R barplot2轴标签

Question

bar33x<- barplot2(pHI, beside=T,width= c(0.1,0.1,0.1), col = c("black", "grey"), ylim = c(0,10),las = 1, xlab = "Site code ", 
                  cex.names=0.7, cex.lab=0.9, cex.axis=0.8,
                  names.arg = c( "R01", "R02", "R04", "R10", "R12", "R13", "R15", "R16","R03", "R05", "R7", "R11", "R14"),
                  space=c(0,0,0.3,0,0.3,0,0.3,0,0.3,0,0.3,0,0.3,0,0.3,0,3,0, 0.3,0,0.3,0,0.3,0,0.3,0))
abline(h=0, lty = 1, lwd = 0.5)
mtext(expression ("pH"), side = 2, line = 2, cex=0.8)

你好，我将names.arg保留在x标签中，但我想旋转它们，如何旋转x轴names.arg标签？