Interactions of elevated [CO 2 ] and night temperature on rice growth and yield

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1 agricultural and forest meteorology 149 (2009) available at journal homepage: Interactions of elevated [CO 2 ] and night temperature on rice growth and yield Weiguo Cheng *, Hidemitsu Sakai, Kazuyuki Yagi, Toshihiro Hasegawa National Institute for Agro-Environmental Sciences, Kannondai 3-1-3, Tsukuba, Ibaraki , Japan article info Article history: Received 14 March 2008 Received in revised form 11 July 2008 Accepted 12 July 2008 Keywords: Dry weight Elevated [CO 2 ] Interaction Night temperature Rice growth Yield abstract To understand how a combination of high night temperature and elevated [CO 2 ] during the reproductive growth period affects rice growth and yield, we conducted a pot experiment in four controlled-environment chambers with two levels of [CO 2 ] (ambient, 380 ppm; and elevated, 680 ppm) and two levels of night temperature (22 and 32 8C). The day temperature was 32 8C in all treatments. As results, the whole plant and stem dry weight were significantly increased by both elevated [CO 2 ] and high night temperature (P < 0.01), while the ear dry weight was significantly increased by elevated [CO 2 ] and decreased by high night temperature (both P < 0.01). The fertilized spikelet number was significantly decreased by high night temperature (P < 0.01), but not affected by elevated [CO 2 ](P = 0.18). The individual grain weight was significantly increased by elevated [CO 2 ](P = 0.03). Consequently, brown rice yield was significantly increased by elevated [CO 2 ](P < 0.01) but decreased by high night temperature (P < 0.01), with a significant interaction of [CO 2 ] and night temperature (P < 0.05). The results indicate that high night temperature will reduce the stimulatory effect of elevated [CO 2 ] on rice production in the future if both continue to increase. # 2008 Elsevier B.V. All rights reserved. 1. Introduction Depending on population growth and energy use scenarios, atmospheric CO 2 concentration ([CO 2 ]) is expected to rise from 380 ppm currently to between 485 and 1000 ppm by 2100 (IPCC, 2001). The projected rise in the global average surface air temperature at the end of the 21st Century relative to will be around C, with a likely range of C (IPCC, 2007). The daily minimum (or night-time) temperature has increased faster than the daily maximum (daytime) temperature in the past century (Kukla and Karl, 1993; Easterling et al., 1997). Rice (Oryza sativa L.) is one of the most important crops in the world and the most important food in Asia. Projected changes in rice production in Asian countries have quite a wide range, depending on the crop models and global climate change scenarios (Matthews et al., 1997; Ohta and Kimura, 2007; Tao et al., 2008). Because both elevated [CO 2 ] and air temperature can have marked effects on rice growth and yield, it is important to quantify these effects. A number of studies have examined the effects of elevated atmospheric [CO 2 ]or combinations of elevated air temperature and [CO 2 ] on rice yield and growth during the last several decades (Yoshida, 1973a,b; Imai et al., 1985; Baker et al., 1992; Ziska et al., 1996; Horie et al., 2000; Kim et al., 2003; Baker, 2004; Yang et al., 2006; Sakai et al., 2006; Sasaki et al., 2007). Most results showed that elevated [CO 2 ] increased yield. Conversely, several studies have shown that high air temperatures can reduce grain yield even under CO 2 enrichment (Baker et al., 1992; Ziska et al., 1996; Matsui et al., 1997; Horie et al., 2000, Prasad et al., 2006) owing to increased spikelet sterility (Satake and Yoshida, 1978; Kim et al., 1996; Matsui et al., 1997; Ohe et al., 2007; Jagadish * Corresponding author at: Agro-Meteorology Division, National Institute for Agro-Environmental Sciences, Kannondai 3-1-3, Tsukuba, Ibaraki , Japan. Tel.: ; fax: address: cheng@niaes.affrc.go.jp (W. Cheng) /$ see front matter # 2008 Elsevier B.V. All rights reserved. doi: /j.agrformet

2 52 agricultural and forest meteorology 149 (2009) et al., 2007). A correlation study showed a yield decline with higher night temperatures due to global warming from 1979 to 2003 (Peng et al., 2004). However, no study has examined the interactions of increased [CO 2 ] and increased night air temperature on rice growth and yield, especially during rice reproductive stage. A theoretical analysis of the effect of day temperature on photosynthesis indicated that the enhancement of photosynthesis due to elevated [CO 2 ] is larger at higher temperature (Long, 1991; Morison and Lawlor, 1999). However, increased night temperature can counter this because of the heavier respiratory cost, increased by the larger biomass. Therefore, we hypothesized that an increased night temperature would reduce the stimulatory effect of elevated [CO 2 ] on both rice biomass and grain yield. We tested this hypothesis by examining growth, respiration, yield and yield components of rice grown at two CO 2 concentrations and two night air temperatures during the reproductive stage. Our objective was to understand how rice growth, fertilized spikelet percentage and yield respond to increased [CO 2 ] and high night temperature and their interaction. 2. Materials and methods 2.1. Experimental schedule, cultural practices, rice cultivar and soil This research was conducted at the National Institute for Agro-Environmental Sciences, Tsukuba, Japan ( N, E). Seedlings were raised in an outdoor water tank and then grown in controlled-environment chambers during the reproductive growth stage (Fig. 1). We grew a semi-dwarf rice, cv. IR72, an indica cultivar popularly grown in South-East Asia (Peng et al., 1999). On 5 June 2006, germinated seeds were sown in a seedling tray (three seeds per cell). At 3 weeks after sowing, the seedlings (three plants) were transplanted to 15 plastic pots (19.5 cm inside diameter, 27.0 cm height, 0.2 cm thickness) filled with 7.4 kg grey sandy soil. The plants growing in each pot was defined as one hill for the whole rice growing period. The sandy soil was collected from the plough layer (15 cm of the top layer) of a rice field in Kujukuri, Chiba Prefecture, Japan, that contained 8.1 g kg 1 organic C and 0.9 g kg 1 total N, and the average ph was 6.3. Before transplanting, 9.0 kg (7.4 kg dry soil equivalent) of soil was mixed with 1.53 g NH 4 Cl and 0.87 g KH 2 PO 4 and placed in each pot. The NPK levels were 0.40:0.20:0.25 g per pot. At 35 and 49 days after transplanting (DAT), we top-dressed with 0.62:0.10:0.13 g per pot. The water depth was maintained at about 5 cm throughout the cultivation period. We applied the treatments during the reproductive stage only, because the climatic factors, such as high or low temperatures during this stage strongly affect rice yield (Matsui et al., 1997). Treatments were started at 59 DAT, when three pots were randomly moved to each of four controlledenvironment chambers (see below) and plants in the other three pots were destructively sampled. Grain was harvested at 107 and 114 DAT in the high and low night temperature treatments, respectively, depending on the physiological maturity Experimental design and controlled-environment chambers We used four controlled-environment chambers (Climatrons, made by Shimadzu, Kyoto, Japan) to apply the two [CO 2 ] and two night temperature treatments. Each chamber measured 4m 2m 2m(L W H). Each housed two stainless-steel containers (1.5 m 1.5 m 0.3 m; L W D) filled with water to hold the pots. We have used these chambers since 1996 to carry out elevated CO 2 experiments with rice (Cheng et al., 2001, 2006; Sakai et al., 2001, 2006). Because there were no chamber replicates (i.e., true replicates) in this study, we rotated the treatments among the four chambers every 3 weeks (changed the environmental settings and moved the Fig. 1 Experimental schedule, changes in daily average air temperature (before treatment in outdoor water tank), and daily air temperature variation (during treatment in controlled-environment chambers).

3 agricultural and forest meteorology 149 (2009) pots so that the pots received the same treatment) during the treatment period, so as to minimize variation due to the controlling system. The four treatments and their abbreviations were as follows: (1) Elevated [CO 2 ] at 680 ppm and High night temperature at 32 8C (EH); (2) Ambient [CO 2 ] at 380 ppm and High night temperature at 32 8C (AH); (3) Elevated [CO 2 ] at 680 ppm and Low night temperature at 22 8C (EL); (4) Ambient [CO 2 ] at 380 ppm and Low night temperature at 22 8C (AL). As implied in Fig. 1, the temperature was maintained at a constant 32 8C in the high night air temperature treatment. In the low night air temperature treatment, it was maintained at 32 8C from 08:00 h until 16:00 h, decreased at 2.5 8Ch 1 to 20:00 h, maintained at 22 8C from 20:00 h until 04:00 h, then increased at 2.5 8C h 1 to 08:00 h. Air and soil (at 10 cm depth) temperatures during 9 11 September 2006 in both temperature treatments were recorded every 10 min by a Thermo Recorder (TR-71U, T&D Corp., Tokyo, Japan) (Fig. 2). The actual average air temperatures were 30.3 and C, respectively; and the soil temperatures were 28.4 and C for high and low night temperature treatments, respectively. The differences of daily average air and soil temperatures between the high and low night temperature treatments were 3.8 and 4.2 8C, respectively, close to values predicted in global climate change scenarios at the end of the 21st century (IPCC, 2007) Growth, destructive sampling and yield measurements Plant height and tiller number were measured once a week. At the beginning of treatment, 59 DAT and final harvest, we collected plants from three pots, carefully washed the soil from the roots in running water, then separated the plants into stems, leaves, roots and ears (final harvest only). The parts were then oven-dried at 80 8C for 3 days and weighed. To measure yield, we air-dried the ears for 4 weeks, counted the number of panicles and carefully threshed the grain. Grain was soaked in tap water and the numbers of sunken and floating grains were counted to determine the grain-filling rate. The dry weight of sunken grain was determined after drying at 80 8C in a forced-air oven for 1 week. Gross yield was defined as the dry weight of filled grain. After hulling, the weight of the edible portion was defined as the brown rice yield (expressed on the basis of 15% moisture content). The floating grain was used to determine grain fertility by iodine reaction with starch (Matsushima and Tanaka, 1960). Harvest index (HI) was calculated from the gross yield and the plant total dry weight Night-time respiration measurements Night respiration was measured as the CO 2 flux in a cylindrical closed-top flux chamber (20.5 cm inside diameter, cm high, 0.3 cm thick) each week during the treatment period at around 22:00 h. We covered each pot within the growth chamber for 30 min. At 0, 15 and 30 min after the chamber was put in place, we withdrew about 30 ml of gas with a 50 ml plastic syringe through a capillary tube at the top of the chamber and injected it into a 19 ml vacuum bottle with a rubber stopper and screw cap. Back at the laboratory, the CO 2 was measured by gas chromatograph (Shimadzu GC-7A, Kyoto, Japan) with a thermal conductivity detector (TCD). The flux rate was calculated from the increase in CO 2 concentration inside the flux chamber for each pot or hill (Cheng et al., 2006) Statistical analysis We calculated the analysis of variance (ANOVA) of plant height, tiller number and night respiration for each week during the treatment period. [CO 2 ] and night temperature were main-plot factors, and DAT was a split-plot factor. We excluded the data on 113 DAT because the high night temperature treatment had finished. We conducted a twoway ANOVA of the dry weight of each organ and whole plants, grain yield and yield components at harvest for effects of [CO 2 ], night temperature and [CO 2 ] night temperature. The analysis was carried out with the statistical package SPSS 14 (SPSS Inc., Chicago, IL, USA). 3. Results Fig. 2 Air temperature and soil temperature at 10 cm over 72 h (recorded every 10 min) in (a) low night temperature and (b) high night temperature treatments during 9 11 September Plant height and tiller number Plant height increased steadily until the grain-filling stage (90 DAT) in all four treatments. It was significantly increased

4 54 agricultural and forest meteorology 149 (2009) Fig. 3 Changes in (a) plant heights and (b) tiller numbers of rice plants throughout the experiment. Bars indicate standard deviation (n = 3). Bef: before treatment; EH: elevated [CO 2 ] and high night temperature; AH: ambient [CO 2 ] and high night temperature; EL: elevated [CO 2 ] and low night temperature; AL: ambient [CO 2 ] and low night temperature. ANOVA results are inset. ns: not significant; **, P < (by 7 cm) by high night temperature (P < 0.01, Fig. 3a), but there was no significant effect of elevated [CO 2 ](P = 0.26). The tiller number increased to a maximum at 35 DAT, 24 days before treatment start, then decreased until heading stage. The tiller number (=panicle number) at harvest was not affected by either elevated [CO 2 ] or high night temperature (Fig. 3b, Table 1) Night respiration Night respiration ranged between 4 and 18 mg C per hill per hour throughout the treatment period and changed significantly with growth stage among treatments and with daily solar radiation (Fig. 4). ANOVA results show that night respiration was significantly increased by elevated [CO 2 ] (by 12% before heading and 13% after) and high night temperature (by 35% before heading and 17% after) (both P < 0.01, Fig. 4). The effect of temperature was notable before heading, but decreased after. There was no significant interaction between elevated [CO 2 ]and night temperature in night respiration (P = 0.16), but after heading the effect of temperature tended to be smaller Dry weights Leaf and root dry weights were not affected by either [CO 2 ]or night temperature, since they were determined largely during Table 1 Effects of elevated CO2 and night temperature on yield and its components of IR72 rice crop HI (%) Brown rice yield (g per hill) Individual grain weight (mg) Fertile spikelet Filled spikelet Filled/fertile spikelet (%) Total spikelet no. per hill Spikelet no. per panicle Panicle no. per hill CO2 (abbrev.) Night temperature Filled/total spikelet (%) No. per hill Fertile/total spikelet (%) No. per hill High (32 8C) Elevated (EH) Ambient (AH) % change Low (22 8C) Elevated (EL) Ambient (AL) % change ANOVA results Temperature ns ns ns ** ** ** ** ** ns ** ** CO 2 ns ns ns ns ns ** + ** * ** ns Temperature CO 2 ns ns ns ns ns + ns ** ns * ns ns: no significance; +, P < 0.1; *, P < 0.05; **, P < 0.01.

5 agricultural and forest meteorology 149 (2009) the vegetative growth stage (Fig. 5d and e). Ear dry weight was significantly increased by elevated [CO 2 ] and decreased by high night temperature (both P < 0.01), and stem dry weight was increased by both treatments (both P < 0.01, Fig. 5b and c). The whole plant dry weight at harvest was significantly increased by both treatments (P < 0.01, Fig. 5a). There were no interactions between [CO 2 ] and night temperature in dry weight of organs or whole plants. (Note that ear dry weight is different from rice yield, where there was an interaction; see Section 3.4.) The net whole plant dry weight increase during treatment was due to both ear formation and stem biomass accumulation Grain yield and yield components Fig. 4 Changes in night respiration of rice plants. Bars indicate standard deviation (n = 3). Arrows indicate heading date in each treatment. EH: elevated [CO 2 ] and high night temperature; AH: ambient [CO 2 ] and high night temperature; EL: elevated [CO 2 ] and low night temperature; AL: ambient [CO 2 ] and low night temperature. ANOVA results are inset. ns: not significant; **, P < The solar radiation on sampling days is shown in the bottom part of the figure. The number of spikelets per panicle and the total number per pot were not affected by either elevated [CO 2 ] or night temperature (Table 1). The number of fertile spikelets was not affected by elevated [CO 2 ] but was significantly decreased by high night temperature (P < 0.01): from 87% at low night temperature to 70% at high night temperature. The number of filled spikelets was significantly affected by both elevated [CO 2 ] and night temperature (both P < 0.01): it was increased by elevated [CO 2 ] by 4.4% at high night temperature and by 19% at low night temperature; and decreased by high night temperature by 8.1% under ambient [CO 2 ] and by 20% under elevated [CO 2 ]. There was a slight interaction between [CO 2 ] and night temperature (P = 0.06). Individual grain weight was significantly increased by elevated [CO 2 ] (by 5.2% on average), but was not affected by night temperature. Overall, brown rice yield was significantly increased by elevated [CO 2 ] and Fig. 5 Dry weight of (a) whole plant, (b) ear, (c) stem, (d) leaf and (e) root before treatment (Bef.) and at harvest. EH: elevated [CO 2 ] and high night temperature; AH: ambient [CO 2 ] and high night temperature; EL: elevated [CO 2 ] and low night temperature; AL: ambient [CO 2 ] and low night temperature. Bars indicate standard deviation (n = 3). ANOVA results are inset. ns: not significant; **, P < The units of Y-axes were similar.

6 56 agricultural and forest meteorology 149 (2009) decreased by elevated night temperature (both P < 0.01). Although the interaction of [CO 2 ] and night temperature in terms of ear dry weight was not significant (Fig. 5b; P = 0.12), the interaction in brown rice yield was significant (Table 1; P < 0.05). 4. Discussion 4.1. Effects of elevated [CO 2 ] and high night temperature on rice growth Although many elevated [CO 2 ] experiments were carried out on rice during the last several decades, no paper reported that the plant height of rice was increased or decreased by elevated [CO 2 ]. This lack of attention in the literature implies that elevated [CO 2 ] likely does not affect the plant height of rice, as our results show in Fig. 3a. However, plant height of rice was significantly increased by high night temperature, which is similar to the height increases due to high daily temperature as reported by Osada et al. (1973) and Ohe et al. (2007). The elongated rice stems retained more photosynthate than did ears under high night temperature (Fig. 5). The tiller (=panicle) number at harvest was not affected by either elevated [CO 2 ]or high night temperature in this present study. However, the apparent lack of tiller response undoubtedly was due to our not imposing the CO 2 and temperature treatments until after the rice vegetative stage, which is the stage for tiller formation (Fig. 3b). Rice biomass production is determined by the balance between net photosynthesis rate and night respiration (Yamagishi, 1994; Sakai et al., 2001). Previous studies have shown that elevated [CO 2 ] promotes photosynthesis and thus biomass production, whereas high temperatures increase respiration, potentially reducing biomass production (Sakai et al., 2001; Peng et al., 2004). In the present study, however, both elevated [CO 2 ] and high night temperature increased biomass production (both P < 0.01, Fig. 5a). The total dry weight increase under high night temperature resulted from the increase in stem biomass (Fig. 5c), because the ear dry weight decreased under high night temperature (P < 0.01, Fig. 5b). Three reasons might explain this result. First, as shown in Fig. 4, night respiration increased at high night temperature, but the magnitude was modest, particularly after heading (17%), and was much smaller than is generally expected from the temperature dependence of respiration (typical Q 10 values of two: Yamagishi, 1994). Secondly, high night temperature might have decreased N accumulation in the panicles through lower N translocation from the vegetative organs under high night temperature, thus resulting in a higher N concentration in the leaves and stems (P < 0.01, data not shown). These higher N concentrations might have enhanced photosynthesis and maintained vegetative growth during the later growth stage, and thus increased the total dry weight in the high night temperature treatment. Thirdly, the elongated rice stem under high night temperature lead to a more efficient plant architecture for rice photosynthesis where mutual shading between leaves was reduced Elevated [CO 2 ] and night temperature affected rice yield Numerous controlled-environment experiments have shown that elevated CO 2 increases tiller and panicle numbers in rice (Baker et al., 1992; Ziska et al., 1997; Moya et al., 1998; Kim et al., 2003; Yang et al., 2006), but that increased daily mean temperature does not change the spikelet number per panicle or yield of rice (Yoshida, 1973a; Ziska et al., 1997). The increase in air temperature often offsets the stimulation of rice biomass and grain yield due to elevated [CO 2 ](Kim et al., 1996; Ziska et al., 1996; Moya et al., 1998). Only limited information on the direct effects of night temperature is available, but Morita et al. (2004) reported that increased night temperature alone reduced the size and weight of grain. Here, we have determined the interaction of elevated [CO 2 ] and night temperature on rice yield. Rice yield is determined by panicle number per land area, spikelet number per panicle, filled spikelet percentage and individual grain weight. Usually, productive tiller number is determined by the maximum tiller number that is formed during the vegetative growth period and tiller degeneration during the reproductive growth period. In rice FACE experiments, yield increases caused by elevated [CO 2 ] are related most strongly to larger productive panicle number per area and larger spikelet number per panicle (Kim et al., 2003; Yang et al., 2006). We applied the [CO 2 ] and night temperature treatments during the reproductive growth stage, so the benefit of elevated [CO 2 ] on sink formation was negligible. In fact, the numbers of tillers (panicles) and total spikelets per pot at harvest were not different between the treatments (Fig. 3, Table 1). Our results must be interpreted as the effects of elevated [CO 2 ] and night temperature on the grain setting and filling processes only. The major determinant of grain set is spikelet fertilization just after flowering. Night temperature has a strong effect on grain set by increasing spikelet sterility, whereas elevated [CO 2 ] has virtually no effect. Satake and Yoshida (1978) showed that night temperature higher than 30 8C reduced spikelet fertility. Our study shows that this can occur under both ambient and elevated [CO 2 ]. Kim et al. (1996) and Matsui et al. (1997) showed that spikelet sterility caused by daytime heat was exacerbated by elevated [CO 2 ], but the present study shows that sterility caused by night-time heat does not have a significant interaction with [CO 2 ]. The reason for this difference is not clear, but elevated [CO 2 ] may exacerbate daytime-heatinduced sterility because of indirect effects of increased crop surface and panicle temperatures (Yoshimoto et al., 2005). We found a significant interaction between [CO 2 ] and night temperature in the ratio of filled grain to fertile spikelets: there was a positive effect of elevated [CO 2 ] only under low night temperature. This could be related to the fact that the number of fertile spikelets was significantly reduced by high night temperature, so enhanced photosynthesis under elevated [CO 2 ] did not translate into filled grain percentage. This result reflects the responses of brown rice yield to elevated [CO 2 ]. These results have shown for the first time that limitation of grain setting under high night temperature limits the sink

7 agricultural and forest meteorology 149 (2009) capacity, reducing the advantage of grain yield due to elevated [CO 2 ]. 5. Conclusions Our results show that high night temperature during the reproductive growth stage reduced the stimulatory effect of elevated [CO 2 ] on brown rice yield. This was not due to reduced enhancement of biomass, but due to decreased dry matter allocation to grain as a result of reduced spikelet fertility. The enhanced vegetative growth and a smaller-than-expected temperature effect on night respiration were reasons for increased total biomass by high night temperature during the reproductive period. Note, however, that our results are based on a growth chamber experiment, and the way in which elevated night temperature decreases the fertile spikelet percentage is still not understood. Further studies on the interactive effects of elevated [CO 2 ] and night temperature should be carried out to confirm our results in the field under future climate warming scenarios. Acknowledgements This research was funded by the Global Environment Research Program of the Ministry of the Environment, Japan. We thank Drs M. Yoshimoto and M. Fukuoka of NIAES for their comments and discussion. references Baker, J.T., Yield responses of southern US rice cultivars to CO 2 and temperature. Agric. For. Meteorol. 122, Baker, J.T., Allen Jr., L.H., Boote, K.J., Temperature effects on rice at elevated CO 2 concentration. J. Exp. Botany 43, Cheng, W., Inubushi, K., Yagi, K., Sakai, H., Kobayashi, K., Effect of elevated CO 2 on biological nitrogen fixation, nitrogen mineralization and carbon decomposition in submerged rice soil. Biol. Fertil. 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