Pressure-volume curves
Pressure-volume curves were undertaken to determine the degree of osmotic adjustment in response to long term drought prior to drought and in leaves collected from the same plants that had experienced long-term drought sufficient to reduce ABA levels to initial levels measured prior to the drought (Tyree & Hammel, 1972). Five individual leaves or leafy shoots from the same individual were collected and rehydrated overnight to a hydrated state (full hydration was considered when initial Ψl was greater than -0.05 MPa). Tissue was scanned to obtain hydrated area then leaves or shoots were dehydrated on the bench, and measurements of weight and water potential were periodically recorded as water potential progressively declined (Tyree & Hammel, 1972). Ψtlp was calculated from the P-V curves as the Ψl at which the relationship between the inverse of relative water content and Ψl deviates from a linear regression.
Data analysis
Generalized additive models and standard errors were fitted for ABA level, PA level, and gs using the gam() function in the MGCV package (Wood, 2011) of R software (v.4.0.5, R Core Team, 2018). ANOVA was perfomed for all comparisons using the aov() function, and significant interactions were determined using the TukeysHSD() funtion of the multcomp package (Hothorn et al. , 2008) in R software. Correlation analysis for ABA and PA levels was performed using the cor.test() funtion in R software. Graphs were generated using the Sigmaplot software (v.10, Systat Software, Chicago, IL, USA).