Fig. 3 Percent inhibition is a measure of trypsin protease inhibitor activity, with high inhibition indicating high levels of protease inhibitor activity. Tomato plants grown without mycorrhizae induced protease inhibitors strongly, while plants grown with mycorrhizae did not show significant induction. Symbols represent mean +/- SE.
Since mycorrhizae and competition interacted to affect leaf consumption and affected both plant nutritional content and resistance traits, we tested which traits quantitatively correlated with leaf damage. Cabbage loopers consumed less leaf tissue when C/N ratios were high (F1,31=6.99, p=0.013). While we saw a similar effect with nitrogen alone (F1,35=5.50, p=0.025), the C/N ratio explained a higher proportion of the variation (R2=0.16). While treatments with high protease inhibitors also had low cabbage looper leaf consumption, neither constitutive or induced protease inhibitor levels correlated with either cabbage looper feeding or mass gain (F1,29=0.781, p=0.383, F1,34=0.365, p=0.550).