I am building a glmm where I have 3 PCs (principal components) as predictors in the model. These PCs are based on soil variables (pH, CEC, nutrients) so I have reason to believe they may interact with other environmental predictors in the model (i.e. soil moisture, canopy gap index). Would the following be valid:
$$ y = x_{1} + x_{2} + x_{3}PC_{1} + x_{4}PC_{2} + \epsilon $$
whereby, $x_{3}$ and $x_{4}$ are soil moisture and canopy gap index and they are interacting with the principal components.