Code for this notebook is here.

Model setup

The P-hydro model (Joshi et al., 2022) is used here to illustrate the effect of acclimating P50 (leaf water potential at 50% loss of conductivity) and K (whole plant conductivity) on the response of stomatal conductance and transpiration to VPD and soil moisture.

# other environmental factors held constant
kphio = 0.087;       # quantum yield efficiency
ppfd = 300;          # umol/m2/s
vpd  = 1000;         # Pa
co2  = 400;          # ppm
elv  = 0;            # m.a.s.l.
fapar = 0.7;         # fraction
rdark = 0.015;
tc = 25;
vwind = 3;
netrad = ppfd/2

# cost parameters for the optimality model (not directly observable)
par_cost = list(alpha = 0.1, gamma = 1)

# model options
options = list(gs_method = "GS_IGF", 
               et_method = "ET_DIFFUSION",
               ftemp_vj_method = "FV_kumarathunge19",
               ftemp_rd_method = "FR_heskel16",
               ftemp_br_method = "FB_atkin15",
               scale_alpha = FALSE
               )

# long-term average VPD to which Vcmax25 and Jmax25 are acclimated
vpd_acc = 100

Reference simulation

With P50 and K at reference values, calculate stomatal conductance and transpiration in response to VPD at two different soil moisture levels (-0.1 kPa and -3 kPa).

par_plant_no_acclim = list(conductivity = 3e-17, 
                           psi50 = -2, 
                           b = 2)

(Code to run model not shown.)

Acclimated hydraulic traits

Assume that the acclimation of hydraulic traits to sustained hydraulic stress leads to a more negative P50 and a lower conductivity.

par_plant_acclim = list(conductivity = 1.2e-17, 
                        psi50 = -4, 
                        b = 2)

(Code to run model not shown.)

Plot

## Warning: Using `size` aesthetic for lines was deprecated in ggplot2 3.4.0.
## ℹ Please use `linewidth` instead.
## This warning is displayed once every 8 hours.
## Call `lifecycle::last_lifecycle_warnings()` to see where this warning was
## generated.