Interaction between Atmospheric CO2 Concentration and Night
Temperature Rise on CH4 Emission from Paddy Fields
Abstract
Carbon dioxide (CO2) concentration increase in the atmosphere promotes methane
(CH4) emission from paddy soils. Through the controlled-environment chamber
experiment, we clarified that CH4 emission is controlled by high night temperature. The
study helps to predict global warming and understand the feedback effect on CH4
emission caused by climate change.
Research Institute: Toshihiro Hasegawa, Ikoku Tei, Hidemitsu Sakai, Kazuyuki Yagi
National Institute for Agro-Environmental Sciences
Background and Purposes
The paddy field is considered as one of the major sources of CH4. Although we all
know that CH4 emission from paddy fields will increase when temperature rises, it is
not very clear that CO2 increase in the atmosphere will enhance CH4 emission. There is
limited knowledge about the influence on CH4 emission of the combination of CO2
concentration and temperature, In particular, the influence of night temperature
increase is unknown. So it will contribute to making estimates of future CH4 emission.
For this reason, we used the semi-enclosed and natural light controlled-environment
chamber (Climatron) to control CO2 concentration and night temperature, and
investigated the effects on methane emission from paddy fields.
Achievements and Features
The seedling (cultivar IR27), which was transplanted in a pot, was sown outdoors.
The rice was put in the Climatron from the middle period of the generative growth
period (59 days after transplanting). Then the rice was cultivated under 4 conditions of
two sets of night temperature (high night temperature of 32°C, low night temperature
of 22°C, day temperature of 32°C) and two sets of CO2 level (ambient concentration at
380ppm, elevated concentration at 680ppm). (Figure 1) CH4 flux sharply increased
around the heading stage five weeks after transplanting, and then decreased until
harvest (Figure 2). High night temperature was highly influential and CH4 emission
increased by up to 50% of the average. In addition, elevated CO2 concentration also
promoted CH4 emission. Even in conditions where there was no difference in the
number of stems, this was the first time the influence of elevated CO2 was most obvious.
Elevated CO2 caused CH4 emission increase by 32% and 4% under low and high night
temperature, respectively. However, the high night temperature restrained the
promotion of CH4 emission by elevated CO2 (Table 1). Although rice biomass increase is
one of the reasons to enrich CH4 emission, the high night temperature repressed the
rice dry weight increase by elevated CO2. The study implies that the high night
temperature reduced the effect of elevated CO2 on CH4 emission because photosynthesis
and dry weight growth in response to CO2 concentration was low. Based on the above
results, we can obtain useful knowledge to clarify and predict the feedback effect of
climate change on CH4 emission.
Figure 1. Experimental schedule of elevated CO2 concentration and high night
temperature by using the Climatron of NIAES, Tsukuba, Ibaraki and daily air
temperature variation. Because the night temperature and CO2 treatment started after
the highest tillering stage, the effect of the treatment in the number of stems, which has
an effect on CH4 emission was not found.
Figure 2. Changes in daily CH4 flux. Vertical bars indicate standard deviation (n=3).
EH: elevated CO2 and high night temperature; AH: ambient CO2 and high night
temperature; EL: elevated CO2 and low night temperature; AL: ambient CO2 and low
nigh temperature. Transplanting was performed on June 26, 2006. Arrows indicate
heading days.
Table 1. Effects of elevated CO2 and night temperature on CH4 emission and net dry
weight increase after treatment, as well as the on total rice dry weight and stem dry
weight at harvest.
Night
CO2
CH4
Net total
Total dry
Stem dry
temperature
concentration
emission
dry weight
weight at
weight at
(℃)
(ppm)
(g C/hill-1)
increase
harvest
harvest
32
(g hill-1)
(g hill-1)
(g hill-1)
680 (EH)
1.00 a*
61 a
122 a
51 a
380 (AH)
0.96 a
54 a
115 a
47 a
Growth rate
3.5
13
5.9
7.7
680 (EL)
0.74 b
58 a
119 a
42 a
380 (AL
0.56 c
42 b
103 b
33 b
Growth rate
32
38
16
26
(%)
22
(%)
*: Identical letters indicate that there is no significant difference (5% of the standard)
between treatments.