title: How to make a multi-line x axis title with mathematical expressions in ggplot2
body: <pre><code>xlab(expression(paste("CO"^"2", " concentration", "\n Lolium perenne")))
  </code></pre>
  
  <p>This is my current coding.
  With my xlab I want to have CO^2 concentration on one line, and then "Lolium perenne" beneath that but it also needs to be in italics. Currently this code places "concentration" on the line above "CO^2" and "Lolium Perenne".
  Please help!</p>