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RESEARCH: RESPIRATION /
CARBON USE EFFICIENCY |
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Growth depends
on efficient photosynthesis and adequate respiration. The effect of
temperature on photosynthetic efficiency is well characterized. In
contrast, respiration is widely accepted to double with each 10 șC
increase in temperature, but this relationship is derived from
short-term (hours) measurements in mature organisms. These
short-term data are then extrapolated over whole life cycles to model
the influence of temperature on plant growth. Using continuous
canopy gas exchange, we found that night temperature has a minimal
effect on respiration and growth in rapidly growing plants. This
finding has profound implications for crop production in controlled
environments. |
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THE ABSTRACTS BELOW:
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Determining
the Environmental Factors Controlling
Respiration: Interpreting the
Temperature Response
Jonathan Frantz, M. van Iersel, and B. Bugbee
Presentation: Agronomy Society of America
Nov. 10-14, 2002; Indianapolis, IN
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ABSTRACT
Light and temperature influence plant respiration. Exactly how
much each influences respiration has been reported to be
anywhere from no effect to quadrupling for a 10 șC rise in
temperature. Models often assume a doubling of maintenance
respiration for each 10 șC increase in temperature and no effect
of temperature on growth respiration. Our studies over the past
three years, have investigated both short term (hours) and long
term (days to weeks) temperature changes on respiration. Our
results indicate that the maintenance coefficient only increased
by at most 50% for a 10 șC rise in day/night temperature during
growth. There was no difference in the maintenance coefficient
between two canopies grown in different constant temperatures.
Surprisingly, the growth respiration coefficient was influenced
by temperature. Carbon use efficiency (CUE: daily carbon gain /
gross photosynthesis) did change in response to different day
night temperatures during growth, but there was no difference in
CUE among canopies grown in different constant temperatures.
These results indicate either a rapid acclimation to temperature
on a whole canopy level or a lack of whole canopy sensitivity to
temperature fluctuations.
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Night
Temperature Has A Minimal Effect on Respiration
and Growth in
Rapidly Growing Plants
Jonathan Frantz and B. Bugbee
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ABSTRACT Carbon gain depends on efficient photosynthesis, adequate
respiration, and the proper balance between the two. The effect
of temperature on photosynthetic efficiency is well understood.
Respiration is widely accepted to double with each 10C increase
in temperature (a 100% increase), but this relationship is
derived from short-term (hours) measurements in mature
organisms. These short-term data are then used to extrapolate
over whole life cycles to predict the influence of temperature
on plant growth, in spite of the likelihood of acclimation to
temperature over time. In this study, we either increased or
decreased the night temperature of plant canopies for up to 20
days. We continuously monitored CO2 gas-exchange to
quantify the effect of night-temperature on respiration,
photosynthesis, and the efficiency of carbon gain (carbon use
efficiency). We found that respiration in rapidly growing
plants increased only 20 to 46% for each 10C rise in
temperature. This change resulted in a small, but permanent
change in carbon use efficiency. However, there was no
significant effect on carbon gain even after 20 days. These
findings have significant implications for our understanding of
the effect of temperature on respiration in whole plants.
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Acclimation to
Shade: Photosynthesis, Respiration,
and Carbon Use Efficiency
Jonathan Frantz and B. Bugbee
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ABSTRACT Photosynthesis,
respiration, and the balance between the two change in response
to the environment. Surprisingly few studies have examined how
quickly and how completely plants acclimate to the environment
on a whole plant or canopy basis. Canopies of tomato and
lettuce were subjected to a range of shade upon canopy closure.
Using CO2 gas exchange, photosynthesis, respiration,
and carbon use efficiency (ratio of carbon gain to carbon fixed)
were measured for up to 18 days after shade was applied. In
contrast to popular growth models, we found that canopies did
not immediately acclimate, and species acclimate in different
ways. Lettuce grown in 80% shade never completely acclimated,
whereas similar shade for tomato acclimated after 12 days. Both
acclimated in part due to more efficient photosynthesis (canopy
quantum yield). These results suggest that some species can
adjust C partitioning, relative growth rates, growth, or
maintenance respiration to maintain carbon use efficiency, but
do so at a much slower rate than currently modeled.
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Exploring the limits of crop productivity: quantum
yield,
radiation capture, and carbon use efficiency of lettuce
in
a high light, temperature, and CO2 environment
Jonathan Frantz, G. Ritchie, N. Cometti, J. Robinson and B. Bugbee
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ABSTRACT There have been several
analyses to determine the theoretical maximum yield of a crop
community. Many crops are grown in sub-optimal conditions and
maximum growth rates are sacrificed in order to improve some
other characteristic of crop production (e.g. timing for the
market). As a result, theoretical maximum yields have not been
analyzed for several important crops and breeders have little
information as to what, if anything,
may be most limiting to productivity. Most productivity studies
are performed under ambient or field CO2
concentrations. Photorespiration is reduced substantially by
elevating CO2, even in warm temperatures, and
electron transport becomes the rate limiting factor in CO2
fixation. As a consequence, crops photosynthetic rate can be
much higher in elevated rather than in ambient CO2.
Radiation capture is also a critical component of productivity
models. Leaf expansion rate is greatly influenced by
temperature and along with leaf emergence rate, provide a plant
the means to effectively capture light as it develops from
seedlings. The temperature optimum for leaf expansion differs
for different crops. Carbon use efficiency (CUE) is a measure
of how well a plant incorporates newly fixed carbon into new
biomass. Little information exists for lettuce CUE in different
environments. We examined growth of lettuce canopies at five
constant temperatures: 21, 25, 30, 32.5, &
35 C with two replicate chambers at each temperature. Our
studies indicate that the temperature optimum for leaf
expansion, light interception, and growth is 30 C, which is much
higher than used in previous studies. The growth rate increased
by more than 3-fold from 21 to 25 C and by 40% from 25 to 30 C;
but decreased by 20 % from 30 to 32.5 C. These results indicate
that the temperature optimum for lettuce growth and appearance
is 5 to 10 C above that used in previous studies. In a separate
study, PPF levels were increased up to 1000
umol m-2 s-1. Lettuce productivity continued to increase
with higher light. These results indicate that lettuce can be
pushed with high light, temperature, and CO2 by improving
radiation capture, QY, and CUE.
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Respiration
and Carbon Use Efficiency:
Adaptation to Fluctuating Environments
Jonathan Frantz and B. Bugbee
Presentation: Agronomy Society of America - 2001
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ABSTRACT must be
balanced between supplying enough energy and consuming too much
substrate for growth. Supply (photosynthate
availability) or demand (temperature dependent) limitations are
used to describe the control of respiration and carbon use
efficiency (CUE: daily carbon gain / gross photosynthesis).
Both limitations play a role in determining carbon gain, but
their relative effects are poorly characterized. This means we
do not understand short and long-term respiratory adaptation to
environmental changes such as cool cloudy days followed by warm
sunny days. Studies with soybean, lettuce, and tomato indicated
that plant canopies lower their respiration rates with cooler
night temperatures and therefore improve CUE. In another study,
constant day and night temperatures between 21 and 35 șC
resulted in the same CUE. Shading lowered respiration and CUE
temporarily decreased by as much as 100% with 80% shading. Over
the next several days, the respiration rate declined and CUE
adapted close to its pre-treatment level. Interestingly, high
shade treatments (>50%) did not completely adapt after ten days. |
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Determining the
Factors Controlling Respiration and
Carbon Use Efficiency in Crop
Plants
Jonathan Frantz, T. Dougher, and B. Bugbee
American Society
of Agronomy - 2000
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ABSTRACT Two viewpoints describe
the control of respiration and carbon use efficiency: supply (photosynthate
availability) or demand (temperature dependent) limitations.
While both components may play a role in determining respiration
rates, their relative contributions are poorly characterized,
and we do not understand the short-term respiratory
adaption of plant communities to environmental changes
such as warm sunny days followed by cool cloudy days. Our
studies indicate that carbon use efficiency (CUE: daily carbon
gain / gross photosynthesis) is temporarily decreased by 20% as
a result of 80% shading, but the respiration rate declines
gradually over seven days, and CUE recovers to its pre-treatment
level. Our studies also indicate that CUE and respiration
rates are strongly influenced by night-time temperatures (either
warmer or cooler), but CUE adapts over one week to return to its
pre-treatment level.
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Estimating Growth and Maintenance
Respiration Coefficients
from Soybean Canopy Gas Exchange Data:
A New Approach
Tracy Dougher, M. van Iersel, J. Frantz, and B. Bugbee
Presentation: American Society
of Agronomy - 2000
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ABSTRACT Estimating growth and
maintenance respiration coefficients in respiration models has
been difficult using traditional methods due to variance during
plant development and variance from environmental conditions. A
ten chamber, whole-canopy, flow-through gas exchange system
provided us with a unique opportunity to continuously measure
soybean net photosynthesis and respiration over the entire life
cycle under a range of environmental conditions. Several models
for estimating the respiration coefficients were tested,
including a new approach that takes advantage of continuous gas
exchange data. This approach indicates that maintenance
respiration is not always determined by the mass of the plant.
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