Rice carbon balance under elevated CO

Transcription

1 Research Rice carbon balance under elevated CO Blackwell Science Ltd 2 Hidemitsu Sakai 1, Kazuyuki Yagi 2, Kazuhiko Kobayashi 1 and Shigeto Kawashima 1 1 National Institute of Agro-Environmental Sciences, Kannondai, Tsukuba , Japan; 2 Japan International Research Center for Agricultural Sciences, 1 2 Ohwashi, Tsukuba , Japan Summary Author for correspondence: Hidemitsu Sakai Tel: Fax: hsakai@niaes.affrc.go.jp Received: 8 August 2000 Accepted: 3 November 2000 Season-long effects of elevated concentration ( ) on the carbon balance of the rice (Oryza sativa) canopy are reported here. The experiment was conducted in six sunlit, semiclosed growth chambers for an entire growing season. Rice plants (cv. Nipponbare) were grown at 350 µmol mol 1 (ambient) in three chambers, or at 650 µmol mol 1 (elevated) in the other three chambers. Canopy net photosynthesis and night-time respiration were determined in the chambers by mass balance. Both canopy gross photosynthesis and total respiration, through the entire growing season, were increased by the enrichment. But -induced variations in canopy carbon gain were mainly caused by changes in canopy photosynthesis. The enhancement of daily canopy gross photosynthesis by elevated was 33.4% for the first 3 week, but it declined gradually and disappeared by heading. Enhancement of daily net carbon gain also decreased as rice plants grew. These results show that the increase in rice biomass by elevated results more from the increase in carbon gain at early rather than later stages of growth. Key words: carbon balance, rice (Oryza sativa), elevated, canopy photosynthesis, canopy respiration. New Phytologist (2001) 150: Introduction Many studies have examined plant responses of photosynthesis and respiration to elevated at the single-leaf and cellular levels (e.g. Stitt, 1991; Wolfe et al., 1998). However only a limited number of studies have examined the photosynthetic and respiratory responses at the whole-plant or canopy level, probably because of technical difficulties. Responses to elevated at the whole-plant level may be different from those at single-leaf and cellular levels, because there are some variations of physiological (nitrogen content, sugar content, etc.) and environmental (light, temperature, etc.) factors between plant organs and even between single leaves in a canopy. The effects of elevated on canopy exchange rates have been studied in wheat (Gifford, 1995; Monje & Bugbee, 1998), soybean (Jones et al., 1984; Reddy et al., 1989), sunflower (Luo et al., 2000) and grasslands (Wolfenden & Diggle, 1995). Relatively few experiments have been conducted on rice (Baker et al., 1990b; Baker et al., 1992; Baker et al., 1997; Baker et al., 2000). Enhancement of canopy photosynthesis by elevated was commonly observed in these studies (Jones et al., 1984; Reddy et al., 1989; Baker et al., 1990b; Wolfenden & Diggle, 1995; Monje & Bugbee, 1998; Luo et al., 2000). Baker et al. (1990b) grew rice plants in subambient (160, 250), ambient (330), and superambient (500, 660 and 900 µmol mol 1 ) treatments. They reported that canopy photosynthetic rates increased with increasing from 160 to 500 µmol mol 1, but saturated beyond 500 µmol mol 1. Enhancement of canopy quantum yield was also observed in wheat (Monje & Bugbee, 1998) and sunflower (Luo et al., 2000). However the long term response of canopy photosynthesis to elevated is inconsistent. Baker et al. (1990b) and Wolfenden & Diggle (1995) observed a decline in the enhancement in canopy photosynthesis under long-term elevated, but such decline was not found in other studies (Jones et al., 1984; Baker et al., 1997; Monje & Bugbee, 1998). The response of canopy respiration to long-term elevated has been reported in few experiments (Baker et al., 1992; Gifford, 1995; Baker et al., 2000). Baker et al. (1992) examined the effects of daytime enrichment on canopy respiration, and reported that canopy respiration rate on a New Phytologist (2001) 150:

2 242 Research ground area basis increased with increasing, but specific respiration rate decreased slightly under elevated. Gifford (1995) conducted an experiment for wheat canopy and reported that maintenance and basal respiration coefficients decreased in elevated, but the respiration : photosynthesis ratio was unchanged. Clearly the current information is insufficient for understanding fully the effects of elevated on canopy respiration. Most canopy-level investigations of exchange rates addressed photosynthesis and respiration separately. It is necessary to address both photosynthetic and respiratory responses to elevated because respiration is closely linked to photosynthesis (Amthor, 1989; Gifford, 1995), and canopy carbon gain is the balance between photosynthesis and respiration. The objective of this study on rice was to examine the effects of long-term elevated on canopy photosynthesis, respiration and carbon gain in relation to growth responses. Materials and Methods Controlled environment chambers Rice plants (Oryza sativa L., cv. Nipponbare) of Japonica-type were grown in six naturally sunlit, semiclosed growth chambers for an entire growing season. Chamber dimensions were m (L W H) with the space for plant growth m. Each chamber housed two stainless-steel containers ( m; L W D) filled with paddy soil. The frames, rear (north) walls, and floor of the chamber were made of stainless steel. The frames were glazed with 5-mm-thick tempered glass whose transmittance of visible light were > 80%. Air temperature and rh in each chamber were controlled by electrical resistive heaters (with bubbling system for humidification) and cold-water heat exchangers using PID (Proportional + Integral + Derivative) controllers (DB1000, CHINO, Tokyo, Japan). Air temperature and rh in each chamber were measured with temperature-humidity sensors (HN-Q500-1, CHINO, Tokyo, Japan) shielded against direct solar radiation and mounted above a rice canopy. In this experiment, air temperature was controlled to track ambient air temperature with the seasonal mean temperature being 23.4 C and a rh of 80 ± 1.9%. was maintained at 353 ± 15/396 ± 23 µmol mol 1 (day/night) in three ambient chambers and 667 ± 36/700 ± 41 µmol mol 1 (day/ night) in three elevated chambers. Daytime was maintained by a computer-controlled pure injection system, which compensated for uptake by the rice canopy. During night-time, increased due to plant respiration, but was kept below 100 µmol mol 1 higher than the daytime by a computer-controlled air ventilation system, which introduced ambient air to reduce. Ambient air temperature was measured with a platinum resistance thermometer which was shielded, aspirated and placed outside the chambers. Environmental data in each chamber and ambient air temperature were monitored every 10 s, and 5 min means were recorded. Ambient data were provided by the laboratory of Micrometeorology of NIAES. They monitored ambient every 10 s at several heights on an observation tower, which was located c. 50 m south of these chambers. Plant culture Germinated seeds of rice were sown on 20th April in Seedlings were grown in plug pots at 23 C, 80% rh and 350 or 650 µmol mol 1. On 15th May, they were transplanted in the containers in chambers with 3 seedlings per hill at cm spacing. Plants were fertilized with 5 g N, 15 g P 2 O 5, and 15 g K 2 O per m 2 just before transplanting, and 3 g N per m 2 on 56 d after transplanting (DAT). The amount of fertilizer was based on local agronomic practices. The containers were flooded with water at 1 5 cm depth throughout the season. When leaf area index of rice canopy reached 3, shading nets (50% light transmittance) were installed at canopy height along the outside of each chamber to make a light environment similar to that in a field. The rice plants were harvested on 15th October (153 DAT). Growth and yield measurement Three rice hills were destructively sampled from each chamber at 20, 40, 67, 98, 122 and 153 DAT. The gaps of the sampled plants were filled with potted plants grown outdoors with the same nitrogen application as those in the chambers. These pot-grown plants were not included in any further sampling. After leaf area was measured for each sampled plant, plants were detached into leaf blade, leaf sheath + stem, root, ear and dead leaf blade. Then each sample was oven-dried for > 48 h at 80 C and d. wt was determined. Samples of one chamber from each treatment were used for carbon (C) and nitrogen (N) analysis. After grinding samples, C and N concentration were determined by a CN coder (MT-700, Yanako, Kyoto, Japan). At harvest, 12 rice hills were destructively sampled from each chamber and the yield was determined for each chamber. Canopy exchange rate in each chamber was monitored every 10 s by an infrared controller (ZFP9GD11, Fuji-denki, Tokyo, Japan) and recorded every 5 min as a 5-min average. For a more precise measurement of in the chambers than the controllers, sample air from each of the six chambers was taken to the control house, and was determined by an infra-red gas analyser (IRA-107, Shimadzu, Kyoto, Japan), which was automatically calibrated three times a day against nitrogen (zero) gas and standard gas (700 µmol mol 1 ). It took 5 min to determine in each chamber and 30 min to scan all the six chambers. The thus determined New Phytologist (2001) 150:

3 Research 243 was recorded and used to describe the regimes in the chambers. The rate of pure injection to maintain in each chamber constant at the target level was controlled and measured by a mass flow controller (SEC-400MARK3, STEC, Kyoto, Japan), and recorded every 5 min for each chamber. The net photosynthetic rate of the rice canopy on a ground area basis was determined as: P net = C in L + R soil Eqn 1 (P net, canopy net photosynthesis rate (mg m 2 min 1 ); C in, carbon injection rate to keep in a chamber (mg m 2 min 1 ); L, chamber leakage rate (mg m 2 min 1 ); R soil, flux out of the paddy water and soil (mg m 2 min 1 ).) Canopy dark respiration rate on a ground area basis in night-time was determined as: R night = C + L R soil Eqn 2 (R night, canopy dark respiration rate in night-time (mg m 2 min 1 ); C, increase of in a chamber (mg m 2 min 1 ) while the air-ventilation is closed.) The airventilation system was programmed to allow for the measurement of C, while maintaining the night-time at desired level. The rate of leakage (L) out of a chamber was estimated by modification of the method of Acock & Acock (1989) and Kimball (1990). Every few weeks pure N 2 O was injected into each chamber, and the decay of N 2 O concentration was measured by using the air sampling system described above and an infra-red gas analyser (ZRC1ZC11, Fuji-denki, Tokyo, Japan) for N 2 O. L was calculated from the measured leakage rate and the gradient between ambient air and chambers by mass balance. The flux out of the paddy water and soil was measured at air temperatures between 15 to 35 C with a 5 C step under flooded conditions, after all aboveground plant material had been removed at the end of the growing season. The canopy dark respiration rate during the daytime (R day ) was calculated by assuming the same rate as that at night-time and at a corresponding temperature (Baker et al., 1997; Monje & Bugbee, 1998). Gross photosynthesis rate (P gross ) was estimated as P net plus R day. The daily total respiration (R total ) was estimated as R day plus R night and the daily carbon gain of a canopy (C gain ) was calculated as: C gain = ΣP gross (ΣR day + ΣR night ) = ΣP net ΣR night Eqn 3 The canopy net photosynthesis rate per unit leaf area (P net / Leaf area; P leaf ) and specific respiration rate (R total /Total d. wt; R dw ) were calculated from destructive sampling date and a P net and R total of few days before and after sampling. Data analysis Daily values of canopy photosynthesis, respiration and carbon gain were compared between the two treatments for five periods: 11 40, 41 70, , , DAT, and the entire growing season by one-way ANOVA with the variance between the chambers as the error variance. Destructive sampling data, P leaf and R dw were also tested for significant effects of the treatment by one-way ANOVA, but data of C and N analysis were tested by one-way ANOVA with the variance between the plants as error. Graphing and smoothing of the daily measurement data were done with the computer software Kaleida Graph (SYNERGY SOFTWARE, Reading, Pennsylvania, USA). Results Plant growth and yield Total d. wt was increased by elevated, but difference between elevated and ambient treatment was not statistically significant before harvest, probably due to the limited number of samples. At harvest, total d. wt was significantly increased by 10.0% (P = 0.008; Fig. 1a) by the elevated treatment. Brown rice yield was 467 ± 33 and 568 ± 19 g m 2 under ambient and elevated, respectively, and significantly increased by the elevated treatment (P = ). Leaf area did not respond to elevated in the early stages of growth, but decreased significantly after heading (P = 0.04; Fig. 1b) under the elevated treatment. The number of tillers increased under elevated by 22% (P = 0.006) at the maximum tiller number stage (45DAT) and 8% (P = 0.03) at harvest. Carbon and nitrogen concentration The C and N concentration in leaves and the whole plant decreased with time as rice plants grew under both ambient and elevated. Compared with ambient, C concentrations were c. 2% higher at elevated for both leave and whole plants, almost through the growing season, whereas N concentrations gradually decreased under elevated with the decrease being greatest (12% for leaf, 9% for whole plant) in the middle of the grain filling stage. Leaf N contents per unit leaf area were significantly decreased by elevated (Fig. 2) with the decrease being greatest (23%, P = 0.008) in the middle of grain filling stage. Measured and estimated carbon gain The final C gain of the rice canopy under ambient and elevated was calculated (from harvest biomass and C concentration) and compared with C gain estimated by integrating the New Phytologist (2001) 150:

4 244 Research Fig. 1 Seasonal trends of (a) total dry weight and (b) leaf area index of rkce (Oryza sativa L.) under elevated (closed circles, bold solid line) and ambient (open circles, thin solid line) treatments. The error bars represent the SE of the mean. Asterisk, indkcates significant dkfferences at P = Fig. 2 Nitrogen contents on the leaf area basis of leaf blade of rkce (Oryza sativa L.) under elevated and ambient treatments. The error bars represent the SE of the mean. **, significant dkfferences at P = Open bars, ambient; closed bars, elevated. New Phytologist (2001) 150:

5 Research 245 (Fig. 4d). At the late grain filling stage, P gross and P net were significantly decreased by enrichment (Table 1). Seasonally-integrated P gross and P net were increased 8.9 and 11.3% respectively, by the elevated. P leaf was significantly enhanced by elevated, but its enhancement rate gradually decreased through the growing season (Fig. 5). R total and R night were significantly increased by elevated before panicle initiation (70 DAT) and after heading, but were unaffected between these stages (Table 1). Seasonallyintegrated R total and R night were increased by 7.1 and 4.5%, respectively. Specific respiration rate (R dw ) was significantly enhanced by elevated early in the growing season, but decreased significantly around heading (Fig. 5). Fig. 3 Comparison between measured and estimated total carbon gain of rice canopy at harvest. Open circles, ambient; closed circles, elevated. daily canopy C gain in Eqn 3 (Fig. 3). Differences between the measured and estimated C gain were small (RMSE = 1.9%). Canopy exchange rate Daily P gross, P net, R total and R night gradually increased until 50 DAT, and after a 50-d period of minor fluctuation, began to decrease around heading (100DAT) under both ambient and elevated (Fig. 4b,c). P gross and P net were significantly increased by elevated for the periods before heading (Table 1), but their enhancement by enrichment was diminished at heading Canopy carbon balance Daily C gain increased gradually after transplanting and reached a maximum at about 80 DAT under both ambient and elevated and declined thereafter (Fig. 6). In the early growth stages, daily C gain was increased by elevated, but the increase diminished by heading (100 DAT), and then C gain decreased under elevated at the late grain filling stage (Table 1). Discussions Carbon gain under elevated Canopy carbon gain was increased by elevated before heading (Fig. 6, Table 1), however the initial enhancement rate of daily carbon gain by elevated gradually decreased with time. This indicates that the increase in rice biomass by elevated resulted more from the increase in carbon gain during the early growth stages than at late stages. Table 1 Average P gross, P net, R total, R night, C gain, air temperature and incident PAR at intervals during the growing season of rice (Oryza sativa L.) under elevated and ambient treatments. Growing season was divided into five stages: early vegetative [11 40 DAT, late vegetative [41 70 DAT, panicle formation [ DAT, early grain filling [ DAT, and late grain filling [ DAT Period (DAT) P gross (g P net (g R total (g R night (g C gain (g Air temp ( C) PAR (mol Ambient Total Elevated ** 11.59** 5.71** 3.19** 2.29** ** 35.14** 18.48** ** ** 41.15** ** ** 6.42** 3.91** 1.17** Total ** 12.65** 5.57** 4.94** **, Significantly different from ambient at P = New Phytologist (2001) 150:

6 246 Research New Phytologist (2001) 150:

7 Research 247 Fig. 5 Relative response of net photosynthesis rate per unit leaf area (P leaf ; closed circls on solid line) and specific respiration rate (R dw ; open circles on dashed line) to enrichment. Fig. 6 Seasonal trends of incident PAR (dashed line) and daily carbon gain of rice (Oryza sativa L.) canopy under elevated (closed circles, bold solid line) and ambient (open circles, thin solid line) treatments. Smoothing curves by using stineman function are shown to help the contrast between the treatments. PAR, dashed line. No enhancement or even decline in canopy carbon gain after heading was observed under elevated (Fig. 6), although yield was increased by elevated. These changes are apparently in conflict, since a major portion of the carbohydrate in rice grains comes from the carbon assimilated after Fig. 4 (a) Air temperature (open circles on thin solid line), incident PAR (closed circles on bold solid line), (b) Daily P gross (canopy gross photosynthesis: closed squares on bold solid line, elevated; open squares on thin solid line, ambient), P net (canopy net photosynthesis: closed circles on bold dashed line, elevated; open circles on thin dashed line, ambient) and (c) R total (canopy total respiration: closed squares on bold dashed line, elevated; open squares on thin dashed line, ambient), R night (canopy night-time respiration: closed circles on bold dashed line, elevated; open circles on thin dashed line, ambient) under elevated and ambient treatments during growing season of rice (Oryza sativa L.). (d) Enhancement rate of elevated in P gross (closed circles on bold solid line) and R total (open circles on thin solid line). Smoothing curves by using stineman function are shown to help the contrast between the treatments. heading. It must be noted, however, that rice yield has been related to the level of carbohydrates stored in the stem before heading, and to the ability of the plant to translocate this storage to the ear (Yoshida, 1972). In this experiment, accumulated starch content in the stem and leaf sheath just before heading was about two times higher under elevated than ambient (H. Sakai et al., unpublished). The contribution of the stored starch to starch accumulation in the ear at harvest could be up to 17% under elevated and 5% under ambient. Grüters (1999) reported that the contribution of stem carbohydrate reserves to yield was enhanced by elevated in wheat. Long-term response of canopy photosynthesis At the single leaf level photosynthetic acclimation to longterm enrichment has often been reported (Stitt, 1991; Wolfe et al., 1998). Few studies have examined the response New Phytologist (2001) 150:

8 248 Research of canopy photosynthesis to long-term elevated. Baker et al. (1990b) reported that differences in the net photosynthesis of the rice canopy between ambient and elevated treatments had disappeared after flowering (Fig. 4 in Baker et al., 1990b). However, Baker et al. (1997) found no photosynthetic down-regulation when they conducted cross-switching experiments with the rice canopy. Continued enhancements of canopy photosynthesis by long-term enrichment have been reported in wheat (Monje & Bugbee, 1998), and soybean ( Jones et al., 1984). The elevated rates of photosynthesis seem to be maintained in -enriched plants when the sink capacity becomes sufficiently large to prevent feed-back inhibition (Monje & Bugbee, 1998). In our study, we found higher starch accumulation in -enriched plants throughout the season (H. Sakai et al., unpublished), although d. wt and tiller number were enhanced by elevated. Rice plants in this experiment may, therefore, be sink-limited. The reduction of active rubisco has been frequently reported as an acclimation response to elevated (Lawlor & Mitchell, 1991; Rowland-Bamford et al., 1991; Sage, 1994; Nakano et al., 1997; Vu et al., 1997; Wolfe et al., 1998). A decrease of leaf N content has also been reported (Rowland- Bamford et al., 1991; Nakano et al., 1997; Wolfe et al., 1998). Nakano et al. (1997) reported no difference between ambient and elevated treatments in the relationship between rubisco and leaf N content of rice and that a decrease of rubisco was the result of the decrease in leaf N content. Makino et al. (1997, 2000) reported that the decrease in leaf N content is not due to dilution of N caused by relative increases in leaf area or plant mass, but the result of a change in N allocation at the morphogenetic level of the whole-plant. In this study, the partitioning rate of N to leaf blade was also decreased throughout the growing season (data not shown). A decrease in leaf N content by elevated was also found (Fig. 2), and the ratio of [elevated : ambient gradually decreased with rice development. Because the relationship between leaf N content and photosynthesis rate under elevated is not available, we could not estimate the effect of a decrease in leaf N content on canopy photosynthesis under elevated. A decrease in the enhancement of canopy photosynthesis under elevated might be partly due to a decrease in leaf N, and it is suggested that canopy photosynthetic responses to elevated are closely related to plant resource partitioning within a canopy. Canopy net photosynthesis rate per unit leaf area (P leaf ) was enhanced by elevated at heading (Fig. 5) when the enhancement of canopy photosynthesis had diminished. While the number of tillers and total d. wt of rice plants were increased, leaf area development did not respond to elevated at the growth stage before heading. This phenomenon has been observed in many other studies with rice (Imai et al., 1985; Baker et al., 1990a; Kim et al., 1996; Ziska et al., 1997). At heading and after, leaf senescence was enhanced by elevated (Fig. 1b), a response also reported by Baker et al. (1990a) and Sicher (1998). This enhanced leaf senescence should have contributed to the decrease in canopy photosynthesis under elevated after heading. The mechanisms of the enhanced leaf senescence under elevated may involve acceleration of plant development due to the higher plant temperatures resulting from partial stomatal closure under elevated. The increased number of ears in elevated should have required leaf N to be re-translocated to ears at a higher rate, which should have also contributed to the enhanced leaf senescence. However the detailed analyses of these mechanisms are beyond the scope of this paper. Long-term response of canopy respiration Knowledge about the effects of elevated on plant respiration is quite limited, especially at the whole-plant level. In this study, canopy respiration rates on a ground area basis were increased by elevated (Table 1) because of increased biomass, but specific respiration rate (R dw ) was significantly decreased in the middle of growing season (Fig. 5). This result is consistent with Baker et al. (1992), who reported that the differences in the specific respiration rate among treatments were influenced by differences in the N concentration of aboveground biomass. In this study, however, the relationship between specific respiration rate and N concentration of total biomass was different among treatments (data not shown). Gifford (1995) reported that the respiration : photosynthesis ratio was not affected by elevated. The respiration : photosynthesis ratio through the growing season averaged 0.43 and 0.40 under ambient and elevated, respectively. While total respiration was up to 40% of canopy gross photosynthesis, the change in respiration due to elevated did not contribute significantly to -induced variations in canopy carbon gain (Table 1). Conclusion In conclusion, this study reports the long-term response of canopy carbon gain to elevated. -induced variations in canopy carbon gain were mainly due to changes in canopy photosynthesis. The long-term response of canopy photosynthesis may be caused by both a decline in carbon assimilation per unit leaf area (P leaf ) and the loss of leaf area due to enhanced leaf senescence. Acknowledgements This work was supported by the Rice-FACE project under the CREST program of Japan Science and Technology Corporation. We appreciate the laboratory of Micrometeorology of NIAES for providing us with the data of ambient which were needed for chamber leakage calculation. The authors thank anonymous reviewers for valuable suggestions. New Phytologist (2001) 150:

9 Research 249 References Acock B, Acock MC Calculating air leakage rates in controlledenvironment chambers containing plants. Agronomy Journal 81: Amthor JS Respiration and crop productivity. Berlin, Germany: Springer-Verlag. Baker JT, Allen LH Jr, Boote KJ. 1990a. Growth and yield responses of rice to carbon dioxide concentration. Journal of Agricultural Science 115: Baker JT, Allen LH Jr, Boote KJ, Jones P, Jones JW. 1990b. Rice photosynthesis and evapotranspiration in subambient, ambient, and superambient carbon dioxide concentration. Agronomy Journal 82: Baker JT, Allen LH Jr, Boote KJ, Pickering NB Rice responses to drought under carbon dioxide enrichment. 2. Photosynthesis and evapotranspiration. Global Change Biology 3: Baker JT, Allen LH Jr, Boote KJ, Pickering NB Direct effects of atmospheric carbon dioxide concentration on whole canopy dark respiration of rice. Global Change Biology 6: Baker JT, Laugel F, Boote KJ, Allen LH Jr Effects of daytime carbon dioxide concentration on dark respiration in rice. Plant, Cell & Environment 15: Gifford RM Whole plant respiration and photosynthesis of wheat under increased concentration and temperature: long-term vs shortterm distinctions for modelling. Global Change Biology 1: Grüters U On the role of wheat stem reserves when source-sink balance is disturbed by elevated. Journal of Applied Botany 73: Imai K, Coleman DF, Yanagisawa T Increase in atmospheric partial pressure of carbon dioxide and growth and yield of rice (Oryza sativa L.). Japanese Journal of Crop Science 54: Jones P, Allen LH Jr, Jones JW, Boote KJ, Campbell WJ Soybean canopy growth, photosynthesis, and transpiration response to whole-season carbon dioxide enrichment. Agronomy Journal 76: Kim HY, Horie T, Nakagawa H, Wada K Effects of elevated concentration and high temperature on growth and yield of rice. I. The effect on development, dry matter production and some growth characters. Japanese Journal of Crop Science 65: Kimball BA Exact equations for calculating air leakage rates from plant growth chambers. Agronomy Journal 82: Lawlor DW, Mitchell AC The effects of increasing on crop photosynthesis and productivity: a review of field studies. Plant, Cell & Environment 14: Luo Y, Hui D, Cheng W, Coleman JS, Johnson DW, Sims DA Canopy quantum yield in a mesocosm study. Agricultural and Forest Meteorology 100: Makino A, Harada M, Kaneko K, Mae T, Shimada T, Yamamoto N Whole-plant growth and N allocation in transgenic rice plants with decreased content of ribulose-1,5-bisphosphate carboxylase under different partial pressures. Australian Journal of Plant Physiology 27: Makino A, Harada M, Sato T, Nakano H, Mae T Growth and N allocation in rice plants under enrichment. Plant Physiology 115: Monje O, Bugbee B Adaptation to high concentration in an optimal environment: radiation capture, canopy quantum yield and carbon use efficiency. Plant, Cell & Environment 21: Nakano H, Makino A, Mae T The effect of elevated partial pressures of on the relationship between photosynthetic capacity and N content in rice leaves. Plant Physiology 115: Reddy VR, Acock B, Acock MC Seasonal carbon and nitrogen accumulation in relation to net carbon dioxide exchange in a carbon dioxide-enriched soybean canopy. Agronomy Journal 81: Rowland-Bamford AJ, Baker JT, Allen LH Jr, Bowes G Acclimation of rice to changing atmospheric carbon dioxide concentration. Plant, Cell & Environment 14: Sage RF Acclimation of photosynthesis to increasing atomospheric : The gas exchange perspective. Photosynthesis Research 39: Sicher RC Yellowing and photosynthetic decline of barley primary leaves in response to atmospheric enrichment. Physiologia Plantarum 103: Stitt M Rising levels and their potential significance for carbon flow in photosynthetic cells. Plant, Cell & Environment 14: Vu JCV, Allen LH Jr, Boote KJ, Bowes G Effects of elevated and temperature on photosynthesis and rubisco in rice and soybean. Plant, Cell & Environment 20: Wolfe DW, Gifford RM, Hilbert D, Luo Y Integration of photosynthetic acclimation to at the whole-plant level. Global Change Biology 4: Wolfenden J, Diggle PJ Canopy gas exchange and growth of upland pasture swards in elevated. New Phytologist 130: Yoshida S Physiological aspects of grain yield. Annual Review of Plant Physiology 23: Ziska LH, Namuco O, Moya T, Quilang J Growth and yield response of field-grown tropical rice to increasing carbon dioxide and air temperature. Agronomy Journal 89: New Phytologist (2001) 150: