10.7280/D12H50
Navarro, Jocelyn
University of Arizona
Powers, John
0000-0001-9926-4548
University of California, Irvine
Paul, Ayaka
Colorado State University
Campbell, Diane
0000-0002-1147-846X
University of California, Irvine
Leaf gas exchange in Ipomopsis aggregata under manipulated snowmelt timing
and summer precipitation
Dryad
dataset
2021
FOS: Biological sciences
National Science Foundation
https://ror.org/021nxhr62
DEB-1654655
2022-03-08T00:00:00Z
2022-03-08T00:00:00Z
en
https://doi.org/10.5281/zenodo.6335942
59107 bytes
11
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Vegetative traits of plants can respond directly to changes in the
environment, such as those occurring under climate change. That phenotypic
plasticity could be adaptive, maladaptive, or neutral. We manipulated the
timing of spring snowmelt and amount of summer precipitation in factorial
combination and examined the responses of photosynthetic rate, stomatal
conductance, and intrinsic water-use efficiency (iWUE) in the subalpine
herb Ipomopsis aggregata. The experiment was repeated in three years
differing in natural timing of snowmelt. A 50% reduction in summer
precipitation reduced stomatal conductance and iWUE. Combining natural and
experimental variation, earlier snowmelt reduced soil moisture,
photosynthetic rate and stomatal conductance, and increased iWUE. Earlier
snowmelt is a strong signal of climate change and can change expression of
leaf morphology and gas exchange traits, just as reduced precipitation
can. Stomatal conductance showed adaptive plasticity under some
conditions.
We established an experimental manipulation of summer precipitation and
snowmelt and then measured floral traits over three years, 2018 - 2020. We
used a replicated split‐plot design, with snowmelt manipulated at the plot
level and precipitation manipulated at the subplot level. The treatments
were applied to the same plots each year. Six 7 m ⨉ 7 m plots were
established within a 45 m ⨉ 25 m area of Maxfield Meadow, Gothic, CO, USA
and three were randomly assigned early snowmelt treatments; a black 55%
woven shade cloth was applied over the entire plot in the spring to
accelerate snowmelt. Cloths were set out during spring melt off when snow
height reached an average of 100 cm across the study site, monitored, and
removed right after bare ground became visible. In 2019, a large avalanche
ran through the site and deposited snow and debris, resulting in a later
deployment and removal of shade cloth in two plots. The 2019 avalanche
added snow that prevented early snowmelt in one plot, so for analysis we
recoded it as having normal snowmelt timing. Within each of the six
snowmelt plots, four 2 m ⨉ 2 m subplots arranged in a square were randomly
assigned one of four summer precipitation treatments. First, a water
addition treatment simulated doubled summer precipitation based on the
historical average in July from 1989 - 2006 measured at the EPA CASTNET
weather station GTH161, 0.9 km northeast of Maxfield Meadow
(www3.epa.gov/castnet/site_pages/GTH161.html). We added 14 L of tap water
evenly to each 4 m2 subplot every 2 days to supplement daily precipitation
by 1.75 mm. Second, a water reduction treatment intercepted approximately
50% of incoming precipitation using a half-covered 2 m × 2 m rainout
shelter. The rainout shelters were constructed with a PVC pipe skeleton,
with sloping clear corrugated plastic greenhouse roofing slats spaced
evenly on top to cover half of the plot's surface area. Intercepted
rainwater ran down these slats into an attached gutter, which then fed
into a bucket on the ground. The shelter frames were camouflaged with
green and brown paint to avoid deterring or attracting pollinators and
herbivores. Third, mock rainout treatments controlled for any effects of
the physical PVC structures but lacked slats to intercept rain. Fourth,
control subplots were unmanipulated and received ambient rainfall. We
measured leaf-level gas exchange on non-flowering plants on 5 - 8 days
each year for a total of 315 measurements of 275 unique plants.
Measurements were taken the following number of days after the average
unmanipulated snowmelt plot melted: 2018: 47 - 78, 2019: 33 - 60, 2020: 45
- 94. Each day we took measurements from subplots in random order and
measured the longest leaf on one haphazardly selected rosette per subplot
that had not been previously measured that year and had a leaf longer than
25 mm. Two consecutive measurements were recorded per leaf and averaged.
We excluded measurements where the estimated intercellular CO2
concentrations or photosynthetic rates were negative. Leaf gas exchange
was measured using a Li-Cor 6400 XT Portable Photosynthesis system (Licor,
Lincoln, Nebraska, USA). All leaf gas exchange measurements taken between
08:00 to 12:00 with saturating light conditions (PAR = 1800 μmol m-2 s-1),
a leaf temperature of 27 °C, and a sample CO2 concentration of 400 ppm,
following Wu and Campbell (2007). Gas fluxes were calculated by dividing
by the leaf area inside the leaf chamber, measured in ImageJ (National
Institute of Health, Bethesda, Maryland, USA). Each value reported is a
mean across the plants measured in that subplot and year.
"ReadMe file for Leafgasexchange_by subplot.txt" explains the
variables.