Adaptation of Growth and Respiration of Three Varieties of Caragana to Environmental Temperature
Lee D. Hansen,
E. Durant McArthur
Growth and respiratory characteristics of Caragana
korshinskii from Wushen and two different seed sources of C. davazamcii
from Helinger and Yijinhuole, all grown at the same conditions, were determined
by measuring metabolic heat and CO2 production rates by isothermal
calorimetry at 5°C intervals from 10 to 40°C. Substrate carbon
conversion efficiencies and growth (anabolic) rates were calculated from
the measured data. Differences in substrate carbon conversion efficiency,
respiratory rates and temperature responses of respiratory rates among
the three accessions all contribute to produce differing temperature responses
of growth rate. Planting seeds from these seed sources outside their native
ranges will probably not be successful because of the differences in temperature
Temperature is one of the most significant determinants of plant distribution.
Plants adapt their growth to their niche by adapting their respiratory
metabolism to the temperature pattern of the environment (Criddle et
al., 2005). Altering rates and the temperature dependence of metabolism
and metabolic efficiency may all be important in adapting growth characteristics
to the local climate. This study compares growth and respiration characteristics
of Caragana korshinskii from Wuhen and C. davazamcii from
Helinger and Yijinhuole, Inner Mongolia. These shrubs are used for combating
desertification, for water and soil conservation (Zhang et al.,
2002; Niu, 2002), as feed for cattle and wild animals in deserts and grasslands
and are the main shrub used for rangeland restoration in Inner Mongolia.
C. korshinskii and C. davazamcii are distributed from the
west to the middle of Inner Mongolia. C. davazamcii is a species
of the eastern Gobi, occurring in the steppe desert and desert steppe
zones on sand lands and Loess hills of the Ordos Plateau and northern
Loess Plateau where it is a dominant species of shrub vegetation. C.
korshinskii is a species of the southern Alashan and western Ordos
where it occurs in fixed and semi-fixed dunes of the steppe desert and
the typical desert zone. The zonal distribution of Caragana forms
an obvious geographic substituted distribution from east to west or from
north to south (Zhao, 2005). C. korshinskii and C. davazamcii
are distinguished by characteristics of flowers, seeds, leaves and especially
bark and height. C. korshinskii has yellow-gold, lustrous bark
and grows taller (300-500 cm, Zhao, 2005) than C. davazamcii (50-150
cm, Zhang et al., 2002). The morphology of leaves of Caragana
show a regular geographic gradient, leaf area becomes smaller and well
developed palisade tissue in the intercellular space also tends to become
smaller from east to west (Yan et al., 2002). Drought tolerance
also increases from east to west. There are disagreements on the taxonomy
of C. davazamcii and C. korshinskii; Sanchir (1974), Fu
(1977), Liu (1984) and Zhao (1990) argue that they are independent species,
Yakovlev (1988) argues that they are the same species and Zhang and Zhu
(2004) argue that C. davazamcii is a variant of C. korshinskii.
For nomenclature purposes only, in this study C. korshinskii and
C. davazamcii are considered to be independent species.
In this study, CO2 production rates (RCO2) and
metabolic heat rates (Rq) are measured as a function of temperature
by calorespirometry on young, growing leaf tissue of C. korshinskii
and C. davazamcii. These data allow calculation of growth (or
anabolic) rates and substrate carbon conversion efficiencies as functions
of temperature. Selection of accessions for restoration can then be done
by matching growth responses to local temperature patterns to maximize
the likelihood of success. This laboratory method cannot completely replace
field experiments, but can save much time and effort and make field experiments
much more efficient. Determining the relationship between metabolism and
growth and thence the mechanism of adaptation of different accessions
to environmental temperature patterns will provide better understanding
for use of these shrubs.
MATERIALS AND METHODS
This study was conducted at the Shrub Sciences Laboratory of the USDA
Forest Service and the Department of Chemistry and Biochemistry of Brigham
Young University, both in Provo, Utah, USA.
Theory: Plant growth depends on photosynthesis to supply substrate
carbon, but under many conditions the limiting factor for growth is not
photosynthate, but micronutrients and/or the rate of utilization of photosynthate
by respiration (Vitousek and Howarth, 1991; Hansen et al., 1998).
Further, because the processes of photosynthesis and respiration are separated
in time, photosynthesis rate cannot be used to predict growth rate. However,
growth rate of vegetative tissue is equal to the anabolic rate in respiration
and calorespirometry can be used to obtain both the anabolic and catabolic
rates and thus the growth rate and substrate carbon conversion efficiency
(Hansen et al., 2004, 2005). Catabolism of photosynthate provides
the energy to drive anabolism and anabolism produces structural biomass
from photosynthate. Because nearly all of the heat of respiration is produced
by catabolism, the metabolic heat rate (Rq) measures the rate
CS + O2 +
xADP + xPi → CO2 + H2O + xATP + heat
Where, Cs is the carbon substrate (assumed to be carbohydrate
in this reaction as written). ATP generated during catabolism supplies
energy to drive anabolism,
CS + yATP → zCBio
+ (1-z)CO2 + yADP + yPi
||Carbon substrate which is assumed to be carbohydrate in this reaction
||New growth, i.e., the rate of formation of Cbio is equal
to the rate of growth or development
Heat energy stored in ATP by the catabolic reaction is released in the
anabolic reaction, but, because the ATP reactions cancel in the overall
process, this heat can be assigned to either reaction and the calculations
are greatly simplified if it is assigned to catabolism.
The sum of the catabolic and anabolic reactions is:
CS + aO2 +
(N,P,K, etc.) → εCBio +(1-ε)CO2
Where, ε is the substrate carbon conversion efficiency, i.e., the
fraction of Cs converted to CBio.
Equations relating mass-specific growth (anabolic) rate (RSG)
to ε and to measured RCO2 and Rq have been
derived (Hansen et al., 2005, 2004);
ε/(1-ε) or RSG = RCO2 [ε/(1-ε)]
RSG= [-ΔHCO2 RCO2-Rq]/ΔHB
Where, ΔHB and ΔHCO2 are, respectively,
enthalpy changes for the difference in heats of combustion of substrate
and biomass and for the heat of combustion of substrate to CO2.
For closely related tissues, ΔHB can be regarded as a
constant and for vegetative tissue similar to that used in this study,
can be assumed equal to +30 kJ Cmol-1 (Lamprecht, 1999). From
Thornton`s rule, ΔHCO2 is approximately equal to -455(1-γs/4)kJ
Cmol-1 where γs is the chemical oxidation state
of carbon in the substrate (e.g., for carbohydrate γs
= 0, for lipid γs ≈ -1.8 and for protein γs
≈ -1.0). Specifically for carbohydrate, ΔHCO2 is
-470 kJ Cmol-1; so in the absence of evidence for other substrates,
ΔHCO2 is assumed equal to -470 kJ Cmol-1.
Combining Eq. 4 and 5 to eliminate RSG gives an equation for
ε/(1-ε) = [(-Rq/RCO2)
Determination of anabolic and catabolic rates and ε as functions
of temperature for different genotypes grown under the same conditions
allows determination of the influence of genotype and thus of natural
selection by environmental temperature on these characteristics.
Materials: Seeds of Caragana korshinskii were collected
near and Northwest of Wushen, Inner Mongolia and
||Results of linear least squares fitting (Excel, linest function)
of plots of average values of RCO2 versus Rq
at 10, 15, 20, 25, 30, 35 and 40°C. Uncertainties are given as
the standard deviation
|a: The substrate carbon conversion efficiency
ε was calculated with equation 6 assuming ΔHCO2
= -470 kJ Cmol-1 and ΔHB = +30 kJ Cmol-1,
*: Indicates these values differ significantly from the others in
seeds of Caragana davazamcii were collected near Helinger and
east Yijinhuole, Inner Mongolia (Table 1). Seeds were planted in
small containers with potting soil and grown in a greenhouse to a seedling
height of 10-15 cm. Stems with attached leaves from the top branch were
used for the calorespirometric measurements.
Measurement method: Hart Scientific Model 7707 and Calorimetry
Sciences Corporation Model 4100 calorimeters, each with three 1 mL sample
and one reference ampule, w ere used in isothermal mode. Seventy to 110
mg fresh tissue was placed into a sample ampule and the ampule inserted
into the calorimeter. The calorimeter was set to a selected temperature
and allowed to equilibrate for 20-30 min to obtain a steady-state metabolic
heat rate which was obtained during the last 5-10 min of this period.
The ampule was then taken out and a 40 μL vial of 0.4 M NaOH placed
in the ampule with the tissue, the ampule was replaced in the calorimeter
and the heat rate measured again. The heat rate from this second measurement
is the sum of metabolic heat and heat from NaOH reacting with CO2,
CO2 (g) + 2OH-1(aq) =
CO3 2–(aq) + H2O(aq)
ΔH = -108.5 kJ mol-1
After removing the vial of NaOH, the metabolic heat rate is measured
again. The metabolic heat rates from the first and third measurements
are averaged and subtracted from the heat rate from the second measurement
to obtain the heat rate for formation of carbonate (in μW or μJ
sec-1). Dividing this rate by 108.5 μJ nmol-1
gives the production rate (RCO2) of CO2 in nmol
sec-1. Averaging the two measurements of metabolic heat rate
corrects for any small drift in the rate during the measurement period.
This protocol was repeated at 10, 15, 20, 25, 30, 35 and 40°C for
each seed source. A given tissue sample was measured in sequence at 20,
15 and 10°C, at 20, 25 and 30°C, or at 30, 35 and 40°C. To
verify that sample history had no effect, additional samples were measured
at only one temperature. Because the calorimeters measure the heat rates
from three samples simultaneously, there were three to nine replicates
for each species and seed source, with each ampule being a unit. Dry Weights
(DW) were obtained after drying the samples for 24 h in a vacuum oven
at 70-80°C. Metabolic heat and CO2 rates were divided by
the dry weights to obtain mass-specific rates.
Figure 1 and 2, respectively show the average heat and CO2 production
rates versus temperature. These plots are not linear when plotted on Arrhenius
axes, i.e., ln(rate) versus reciprocal absolute temperature. The metabolic
heat and CO2 rates have similar responses to temperature, but
the responses differ among the three accessions. At temperatures below
25°C, Rq and RCO2 of the three accessions are
comparable. At temperatures above 25°C, Rq and RCO2
of Yijinhuole are higher than those of Helinger, which are higher than
those of the Wushen variety.
To determine whether the substrate carbon conversion efficiency (ε)
changed with temperature, plots of RCO2 versus Rq
were constructed and fit to a linear equation by least squares. The results
are shown in Table 1. If such a plot is linear and has a zero intercept,
||Metabolic heat rates (μW or μJ sec-1 mg-1
dry weight) of leaf tissue from Caragana korshinskii from Wushen
(WNJ) and C. davazamcii from Helinger (HXJ) and from Yijinhuole
(YXJ), Inner Mongolia. Error bars show the 95% confidence intervals.
The scatter is largely due to differing responses of tissue samples
since the instrument scatter is <5%
||CO2 production rates of leaf tissue from Caragana
korshinskii from Wushen (WNJ) and C. davazamcii from Helinger
(HXJ) and from Yijinhuole (YXJ), Inner Mongolia. Error bars show the
95% confidence intervals. The scatter is largely due to differing
responses of tissue samples since the instrument scatter is <10%
||Growth rates calculated from average metabolic heat
and CO2 production rates of leaf tissue from Caragana
korshinskii from Wushen (WNJ) and C. davazamcii from Helinger
(HXJ) and from Yijinhuole (YXJ), inner Mongolia. The temperature ranges
estimated from the growth curves indicate the range for optimal growth
can be concluded that ΔHCO2, ΔHB and
ε do not change with temperature (Eq. 6) and thus that the substrate
and biomass composition and catabolic-anabolic coupling do not change
with temperature over the linear range of the plot. The intercepts in
Table 1 are near zero and the plots are linear, showing that none of these
characteristics change significantly with temperature.
||Monthly average temperatures for Wushen (WNJ), Helinger
(HXJ) and Yijinhuole (YXJ), Inner Mongolia
Because it is highly unlikely that ΔHCO2 or ΔHB
differ among the accessions, we conclude that the substrate carbon conversion
efficiency and thus the anabolic-catabolic coupling of the Wushen variety
is significantly greater than the substrate carbon conversion efficiencies
of the Yijinhuole and Helinger varieties.
Figure 3 shows that the temperature of maximum growth
rate is similar among the three accessions, but the maximum growth rate
differs. The maximum growth rate decreases in the order Yijinhuole>Wushen>Helinger,
but note that total growth is proportional to the integral of the growth
rate over the temperatures and time of the growth season. These curves
show Wushen is adapted to grow at environmental temperatures from 12-43°C;
Yijinhuole from 18-41°C and Helinger from 5-46°C. Yijinhuole may
have a second, lower growth rate maximum around 10°C. Such bimodal
curves of growth rate versus temperature have previously been found for
plants adapted to climates with large, consistent diurnal temperature
variations (McCarlie et al., 2003; Ward, 2007). In agreement with
these results, Helinger is native to the coldest region, Yijinhuole is
in the middle and Wushen is native to the warmest climate. Monthly
average temperature and precipitation during the growth season are given
in Fig. 4 and 5. Wushen is slightly
warmer on average and the average temperatures are not significantly different
between the other two sites, but averaging apparently hides significant
differences in the temperature patterns. It is unfortunate that data on
high and low temperatures at these sites are not available to compare
with the temperature ranges derived from the growth curves
||Monthly precipitation for Wushen (WNJ), Helinger (HXJ)
and Yijinhuole (YXJ), Inner Mongolia
As shown in Eq. 4, growth rate is equal to the respiratory CO2
production rate times an efficiency factor. Quantitative differences in
efficiency and respiratory rate and differences in the temperature response
of the respiration rate all contribute to the differences in growth characteristics
of the three populations. Because the plants used in this study were grown
from seed in a common environment, the differences in the growth curves
are due to genetic adaptations and show the plants have limited ability
to acclimate. The curves of growth rate versus temperature in Fig.
3 show that plants from the three sites are adapted to very different
temperature patterns. That is, the maximum and minimum temperatures for
growth are expected to match the extreme temperatures commonly encountered
during the growth season and total seasonal growth is expected to be optimal
when the curve of growth rate versus temperature matches the shape of
the distribution curve for environmental temperatures at the native site
(Criddle et al., 2005; Criddle and Hansen, 1999). The areas under
the growth curves in Fig. 3 are approximately the same
as expected for plants that grow to a similar size during the same length
of growth season. The other principle governing the shape and position
of curves of growth rate versus temperature for well adapted plants is
that plants grow at the temperatures extant when water is available. The
differences in the temperature patterns at the native sites as indicated
by the growth curves in Fig. 3 are not captured in the
average temperature and precipitation data in Fig. 4
and 5 because averaging data over time can hide large
differences in temperature and precipitation patterns.
In conclusion, this study shows that no simple relation exists between
any one respiratory characteristic and the growth properties of these
three accessions of closely related plants. The temperature responses
of the growth rates result in similar total seasonal growth of plants
of each accession when grown in the native climate, but planting seeds
from these seed sources outside their native ranges will probably not
be successful because of the differences in temperature adaptation.
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