4.1 Assessment of field warming and the impact on rice quality
formation
Since 2009, we have continuously carried out warming experiments in rice
fields based on the open-field free air temperature enhancement system
(FATE), and the effects of increased temperature on rice growth and
development were guardedly studied. The ultimate goal of our study is to
find key regulatory factors or metabolic pathways involved in rice
growth process and apply appropriate field cultivation measures to
reasonably respond to the challenge of climate warming on rice. The FATE
device is suspended above the field and uses 12 sets of ceramic infrared
heaters to perform uniform heating in an area of
7.1m2. In the fully activated state, the daytime
canopy temperature of rice can be increased by 2.4℃ on the basis of
natural temperature, and the rice canopy night temperature can be
increased by 5.4℃. This warming range is within the prediction of
possible temperature increase by 1.4-5.8 °C at the end of the 21st
century by IPCC (IPCC, AR5, 2014). Furthermore, the increase in night
temperature is significantly greater than that during the day and that
is consistent with the asymmetric trend of climate warming
(Pachauri et al., 2014). Compared
with closed or semi-closed warming scenario, the warming method and
effect adopted in this project could closely simulate climate warming
characteristics and that provides a more reliable platform for us to
conduct related experiments in the actual field.
Rice quality is a complex characteristic, including appearance, milling,
nutrition, cooking and eating quality. Our field evidence shows that the
overall temperature increase has a relatively negative effect on rice
quality, including significantly increased chalky rate, chalky area and
chalkiness. Meanwhile, the milling quality indicators milled rice rate
and head rice rate were decreased significantly, and that would
exceedingly reduce the market recognition of rice. Our previous
researches have been devoted to exploring the mechanism of the influence
of increased temperature on rice quality and to our knowledge, the
changes of external temperature inevitably affect the morphological
composition and structure of the grain storage material, and that
further induce the changes of related quality traits (Dou et al., 2017;
Dou et al., 2018; Tang et al., 2018; Tang et al., 2019). Among these
attributes, eating and cooking quality (ECQ) is one of the most
important indicators, especially from the consumer’s perspective. The
eating quality refers to the sensory perception of consumers on rice,
and is related to the gloss, flavor, and viscosity of rice. Although the
physical and chemical properties of starch in rice endosperm can be used
as an indirect indicator of ECQ, it is still a difficult task to assess
ECQ through these traits. At the same time, the increase of glutelin
content in rice grain is particularly obvious under the condition of
increased temperature, which leads to a change in the overall balance of
grain storage materials and has a negative impact on the taste and
appearance quality of the rice.