Analysis of Temperature and Atmospheric CO2 Effects on Radiation Use Efficiency in Chickpea (Cicer arietinum L.)
In this study, a simple theoretical framework was extended to account for the effects of temperature and atmospheric CO2 concentration on RUE. A general test of the model showed that simulated and observed daily biomass productions under average daily temperatures ranged from 11 to 28°C are similar. The calculated RUEs for 13-23°C were similar to measured ones and percentage increase in RUE for CO2 concentration of 640 ppm relative to 330 ppm was in agreement with the measured percentage increase in biomass production. By using the framework, RUE response functions to average daily temperature and CO2 concentration were calculated for chickpea. RUE of chickpea at temperatures lower than 3°C and higher than 36°C is zero. RUE rapidly increased (9.5%°C-1) with increasing temperature from 3 to 14°C. With further increase in temperature to 22°C, RUE slowly (1.4%°C-1) decreased and temperature increase between 22 to 36°C resulted in sharp decrease (7.4%°C-1) in RUE. Response of RUE to CO2 concentration was curvilinear. At low concentrations of CO2 (60 to 400 ppm), RUE was especially sensitive to increases in CO2 concentration, but increases in CO2 greater than 700 ppm were predicted to result in only small increases in RUE. The functions obtained can be used in simulation studies of chickpea crop response to projected climate change.
Chickpea (Cicer arietinum L.) is one of the major pulse crops in arid
and semiarid environments of West Asia and North Africa (WANA) region and has
considerable importance as food, feed and fodder. Due to the increasing need
for legumes, chickpea is no longer considered a subsistence crop (Saxena
et al., 1996). Projected global climate change may have major influences
on cropping aspects of this crop in the region. In order to ensure a balanced
growth and development in agriculture in the region, a comprehensive assessment
of the vulnerability of chickpea cropping due to projected climate change is
Radiation use efficiency (RUE, g MJ-1) is the amount of biomass
accumulated for each unit of total solar radiation intercepted by leaf canopy
(Choudhury, 2000). Recently, a simple mechanistically
based model was developed for chickpea in which the daily biomass production
is calculated using RUE (Soltani et al., 1999).
In this model, the effect of supra-optimal temperatures and atmospheric CO2
concentrations were not included and the effect of low temperature was only
considered. The effect of temperature and CO2 on RUE is especially
important in climate change studies using RUE based models. However, there is
no report on the response functions of RUE to temperature and CO2
concentration in chickpea.
Sinclair and Horie (1989), Sinclair
(1991), Sinclair et al. (1992) and Hammer
and Wright (1994) developed and extended a framework to analyze the effects
of radiation, leaf nitrogen, fraction diffuse radiation and leaf light-saturated
CO2 assimilation rate on RUE. This framework provides a simple and
effective method to analyses the variation of RUE between species and under
different conditions. The framework, however, does not account for the effects
of temperature and CO2 concentration.
Our objectives of this study were: (1) to extend and test the theoretical framework to model the effects of average daily temperature and atmospheric CO2 concentration on RUE and (2) to use the extended framework to produce the response functions of chickpea RUE to average daily temperature and atmospheric CO2.
Materials and Methods
The Theoretical Framework Used
Crop radiation use efficiency on any day is calculated as the ratio of crop
biomass produced that day to total solar radiation intercepted by the canopy
that day. Crop biomass increment is determined from canopy gross CO2
assimilation rate, daily rate of maintenance respiration costs and the assimilate
requirement for dry matter production (Goudriaan and van Laar,
1994; Choudhury, 2000). Growth respiration and the
efficiency of conversion of glucose to plant tissue was computed using the procedure
of Penning de Vries et al. (1989). The maintenance
coefficients for chickpea were considered as 0.03 for leaves, 0.015 for stems,
0.015 for roots and 0.01 for storage organs based on Penning
de Vries et al. (1989) and Goudriaan and van Laar
(1994). When organs dry matter are not available, maintenance respiration
is calculated as a fraction of the daily total hexose production. The fraction
has a value of 0.15-0.2 (Sinclair and Horie, 1989).
Canopy gross assimilation is calculated by integrating the instantaneous assimilation
rates of sun leaves and shade leaves over the day light periods. The instantaneous
assimilation rates are calculated from the product of leaf area index of sunlit
or shade leaves and the assimilation rate per unit leaf area (P). P is given
by an asymptotic exponential equation of radiation flux density incident on
either sun or shade leaves (KJ m-2 sec-1) (Boote
and Loomis, 1991):
where Pmax (mg CO2 m-2 sec-1) is the assimilation rate per unit leaf area asymptote to leaf potential for CO2 assimilation rate per unit leaf area corrected for temperature and CO2 concentration and QEc (mg CO2 kJ-1) is the light use efficiency at low light corrected for temperature and atmospheric CO2.
The leaf area index of sun or shade leaves is calculated by considering the
sun angle elevation, the proportion of intercepted radiation and shadow projection
function (Boote and Loomis, 1991). The radiation flux
density, incident on either sun or shade leaves is calculated from the incident
direct and diffuse radiation, the proportion of incident radiation intercepted
by the leaf canopy and the leaf area index of sun or shade leaves in a manner
similar to Sinclair et al. (1992). The direct
and diffuse components of the total incident radiation at any time are calculated
in a manner similar to that of Goudriaan and van Laar (1994).
Pmaxc and QEc, required in Eq. 1 are calculated by:
where Pmax is leaf light-saturated CO2 assimilation rate
(mg CO2 m-2 sec-1), Ptmp is a correction
factor (between 0 to 1) of Pmax for temperature,is
a correction factor of Pmax for atmospheric CO2 concentration,
QE is the light use efficiency at low light which was set at 5 mg CO2 KJ-1
(Sinclair and Horie, 1989) and is
a correction factor of QE for CO2 concentrations.
The correction of the Pmax and QE for the effect of atmospheric
CO2 is modeled using Farquhar and von Cammerer
(1982) procedure for limiting RuBP as used by Boote
and Pickering (1994) and Yu et al. (2003):
where CiPmax is internal CO2 concentration
for the computation of with
a Ci/Ca ratio of 0.7, CiQE is internal
CO2 concentration for the computation of with
a Ci/Ca ratio of 1 and Γ* is CO2 compensation
point in absence of dark respiration. The factors 6.5382 and 5.7768 scaleandto
1 at 25°C and 350 ppm CO2, respectively. CiPmax
and CiQE are calculated as:
where CO2 is atmospheric CO2 concentration (ppm). The
Γ* depends on the specificity factor (calculated according to Evans
and Farquhar, 1991) and the O2 concentration.
Photosynthesis response to temperature is modeled as Goudriaan
and van Laar (1994). Considering a lack of data for chickpea, the Pmax
response function to temperature was borrowed from Penning de Veris et al.
(1989) based on a fababean (a cool season legume crop like chickpea) photosynthesis
response to temperature; Ptmp increases from 0 at 3°C to relative
rate of 1 between 14°C and 22.5°C, declines with rising temperature
above 22.5°C and reaches to 0 at 35°C. The average temperature during
daytime is used to determine the relative response of Pmax to temperature
(Ptmp). QE was related to temperature using the function for C3
plants cited in Penning de Veris et al. (1989).
A detailed description of the model equations and source codes of the model are obtainable from the authors.
Test of the Model
To conduct a general test of the model, Pmax was firstly estimated
as 0.85 mg CO2 m-2 sec-1 for chickpea cultivars
Jam and Kaka using crop growth rate data of K. Ghassemi-Golezani (unpubl. data).
For testing of the model, crop growth rate data of Movahhedi
(1996) was used. To do this, average daily crop growth rates (g m-2
day-1) were calculated using weekly samples of crop dry matter. In
each case meteorological observations of maximum and minimum temperatures and
sunshine hours were available and LAI for each day between samplings was estimated
using linear interpolation. Then average simulated crop growth rates for different
intervals were calculated and compared with observed ones.
For specific test of the model, calculated RUEs at temperatures between 13
and 23°C were compared to the measured values by Soltani
et al. (2006) for the same average temperatures. Similarly, percentage
increase in RUE calculated for CO2 concentrations of 640 ppm relative
to 330 ppm was compared to percentage increase in biomass production measured
by Khana-Chopra and Sinha (1987) in three chickpea cultivars
at the same CO2 concentrations.
||Typical characteristics of a chickpea crop between flowering
and beginning seed growth in Tabriz, NW Iran (K. Ghassemi-Golezani, unpubl.
data of 2 years growth analysis of 9 chickpea cultivars at the University
of Tabriz, Tabriz, Iran; Movahedi, 1996)
|*Estimated using a root/shoot ratio of 0.2 (Gregory,
Simulation for Chickpea
The model was run for chickpea crops at different latitudes and days of
year with varying LAI and crop weight. Results showed that RUE is changed little
with variation of latitude, day of year and LAI (data not shown), thus a typical
chickpea crop between flowering and beginning seed growth stages in Tabriz (38°N),
NW Iran, with characteristics presented in Table 1 was considered.
In this stage which occurs at day of year 177 (with a range of 170 to 190),
vegetative organs are dominant. Long-term (1965-1997) averages of temperature
and solar radiation at this time are 25°C and 27.7 MJ m-2 day-1,
respectively. The latitude was set at 38°N, which corresponds to the chickpea
growing area in NW Iran and the location of the crop presented in Table
1. To generate the response functions of RUE, daily average temperatures
from 0 to 40°C and ambient CO2 concentrations from 20 to 1200
ppm were inputted to the model.
Results and Discussion
Figure 1 shows a plot of simulated versus observed crop growth
rates. The crop growth rate data were observed under (and simulated for) average
daily temperatures ranged from 11 to 28°C. Good agreement between simulated
and observed crop growth rates was obtained.
||Simulated versus observed Crop Growth Rates (CGR) for chickpea
cultivars Jam and Kaka. The solid line is 1:1 line and the thick line is
the regression line
||Simulated curve of RUE response to temperature and experimental
RUE values. Squares are RUE values from Exp. 1 and circles from Exp. 2 of
Soltani et al. (2006)
This test show the ability of the model to simulate daily biomass production
under a range of temperatures. Of course, it should be noted that under field
conditions temperature is normally associated positively with solar radiation
and negatively with vapor pressure deficit.
The calculated RUEs for temperatures of 13 to 23°C were similar to that
measured by Soltani et al. (2006) in chickpea
under the same temperature averages (Fig. 2). Soltani
et al. (2006) measured RUE in 2 experiments each with 4 plant densities
and 3 sowing dates at Gorgan in the west part of the Caspian Sea Coast of Iran.
There was no significant difference between sowing densities, but sowing dates
differed significantly. Variability of RUE between sowing dates was related
to temperature. Khana-Chopra and Sinha (1987) found, in
three chickpea genotypes, that with increase in CO2 concentration
from 330 to 640 ppm, biomass production increases by 20 to 33%. The model predicts
a 25% increase in RUE for the same concentrations, midway between the reported
values. From these tests we concluded that model performance is acceptable and
can be used to produce response of RUE to temperature and CO2 concentration.
With mean daily temperature of 25°C and radiation of 27.7 MJ m-2 day-1
the crop presented in Table 1 produced 23.8 g DM m-2.
RUE was 0.95 g MJ-1 that was obtained with a Pmax of 0.85
mg CO2 m-2 sec-1. This value of RUE is also
equal to that reported for chickpea by Hughes et al.
Figure 2 shows the dependence of RUE to average daily temperature. At temperatures lower than 3°C and higher than 36°C RUE is zero. RUE is sharply increased (9.5%°C-1) with increasing temperature from 3 to 14°C, where it has maximum of its value. With further increase in temperature to 22°C, RUE is slowly decreased (1.4%°C-1). Rising temperature from 22 to 36°C is resulted in the sharp decrease (7.4%°C-1) of RUE. This sharp decrease is a result of increasing respiration and declining photosynthesis with increase in temperature.
Figure 3 shows response to atmospheric CO2 of
RUE in chickpea. At CO2 concentrations lower than 60 ppm, RUE is
zero, a similar value presented by Wolfe (1994) for net
photosynthesis response to CO2. With increasing CO2, RUE
is increased by a diminishing rate and saturated at CO2 greater than
700 ppm. This response also is very similar to that reported for C3
plants (net photosynthesis) by Wolfe (1994). Figure
3 shows that a doubling atmospheric CO2 (from 350 to 700 ppm)
increases RUE of chickpea by 23%. Kimball et al.
(2002) summarizing data from experimental studies, found a 25% increase
in growth rate with a doubling of CO2 concentration. Melkonian et
al. (1998), using three formulations for estimating the impact of elevated
CO2 on daily net canopy carbon assimilation, found that with doubling
CO2 concentration 15-48% increase in net carbon assimilation is occurred.
||Simulated Radiation Use Efficiency (RUE) of chickpea as a
function of atmospheric CO2 concentration
Overall, by integrating quantitative relationships that capture the physiological
responses, a simple, suitable theoretical framework was extended to allow the
effects of temperature and CO2 on RUE. By using the framework, response
functions of RUE to temperature and atmospheric CO2 concentration
were calculated for chickpea. The RUE response to temperature and CO2
concentration is consistent with the results obtained for some other C3
crops. These functions can be used for describing the response of RUE to temperature
and CO2 concentration in climate change studies.
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