Data from: Does stomatal patterning in amphistomatous leaves minimize the CO2 diffusion path length within leaves?

Photosynthesis is co-limited by multiple factors depending on the plant
and its environment. These include biochemical rate limitations, internal
and external water potentials, temperature, irradiance, and carbon dioxide
(CO2). Amphistomatous leaves have stomata on both abaxial and adaxial leaf
surfaces. This feature is considered an adaptation to alleviate CO2
diffusion limitations in productive environments as the diffusion path
length from stomate to chloroplast is effectively halved in amphistomatous
leaves. Plants may also reduce CO2 limitations through other aspects of
optimal stomatal anatomy: stomatal density, distribution, patterning, and
size. A number of studies have demonstrated that stomata are overdispersed
compared to a random distribution on a single leaf surface; however,
despite their prevelance in nature and near ubiquity among crop species,
much less is known about stomatal anatomy in amphistomatous leaves,
especially the coordination between leaf surfaces. Here we use novel
spatial statistics based on simulations and photosynthesis modeling to
test hypotheses about how amphistomatous plants may optimize CO2 diffusion
in the model angiosperm Arabidopsis thaliana grown in different light
environments. We find that 1) stomata are overdispersed, but not ideally
dispersed, on both leaf surfaces across all light treatments; 2) the
patterning of stomata on abaxial and adaxial leaf surfaces is independent;
and 3) the theoretical improvements to photosynthesis from abaxial-adaxial
stomatal coordination are miniscule (≪ 1%) across the range of feasible
parameter space. However, we also find that 4) stomatal size is correlated
with the mesophyll volume that it supplies with CO2, suggesting that
plants may optimize CO2 diffusion limitations through alternative pathways
other than ideal, uniform stomatal spacing. We discuss the developmental,
physical, and evolutionary constraits which may prohibit plants from
reaching this theoretical adaptive peak of uniform stomatal spacing and
inter-surface stomatal coordination. These findings contribute to our
understanding of variation in the anatomy of amphistomatous leaves.