different drought patterns and how these vary within species.Two main plant water use strategies are distinguished in the literature, referred to as “risk – taking” (anisohydric) and “conserving” (isohydric). Under well-watered conditions, risk takers exhibit a higher transpiration rate (TR) associated with a greater CO₂ assimilation rate, and hence, greater dry matter production than conserving plants which have a tighter stomatal control. Depending on the root traits the transpiration-limiting soil moisture level (θ_crit) can differ between plants with similar shoot traits. A high θ_crit (e.g. due to shallow roots) entails early stomata closure. This study aimed at examining the drought response of four high-yielding European spring barley cultivars considered to exhibit different response behavior.

We collected detailed plant physiological data with a high- throughput functional phenotyping platform (Plantarray®, Plant-Ditech) and analyzed final yield parameters. Around flowering cv. Chanelle (CHAN), RGT Planet (RGT), Formula (FORM), and Baroness (BAR) were exposed to 12 days of drought. Based on higher TR, higher biomass and grain yield under well-watered conditions and the faster TR reduction below θ_crit ,CHAN ranked as very risk taking and RGT as risk taking in contrast to conserving FORM and very conserving BAR.

Drought effects on final yield are closely linked to the plants recovery potential, i.e. the ability to increase TR to control plant levels upon re-irrigation. The highest yielding cultivar under ample water supply, CHAN, showed a significantly impaired recovery potential and suffered notable yield penalties under drought (24%). The very conserving response behavior of BAR resulted in good recovery, minimal yield loss (-2% yield) and a final grain yield that was almost similar to very risk taking CHAN (Δ 5g/pot). FORM produced the lowest yields under control and stress conditions yet suffered no drought induced yield penalties, probably due to a better adapted root system. The lower θ_crit of FORM delayed stomata closure and the breakdown of assimilation. FORM and RGT had similar recovery rates.

RGT produced the second highest yield under well-watered conditions and drought did not cause any yield losses. Under ample water supply, RGT behaved like a risk taker, whereby the high TR allowed it to be more productive than the conserving cultivars. RGT switched to a more conserving behavior under drought where it only gradually (same slope as FORM) decreased TR below θ_crit and was thereby more productive than very risk taking CHAN. This rather dynamic water use behavior made RGT the best performing cultivar in the here examined drought scenario.

A higher number of seeds per spike (along with reduced kernel size) likely contributed to the yield stability observed under drought in FORM and RGT the exact physiological mechanisms of which still require more investigation. Prospective studies will examine different drought patterns and durations and implement the gained knowledge into crop simulation models for upscaling.

 

Keywords: water-response behavior, isohydric; anisohydric; spring barley, drought