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

Estela Pasuquin

    Research output: ThesisDoctoral Thesis

    123 Downloads (Pure)

    Abstract

    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
    Supervisors/Advisors
    • 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
    Publisher
    Publication statusPublished - 2014

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