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CHAPTER 18 Growth and Yield of Paddy Rice Under Free-air CO 2 Enrichment Kazuhiko Kobayashi, Mark Lieffering, and Han Yong Kim CONTENTS Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 Atmospheric CO 2 and Rice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371 Objectives of the Rice FACE Experiment . . . . . . . . . . . . . . . . . . . . . . 373 Growing Crops under Elevated [CO 2 ]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 Chamber Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 FACE Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 Rice FACE System: Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375 Ring Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376 CO 2 Control and Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376 Temporal and Spatial Control of [CO 2 ] (1999) . . . . . . . . . . . . . . 377 The Effects of FACE on the Growth and Yield of Paddy Rice . . . . . . . . . . . 378 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387 Conclusions and Implications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392 INTRODUCTION Atmospheric CO 2 and Rice It is estimated that up until the industrial revolution in the eighteenth century,atmospheric CO 2 concentrations ([CO 2 ]) were about 280 ppmV (parts 371 0-8493-0904-2/01/$0.00+$.50 © 2001 by CRC Press LLC 920103_CRC20_0904_CH18 1/13/01 11:21 AM Page 371 372 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT per million by volume). Since then, the [CO 2 ] has risen to 370 ppmV at pres- ent and is expected to keep increasing at a rate of about 15 ppmV per decade. The increase in [CO 2 ] is attributed to human activities such as fossil fuel burn- ing and deforestation (Houghton et al., 1996). It is predicted that the increase will continue into the twenty-first century, resulting in a [CO 2 ] concentration somewhere between 450 and 550 ppmV around the year 2050 (Houghton et al., 1996). Because CO 2 is a “greenhouse” gas, the increase in [CO 2 ] is pre- dicted to affect the global radiation energy balance and thereby climate. The predicted changes in climate most notably include an increase in the Earth’s mean surface temperature and alterations in rainfall patterns, both factors which strongly affect biomass production in both agricultural and natural ecosystems worldwide (Reilly, 1996). Besides the indirect effects on plant growth induced by climate change, elevated [CO 2 ] can also directly alter plant processes, most importantly pho- tosynthesis and stomatal conductance. Because photosynthesis in plants uti- lizing the C 3 pathway is limited by current [CO 2 ] levels, elevating [CO 2 ] increases rates of carbon (C) fixation, leading to greater plant biomass pro- duction (Drake et al., 1997). Elevated [CO 2 ] also tends to reduce stomatal con- ductance which, coupled with the increase in photosynthesis, leads to an increase in water use efficiency. In terms of both area and tonnage harvested, rice, oryza sativa, h, is the primary crop in Asia and is among the world’s three major crops (the other two are wheat, Triticum aestivum L., and maize, Zea mays L.). Rice is unique in that 95% of the world’s total production occurs in developing countries, and the majority of that grown is consumed locally (Alexandratos, 1995). In most of the countries where it is produced, rice provides a major part of the human dietary needs, and its production is usually a large factor in the economy. Rice production in Asia has increased almost linearly since 1960 and had risen by 150% by 1995 (FAOSTAT; The harvested area has increased by only 20%, hence the increased production has mostly come from a 100% increase in yield per unit harvested area. This large yield increase can be ascribed to technological advances such as the breeding of new, high-yielding varieties, the development and expansion of irrigation systems, increased fertilizer use and efficiency, and improved pest manage- ment (Greenland, 1997). It has been estimated that in the next 30 years the growing population in Asia may need nearly 70% more rice (Hossain, 1997). Because the area avail- able for cultivation is predicted to decrease, yield per unit harvested area must increase more than the growth in population. However, there is evi- dence that the impressive yield increases since 1960 may be plateauing (Cassman et al., 1997), and there appears to have been little increase in poten- tial crop yields in recent times (Khush and Peng, 1996). Therefore, it is spec- ulated that further increases in yield may be achieved only by optimizing the supply of resources limiting crop growth, such as water and nitrogen (N) (Sinclair, 1998a). 920103_CRC20_0904_CH18 1/13/01 11:21 AM Page 372 GROWTH AND YIELD OF PADDY RICE UNDER FREE-AIR CO 2 ENRICHMENT 373 The effects of elevated [CO 2 ] on rice growth have been studied since the 1960s (e.g., Murata, 1962). In these early experiments, higher [CO 2 ] was shown to enhance both biomass growth (Imai and Murata, 1976) and yield (Yoshida, 1973). It was also found that environmental variables such as N (Imai and Murata, 1978) and temperature (Imai and Murata, 1979) can affect growth enhancement due to higher [CO 2 ]. In these studies, plants were grown under higher [CO 2 ] for only a portion of the growth duration. It was later confirmed that rice yield also increases when plants are grown under higher [CO 2 ] throughout the growth duration (Imai et al., 1985; Baker et al., 1990; Ziska and Teramura, 1992; Baker and Allen, 1993a, b; Seneweera et al., 1994; Kim et al., 1996a,b; Ziska et al., 1997; Moya et al., 1998). The studies cited above have identified some common factors which result in the increase in yield with elevated [CO 2 ]. Individual leaf area and the number of leaves per stem are usually decreased but a greater tiller number results in an increase in leaf area per plant (Imai, 1995). Photosynthesis per unit leaf area is usually increased with elevated [CO 2 ], though rates may decrease as the leaf matures (photosynthetic acclimation) (Imai and Murata, 1978b). The net result is an increase in photosynthesis per plant, resulting in greater carbohydrate accumulation and dry matter production (Rowland- Bamford et al., 1990; Baker et al., 1993). Frequently, the increase in root dry weight (d.wt) with elevated [CO 2 ] is greater than the increase in shoot d.wt (Imai et al., 1985). The greater tiller number leads to an increase in the pro- duction of panicles, an important determinant of grain yield (e.g., Ziska et al., 1997). Increased carbohydrate supply leads to an increase in both grain num- ber per panicle and the percentage of mature grains that develop (Yoshida, 1981). Elevated [CO 2 ] rarely increases individual grain weight because of the physical limitations imposed by the grain and husk characteristics (Yoshida, 1981). Objectives of the Rice FACE Experiment In view of the importance of rice in the lives of a large proportion of the world’s population and the anticipated decreases in per capita yield, there is a need to determine the effects of the predicted elevated [CO 2 ] on rice growth and yield under field conditions. An important question is by how much will elevated [CO 2 ] increase rice yields under field conditions and to what extent will these increases satisfy the predicted demand? Also, will there be interac- tions between elevated [CO 2 ] and the other factors that limit rice yields, and if so how can these be utilized to maximize yields? In this chapter we briefly review the techniques that have been used in past research efforts on the effects of elevated [CO 2 ] on rice growth and yield. All these studies have grown rice in some kind of enclosure fumigated with air containing elevated [CO 2 ]. We highlight some of the drawbacks in using enclosures to grow plants and then introduce the free-air CO 2 enhancement (FACE) technique as 920103_CRC20_0904_CH18 1/13/01 11:21 AM Page 373 374 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT a method to grow large areas of crops under elevated [CO 2 ]. We then present some results from the first experiment to grow rice using the FACE technique and discuss their implications. GROWING CROPS UNDER ELEVATED [CO 2 ] Chamber Studies Much information on the response of rice to elevated [CO 2 ] has come from experiments conducted using chambers or enclosures which were fumigated with either ambient or CO 2 enriched air. The types of enclosures that have been used include temperature gradient chambers (TGCs); (Kim, 1996a,b), soil-plant-air research (SPAR) units (e.g., Baker et al., 1992; Gesch et al., 1998) and open-topped chambers (OTCs) (e.g., Moya et al., 1998). However, to iso- late the effects of elevated [CO 2 ] on plant growth, it is important that the experimental system imparts minimal effects on other abiotic environmental parameters that may influence growth. In many of the early experiments con- ducted in fumigated glasshouses (e.g., Imai et al., 1985), plants were grown in pots. The soil environment in pots differs markedly from that under field conditions, with differences in factors such as nutrient availability, water drainage, and soil temperature. In fact, the response of plants to elevated [CO 2 ] has been shown to decrease with decreasing pot size (Arp, 1991). Chambers and enclosures can affect abiotic environmental factors such as temperature, solar radiation, humidity, and wind (McLeod and Long, 1999). Frequently, compared to outside conditions, within the chamber there is less light, the air is drier, and temperatures are higher. These differences can affect plant growth (commonly called a “chamber effect”) to as large an extent as the effect of the elevated [CO 2 ] (e.g., Knapp et al., 1994). The cham- ber effect can influence many aspects of the response of plants and crops to elevated [CO 2 ], including photosynthesis, metabolism, biomass production, and crop water and energy balances (McLeod and Long, 1999), making the translation of results to outside conditions difficult. For example, Van Oijen et al., (1999) found that the response of wheat grain yield to elevated [CO 2 ] was less in OTCs cooled to very close to the ambient temperature compared to uncooled OTCs. However, the yield of plants in the cooled OTCs was still different from those grown outside, suggesting that abiotic factors other than temperature also contributed to the chamber effect. FACE Systems To overcome the limitations of chamber methods, the FACE method was developed in the mid 1980s (Lewin et al., 1994). The first full scale field exper- iment was established at Maricopa (Arizona, U.S.) using cotton as the crop 920103_CRC20_0904_CH18 1/13/01 11:21 AM Page 374 GROWTH AND YIELD OF PADDY RICE UNDER FREE-AIR CO 2 ENRICHMENT 375 (Nagy et al., 1994). Generally, FACE systems involve fumigating a circular area of vegetation with pure CO 2 or CO 2 /air mixtures, thereby generating a zone having [CO 2 ] higher than that of the surrounding ambient atmosphere. The CO 2 is usually emitted from a structure (sometimes referred to as a ring) constructed from pipes or tubes that surrounds the crop. The CO 2 is emitted from the upwind direction of the ring, relying on the wind to mix and dis- perse it over the whole ring. The target [CO 2 ] in the fumigated zone may be either static (e.g., a constant 500 ppmV) or dynamic, whereby the target is set at a certain level (e.g., 200 ppmV) above the real-time ambient [CO 2 ]. A con- trol system regulates the amounts of CO 2 emitted by monitoring and inte- grating wind speed and direction together with [CO 2 ] levels at ring center. The system must be able to deal with short-term changes in the weather, most notably differences in wind speed and direction, both of which may change over very short periods of time. The control system must also be able to cope with longer term temporal variations in [CO 2 ], which may be caused by fac- tors such as diurnal and seasonal changes in the relative amounts of crop photosynthesis and respiration. The FACE method has been successfully used to study the effects of ele- vated [CO 2 ] on a variety of vegetation types. These include agriculturally important crops such as cotton (Lewin et al., 1994), wheat (Kimball et al., 1995), and pastures (Hebeisen et al., 1997), as well as harvestable tree species (Hendrey et al., 1999). FACE has also been used in more natural vegetation types such as desert vegetation (Jordan et al., 1999). The most important advantage of FACE systems over other methods of growing vegetation under elevated [CO 2 ] is that the vegetation is not unduly influenced by the effects of enclosures on environmental factors such as solar radiation, temperature, and wind (McLeod and Long, 1999). Also, relatively large areas of vegetation can be treated, meaning that a large number of sam- ples can be collected for analyses and a range of experiments can be con- ducted in one season. The major disadvantage of FACE systems is their relatively high cost, both to build and run, the latter due primarily to the large amounts of CO 2 required for fumigation. However, expressed on the basis of cost per usable fumigated crop area, FACE systems can be more cost effective than other methods of growing plants under elevated CO 2 (Kimball, 1992). Rice FACE System: Description The Rice FACE project was established in 1996 to study the effects of ele- vated [CO 2 ] concentrations on rice crop growth, yield, and ecosystem processes. It is the first FACE experiment to be conducted on rice. After design trials in 1997, a facility consisting of four FACE rings and their associ- ated ambient (control) plots was constructed for use during the 1998–2000 rice growing seasons. 920103_CRC20_0904_CH18 1/13/01 11:21 AM Page 375 376 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Ring Description Each Rice FACE ring consists of a CO 2 emission structure, a CO 2 moni- toring system, and a computerized control system. In order to minimize atmospheric contamination of the control plots, there is at least 90 m between the controls and the nearest ring. Each emission structure consists of a 12-m diameter octagon made of eight 5-m long, 3.8-cm diameter polyethylene tubes. Each tube is horizontally supported by a 5-m long, 2.2-cm diameter galvanized steel pipe, which is supported at each end by similarly sized, upright pipes dug 40 cm into the soil. The polyethylene tubes have 0.6–0.9- mm diameter CO 2 -release holes located approximately every 4 cm on the side facing into the crop. The height of the emission tubes above ground level is set at approximately 50 cm above the canopy. Liquid CO 2 contained in a hold- ing tank passes through a vaporizer, and the CO 2 gas is delivered to the emis- sion tubes via valves to the emission tubes. Pure CO 2 at a maximum pressure of 0.13 MPa is “sprayed” from the tubes; preliminary simulation studies have shown that, depending on wind speed and emission pressure, concentrations drop from 100% to 2000 ppmV within 20 cm of the emission tube (M. Yoshimoto, pers. comm.). The use of pure CO 2 in the Rice FACE experiment is different from that used in many other FACE designs, which emit a CO 2 /air mixture into the ring using blowers. Under some circumstances this can influence the microclimate within the FACE ring (“blower effects”) (McLeod and Long, 1999), and the control plots must have blowers installed to cancel out the blower effects. There is no such problem with the pure-CO 2 FACE. The total area within each FACE ring is approximately 120 m 2 . Walkways, situated approximately 15 cm above the paddy water level, extend from one of the surrounding earth dikes to the ring center and pro- vided access to the crop and monitoring equipment. Preliminary studies indicate that canopy microclimate such as wind and canopy temperature do not appear to be affected by the presence of the ring structures (M. Yoshimoto, personal communication). CO 2 Control and Monitoring The main objective of the Rice FACE experiment is to determine the influ- ence of elevated [CO 2 ] on various crop and ecosystem processes. It is there- fore crucial to have control over the amounts of CO 2 applied and also to know with confidence what the level of [CO 2 ] is at any time and location within the ring over the duration of the experiment. Because a dynamic target (200 ppmV above ambient) is being used, both ambient and ring [CO 2 ] levels must be monitored. Ambient [CO 2 ] concentra- tions are measured at the center of the two distal control plots using infrared CO 2 gas analyzers. [CO 2 ] in the FACE rings is monitored at ring center, together with wind speed and direction, which are measured every second. 920103_CRC20_0904_CH18 1/13/01 11:21 AM Page 376 GROWTH AND YIELD OF PADDY RICE UNDER FREE-AIR CO 2 ENRICHMENT 377 Table 18.1 Mean CO 2 above ambient (target ؍ 200 ppmV) at ring center and 2.5 m (average of 4 locations) and 5 m (average of 8 locations) from the center for the 4 Rice FACE rings from May 21 until August 20, 1999. Ambient [CO 2 ] concentration during the same time period was 391.1 ppmV. CO 2 concentrations above ambient (ppmV) Ring center 2.5m 5m A 185.9 201.8 251.8 B 201.5 216.6 278.9 C 191.2 213.8 273.5 D 213.5 238.0 309.6 mean 198.0 217.6 278.5 The data generated is sent to data acquisition and control equipment which determines the target and regulates how much and from which emission tubes CO 2 is emitted, with the latter depending on wind direction. When speeds are above 0.3 ms Ϫ1 , the three tubes in the upwind direction emit the required amount of CO 2 , while at wind speeds below 0.3 ms Ϫ1 emission is switched between every other tube every 10 sec. Because a number of different experiments are conducted in various sub- plots within each FACE ring, it is important to know what the [CO 2 ] levels are at these sites over the season. For each ring a separate infrared CO 2 analyzer samples the atmosphere at canopy height at 13 locations. Sampling tubes are located at the center and equidistantly spaced in two concentric circles 2.5 m (4 locations) and 5 m (8 locations) from the center. [CO 2 ] levels at any location within the ring can be estimated by interpolating the actual [CO 2 ] at each of the sampling locations. Temporal and Spatial Control of [CO 2 ] (1999) The ability of the FACE system to control [CO 2 ] can be assessed by com- paring the actual and target [CO 2 ] at any location for a given time period. Performance can be expressed as the average [CO 2 ] concentration above ambient for the time period, or the percentage of the time that all the actual values were within 10 and 20% of the target can be calculated. During the first half the 1999 season (up to the time of writing), [CO 2 ] levels at ring center were between 185 and 213 ppmV above ambient (Table 18.1) and about 55 and 85% of the samples were within 10 and 20% of the target, respectively (data not shown). Within 2.5 m of the center, [CO 2 ] averaged 220 ppmV above ambient, and around 50% of the samples were within 10% of the target. At 5 m fromthe center, [CO 2 ] averaged 280 ppmV above ambient, and only about 30% of the samples were within 10% of the target. (A different control algo- rithm was used in 1998 which resulted in less satisfactory performance, with 920103_CRC20_0904_CH18 1/13/01 11:21 AM Page 377 378 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT CO 2 levels averaging 224 and 340 ppmV above ambient at the center and out- lying yield plots respectively.) CO 2 levels at 2.5 and 5 m from the center were around 3.5 and 13% greater than at the center (Table 18.1), resulting in a “bowl shaped” [CO 2 ] distribu- tion pattern. CO 2 is released from the peripheries of the ring and dispersed towards the center, and, as long as wind speeds and directions are evenly dis- tributed over the season, such a distribution pattern is typical for FACE rings. The size and shape of the [CO 2 ] gradient from the ring edge to the center will depend on factors such as ring architecture, the force of CO 2 emission, wind speed, and the control algorithm used. The CO 2 control performance of the Rice FACE in terms of the percent- age of observations that were within 10% of the target at ring center was not as good as those reported for other FACE systems of similar size. For exam- ple, for the Maricopa FACE experiment, [CO 2 ] levels at ring center were within 10% of the target 90% of the time (Nagy et al., 1994), compared to only 55% for the Rice FACE experiment. This difference in performance can be partially attributed to differences in the wind characteristics of the two sites. Greater average wind speeds result in better CO 2 distribution and mixing. At the Maricopa site, average daily wind speeds were about 1.7 ms Ϫ1 (Nagy et al., 1994) with calm periods (Ͻ 0.4 ms Ϫ1 ) occurring about 19% of the fumigation time (Nagy et al., 1992). In contrast, at the Rice FACE site, average daily wind speed ranged from 1.1 ms Ϫ1 in June to 0.5 ms Ϫ1 in September (season average of 0.7 ms Ϫ1 ), while calm (Ͻ 0.3 ms Ϫ1 ) periods ranged from 30% of the time early in the season to nearly 60% near the end (season average 45%). This lower average wind speed and greater calm percentage makes effective tem- poral control and uniform spatial distribution difficult and is probably a major reason for the differences in CO 2 performance between the Rice FACE and other FACE experiments. THE EFFECTS OF FACE ON THE GROWTH AND YIELD OF PADDY RICE Materials and Methods a. Site description. The Rice FACE experiment is located at Shizukuishi, Iwate Prefecture, in the northern part of Honshu, Japan (39° 38’ N, 140° 57’ E). It is situated in a valley at an altitude of about 200 m, surrounded by 600-m high hills to the south, west, and north. The site was chosen because it is typ- ical of the agroenvironment that grows a large proportion of the Japanese rice crop. It is also close to existing research facilities at the Tohoku National Agricultural Experiment Station near Morioka. The climate is best described as humid continental with a summer precipitation maximum and a cold, dry winter. Over the year, daily average air temperatures range from Ϫ2.5 (January) to 23.2°C (August); meteorological data from the 1998 growing 920103_CRC20_0904_CH18 1/13/01 11:21 AM Page 378 GROWTH AND YIELD OF PADDY RICE UNDER FREE-AIR CO 2 ENRICHMENT 379 Table 18.2 Meteorological profiles of the Rice FACE site, 1998 Air temperature a Solar radiation Rainfall c mean min max mean daily b monthly Month (°C) (MJ m ؊2 d ؊1 ) (mm) May d 16.1 9.4 22.6 18.3 34.1 Jun 16.8 13.4 20.9 12.4 219.3 Jul 21.3 17.4 26.2 14.0 206.0 Aug 21.5 18.0 26.4 11.8 446.5 Sep 20.2 16.5 25.1 10.1 270.2 Season mean 19.7 15.9 24.5 12.5 1176.1 e a Monthly average of the daily mean, minimum, and maximum air temperatures. b Monthly average of the daily mean solar radiation. c Monthly accumulated rainfall. d For last 10 days of the month only. e Season accumulated rainfall. season is shown in Table 18.2. The soils of the site are derived from volcanic ash and have been tentatively classified as humic Andosols. b. Experimental design. In both 1998 and 1999, the experiment was a completely randomized block design with two levels of [CO 2 ] (ambient [CO 2 ] (control) and elevated [CO 2 ] within the FACE rings) replicated four times. FACE and control plots were located in eight paddies blocked by location; the four blocks consisted of paddies with similar agronomic histories and soil characteristics. c. Seedling establishment. In both years, presoaked seeds of rice cv. Akitakomachi (a commonly grown variety in northern Japan) were sown into seedling trays and grown under flooded conditions. Trays were placed in plastic chambers fumigated either with air containing ambient or elevated (ϩ200 ppmV) [CO 2 ]. The duration of seedling growth was 14 and 23 days at average air temperatures of 19.35°C and 18.25°C in 1998 and 1999, respec- tively. d. Crop establishment and management. Seedlings were hand-trans- planted into either control or FACE plots on 21 May 1998 and 20 May 1999. Although most Japanese farmers use mechanical transplanters in establish- ing rice crops, hand transplanting was used in the experiment to ensure an even number of seedlings per hill and regular hill spacing. In both years, there were three seedlings per hill and 17.5 and 30 cm between hills and rows, respectively (Ϸ 19 hills m Ϫ2 ). This spacing is commonly used by farmers in this district. Three levels of N were supplied as ammonium sulfate: 4g (low), 8g (medium), and 12g N m Ϫ2 (high) in 1998, and 4, 9, and 15 g N m Ϫ2 in 1999. The medium N level is typical of the standard rate used by local farmers. In both years N was applied as a basal dressing (63% of the total), at mid-tiller- ing (20%) and at panicle initiation (17%). Levels of phosphorus and potas- sium fertilizer were similar for all N levels and adequate for the high N 920103_CRC20_0904_CH18 1/13/01 11:21 AM Page 379 380 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT treatment. Flooded paddy fields were maintained throughout the season except for a midsummer drainage conducted in mid-July in both years and from 10 days prior to harvest in 1998. Herbicides, insecticides, and fungicides were applied when necessary. e. Sampling and harvesting. To determine the influence of elevated [CO 2 ] on vegetative growth, in both years seedlings were sampled on the day of transplanting and established plants were sampled from the medium N treatment of FACE and control plots at 25, 53, 81, 109, and 131 days after transplanting (DAT) from three locations in 1998. In addition, plants in the high N plots were harvested at 83 and 137 DAT, while low N plants were only harvested at grain maturity. Plants were separated into living and dead leaf blades, stems (including leaf sheath), panicles (when present), and roots; d.wt of the plant parts as determined separately. The number of tillers and panicles (when present) as determined and leaf area was measured. At final harvest, the number of spikelets per panicle was also determined. To deter- mine crop N uptake, the dried plant parts were milled and total N in each part was determined (micro-Kjeldahl technique). In order to determine flowering date, two or three locations within each [CO 2 ] plot were investigated daily for panicle appearance in 1999, but only once in 1998. Flowering date was defined as when panicles had emerged from 50% of the effective tillers (potential panicle bearing). The effect of FACE on grain maturity was investigated by checking the color of the pani- cles by eye during grain filling in 1998. The date of maturity was defined by a “yellow index” in which maturity was defined as when 90% of the panicles at a location had greater than 80% yellow grains. For grain yield determination, subplots were set aside within both FACE and control plots and not disturbed until final harvest. Plants were sampled at grain maturity; total and fertile spikelet number per hill together with mean grain weight were determined. Mean [CO 2 ] (four replicates) in 1998 for these grain yield plots over the season were 726 and 387 ppmV for FACE and control, respectively. In this chapter we present seedling and phenological data from both years, but only 1998 data for crop dry matter and grain yield investigations. Results a. Seedling growth. When rice crops are established by transplanting, early seedling growth and vigor under nursery conditions are important fac- tors in the successful establishment and eventual yield of the crops. However, there is little information on the effects of elevated [CO 2 ] on the growth of rice seedlings cultivated for transplanting using commercial agricultural condi- tions and techniques. In both years, elevated [CO 2 ] increased total and root d.wt (Table 18.3). In 1998, leaf blade d.wt increased with elevated [CO 2 ], while leaf area decreased, leading to an increase in specific leaf weight (leaf d.wt 920103_CRC20_0904_CH18 1/13/01 11:21 AM Page 380 [...]... yield increase with FACE Grain number was also increased with increasing applied N It is important to provide high levels of plant N prior to anthesis in order to produce and maintain spikelet number in rice crops (Kobayashi and Horie, 1994) In both FACE and control plots, grain number increased linearly with increasing N uptake during vegetative development (from transplanting to flowering; Figure 18. 8a)... both a drop in Rubisco activity and Rubisco amount relative to other leaf proteins and an increase in nonstructural carbohydrates in the leaf blades and sheaths (Rowland-Bamford et al., 1990, 1991) The increase in nonstructural carbohydrates leads to increases in SLW (Pritchard et al., 1999); for rice SLW increased by approximately 2% with increasing [CO2] from 330 ppmV to 500 ppmV (Rowland-Bamford et... was greater with increasing applied N level, with FACE increasing yields of low, medium, and high N levels 12%, 16%, and 21%, respectively These increases in yield were similar to the increases in grain numbers (Figure 18. 5a), indicating that higher yield with elevated [CO2] depends mainly on increased grain number Similar responses have been found in a previous study conducted using temperature gradient... climate and agronomic practices Because more than a half of the world’s rice is grown in China and India, where the climate, soils, and agricultural practices are quite different from those in northern Japan, we believe that FACE experiments must also be done in these major rice-producing countries Indeed, there is a rice-wheat cropping system FACE project at the designing and testing stage in India... O.S., Pamplona, R.P., and Weerakoon, W M., 1995 Interactive effects of elevated carbon dioxide and temperature on rice growth and development, in S Peng et al., (Eds.), Climate Change and Rice, 278 –287 Springer-Verlag Berlin 920103_CRC20_0904_CH18 394 1/13/01 11:22 AM Page 394 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Jordan, D.N., Zitzer, S.F., Hendrey, G.R., Lewin, K.F., Nagy, J.,... 920103_CRC20_0904_CH18 386 1/13/01 11:22 AM Page 386 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Figure 18. 5 The effect of CO2 (ambient [CO2] (control) and free-air CO2 enrichment (FACE)) and nitrogen application on grain number and grain yield per m2 Error bars are Ϯ1 standard error of the mean “ns” and “**” denote not significant and significant at p Ͻ 0.01, respectively despite the... FACE and control, NUE declined exponentially with increasing N uptake (Figure 18. 8b) Overall, FACE resulted in a significant increase in tiller number, crop biomass, and grain yield The number of days to flowering was significantly decreased by FACE, but there was no difference in the grain filling period The increase in grain yield with FACE was greater with higher levels of applied N This yield increase... flowering, grain filling and finally grain maturity Grains are composed mainly of carbohydrates which are derived from two sources: those stored in the vegetative parts before flowering, and those produced after flowering The contribution 920103_CRC20_0904_CH18 1/13/01 11:21 AM Page 383 GROWTH AND YIELD OF PADDY RICE UNDER FREE-AIR CO2 ENRICHMENT 383 Figure 18. 2 The effect of ambient [CO2] (control) and. .. not shown) 920103_CRC20_0904_CH18 384 1/13/01 11:21 AM Page 384 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Figure 18. 3 The effect of ambient [CO2] (control) and free-air CO2 enrichment (FACE) on the time to flowering in 1998 and 1999 (see text for details) Average temperature up to flowering is shown Plant population ϭ 19 mϪ2 Error bars are Ϯ 1 standard error of the mean “ **” denotes... A FACE experiment in China is also being set up Knowledge obtained from Rice FACE experiment will improve our understanding of the rice crop and ecosystem processes in a world with elevated [CO2] A better understanding of these processes will hopefully help us predict the changes in rice production and rice ecosystems, thereby enabling planning for, adapting to, and possibly utilizing the future elevated . 379 380 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT treatment. Flooded paddy fields were maintained throughout the season except for a midsummer drainage conducted in mid-July in. (Kobayashi and Horie, 1994). In both FACE and control plots, grain number increased lin- early with increasing N uptake during vegetative development (from trans- planting to flowering; Figure 18. 8a) 385 386 STRUCTURE AND FUNCTION IN AGROECOSYSTEMS DESIGN AND MANAGEMENT Figure 18. 5 The effect of CO 2 (ambient [CO 2 ] (control) and free-air CO 2 enrichment (FACE)) and nitrogen application on grain
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