Responses of Rice (Oryza sativa L.) Cultivars to Altered Climatic Conditions, Particularly Elevated Temperature

Estela Pasuquin

Research output: ThesisDoctoral Thesis

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Changes in the environment can affect food crop production, including
rice, the staple of more than half of the world’s population. Anticipated
changes in climate are predicted to affect temperature and rainfall patterns
as well as other climate factors. The effects of the combined changes of
climate on agricultural production are difficult to predict, but scientists
anticipate food production to likely be affected. One strategy to aid in
accommodating a changing climate is to select better adapted cultivars, or
develop new cultivars better adapted to heat and variable rainfall. To do
this, more knowledge on the responses of crops to sets of climatic
components need to be established. This study evaluated the responses of a
series of rice cultivars to elevated temperatures in a controlled environment
and in field-based chambers. The first experiment aimed at examining the
effect of maintaining constant day/night temperature under two light
regimes in growth rooms with artificial light at Wagga Wagga, and with
natural light at Yanco, NSW, Australia. A total of 18 cultivars of different
genetic backgrounds (indica, japonica, indica/japonica, and
glaberrima/japonica) were used. Part 1 of the second experiment focused on
the effects of varying temperatures under similar relative humidity, and Part
2 examined the effects of varying relative humidity under a similar
temperature. This study was conducted in highly controlled growth rooms
(Climatron) at the National Institute for Agro-Environmental Sciences in
Tsukuba, Japan. The third experiment aimed to determine the effects of day
temperature elevation in field-based chambers during the panicle
differentiation stage in Wagga Wagga, NSW, Australia. The cultivars that
performed better in these highly contrasting conditions are anticipated to be
better adapted to future climatic events.

There was interaction between light intensity and temperature in
biomass production. The total shoot biomass was highest at 31 ºC under
artificial light and at 25 and 28 ºC under natural light. From among the 18
cultivars, total shoot biomass was consistently higher in IR64, IR72, N22,
Vandana (all indica), and Takanari (indica/japonica) at tested light intensity
and temperature. This was highly related to leaf area.

The responses were more variable at the high- than at the lowtemperature
experiment. The increase in temperature from 28/22 ºC to 32/22
ºC at 70% relative humidity did not affect total plant biomass in the four
cultivars selected from the initial experiment (Akihikari, IR64, N22, and
Takanari). These were attributed to the unaffected photosynthesis and
assimilate (sucrose) concentration in the stem. On the other hand, the
increase in temperature from 32/22 ºC to 35/22 ºC at 70% relative humidity
increased total plant biomass in N22 only. This was linked to the increase in
stomatal conductance, intercellular CO2 concentration, photosynthesis, and
leaf area. This increase in temperature did not affect organ and total plant
biomass in Takanari as did stomatal conductance, photosynthesis, and leaf
area. In contrast, the increase in temperature reduced total plant biomass in
Akihikari and IR64, consistent with the reduction in stomatal conductance
and photosynthesis even when leaf area was unaffected.

Stable physiological and morphological responses determined the
cultivars’ better adaptation to decrease in relative humidity. The
photosynthesis in N22, and the photosynthesis and transpiration in Takanari
were unaffected by the decrease in relative humidity from 72 to 50% at
32/22 ºC. These were regarded to contribute to higher total plant biomass,
and to support the filling of a high total number of spikelet in these
cultivars. The stem length in Takanari was also unaffected. The comparable
filled-grain biomass of IR64 with N22 and Takanari at 50% relative
humidity, despite the significant decrease in stomatal conductance,
photosynthesis, and intercellular CO2 concentration during the treatment
period, was attributed to high leaf area at maturity. The reduced stomatal
conductance, photosynthesis, and intercellular CO2 concentration in
Akihikari and IR64 reduced the leaf area, specific leaf area, and stem length.
These also reduced organ (leaf, stem, and root) and total plant biomass.

Plants can modify their environments to avoid the negative effects of
elevated temperature. A higher mean maximum day temperature of 10 ºC
between elevated and ambient temperature chambers at a relative humidity
of around 40% over a 12-day period during the early panicle differentiation
stage did not affect total plant biomass and yield components of IR64, N22,
Takanari, and Vandana. This was related to the cooler lower canopy
temperature (33 ºC) than the above canopy (41 ºC) in the elevated
temperature treatment possible from the transpiration of plants, the
cumulative effects of evaporation of ponded water, and shading by the
upper canopy. The higher photosynthesis and transpiration in Takanari than
the other cultivars before, during, and after the treatment could have
supported the filling of a higher number of spikelets and resulted to higher
dry weight of filled grains at maturity.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Charles Sturt University
  • Eberbach, Philip, Co-Supervisor
  • Hasegawa, Toshihiro, Co-Supervisor, External person
  • Lafarge, Tanguy, Co-Supervisor, External person
  • Wade, Leonard, Co-Supervisor
Award date21 Aug 2014
Place of PublicationAustralia
Publication statusPublished - 2014

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