Genotype-dependent influence of night-time vapour pressure deficit on night-time transpiration and daytime gas exchange in wheat.

In crop plants, accumulating evidence indicates non-marginal night-time transpiration (TRNight) that is responsive to environmental conditions, especially in semiarid areas. However, the agronomical advantages resulting from such phenomenon remain obscure. Recently, drought-tolerance strategies directly stemming from daytime TR (TRDay) responses to daytime vapour pressure deficit VPD (VPDDay) were identified in wheat (Triticum spp.), but the existence of similar strategies resulting from TRNight response to night-time VPD (VPDNight) remains to be investigated, especially that preliminary evidence on this species indicates that TRNight might be responsive to VPDNight. Our study aims at investigating such strategies among a group of diverse lines including drought-tolerant genotypes. The study revealed that: (i) TRNight can be as high as 55% that of the maximal TRDay; (ii) VPDNight is the major driver of TRNight in a genotype-dependent fashion and has an impact on following daytime gas exchange; and (iii) a strong correlation exists between TR sensitivities to VPD under night-time and daytime conditions, revealing that tolerance strategies such as conservative water use do also exist under night-time environments. Overall, this report opens the way to further phenotyping and modelling work aiming at assessing the potential of using TRNight as a trait in breeding new drought-tolerant germplasm.