向 R 图添加指数数

问：

有没有办法在轴标签的中间添加指数数？ 如果我使用

expression(paste("Total Biomass (mg/", m^{3})))

我无法让它看起来像（想象 3 很小）。它看起来只会像没有，我也无法创建一个需要说的标签（想象一下 6 很小）。Total Biomass (mg/m3)Total Biomass (mg/m3)"Total Abundance (x106 cells/L)"

# create a dataset
set.seed(123)
specie <- c(rep("sorgho" , 3) , rep("poacee" , 3) , rep("banana" , 3) , rep("triticum" , 3) )
condition <- rep(c("normal" , "stress" , "Nitrogen") , 4)
value <- abs(rnorm(12 , 0 , 15))
df <- data.frame(specie,condition,value)
df

# Grouped
ggplot(df, aes(fill = condition, y = value, x = specie)) +
  labs(x = "Lakes", y = expression(paste("Total Plankton Biomass (mg/", m^{3})))