Growth rate (fitness)
The plants grew rapidly over the four-week growth assay with an average
doubling time of 6 days across all treatments. Growth rate was affected
by environmental conditions (F3,21=362.6,
p<0.001), with plants growing 1.23x faster in high nutrient
conditions than in low nutrient conditions, and more than 1.95x faster
in high light conditions than in low light (Fig. 1). In the most
favourable environmental conditions (high light - high nutrients),
average doubling time was 4 days, whereas in the most stressful
environmental conditions (low light – low nutrients), it was 10 days.
There was considerable variation in growth rate among genotypes, all of
which responded to light and nutrients in the same direction (increased
growth rate with higher resource levels). The extent of this increase
varied among genotypes however, leading to a significant genotype x
environment interaction (F21,128=2.92,
p<0.001), indicating the presence of a genotype by environment
(GxE) effect. Presence of the microbiome had a strong and consistent
effect on growth rate (F1,7=32.3, p<0.001),
reducing growth rate in all environmental conditions (Fig. 1) and for
seven of the eight genotypes (Fig. 2a). Again, the magnitude of this
negative effect varied among genotypes and environmental conditions
leading to significant interactions between microbiome x genotype
(F7,128=3.39, p=0.002), and microbiome x environmental
condition (F3,128=5.63, p=0.001). Full Anova tables for
all analyses can be found in the Supplementary materials (Table S3).