Free-air CO2 Enrichment Plots Research Articles

Don't panic any more: MORE PANICLES 3 increases rice yield at elevated CO2 levels.

Don't panic any more: MORE PANICLES 3 increases rice yield at elevated CO2 levels.

Canopy warming accelerates development in soybean and maize, offsetting the delay in soybean reproductive development by elevated CO2 concentrations.

Increases in atmospheric CO2 concentrations ([CO2 ]) and surface temperature are known to individually have effects on crop development and yield, but their interactive effects have not been adequately investigated under field conditions. We evaluated the impacts of elevated [CO2 ] with and without canopy warming as a function of development in soybean and maize using infrared heating arrays nested within free air CO2 enrichment plots over three growing seasons. Vegetative development accelerated in soybean with temperature plus elevated [CO2 ] resulting in higher node number. Reproductive development was delayed in soybean under elevated [CO2 ], but warming mitigated this delay. In maize, both vegetative and reproductive developments were accelerated by warming, whereas elevated [CO2 ] had no apparent effect on development. Treatment-induced changes in the leaf carbohydrates, dark respiration rate, morphological parameters, and environmental conditions accompanied the changes in plant development. We used two thermal models to investigate their ability to predict the observed development under warming and elevated [CO2 ]. Whereas the growing degree day model underestimated the thermal threshold to reach each developmental stage, the alternative process-based model used (β function) was able to predict crop development under climate change conditions.

Using FACE Systems to Screen Wheat Cultivars for Yield Increases at Elevated CO2

Because of continuing increases in atmospheric CO2, identifying cultivars of crops with larger yield increases at elevated CO2 may provide an avenue to increase crop yield potential in future climates. Free-air CO2 enrichment (FACE) systems have most often been used with multiple replications of each CO2 treatment in order to increase confidence in the effect of elevated CO2. For screening of cultivars for yield increases at elevated CO2, less precision about the CO2 effect, but more precision about cultivar ranking within CO2 treatments is appropriate. As a small-scale test of this approach, three plots, each of four cultivars of wheat, were grown in single FACE and control plots over two years, and the cultivar rankings of yield at elevated and ambient CO2 were compared. Each replicate plot was the size used in traditional cultivar comparisons. An additional test using four smaller replicate plots per cultivar within one FACE and one ambient plot was used to compare nine cultivars in another year. In all cases, elevated CO2 altered the ranking of cultivars for yield. This approach may provide a more efficient way to utilize FACE systems for the screening of CO2 responsiveness.

Elevated atmospheric CO2 levels affect community structure of rice root-associated bacteria.

A number of studies have shown that elevated atmospheric CO2 ([CO2]) affects rice yields and grain quality. However, the responses of root-associated bacteria to [CO2] elevation have not been characterized in a large-scale field study. We conducted a free-air CO2 enrichment (FACE) experiment (ambient + 200 μmol.mol−1) using three rice cultivars (Akita 63, Takanari, and Koshihikari) and two experimental lines of Koshihikari [chromosome segment substitution and near-isogenic lines (NILs)] to determine the effects of [CO2] elevation on the community structure of rice root-associated bacteria. Microbial DNA was extracted from rice roots at the panicle formation stage and analyzed by pyrosequencing the bacterial 16S rRNA gene to characterize the members of the bacterial community. Principal coordinate analysis of a weighted UniFrac distance matrix revealed that the community structure was clearly affected by elevated [CO2]. The predominant community members at class level were Alpha-, Beta-, and Gamma-proteobacteria in the control (ambient) and FACE plots. The relative abundance of Methylocystaceae, the major methane-oxidizing bacteria in rice roots, tended to decrease with increasing [CO2] levels. Quantitative PCR revealed a decreased copy number of the methane monooxygenase (pmoA) gene and increased methyl coenzyme M reductase (mcrA) in elevated [CO2]. These results suggest elevated [CO2] suppresses methane oxidation and promotes methanogenesis in rice roots; this process affects the carbon cycle in rice paddy fields.

Elevated atmospheric CO2 stimulates soil fungal diversity through increased fine root production in a semiarid shrubland ecosystem.

Soil fungal communities are likely to be central in mediating microbial feedbacks to climate change through their effects on soil carbon (C) storage, nutrient cycling, and plant health. Plants often produce increased fine root biomass in response to elevated atmospheric carbon dioxide (CO2 ), but the responses of soil microbial communities are variable and uncertain, particularly in terms of species diversity. In this study, we describe the responses of the soil fungal community to free air CO2 enrichment (FACE) in a semiarid chaparral shrubland in Southern California (dominated by Adenomstoma fasciculatum) using large subunit rRNA gene sequencing. Community composition varied greatly over the landscape and responses to FACE were subtle, involving a few specific groups. Increased frequency of Sordariomycetes and Leotiomycetes, the latter including the Helotiales, a group that includes many dark septate endophytes known to associate positively with roots, was observed in the FACE plots. Fungal diversity, both in terms of richness and evenness, increased consistently in the FACE treatment, and was relatively high compared to other studies that used similar methods. Increases in diversity were observed across multiple phylogenetic levels, from genus to class, and were distributed broadly across fungal lineages. Diversity was also higher in samples collected close to (5 cm) plants compared to samples in canopy gaps (30 cm away from plants). Fungal biomass correlated well with soil organic matter (SOM) content, but patterns of diversity were correlated with fine root production rather than SOM. We conclude that the fungal community in this ecosystem is tightly linked to plant fine root production, and that future changes in the fungal community in response to elevated CO2 and other climatic changes will be primarily driven by changes in plant belowground allocation. Potential feedbacks mediated by soil fungi, such as soil C sequestration, nutrient cycling, and pathogenesis, are discussed.

Heat-tolerant rice cultivars retain grain appearance quality under free-air CO2 enrichment.

BackgroundHeat-tolerant rice cultivars have been developed as a countermeasure to poor grain appearance quality under high temperatures. Recent studies showed that elevated CO2 concentrations (E-[CO2]) also reduce grain quality. To determine whether heat-tolerant cultivars also tolerate E-[CO2], we conducted a free-air CO2 enrichment (FACE) experiment with 12 rice cultivars differing in heat tolerance.ResultsThe percentage of undamaged grains of five standard cultivars (Akitakomachi, Kinuhikari, Koshihikari, Matsuribare, Nipponbare) averaged 61.7% in the ambient [CO2] (AMB) plot and 51.7% in the FACE plot, whereas that of heat-tolerant cultivars (Eminokizuna, Wa2398, Kanto 257, Toyama 80, Mineharuka, Kanto 259, Saikai 290) averaged 73.5% in AMB and 71.3% in FACE. This resulted in a significant [CO2] by cultivar interaction. The percentage of white-base or white-back grains increased from 8.4% in AMB to 17.1% in FACE in the sensitive cultivars, but from only 2.1% in AMB to only 4.4% in FACE in the heat-tolerant cultivars.ConclusionHeat-tolerant cultivars retained their grain appearance quality at E-[CO2] under present air temperatures. Further improvements in appearance quality under present conditions will be needed to achieve improvements under E-[CO2], because E-[CO2] will likely lower the threshold temperature for heat stress.

Free-air CO2 enrichment (FACE) net nitrogen fixation experiment at a paddy soil surface under submerged conditions

The aim of this study was to evaluate the cumulative net free-living nitrogen (N) fixation and its response to elevated atmospheric carbon dioxide (CO2) in the submerged surface of paddy soil. The study site was an actual paddy area in central Japan that was equipped with a free-air CO2 enrichment (FACE) facility and was composed of four bays, where each bay had an elevated CO2 plot (FACE plot) and an ambient plot. Field incubation was conducted at subplots without N fertilizer application from May 28 to August 18, 2012 (82 days). The CO2 enrichment was an average of +528 ppm during the study period at the subplots. The changes in total N (TN) content in the surface soil (0–1 cm) were determined in comparison to the initial TN content. The cumulative net N fixations during the 82-day study period were 47.1 ± 3.7 and 43.3 ± 5.8 (standard error) kg N ha−1 in the FACE and ambient plots, respectively. The difference between the FACE and ambient plots was not significant (p = 0.05). However, these values were partly affected by the charophyte blooms, which are not involved in N fixation. The results are not conclusive, and the one bay without charophyte blooming displayed a significant increase in the cumulative net N fixation (approximately 10 kg N ha−1) with CO2 enrichment (p < 0.001).

Comment on 'improving ecophysiological simulation models to predict the impact of elevated CO(2) concentration on crop productivity' by X. Yin.

The recent publication by Yin (2013; Annals of Botany 112: 465-475) referred to in the title above provides an excellent review of modelling approaches to predict the impact of elevated CO2 on crop productivity, as well as on the controversy regarding whether yield responses observed in free-air CO2 enrichment (FACE) experiments are indeed lower than those from chamber-based experiments. However, the wheat experiments in the example of fig. 1 in Yin's paper had a flaw as the control plots lacked blowers that were in the FACE plots, which warmed the FACE plots at night and hastened plant development. This Viewpoint seeks to highlight this fact, and to comment on the relative merits of FACE and enclosure experiments.

Pest and disease abundance and dynamics in wheat and oilseed rape as affected by elevated atmospheric CO2 concentrations.

Future atmospheric CO2 concentrations are predicted to increase, and directly affect host plant phenology, which, in turn, is assumed to mediate the performance of herbivorous insects indirectly as well as the abundance and epidemiology of plant diseases. In a 4-year field experiment, spring wheat (Triticum aestivum L. cv. Triso) and spring oilseed rape (Brassica napus L. cv. Campino) were grown using a mini- free-air CO2 enrichment (FACE) system, which consisted of a control (CON), an ambient treatment (AMB) and FACE treatments. The CON and AMB treatments did not receive additional CO2, whereas the FACE plots were moderately elevated by 150μLL-1 CO2. The impact of elevated CO2 was examined with regard to plant phenology, biomass, leaf nitrogen and carbon, abundance of insect pest species and their relative population growth by either direct counts or yellow sticky traps. Occurrence and damage of plants by pathogens on spring wheat and oilseed rape were directly assessed. Disease infestations on plants were not significantly different between ambient and elevated CO2 in any of the years. Plant phenology, aboveground biomass, foliar nitrogen and carbon concentrations were also not significantly affected by CO2 enrichment. In contrast, the abundance of some species of insects was significantly influenced by elevated CO2, showing either an increase or a decrease in infestation intensity.

Will elevated CO2 enhance mineral bioavailability in wetland ecosystems? Evidence from a rice ecosystem

Mineral cycling plays a critical role in wetland ecosystem functions and can be affected by environmental changes, such as CO2 enrichment. Learning the responses of mineral bioavailability in wetlands to elevated CO2 under field conditions will provide enormous benefits to the assessment of climate change impacts on wetland ecosystems. A free-air CO2 enrichment (FACE) experiment was conducted in a rice ecosystem in Jiangsu, China, with two nitrogen (N) application levels. Responses of K, Ca, Mg, Fe, Mn, Zn, and Si in this ecosystem were investigated in situ. CO2 enrichment increased rice biomass Ca, Mg, Fe, Mn, Zn, and Si regardless of N application levels. Dissolved mineral contents in surface water and available mineral contents in the 0–15 cm soil layer were higher in the FACE plots than in the ambient under both N levels. Elevated CO2 reduced the pH values of the 0–15 cm soil layer and surface water, but increased the cation exchange capacity of the soil layer. The effects of N treatment and its interaction with CO2 enrichment were mostly insignificant on the above parameters. Our results indicate that CO2 enrichment can enhance mineral bioavailability in a rice ecosystem through accelerating mineral transformation from the bio-inactive reservoirs to the bioactive ones.

Performance of the enlarged Rice-FACE system using pure CO2 installed in Tsukuba, Japan

Free-air CO2 enrichment (FACE) provides a unique platform for testing the response of future ecosystems to higher atmospheric CO2 concentration ([CO2]) without disturbing various ecosystemscale interactions. To investigate adaptations to climate change, it is crucial to test the responses of diverse cultivars and management conditions to higher [CO2]. The older rice-FACE facility at Shizukuishi had an effective area of about 80 m2 for [CO2] treatment in each replicate, which was not large enough to test multiple genotypes and management practices. We report the first-year performance of the Tsukuba rice-FACE system installed at Tsukubamirai, Ibaraki, Japan. The new system was designed to have twice the usable area (>160 m2) of the Shizukuishi system without deteriorating the ability to control [CO2]. We adopted a pure-CO2 injection type system to elevate [CO2] in the FACE ring by 200 μmol mol-1 above ambient (control) plots. Overall temporal [CO2] control of the Tsukuba FACE system was slightly better than of the Shizukuishi system; mean [CO2] in the FACE plots was 584 μmol mol-1, nearly equal to the target [CO2] of 586 μmol mol-1. The one-minute mean [CO2] deviated by <±10% and <±20% from the target [CO2] 73.9% and 91.3% of the time, respectively. Spatial distribution of [CO2] inside the ring strongly depended on wind direction and speed. Relatively uniform [CO2] was achieved near the ring center and in the northwestern direction, yielding an aerial fraction of 66% that experienced a season-mean [CO2] within ±20% of the target. These aspects of spatio-temporal performance are comparable to those of other FACE facilities, indicating that the Tsukuba system can serve as a useful and reliable platform on which to test various rice genotypes that may be beneficial under projected high [CO2] conditions in the future.

Effect of Elevated [CO2] on Soil Bubble and CH4 Emission from a Rice Paddy: A Test by 13 C Pulse-Labeling under Free-Air CO2 Enrichment

A 13 C pulse-labeling experiment was conducted under ambient CO2 and free-air CO2 enrichment (FACE) conditions to understand how elevated CO2 affects the CH4 in soil bubbles and CH4 emissions from rice paddies. Two hills of rice plants enclosed by frames in ambient CO2 and FACE plots were labeled with 13 CO2 at the panicle formation stage, and plants and soil bubbles were collected 2 and 51 days after the pulse labeling. CH4 and 13 CH4 emissions were also measured by the closed-chamber method between the 2 bubble samplings. Conversion of photosynthate carbon to CH4 entrapped in soil bubbles and CH4 emission to the atmosphere occurred quickly, suggesting that recent photosynthates can be an important source of carbon for methanogenesis. About 1% of the 13 C-labeled C taken up through photosynthesis was emitted as 13 CH4 during the 7 weeks of measurement, most during the first 3 weeks after labeling. Total CH4 and 13 CH4 emissions did not differ between the ambient CO2 and FACE treatments, because the entrapped CH4 in the soil and the root biomass were not affected by elevated CO2 levels in this study.

Elevated Carbon Dioxide and Irrigation Effects on Soil Nitrogen Gas Exchange in Irrigated Sorghum

The impacts of increasing atmospheric CO2, an important greenhouse gas, on soil microbial production and consumption of other greenhouse gases such as N2O are uncertain. This study was conducted during the 1998 and 1999 summer growing seasons at the Free‐Air CO2 Enrichment (FACE) site in Maricopa, AZ. The objective was to measure N2O and denitrification emission rates in a C4 sorghum [Sorghum bicolor (L.) Moench] production system with ample and limited flood irrigation rates under FACE (seasonal mean = 579 μmol mol−1) and control (seasonal mean = 396 μmol mol−1) CO2 Plots were sampled for N2O flux using both chamber and intact incubated soil core techniques. Nitrogen gas (N2O plus N2) emissions were measured using intact incubated soil cores with C2H2 inhibition. Nitrous oxide emissions measured with chambers increased markedly after irrigation and fertilization following prolonged periods without water under both elevated and control CO2 conditions. Within 5 d of fertilization and irrigation, N2O emissions measured with chambers were &lt;250 g N2O‐N ha−1 d−1 until subsequent irrigations. Emissions measured from cores ranged from −0.11 to &gt;250 g N2O‐N ha−1 d−1 Seasonal cumulative N2O‐N emissions measured using chambers were &lt;1.5 kg N ha−1 Seasonal N‐gas losses measured during 1999 were as high as 3.7 kg N ha−1, and were highest with elevated CO2 and the high irrigation treatment. During periods when significant emissions were recorded, the primary end product of denitrification was N2 rather than N2O. Water‐filled pore space (WFPS) was the most important single factor controlling N‐gas emissions, with the largest emissions (&gt;500 g N2O‐N ha−1 d−1) coming with &gt;55% WFPS. Neither soil NO3− nor soil organic C alone limited N gas emissions. Elevated CO2 did not result in increased N2O or N‐gas emissions with either ample or limited irrigation.

Dynamics of labile and recalcitrant soil carbon pools in a sorghum free-air CO 2 enrichment (FACE) agroecosystem

Experimentation with dynamics of soil carbon pools as affected by elevated CO 2 can better define the ability of terrestrial ecosystems to sequester global carbon. In the present study, 6 N HCl hydrolysis and stable-carbon isotopic analysis ( δ 13C) were used to investigate labile and recalcitrant soil carbon pools and the translocation among these pools of sorghum residues isotopically labeled in the 1998–1999 Arizona Maricopa free air CO 2 enrichment (FACE) experiment, in which elevated CO 2 (FACE: 560 μmol mol −1) and ambient CO 2 (Control: 360 μmol mol −1) interact with water-adequate (wet) and water-deficient (dry) treatments. We found that on average 53% of the final soil organic carbon (SOC) in the FACE plot was in the recalcitrant carbon pool and 47% in the labile pool, whereas in the Control plot 46% and 54% of carbon were in recalcitrant and labile pools, respectively, indicating that elevated CO 2 transferred more SOC into the slow-decay carbon pool. Also, isotopic mixing models revealed that increased new sorghum residue input to the recalcitrant pool mainly accounts for this change, especially for the upper soil horizon (0–30 cm) where new carbon in recalcitrant soil pools of FACE wet and dry treatments was 1.7 and 2.8 times as large as that in respective Control recalcitrant pools. Similarly, old C in the recalcitrant pool under elevated CO 2 was higher than that under ambient CO 2, indicating that elevated CO 2 reduces the decay of the old C in recalcitrant pool. Mean residence time (MRT) of bulk soil carbon at the depth of 0–30 cm was significantly longer in FACE plot than Control plot by the averages of 12 and 13 yr under the dry and wet conditions, respectively. The MRT was positively correlated to the ratio of carbon content in the recalcitrant pool to total SOC and negatively correlated to the ratio of carbon content in the labile pool to total SOC. Influence of water alone on the bulk SOC or the labile and recalcitrant pools was not significant. However, water stress interacting with CO 2 enhanced the shift of the carbon from labile pool to recalcitrant pool. Our results imply that terrestrial agroecosystems may play a critical role in sequestrating atmospheric CO 2 and mitigating harmful CO 2 under future atmospheric conditions.

Flowering, seed production and seed mass in a species-rich temperate grassland exposed to FACE and warming

Long-term effects of climate change on plant communities must be mediated by reproductive and recruitment responses of component species. From spring 2003 until autumn 2006, we monitored flowering and seed-production responses to free air CO2 enrichment (FACE) and 2°C warming in a species-rich, nutrient-poor southern temperate grassland, by using the TasFACE experiment. There were no effects of either FACE or warming on the proportion of species flowering in any year. Flowering, seed production and seed mass were not significantly affected by FACE, warming or their interaction in most species. Some species, however, did respond significantly to simulated global changes. These responses generally were not governed by life history, but there were two distinct trends. First, warming increased the proportion of the population that flowered in perennial grasses but not in other species types. Second, flowering and seed production of both perennial woody dicots responded strongly to the interaction of FACE and warming, with Bossiaea prostrata producing most seeds in warmed FACE plots and Hibbertia hirsuta producing the most in unwarmed FACE plots. FACE increased seed mass 4-fold in the perennial C3 grass Elymus scaber (P &lt; 0.01) but substantially reduced seed mass of the perennial C3 grass Austrodanthonia caespitosa (P &lt; 0.02) and the perennial forb Hypochaeris radicata (P &lt; 0.02), with the remainder of species unaffected. Our results indicate that warming and elevated CO2 had little effect on seed production in the temperate grassland ecosystem. The few significant affects there were, however, are likely to have substantial implications for community composition and structure.

Seasonal changes in the effects of free-air CO 2 enrichment (FACE) on dry matter production and distribution of rice ( Oryza sativa L.)

It is reported that stimulating effect of elevated atmospheric [CO 2] on photosynthesis of rice ( Oryza sativa L.) is likely to be reduced during the plant growth period. However, there is little information on seasonal changes in dry matter (DM) production and distribution of rice under elevated atmospheric [CO 2]. A free-air CO 2 enrichment (FACE) experiment was conducted at Wuxi, Jiangsu, China, in 2001–2003, using Wuxiangging 14, a japonica cultivar. The rice was grown at ambient or elevated (ca. 200 μmol mol −1 above ambient) [CO 2] and supplied with 25 g N m 2, which is the normal N application rate for local farmers. DM accumulation of rice in FACE plots was significantly increased by 40, 30, 22, 26 and 16% on average at tillering, panicle initiation (PI), heading, mid-ripening and grain maturity, respectively. Rice DM production under FACE was significantly enhanced by 41, 27, 15 and 38% on average during the growth periods from transplanting to tillering (Period 1), tillering to PI (Period 2), PI to heading (Period 3) and heading to mid-ripening (Period 4), respectively, but significantly decreased by 25% in the period from mid-ripening to grain maturity (Period 5). In general, seasonal changes in crop response to FACE in both green leaf area index (GLAI) and net assimilation rate (NAR) followed a similar pattern to that of the DM production. Under FACE the leaves decreased significantly in proportion to the total above-ground DM over the season, the stems showed an opposite trend, while the spikes depended on crop development stage: showing no change at heading, significant increase (+4%) at mid-ripening and significant decrease (−3%) at grain maturity. Grain yield was stimulated by an average of 13% by FACE, due to increased total DM production rather than any changes in partitioning to the grain. We conclude that the gradual acclimation of rice growth to elevated [CO 2] do not occur inevitably, and it could also be altered by environmental conditions (e.g., cultivation technique).

Effects of Elevated Atmospheric CO 2 on Soil Microbial Biomass, Activity, and Diversity in a Chaparral Ecosystem

This study reports the effects of long-term elevated atmospheric CO2 on root production and microbial activity, biomass, and diversity in a chaparral ecosystem in southern California. The free air CO2 enrichment (FACE) ring was located in a stand dominated by the woody shrub Adenostoma fasciculatum. Between 1995 and 2003, the FACE ring maintained an average daytime atmospheric CO2 concentration of 550 ppm. During the last two years of operation, observations were made on soil cores collected from the FACE ring and adjacent areas of chaparral with ambient CO2 levels. Root biomass roughly doubled in the FACE plot. Microbial biomass and activity were related to soil organic matter (OM) content, and so analysis of covariance was used to detect CO2 effects while controlling for variation across the landscape. Extracellular enzymatic activity (cellulase and amylase) and microbial biomass C (chloroform fumigation-extraction) increased more rapidly with OM in the FACE plot than in controls, but glucose substrate-induced respiration (SIR) rates did not. The metabolic quotient (field respiration over potential respiration) was significantly higher in FACE samples, possibly indicating that microbial respiration was less C limited under high CO2. The treatments also differed in the ratio of SIR to microbial biomass C, indicating a metabolic difference between the microbial communities. Bacterial diversity, described by 16S rRNA clone libraries, was unaffected by the CO2 treatment, but fungal biomass was stimulated. Furthermore, fungal biomass was correlated with cellulase and amylase activities, indicating that fungi were responsible for the stimulation of enzymatic activity in the FACE treatment.

Soil microbial indices as bioindicators of environmental changes in a poplar plantation

An understanding of microbial biomass and microbial activity as part of belowground processes as affected by elevated CO2 is crucial in order to predict the long-term response of ecosystems to climatic changes. The ratio of biomass C to soil organic C (Cmic:Corg), the metabolic quotient (the specific soil respiration of the microbial biomass, qCO2), the C mineralization quotient (the fraction of total organic C mineralized throughout the incubation, qM), the microbial biomass change rate quotient (qC) and soil inorganic nitrogen content were determined on soil samples taken during 3 years (Fall 2000–Fall 2003) in a poplar plantation exposed to increased atmospheric CO2 by means of FACE (Free Air CO2 Enrichment) technique and nitrogen fertilization. A competition for nitrogen between plants and microrganisms, stronger in FACE plots, induced a stress condition within microbial community. FACE treatment provided C for microbial growth (Cmic:Corg), but reducing nitrogen availability, led to a higher microbial loss over time (qC). Nitrogen fertilization decreased microbial mortality lowering energetic maintenance requirements (qCO2) and induced a short-term shift in favour of microrganisms more rapid in the use of the resources. The C mineralization quotient (qM) was not affected by either FACE nor fertilization treatment meaning that the fraction of total organic carbon mineralized during the incubation period did not vary significantly.

Effect of Free-Air CO2 Enrichment (FACE) on the Community Structure of Aquatic Organisms in Floodwater of a Japanese Paddy Field during the Flooding Period of Rice Cultivation

In the present study, the effect of free-air CO2 enrichment (FACE) on the diversity and the community structure of aquatic organisms in the floodwater of a paddy field in northern Japan was evaluated. The varieties and the number of aquatic organisms ranging from 30 μm to 2 cm were compared four times at intervals of 20 d between the FACE (599 ppm CO2) and ambient air (384 ppm CO2) plots during the flooding period of rice cultivation. Aquatic organisms were classified mainly at the order level. Twenty-eight taxonomical groups were detected, and the number of groups in the FACE plots was significantly lower than that in the ambient plots. Zygnematales and Chaetonotida were less frequently detected in the FACE plots. The population densities of Zygnematales, and Chaetonotida also tended to be lower in the FACE plots than in the ambient plots in the late flooding period (after 50 d of flooding). No groups showed a significantly higher population density and frequency of presence in the FACE plots than in the ambient plots. The seasonal variations in the number of taxonomical groups and the community structure of aquatic organisms were less conspicuous in the FACE plots than in the ambient plots. We concluded that the FACE conditions adversely affected the communities of aquatic organisms in paddy fields.

Effect of Free-Air CO2 Enrichment (FACE) on Methanogenic Archaeal Communities Inhabiting Rice Roots in a Japanese Rice Field

The effect of free-air CO2 enrichment (FACE) on the methanogenic archaeal communities inhabiting rice roots was studied in a Japanese rice field by separately collecting rice roots three times (at mid-tillering, panicle initiation, and heading stages) according to their nodal number, extracting DNA from the roots and subjecting it to polymerase-chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) and sequence analyses. Appearance of roots indicated that aging and senescence occurred faster under the FACE conditions than under the ambient conditions. The number of DGGE bands of methanogenic archaeal communities tended to increase with the growth stages. Cluster analysis showed that the succession of methanogenic archaeal communities in the ambient plot preceded that in the FACE plot, while the trend of the appearance of rice roots was opposite. All the closest relatives associated with the DGGE bands belonged to Methanomicrobiales and Rice cluster I, and FACE did not affect the phylogenetic position of the closest relatives associated with the characteristic DGGE bands. Faster succession of methanogenic archaeal communities in the ambient plot and similar phylogenetic members between the plots were observed in rice roots in years with both warmer (1999) and cooler (2003) weather during the rice cultivation period than in average years.