Differential expression of year of sampling effect. Volcano plot of the negative log10 p-value (y-axis) - i.e. log odds ratio - plotted against log2-fold change (x-axis) showing the results of differential expression analysis assayed using RNA-Sequencing comparing samples collected from trees in 2008 and 2010. Gene expression was assayed using samples collected from trees in 2008 and 2010 by RNA-Sequencing. Significant genes are shown as larger brown points. Non-significant genes are coloured to indicate density, which is shaded from yellow (high) to blue (low). The dashed horizontal line represents a 1% False Discovery Rate.