Statistical analysis
The experiment had four response variables: population growth rate, colony size, frond area, and root length. Growth rate was calculated for each flask during the final two-week growth period using the standard formula for exponential growth\(r=\frac{\ln\left(\frac{\text{Nt}}{N0}\right)}{t}\) where N0 is initial population size, t is time in days, and Nt is population size at time t. For each response variable we used a linear mixed-model ANOVA to test the effects of the microbiome and environmental conditions, (two fixed factors), and genotype (one random factor). Expected Mean Squares and estimates of F were evaluated as described by Sokal and Rohlf (1981), Box 12.1 pg.383 ‘Mixed Model’. Since there is only a single measure of growth rate per flask, replicate flask was used as the error variance, and similarly, an average value of frond area and root length of the 10 measured individuals was used as a single measure per flask.