Acclimating response to VPD
Beni Stocker and Jaideep Joshi
2023-09-11
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 = 100Reference 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)
acc2 = rphydro_analytical(tc,
tc,
ppfd,
netrad,
vpd_acc,
co2,
elv,
fapar,
kphio,
0,
rdark,
vwind,
par_plant_no_acclim,
par_cost,
options)
dat2 = list(vpd = exp(seq(log(100), log(5000), length.out = 100 )),
psi_soil = c(-0.1, -3)) %>%
expand.grid() %>%
mutate(dat = purrr::map2(.x = psi_soil,
.y = vpd,
.f = ~rphydro_instantaneous_analytical(acc2$vcmax25,
acc2$jmax25,
tc,
tc,
ppfd,
netrad,
.y,
co2,
elv,
fapar,
kphio,
.x,
rdark,
vwind,
par_plant_no_acclim,
par_cost,
options))) %>%
unnest_wider(dat)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 = 2e-17,
psi50 = -4,
b = 2)
acc1 = rphydro_analytical(tc,
tc,
ppfd,
netrad,
vpd_acc,
co2,
elv,
fapar,
kphio,
0,
rdark,
vwind,
par_plant_acclim,
par_cost,
options
)
dat1 = list(vpd = exp(seq(log(100), log(5000), length.out = 100)),
psi_soil = c(-0.1, -3)) %>%
expand.grid() %>%
mutate(dat = purrr::map2(.x = psi_soil,
.y = vpd,
.f = ~rphydro_instantaneous_analytical(acc1$vcmax25,
acc1$jmax25,
tc,
tc,
ppfd,
netrad,
.y,
co2,
elv,
fapar,
kphio,
.x,
rdark,
vwind,
par_plant_acclim,
par_cost,
options))) %>%
unnest_wider(dat)Plot
tmp <- dat1 %>%
select(vpd, psi_soil, gs, e, a) %>%
mutate(type = "With acclimation") %>%
rbind(dat2 %>%
select(vpd, psi_soil, gs, e, a) %>%
mutate(type = "No acclimation")) %>%
melt(c("vpd", "psi_soil", "type"))
gg1 <- tmp %>%
filter(variable == "gs") %>%
ggplot(aes(x = vpd, y = value, col = factor(psi_soil), group = factor(psi_soil))) +
facet_wrap(facets = c("type"), scales = "fixed", nrow = 1) +
geom_line(size = 1) +
labs(x = "VPD", y = "Stomatal conductance") +
scale_color_manual(labels = c("Dry soil", "Moist soil"),
values = c('#E69F00','#56B4E9'), name = "") +
ylim(0, NA) +
theme_cowplot() +
theme(
axis.text.x=element_blank(),
axis.ticks.x=element_blank(),
axis.text.y=element_blank(),
axis.ticks.y=element_blank(),
legend.position = c(0.75, 0.6))## 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.gg2 <- tmp %>%
filter(variable == "e") %>%
ggplot(aes(x = vpd, y = value, col = factor(psi_soil), group = factor(psi_soil))) +
facet_wrap(facets = c("type"), scales = "fixed", nrow = 1) +
geom_line(size = 1) +
labs(x = "VPD", y = "Transpiration") +
scale_color_manual(labels = c("Dry soil", "Moist soil"),
values = c('#E69F00','#56B4E9'), name = "") +
ylim(0, NA) +
theme_cowplot() +
theme(
axis.text.x=element_blank(),
axis.ticks.x=element_blank(),
axis.text.y=element_blank(),
axis.ticks.y=element_blank(),
axis.line.y = element_line(),
legend.position = "none")
gg3 <- tmp %>%
filter(variable == "a") %>%
ggplot(aes(x = vpd, y = value, col = factor(psi_soil), group = factor(psi_soil))) +
facet_wrap(facets = c("type"), scales = "fixed", nrow = 1) +
geom_line(size = 1) +
labs(x = "VPD", y = "Assimilation") +
scale_color_manual(labels = c("Dry soil", "Moist soil"),
values = c('#E69F00','#56B4E9'), name = "") +
ylim(0, NA) +
theme_cowplot() +
theme(
axis.text.x=element_blank(),
axis.ticks.x=element_blank(),
axis.text.y=element_blank(),
axis.ticks.y=element_blank(),
axis.line.y = element_line(),
legend.position = "none")
cowplot::plot_grid(gg1, gg2, nrow = 2)
ggsave("../fig/acclimating_vpd_response.png", width = 6, height = 5)
cowplot::plot_grid(gg1, gg2, gg3, nrow = 3)
ggsave("../fig/acclimating_vpd_response_with_assim.png", width = 6, height = 7)