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دوشنبه 19 اردیبهشت 1390

4-7

نویسنده: رضا کوشکی   

Fig. 2 Evolution of cardinal temperatures for wheat from vernalisation to grain filling (data source:
Porter and Gawith (1999)). VER vernalisation, SE sowing to emergence, TSI terminal spikelet
initiation, AT anthesis, GF grain filling

Downs (1972) found that grain yield and maximum dry matter production have a
Topt of 27/22◦ C. A recent study by Prasad et al. (2006) found that grain yield, harvest
index, pollen viability and percent seed-set have a Topt of 32/22◦ C and a Tfp of
40/30◦ C, and that vegetative biomass, photosynthesis and seed size has a Topt of
40/30◦ C, 44/34◦ C and 36/26◦ C respectively.
Summer cereal crops such as maize, rice and sorghum have relatively higher Topt
for crop growth and development compared with that of winter cereal crops such as
wheat. Reproductive stage of summer crops has relatively lower Topt compared with
vegetative stage.

 

2.2 Horticultural crops

Broccoli Tan et al. (1999) quantified and assessed the effects of a range of sub
zero Ts for a short period at different stages of crop development on the mortality,
yield and quality of broccoli. Whole plants in pots or in the field were subjected
to sub-zero T regimes from −1 to −19◦ C. It was found that lethal T for pot-grown
broccoli was between −5 ∼ −3◦ C, whereas the lethal T for field-grown broccoli was
between −9 ∼ −7◦ C. This study also found that the floral initiation is more sensitive
to freezing Ts than at florescence buttoning stage. Tan et al. (2000) estimated Tbase
and Topt for broccoli based on experimental studies in southeast Queensland. Three
cultivars (Fiesta, Greenbelt and Marathon) were sown on eight dates from 11 Mar.
to 22 May 1997 and grew under natural and extended (16 h) photoperiods under
non-limiting conditions of water and nutrient supply. This study found that broccoli
has a Tbase of 0◦ C and a Top of 20◦ C during the entire growing cycle. Unlike wheat,
cardinal Ts do not increase with the progression of broccoli life cycle.

Citrus Rosenzweig et al. (1996) summarized Topt ranges for different phenophases
of citrus. It was reported that dormancy stage has a Topt range of −4◦ C to 14◦ C. This
stage includes two sub-stages: hardening and pre-bloom. Their corresponding Topt
is −4◦ C to 8◦ C and 0◦ C to 14◦ C respectively. Flowering time has a Topt of 10–27◦ C.
Fruit set has a Topt of 22–27◦ C and fruit growth has a Topt of 20–33◦ C. Similar to
wheat crops Topt increases with the progression of citrus growth and development.

 

It was also reported that maturation has a Topt of 13–27◦ C for the development of
soluble sugars and 8–18◦ C for the development of colour. Maximum temperature of
35◦ C and minimum temperature of 2◦ C were identified as the temperature thresholds
for citrus across its growing season (Tahir Khurshid, pers. comm.).

It was also reported that maturation has a Topt of 13–27◦ C for the development of
soluble sugars and 8–18◦ C for the development of colour. Maximum temperature of
35◦ C and minimum temperature of 2◦ C were identified as the temperature thresholds
for citrus across its growing season (Tahir Khurshid, pers. comm.).

2.3 Legume crops

Dry bean/common bean Prasad et al. (2002) reported that dry bean seed yield has a
Topt of 23◦ C and a Tfp of 32◦ C. A study by Laing et al. (1984) stated that bean yield
has a Topt of 24◦ C.

 

 

The Tbase for peanut leaf appearance rate and onset of anthesis
is 10◦ C and 11◦ C respectively (Ong 1986). The Topt for leaf appearance rate is above
30◦ C while the Topt for rate of vegetative development to anthesis is between 29◦ C
and 33◦ C (Bolhuis and deGroot 1959). Leaf photosynthesis has a fairly high Topt of
36◦ C. Pollen viability and percent seed-set have a Topt of <31◦ C and a Tfp of 44/34◦ C
(Prasad et al. 2003). Percent fruit-set has a Topt of <33◦ C (bud temperature) and a
Tfp of 43◦ C (bud temperature) (Prasad et al. 2001). Cox (1979) observed that single
pod growth rate and pod size has a Topt of 24◦ C. Williams et al. (1975) found that
peanut yield has a Topt of 20◦ C. Hatfield et al. (2008) summarised that Topt for pod
yield, seed yield, pod harvest index and seed size is in the range of 23 ∼ 24◦ C and
with a Tfp of 40◦ C based on Prasad et al. (2003).

Soybean Reproductive development (time to anthesis) in soybean has a Tbase of
6◦ C and a Topt of 26◦ C (Boote et al. 1998). The post-anthesis phase has a lower Topt
of 23◦ C (Egli and Wardlaw 1980; Baker et al. 1989; Pan 1996; Thomas 2001; Boote
et al. 2005) compared with that of reproductive development. Pan (1996) and Thomas
(2001) found that mean temperature of 39◦ C is lethal to soybean yield production.
Averaged over many cultivars the cardinal temperatures (Tbase, Topt, and Tfp) were
13.2◦ C, 30.2◦ C and 47.2◦ C for pollen germination and 12.1◦ C, 36.1◦ C and 47.0◦ C for
pollen tube growth (Hatfield et al. 2008).

 

2.4 Other crops

It was reported that cotton vegetative development has a Tbase of 14◦ C and a Topt
of 37◦ C (Reddy et al. 1999 and 2005) which is higher than that of other crops due
to its higher adaptability to higher temperature environment (Hatfield et al. 2008).
However, cotton reproductive progression has a lower Topt of 28 ∼ 30◦ C (Reddy
et al. 1997 and 1999). Reddy et al. (2005) found that growth rate per boll has a Topt

 

دوشنبه 19 اردیبهشت 1390

1-3

نویسنده: رضا کوشکی   

 

 

Abstract Temperature thresholds for a range of crops from cereal crops to horti-


cultural crops and to legum crops were identified through an extensive literature
review. Identification of temperature thresholds provides a basis for quantifying the
probability of exceeding temperature thresholds which is a very important aspect of
climate change risk assessment. The effects of extreme temperatures on yield and
yield components were then reviewed and summarised. Through these processes,
critical phenophases were defined based on the sensitivity of crop yield and/or
yield components to extreme high temperatures which were imposed on various
phenophases. Information on the direction and degree of the impact of extreme
temperature on yield/yield components can contribute to the improvement of crop
models in which the effects of extreme temperature on crop production have not
been adequately represented at this stage. Identification of critical phenophases at
which crops yield and/or other economic characteristics are sensitive to extreme
temperatures will help scoping appropriate adaptation options.

1 Introduction

Temperature (T) is one of the major environment factors affecting the growth,
development and yields of crops especially the rate of development. On one hand,
crops have basic requirement for T to complete a specific phenophase or the whole
life cycle. On the other hand, extremely high and low Ts can have detrimental effects
on crop growth, development and yield particularly at critical phenophases such as

Climatic Change

anthesis. Wheeler et al. (2000) pointed out that the effects of hot T episodes close
to the time of anthesis were of more importance to the yield of many crops than
the effects of the increase in mean seasonal T of about 2◦ C. Cardinal T (i.e. base T
(Tbase), optimum T (Topt1 and Topt2), and failure point T (Tfp)) and lethal T (e.g.
lethal minimum T (Tlmin) and lethal maximum T (Tlmax)) are typical Ts associated
with crop production. Crops grow and develop ideally within the range of Topts and
at a slower rate beyond the range (the so-called sub/supra-Topt). It was found that
the rate of many development processes is a positive linear function of T between
Tbase and Topt and a negative linear function of T between Topt2 and Tfp (Roberts
and Summerfield 1987; Wheeler et al. 2000). Figure 1 depicts the relative position of
these temperatures. Tfp represents failure (ceiling) T at which grain yield fails to zero
yield (Hatfield et al. 2008). The difference between lethal Ts and cardinal Ts is that
recovery of function is possible within the range of cardinal Ts but is irrecoverably
lost beyond the lethal limits (Porter and Gawith 1999). Cardinal T and lethal T are
associated with thresholds. What they relate to climate change risk assessment is how
often and much T thresholds will be crossed and what the effects of exceeding those
T thresholds might be in relation to crop yield and yield components including impact
direction and magnitude. Under global warming scenarios, the chances and extent of
crossing T thresholds may be higher and more than those under current temperature
regime.
It seems that there is an urgent need to identify temperature thresholds and the
effects of extreme temperature on crop production. Identification of temperature
thresholds will provide a starting point for assessing extreme temperature related
risks and this will provide a pathway toward to exploring adaptation options. Iden-
tification of the effects of extreme temperature on crop production across various
phenophases will help to define critical phenophases so that impact assessment and
adaptation evaluation/implementation are focus-oriented. Information on the effects
of extreme temperature on crop production under various field/controlled environ-
mental conditions can be used to improve crop models for accurate quantification
of the impacts of temperature change on crop production at regional level. The
impacts of mean T on crop production were represented in some crop models by
growing degree days (GDD). However, the effect of extreme Ts on crop production
is lacking in many models which may bias the projection of the impacts of climate

 

Fig. 1 Relative position of temperature types. Data source: Porter and Gawith (1999). The cardinal
temperatures (Tbase, Topt and Tmax) are associated with terminal spikelet initiation stage

 

change on crop production. This indicates that crop models need to be improved to
accommodate the effects of extreme T on crop production.

From what argued above, this paper aims to identify temperature thresholds and
the effects of exceeding temperature thresholds on crop yield and yield components
for various phenological stages and across a range of crops from cereal crops to
legume crops and to horticultural crops based on an extensive literature review
and to identify the key phenophases which are most sensitive to the exceedance of
temperature thresholds. This kind of information will be very useful for assessing
temperature change impacts and for scoping appropriate adaptation options either
for a specific industry or for a specific region where a range of crops grow.

2 Temperature thresholds

2.1 Cereal crops

Wheat Temperature thresholds in relation to wheat were well defined. Porter
and Gawith (1999) extensively reviewed temperature thresholds across different
components (root, leaf, culm) and phenophases based on worldwide experimental
studies. Key findings from that literature were given in Table 1. It is found that
cardinal temperatures increase as wheat growth and development progress (Porter
and Gawith 1999; Slafer and Rawson 1995). This was demonstrated in Fig. 2.

 

Barley Prasil et al. (2007) evaluated the tolerance of 39 barley cultivars and breed-
ing lines to low temperature by using four direct methods in the Czech Republic: (1)
field survival after five winters 1999–2004; (2) winter survival in a provocation pot
test under natural conditions; (3) lethal temperature (LT50) of plants taken from a
field in winter; and (4) LT50 of plants grown and hardened in a growth chamber. It
was found that barley has a Tlmin50 (at which 50% of samples are killed) of −17.3 ∼
−12.9◦ C across 20 cultivars which is close to the Tlmin (−18 ∼ −16◦ C) of wheat as
given in Table 1.

Maize Several studies found that temperatures of above 35◦ C are lethal to maize
pollen viability (Herrero and Johnson 1980; Schoper et al. 1987; Dupuis and Dumas
1990). Leaf photosynthesis rate of maize has a high Topt of 33◦ C to 38◦ C (Crafts-
Brandner and Salvucci (2002).

Rice The response of rice to temperature has been well studied. Leaf-appearance
rate increases with temperature from a Tbase of 8◦ C, until reaching 36–40◦ C, the
thermal threshold of survival (Alocilja and Ritchie 1991; Baker et al. 1995) with
biomass increasing up to 33◦ C (Matsushima et al. 1964). However, the Topt for grain
formation and yield is lower (25◦ C) (Baker et al. 1995). High percentages of rice
spikelet sterility occur if temperatures exceed 35◦ C at anthesis and last for more than
1 h (Yoshida 1981).

Sorghum The vegetative development of sorghum has a Tbase of 8◦ C and Topt of
34◦ C (Alagarswamy and Ritchie 1991) while reproductive development of sorghum
has a Topt of 31◦ C (Prasad et al. 2006). Maiti (1996) reported that sorghum vegetative
growth has a Topt of 26 ∼ 34◦ C while reproductive growth has a Topt of 25 ∼ 28◦ C.

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