Nighttime evaporative demand induces plasticity in leaf and root hydraulic traits

Abstract

Increasing evidence suggests that nocturnal transpiration rate (TR ) is a non-negligible contributor to global water cycles. Short-term variation in nocturnal vapor pressure deficit (VPD ) has been suggested to be a key environmental variable influencing TR . However, the long-term effects of VPD on plant growth and development remain unknown, despite recent evidence documenting long-term effects of daytime VPD on plant anatomy, growth and productivity. Here we hypothesized that plant anatomical and functional traits influencing leaf and root hydraulics could be influenced by long-term exposure to VPD . A total of 23 leaf and root traits were examined on four wheat (Triticum aestivum) genotypes, which were subjected to two long-term (30 day long) growth experiments where daytime VPD and daytime/nighttime temperature regimes were kept identical, with variation only stemming from VPD , imposed at two levels (0.4 and 1.4 kPa). The VPD treatment did not influence phenology, leaf areas, dry weights, number of tillers or their dry weights, consistently with a drought and temperature-independent treatment. In contrast, vein densities, adaxial stomata densities, TR and cuticular TR, were strongly increased following exposure to high VPD . Simultaneously, whole-root system xylem sap exudation and seminal root endodermis thickness were decreased, hypothetically indicating a change in root hydraulic properties. Overall these results suggest that plants 'sense' and adapt to variations in VPD conditions over developmental scales by optimizing both leaf and root hydraulics.

Increased contribution of wheat nocturnal transpiration to daily water use under drought

“…abscisic acid or ABA). This is consistent with the observation that in some plants, stomata are unable to fully close even following ABA treatment (Santamaria et al , Coupel‐Ledru et al ) and that cuticular transpiration is chiefly related to fixed structural properties such as wax deposition or stomata densities (Muchow and Sinclair , Coupel‐Ledru et al , Claverie et al ).…”

“…The second group of 48 replicate plants per genotype was assigned to a second neighboring glasshouse (G2) that was identical to G1 except that it was equipped with an automatic de‐humidification system that allowed for the imposition of a high VPD N environment independently from temperature (1.4 kPa, Table ). This was achieved using an industrial dehumidifier (model 350S, Trotec, Heinsberg, Germany), equipped with a timer so that it operated only during the nighttime period (Claverie et al ). For each genotype, half of the pots were kept WW, while the other half was allowed to undergo progressive soil drying (i.e.…”

“…Two centimeters of the remaining leaf portion were used for vein density (VD) measurements as in Claverie et al (). Adaxial epidermis and palisade mesophyll were removed with a sharp razor and sections were placed in commercial household bleach for 20–30 min (Carins Murphy et al ).…”

“…Recent genetic analyses on wheat and grapevine confirm the potential benefits resulting from a tighter control of TR N in water‐limited environments. On wheat, there is strong evidence for substantial phenotypic variability in TR N (Rawson and Clarke , Schoppach et al ), and variation in TR N has been recently shown to be developmentally and genetically controlled (Claverie et al , Schoppach et al ). In the latter study, TR N was found to be heritable (H2 = 0.73) and controlled by trait‐specific and more numerous quantitative trait loci than found for daytime TR (TR D ), suggesting the possibility to breed independently for genotypes that minimize TR N with limited consequences on daytime gas exchange.…”

“…In order to examine the relationships between TR N responses to progressive soil drying and drought tolerance, we investigated (1) and (2) for two contrasted Australian wheat genotypes (RAC875: drought‐tolerant; and Kukri: drought‐sensitive). Finally, because long‐term variation in VPD N was found to induce phenotypic plasticity in plant shoot and root traits under WW controlled conditions (Claverie et al ), an additional objective was to investigate the long‐term effect of VPD N on 13 root and shoot traits that are related to plant development and hydraulics under the aforementioned conditions. To address these objectives, we developed an experimental protocol that allowed, under greenhouse conditions, to achieve consistently over relatively long periods of time (2 weeks) two temperature‐independent VPD N regimes (low: 0.9 kPa; high: 1.4 kPa) that minimally influenced daytime conditions.…”