Work

Vapor pressure deficit normalizes diurnal photochemical reflectance index for repeatable drought phenotyping of Prunus rootstocks in Mediterranean climates

Year: 2026

Type: article

Abstract: Breeding programs need field-ready traits to compare rootstock drought performance under fluctuating atmospheric demand, particularly in Mediterranean climates where vapor pressure deficit (VPD) can increase abruptly during the day and confound midday “snapshot” screening. We present a VPD-based method to normalize and decompose diurnal dynamics of the photochemical reflectance index (PRI) into repeatable components. Six Prunus rootstocks genotypes were grown under well-watered (WW) and water-deficit (WD; 40% of field capacity) conditions. Leaf PRI was measured hourly (10:00–18:00) on three days spanning VPDmax ≈ 4.9–3.3 kPa, while midday gas exchange and leaf water potential were measured on two days. PRI relationships with incident radiation were weak and variable across genotypes and dates, whereas PRI–VPD trajectories were structured and consistently separated WW and WD conditions. For each genotype, date, and water-regime, PRI–VPD regressions were fitted and decomposed into (i) basal PRI at a common reference VPD (VPDref = 2.0 kPa), (ii) the diurnal PRI–VPD slope, and (iii) WW–WD separation at VPDref. Basal PRI and WW–WD separation produced stable genotype rankings across days (Spearman ρ ≈ 0.8–0.9). Across genotypes, water-deficit–induced changes in PRI (WD relative to WW) tracked changes in stomatal conductance (gs) and transpiration (E). This VPD-normalized decomposition provides a scalable optical trait to quantify diurnal stress signatures for drought phenotyping in Mediterranean environments.

Source: Frontiers in Plant Science

DOI: 10.3389/fpls.2026.1878667