R 条形图中每个条形和每个组的轴标签

问：

我正在尝试在带有避视图的条形图中为每个条形和每个组创建轴标签。此处的相关问题：条形图中每个条形和每个组的轴标签，带有避视图组

我希望最终结果看起来像这样，但有 3 组，每组有 4 个小节

我在下面添加了示例数据

我玩过，但似乎不起作用。scale_x_discretescale_x_continuous

# create a dataset 
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
set.seed(123)
df

ggplot(df, aes(fill = specie, y = value, x = condition)) +
  geom_bar(stat="identity", position = position_dodge(width = 0.9), width = 0.6) +
  scale_fill_manual(
    "specie",
    values = c("black", "black", "black", "black"),
    
  ) +
  theme_classic() +
  theme(panel.border = element_rect(colour = "black", fill=NA, size=1),
        text = element_text(size = 8, family = "sans"),
  ) + labs(x = "Nitrogen                  normal          stress", y = expression(paste("Total Phytoplankton Abundance (", x10^{6}, "cells/L)"))) +
  scale_y_continuous(expand = c(0,0))  +   
  theme(legend.position="none") + scale_x_discrete("", breaks=c(-0.25,0.25,0.75,1.25,1.75,2.25,2.75,3.25,3.75,4.25,4.75,5.25),
                     labels=rep(c("sorgho","poacee", "banana", "triticum"),times=3)) 

电流输出

'''scale_x_discrete'' 出于某种原因删除所有 x 轴标签。