x-axis expand changes after plot_grid

[arslan9732]

I am using plot_grid() to combine three plots. but after applying plot_grid(), it seems like it change the expand() in scale_x_discrete().

library(ggplot2)
library(cowplot)
library(gggenomes)

data1 <- data.frame(
  Window = as.factor(seq(0,3800, by = 100)),
  Para1 = runif(39, min = 40, max = 50))

data2 <- data.frame(
  Window = as.factor(seq(0,7400, by = 100)),
  Para2 = runif(75, min = 40, max = 50))

p1 <- ggplot(data1, aes(x = as.factor(Window), y = Para1, group = 1)) +
  geom_line(color = "grey") +
  geom_ribbon(aes(ymin = 0, ymax = Para1), fill = "grey", alpha = 1) +
  scale_x_discrete(expand = c(0.01,0.01),
                   breaks = c(0, 3800)  # Show only first and last
  ) +
  scale_y_continuous(
    expand = c(0, 0),
    limits = c(0, 101),
    breaks = seq(0, 100, by = 50)
  ) +
  theme_classic() +
  theme(
    panel.background = element_rect(fill = "transparent", color = NA),
    plot.background = element_rect(fill = "transparent", color = NA),
    ) +
  labs(x = "")
p1


p2 <- ggplot(data2, aes(x = as.factor(Window), y = Para2, group = 1)) +
  geom_line(color = "grey") +
  geom_ribbon(aes(ymin = 0, ymax = Para2), fill = "grey", alpha = 1) +
  scale_x_discrete(expand = c(0.01,0.01),
                   breaks = c(0,7400)  # Show only first and last
  ) +
  scale_y_continuous(
    expand = c(0, 0),
    limits = c(0, 101),
    breaks = seq(0, 100, by = 50)
  ) +
  theme_classic() +
  theme(
    panel.background = element_rect(fill = "transparent", color = NA),
    plot.background = element_rect(fill = "transparent", color = NA),
  ) +
  labs(x = "")
p2

df <- data.frame(
  seq_id = c("a", "b"),
  length = c(3800,7400)
)

p3 <- gggenomes(seqs=df) + 
  geom_seq() +
  scale_x_continuous(expand = c(0.01,0.01), breaks = seq(0, max(df$length)+100 , by = 1000)) +
  scale_y_continuous(expand = c(0,0.4)) +
  theme_classic()

narrow <- plot_grid(p1,
                    NULL, nrow = 1, rel_widths = c(0.5, 0.42))
plot_grid(narrow, p3, p2,
          ncol =  1)