Data from: Atmospheric feedbacks reverse the sensitivity of modeled photosynthesis to stomatal function

Stomata mediate fluxes of carbon and water between terrestrial plants and
the atmosphere. These fluxes are governed by stomatal function and can be
modulated in many Earth system models by an empirical parameter within the
calculation of stomatal conductance, the stomatal slope (g1M).
Intuitively, g1M represents the marginal water cost of carbon, relating it
to the emergent plant property of water use efficiency. Observations show
that g1M can range widely across and within plant types in varying
environments, and this distribution of g1M is not captured within Earth
system models which represent each plant type with a single g1M value.
Here we examine how g1M influences photosynthesis using coupled Earth
system model simulations by perturbing g1M to observed 5th and 95th
percentiles for each plant type. We find that high g1M reduces
photosynthesis nearly everywhere, while low g1M has regionally dependent
responses. Under fixed atmospheric conditions, low g1M increases
photosynthesis in the Amazon and central North America but decreases
photosynthesis in boreal Canada. These responses reverse when the
atmosphere responds interactively due to spatially differing sensitivity
to increases in temperature and vapor pressure deficit. Choice of g1M also
influences photosynthetic response to changes in
atmospheric carbon dioxide (CO2), with lower and higher g1M
modifying total global response to elevated 2x preindustrial CO2 by 6.4%
and -9.6%, respectively. Our work demonstrates that atmospheric feedbacks
are critical for determining the photosynthetic response to
g1M assumptions and some regions are particularly sensitive to
choice of g1M.