Fig. 2. Correlations between phenotypes measured in the field and natural levels of resource availability. A. Average frond area (mm2) as a function of local light availability. Each point is the average of 10 individuals in each of 3 microsites to give a single value of average frond area per site. Light availability is measured as percent transmittance of photosynthetically active radiation. B. Average root length (mm) as a function of water total Phosphorus (µgL-1). Each point is the average of 10 individuals in each of 3 microsites to give a single value of average root length per site.
Plants from the field were taken back to the lab and grown in a common garden assay. Mean generation time in the common garden was 4.1 days which resulted in a total of ~7 generations for the full 30-day common garden assay. Although diverse protists and cyanobacteria were observed in the flasks with microscopy, their densities remained low as the growth media never became green to the naked eye.
Whereas phenotypic variation in the field is due a mixture of environmental and genetic sources, any persistent variation in the common garden can be attributed to genetic differences. There was a major reduction in phenotypic variation among sites, comparing measurements from the field to those in the common garden, for both frond area (Fig. 3 A&B), and root length (Fig. 3 C&D). Frond area generally increased in the common garden compared to field measurements, likely due to the vastly lower irradiance provided by artificial light in the growth chambers (200 µmols/s/m2) compared to natural irradiance, even in shaded sites.