Interacting influences of global change factors on leaf stomatal
response in prairie grasses
Gregory T. Nelson, Zoe Zehner ● Faculty Mentor: Dr. Tali D. Lee
Department of Biology-University of Wisconsin Eau Claire
*nelsongt@uwec.edu
Results
Agropyron repens:
0.13
0.12
0.11
N main effect: P = 0.6043
N x age: P = 0.1160
0.15
Stomatal Index
0.14
(C)
0.14
0.13
0.12
0.11
*
H2O main effect: P = 0.0454
H2O x age: P = 0.6893
0.15
0.14
0.13
0.12
0.11
0.4
(µmol m-2 s-1)
CO2 main effect: P = 0.0413
CO2 x age: P = 0.7490
0.15
Stomatal Index
(B)
Stomatal Conductance
(A)
Stomatal Index
Age main effect: P < 0.001
0.3
0.2
0.1
0
0.1
0.1
0.1
ambient CO2
elevated CO2
ambient N
Carbon Dioxide Treatment
ambient H2O
elevated N
reduced H2O
Water Treatment
Nitrogen Treatment
Treatment
Andropogon gerardii:
Age main effect: P = 0.0248
• Our main objective was to examine leaf stomatal responses when
multiple environmental factors were manipulated, as part of a large
scale ecosystem study, in an attempt to better predict the effects of
changing global factors on plant function and the implications for
carbon and water cycles.
0.11
0.1
0.1
ambient CO2
elevated N
ambient H2O
(µmol m-2 s-1)
reduced H2O
Water Treatment
Treatment
(B)
CO2 main effect: P = 0.5625
CO2 x age: P = 0.2361
0.15
0.14
0.13
0.12
0.11
0.15
0.14
0.13
0.12
0.11
0.1
0.1
ambient CO2
Figure 2. Interaction plots of stomatal index (SI =
# 𝑜𝑓 𝑠𝑡𝑜𝑚𝑎𝑡𝑎
# 𝑜𝑓 𝑡𝑜𝑡𝑎𝑙 𝑒𝑝𝑖𝑑𝑒𝑟𝑚𝑎𝑙 𝑐𝑒𝑙𝑙𝑠
elevated N
Nitrogen Treatment
Carbon Dioxide Treatment
0.15
0.14
0.13
0.12
0.11
ambient H2O
Water Treatment
Results: Newest developed leaves had significantly higher SI than oldest leaves across species. Otherwise, the CO2, H2O, and N treatments had little effect on SI.
Elevated CO2 grown leaves had slightly higher SI than ambient CO2 grown leaves in 2 of the 3 species and in 1 species, leaves grown at reduced H2O availability
had more stomata than those grown at ambient H2O. Additionally, responses to N and H2O availability depended on leaf age in a few cases.
Discussion
• Leaves that develop later in the growth season had greater numbers of
stomata suggesting an affect of ontogeny. In some cases, this response
was dependent on environmental factors, suggesting that grasses are able
to detect and subsequently respond developmentally to seasonal changes.
• Although there has been a historic trend of decreasing stomatal density
with increasing CO21,2, some studies are finding no change or even an
increase in stomatal index3, as we have in this study. There is likely a point
at which further decreases in stomatal densities can compromise basic leaf
function regardless of CO2 concentrations and that other adjustments such
as in changes in physiology become relatively more effective.
• This idea is supported by our results as stomatal conductance was lower in
plants grown under elevated compared to ambient CO2 due to changes in
stomatal physiology.
• Stomatal conductance to H2O was measured using a LiCOR 6400 portable infrared
gas exchange system in the pervious three years.
• Analysis of variance (ANOVA) statistical analyses were performed using JMP v7
(SAS Cary, NC). P <0.1 considered biologically significant.
• In contrast with findings for other plant groups, environmental factors had
little effect on stomatal index in these grasses. Instead grasses seem to
rely on their ability to physiologically control conductance.9
• To improve our understanding of how plants will respond to changing
global environments, ontogeny should be considered. In addition, the
physiological regulation of stomatal function in grasses may become
relatively more important than stomatal density changes as plants
adapt to future global conditions. Finally, as different plant groups
have different stomatal evolutionary histories, responses must be
evaluated per group.
http://www.uniquelyminnesota.com/weekend-away/prairie-waters-mn.htm
0.2
*
0.1
reduced H2O
point represents 32 plants pooled across other treatments. P values for environmental treatment and age main effects and treatment x age interactions are given for each species.
Figure 1. Photograph of a dumb-bell shaped stomata typical of grasses
(left) and a kidney bean shaped stomata of other plants (right).10 Plants
regulate CO2 uptake and H2O loss by controlling the number of stomata
formed during growth as well as the aperture of the stomata as conditions
change.
*
0
, mean ± SE) for three grass species showing age by (A) CO2, (B) N, and (C) H2O treatment interactions. Each
• Experimental treatments were arranged in factorial combination of CO2
concentration (ambient, ambient + 180 ppm), H2O supply (ambient, ambient - 50%
precipitation), and N availability (ambient, ambient + 4g N m-2yr-1).
0.3
H2O main effect: P = 0.9879
H2O x age: P = 0.4959
0.1
ambient N
elevated CO2
(C)
N main effect: P = 0.2275
N x age: P = 0.0188
(µmol m-2 s-1)
(A)
Stomatal Conductance
Age main effect: P = 0.0933
plots representative of grasslands communities.
• Number of stomata per total number of epidermal cells (stomatal index, SI) was
calculated as a fair measure of stomata density to control for unrelated changes in
leaf morphology.
0.11
0.1
Bromus inermis:
(http://www.biocon.umn.edu/).
• Upper fully expanded leaves, “newest”, and oldest functional leaves, “oldest”, were
harvested per plant to make leaf surface impressions using clear acrylic to determine
stomatal and epidermal cell densities visible through a microscope (400x).
0.12
Nitrogen Treatment
Carbon Dioxide Treatment
• Study site: Cedar Creek Ecosystem Science Reserve, east central Minnesota
• Plants were grown in 2x2
0.13
*
*
0.1
ambient N
elevated CO2
Methods
m2
Stomatal Conductance
Stomatal Index
0.11
0.12
0.14
Treatment
Figure 3. Stomatal conductance (mean ± SE) for each species.
Asterisks denote a significant difference between ambient and
altered treatment levels (P < 0.05); data was natural log transformed
for analysis.
Results: Conductance rates were lower in plants grown under
elevated than ambient CO2 and in plants under reduced
compared to ambient H2O. N did not affect conductance.
0
((reduced – ambient)
/ambient)*100
• Agropyron repens, Andropogon gerardii, and Bromus inermis are three grass
species common to new world prairies.14
0.12
0.13
0.2
% change in
conductance
• Previous work has shown that stomatal densities have declined since the
industrial revolution as a result of rising CO2 concentrations.16,17,18 Stomatal
density can also be affected by environmental factors such as H2O12,13 and
nitrogen (N) availability.4
0.13
0.14
H2O main effect: P = 0.3562
H2O x age: P = 0.0615
0.15
Stomatal Index
• The leaf is also the primary site of perception of many environmental
variables and can relay information to guide new leaf development.11
0.15
Stomatal Index
• Plants optimize CO2 uptake and minimize H2O loss through development by
adjusting stomatal densities7,8 and physiology by controlling stomatal
conductance.6,8
0.14
(C)
N main effect: P = 0.9642
N x age: P = 0.1144
0
Stomatal Index
• Plants play an important role in the carbon cycle, fixing atmospheric carbon
dioxide (CO2) into organic compounds.10 Pores in plant leaves called stomata
are the gateway between the atmospheric and biological portions of the
carbon cycle as they modulate gas exchange (CO2 and H2O).5,15
Stomatal Index
0.15
Introduction and Objective
(B)
CO2 main effect: P = 0.0507
CO2 x age: P = 0.1162
Stomatal Index
(A)
http://michaelforsberg.photoshelter.com/image/I00007mBBjm3c2P8
-0.1
aC
elevated CO
eC
ambient CO2
-0.2
-0.3
2
-0.4
-0.5
Figure 4. Percent reductions in stomatal conductance rates due to
reduced H2O availability.
Results: The magnitude of reduction due to reduced water
availability was dependent on the CO2 level for A. gerardii.
Acknowledgements
Funding:
UWEC Office of Research and Sponsored Programs
UWEC Differential Tuition
Cedar Creek Ecosystem Science Reserve
Field and technical support:
Molly Kreiser, Adam Schneider, Susan Barrott, and Kally Worm
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