Free-air CO2 Enrichment Research Articles

Root electrical capacitance as an indicator of wheat growth and yield in a free-air carbon dioxide enrichment (FACE) experiment

Background and aimsThis study was the first to test the efficiency of monitoring root electrical capacitance (CR*) non-destructively in the field to evaluate crop development under different environmental conditions.MethodsA free-air CO2 enrichment (FACE) experiment was performed with two winter wheat cultivars, two levels (low and high) of nitrogen supply and two (ambient and elevated) of [CO2] in three replicate plots over two years. The validity of CR* as a proxy for root uptake activity was confirmed by tracking the ceptometer-based leaf area index (LAI).ResultsRepeated CR* measurements clearly demonstrated the seasonal dynamics in root development, with a peak at flowering, and the delayed growth in the second year caused by the unfavourable meteorological conditions. From the vegetative to flowering stages, CR* was strongly correlated with LAI (R2: 0.897–0.962). The positive effect of higher N supply and elevated [CO2] on crop growth was clearly indicated by the higher CR* values, associated with increased LAI, shoot dry mass (SDM) at flowering and grain yield (GY). The maximum CR* was closely related to GY (R2: 0.805 and 0.867) when the data were pooled across the N and CO2 treatments and the years. Unlike CR* and GY, SDM and LAI were significantly lower in the second year, presumably due to the enhanced root/shoot ratio induced by a severe spring drought.ConclusionsThe present results convincingly demonstrated the potential of the in situ root capacitance method to assess root responses dynamically, and to predict crop GY.

Soil Organic Carbon Isotope Tracing in Sorghum under Ambient CO2 and Free-Air CO2 Enrichment (FACE)

As atmospheric carbon dioxide concentrations, [CO2Air], continue their uncontrolled rise, the capacity of soils to accumulate or retain carbon is uncertain. Free-air CO2 enrichment (FACE) experiments have been conducted to better understand the plant, soil and ecosystem response to elevated [CO2], frequently employing commercial CO2 that imparts a distinct isotopic signal to the system for tracing carbon. We conducted a FACE experiment in 1998 and 1999, whereby sorghum (C4 photosynthetic pathway) was grown in four replicates of four treatments using a split-strip plot design: (i) ambient CO2/ample water (365 μmol mol−1, “Control–Wet”), (ii) ambient CO2/water stress (“Control–Dry”), (iii) CO2-enriched (560 μmol mol−1, “FACE–Wet”), and (iv) CO2-enriched/water stressed (“FACE–Dry”). The stable-carbon isotope composition of the added CO2 (in FACE treatments) was close to that of free atmosphere background values, so the subsequent similar 13C-enriched carbon signal photosynthetically fixed by C4 sorghum plants could be used to trace the fate of carbon in both FACE and control treatments. Measurement of soil organic carbon content (SOC (%) = gC/gdry soil × 100%) and δ13C at three depths (0–15, 15–30, and 30–60 cm) were made on soils from the beginning and end of the two experimental growing seasons. A progressive ca. 0.5‰–1.0‰ δ13C increase in the upper soil SOC in all treatments over the course of the experiment indicated common entry of new sorghum carbon into the SOC pools. The 0–15 cm SOC in FACE treatments was 13C-enriched relative to the Control by ca. 1‰, and according to isotopic mass balance, the fraction of the new sorghum-derived SOC in the Control–Wet treatment at the end of the second season was 8.4%, 14.2% in FACE–Wet, 6.5% in Control–Dry, and 14.2% in FACE–Dry. The net SOC enhancement resulting from CO2 enrichment was therefore 5.8% (or 2.9% y−1 of experiment) under ample water and 7.7% (3.8% y−1 of experiment) under limited water, which matches the pattern of greater aboveground biomass increase with elevated [CO2Air] under the Dry treatment, but no parallel isotopic shifts were found in deeper soils. However, these increased fractions of new carbon in SOC at the end of the experiment do not necessarily mean an increase in total SOC content, because gravimetric measurements of SOC did not reveal a significant increase under elevated [CO2Air], at least within the limits of SOC-content error bars. Thus, new carbon gains might be offset by pre-experiment carbon losses. The results demonstrate successful isotopic tracing of carbon from plants to soils in this sorghum FACE experiment showing differences between FACE and Control treatments, which suggest more dynamic cycling of SOC under elevated [CO2Air] than in the Control treatment.

Impacts of Elevated Atmospheric CO2 and N Fertilization on N2O Emissions and Dynamics of Associated Soil Labile C Components and Mineral N in a Maize Field in the North China Plain

The elevated atmospheric CO2 concentration (eCO2) is expected to increase the labile C input to the soil, which may stimulate microbial activity and soil N2O emissions derived from nitrification and denitrification. However, few studies studied the effect of eCO2 on N2O emissions from maize field under the free-air CO2 enrichment (FACE) conditions in the warm temperate zone. Here, we report a study conducted during the 12th summer maize season under long-term eCO2, aiming to investigate the effect of eCO2 on N2O emissions. Moreover, we tested zero and conventional N fertilization treatments, with maize being grown under either eCO2 or ambient CO2 (aCO2). We hypothesized that N2O emissions would be increased under eCO2 due to changes in soil labile C and mineral N derived from C-deposition, and that the increase would be larger when eCO2 was combined with conventional N fertilization. We also measured the activities of some soil extracellular enzymes, which could reflect soil C status. The results showed that, under eCO2, seasonal N2O and CO2 emissions increased by 12.4–15.6% (p < 0.1) and 13.8–18.5% (p < 0.05), respectively. N fertilization significantly increased the seasonal emissions of N2O and CO2 by 33.1–36.9% and 17.1–21.8%, respectively. Furthermore, the combination of eCO2 and N fertilization increased the intensity of soil N2O and CO2 emissions. The marginal significant increase in N2O emissions under eCO2 was mostly due to the lower soil water regime after fertilization in the study year. Dissolved organic C (DOC) and microbial biomass C (MBC) concentration showed a significant increase at most major stages, particularly at the tasseling stage during the summer maize growth period under eCO2. In contrast, soil mineral N showed a significant decrease under eCO2 particularly in the rhizospheric soils. The activities of C-related soil extracellular enzymes were significantly higher under eCO2, particularly at the tasseling stage, which coincided with concurrent increased DOC and MBC under eCO2. We conclude that eCO2 increases N2O emissions, and causes a higher increase when combined with N fertilization, but the increase extent of N2O emissions was influenced by environmental factors, especially by soil water, to a great extent. We highlighted the urgent need to monitor long-term N2O emissions and N2O production pathways in various hydrothermal regimes under eCO2.

Elevated Co2 Alleviated the Dissemination of Antibiotic Resistance Genes in Sulfadiazine-Contaminated Soil: A Free-Air Co2 Enrichment Study

Elevated Co2 Alleviated the Dissemination of Antibiotic Resistance Genes in Sulfadiazine-Contaminated Soil: A Free-Air Co2 Enrichment Study

Impact of Elevated CO2 and Reducing the Source-Sink Ratio by Partial Defoliation on Rice Grain Quality - A 3-Year Free-Air CO2 Enrichment Study.

Evaluating the impact of increasing CO2 on rice quality is becoming a global concern. However, whether adjusting the source-sink ratio will affect the response of rice grain quality to elevated CO2 concentrations remains unknown. In 2016–2018, we conducted a free-air CO2 enrichment experiment using a popular japonica cultivar grown at ambient and elevated CO2 levels (eCO2, increased by 200 ppm), reducing the source-sink ratio via cutting leaves (LC) at the heading stage, to investigate the effects of eCO2 and LC and their interactions on rice processing, appearance, nutrition, and eating quality. Averaged across 3 years, eCO2 significantly decreased brown rice percentage (−0.5%), milled rice percentage (−2.1%), and head rice percentage (−4.2%) but increased chalky grain percentage (+ 22.3%) and chalkiness degree (+ 26.3%). Markedly, eCO2 increased peak viscosity (+ 2.9%) and minimum viscosity (+ 3.8%) but decreased setback (−96.1%) of powder rice and increased the appearance (+ 4.5%), stickiness (+ 3.5%) and balance degree (+ 4.8%) of cooked rice, while decreasing the hardness (−6.7%), resulting in better palatability (+ 4.0%). Further, eCO2 significantly decreased the concentrations of protein, Ca, S, and Cu by 5.3, 4.7, 2.2, and 9.6%, respectively, but increased K concentration by 3.9%. Responses of nutritional quality in different grain positions (brown and milled rice) to eCO2 showed the same trend. Compared with control treatment, LC significantly increased chalky grain percentage, chalkiness degree, protein concentration, mineral element levels (except for B and Mn), and phytic acid concentration. Our results indicate that eCO2 reduced rice processing suitability, appearance, and nutritional quality but improved the eating quality. Rice quality varied significantly among years; however, few CO2 by year, CO2 by LC, or CO2 by grain position interactions were detected, indicating that the effects of eCO2 on rice quality varied little with the growing seasons, the decrease in the source-sink ratios or the different grain positions.

Elevated CO2 does not necessarily enhance greenhouse gas emissions from rice paddies

Elevated atmospheric carbon dioxide (eCO2) greatly impacts greenhouse gas (GHG) emissions of CH4 and N2O from rice fields. Although eCO2 generally stimulates GHG emissions in the short term (<5 years) experiments, the responses to long-term (≥10 years) eCO2 remain poorly known. Here we show, through a series of experiments and meta-analysis, that the eCO2 does not necessarily increase CH4 and N2O emissions from rice paddies. In an experiment of free-air CO2 enrichment for 13–15 years, CH4 and N2O emissions were decreased by 11–54% and 33–54%, respectively. The decline of CH4 emissions was related to the reduction of CH4 production and enhancement of CH4 oxidation via raising soil Eh and soil-water interface [O2] under eCO2. Moreover, the eCO2 significantly decreased NH4+-N content, suggesting a reduction of soil nitrification and thereby N2O emissions. A meta-analysis showed that CH4 and N2O emissions were stimulated under short-term eCO2 while reduced under long-term eCO2. The eCO2-induced increase in yield and biomass and the ratio of mcrA genes/pmoA genes declined with eCO2 duration, indicating an eCO2-stimulation of methanogenesis lower than that of methanotrophy over time by fewer increased substrates. Upscaling the results of meta-analysis, the eCO2-induced global paddy CH4 and N2O emissions shifted from an increase (+0.17 Pg CO2-eq year−1) in the short term into a decrease (−0.11 Pg CO2-eq year−1) in the long term. Our findings suggest that the effect of eCO2 on GHG emissions changes over time, and this should be considered in future climate change research.

Effect of elevated CO2 and elevated temperature on growth and biomass accumulation in Valeriana jatamansi Jones. under different nutrient status in the western Himalaya

Valeriana jatamansi is an important medicinal and aromatic plant used as sedative in modern and traditional medicines butthere is dearth of literature regarding how elevated CO2 and temperature affect on this plant. Therefore,an experiment was conducted to study the effect of elevated CO2 (550±50 µmol mol-1) and elevated temperature (2.5±0.5°C above ambient) and vermicompost on growth, phenology and biomass accumulation in V. jatamansi under Free Air CO2 Enrichment (FACE) and Free Air TemperatureIncrement (FATI) facilities at Palampur, India, during 2013-2015. Growth parameters and biomass accumulation into different parts were observed at 4, 12 and 16 months after exposure (MAE). Plant height, total dry biomass and leaf area plant -1 increased in elevated CO2 treatment applied with vermicompost as compared to the other treatments. Elevated CO2 significantly enhanced leaf area (3.5-23.5%), leaf biomass (12.7-33.2%), stem (15.3-15.6%), root (3.2-72.5%), rhizome (2.1-42.2%) and total biomass (7.7-52.7%), whereas elevated temperature increased aboveground biomass (15.0-45.3%), belowground biomass (11.6-55.5%) and total biomass (12.4-7.9%), respectively, as compared to ambient. Phenological stages were advanced by 1.2-3.9 days under FACE and FATI as compared to ambient. The results indicate that aboveground, belowground and total biomass increased under elevated CO2 and elevated temperature as compared to ambient.

Enhanced drought resistance of vegetation growth in cities due to urban heat, CO2 domes and O3 troughs

Sustained increase in atmospheric CO2 is strongly coupled with rising temperature and persistent droughts. While elevated CO2 promotes photosynthesis and growth of vegetation, drier and warmer climate can potentially negate this benefit, complicating the prediction of future terrestrial carbon dynamics. Manipulative studies such as free air CO2 enrichment (FACE) experiments have been useful for studying the joint effect of global change factors on vegetation growth; however, their results do not easily transfer to natural ecosystems partly due to their short-duration nature and limited consideration of climatic gradients and potential confounding factors, such as O3. Urban environments serve as a useful small-scale analogy of future climate at least in reference to CO2 and temperature enhancements. Here, we develop a data-driven approach using urban environments as test beds for revealing the joint effect of changing temperature and CO2 on vegetation response to drought. Using 75 urban-rural paired plots from three climate zones over the conterminous United States (CONUS), we find vegetation in urban areas exhibits a much stronger resistance to drought than in rural areas. Statistical analysis suggests the drought resistance enhancement of urban vegetation across CONUS is attributed to rising temperature (with a partial correlation coefficient of 0.36) and CO2 (with a partial correlation coefficient of 0.31) and reduced O3 concentration (with a partial correlation coefficient of −0.12) in cities. The controlling factor(s) responsible for urban-rural differences in drought resistance of vegetation vary across climate regions, such as surface O3 gradients in the arid climate, and surface CO2 and O3 gradients in the temperate and continental climates. Thus, our study provides new observational insights on the impacts of competing factors on vegetation growth at a large scale, and ultimately, helps reduce uncertainties in understanding terrestrial carbon dynamics.

Genotypic variation in the response of soybean to elevated CO2.

The impact of elevated CO2 (eCO2) on soybean productivity is essential to the global food supply because it is the world's leading source of vegetable proteins. This study aimed to understand the yield responses and nutritional impact under free-air CO2 enrichment (FACE) conditions of soybean genotypes. Here we report that grain yield increased by 46.9% and no reduction in harvest index was observed among soybean genotypes. Elevated CO2 improved the photosynthetic carbon assimilation rate, leaf area, plant height, and aboveground biomass at vegetative and pod filling stages. Besides the positive effects on yield parameters, eCO2 differentially affected the overall grain quality. The levels of calcium (Ca), phosphorous (P), potassium (K), magnesium (Mg), manganese (Mn), iron (Fe), boron (B), and zinc (Zn) grain minerals decreased by 22.9, 9.0, 4.9, 10.1, 21.3, 28.1, 18.5, and 25.9% under eCO2 conditions, respectively. Soluble sugars and starch increased by 9.1 and 16.0%, respectively, phytic acid accumulation increased by 8.1%, but grain protein content significantly decreased by 5.6% across soybean genotypes. Furthermore, the antioxidant activity decreased by 36.9%, but the total phenolic content was not affected by eCO2 conditions. Genotypes, such as Winsconsin Black, Primorskaja, and L-117, were considered the most responsive to eCO2 in terms of yield enhancement and less affected in the nutritional quality. Our results confirm the existence of genetic variability in soybean responses to eCO2, and differences between genotypes in yield improvement and decreased sensitivity to eCO2 in terms of grain quality loss could be included in future soybean selection to enable adaptation to climate change.

Projected Elevated [CO2] and Warming Result in Overestimation of SPAD-Based Rice Leaf Nitrogen Status for Nitrogen Management

Nitrogen (N) has a unique place in agricultural systems with large requirements. To achieve optimal nitrogen management that meets the needs of agricultural systems without causing potential environmental risks, it is of great significance to increase N use efficiency (NUE) in agricultural systems. A chlorophyll meter, for example, the SPAD-502, can provide a simple, nondestructive, and quick method for monitoring leaf N status and NUE. However, the SPAD-based crop leaf’s N status varies greatly due to environmental factors such as CO2 concentration ([CO2]) or temperature variations. In this study, we conducted [CO2] (ambient and enriched up to 500 μmol moL1) and temperature (ambient and increased by 1.5~2.0 °C) controlled experiments from 2015 to 2017 and in 2020 in two Free-Air CO2 Enrichment (FACE) sites. Leaf characters (SPAD readings, chlorophyll a + b, N content, etc.) of seven rice cultivars were measured in this four year experiment. Here, we provide evidence that SPAD readings are significantly linearly correlated with rice leaf chlorophyll a + b content (chl a + b) and N content, while the relationships are profoundly affected by elevated [CO2] and warming. Under elevated [CO2] treatment (E), the relationship between chl a + b content and N content remains unchanged, but SPAD readings and chl a + b content show a significant difference to those under ambient (A) treatment, which distorts the SPAD-based N monitoring. Under warming (T), and combined elevated [CO2] and warming (ET) treatments, both of the relationships between SPAD and leaf a + b content and between leaf a + b content and N content show a significant difference to those under A treatment. To deal with this issue under the background of global climate change dominated by warming and elevated [CO2] in the future, we need to increase the SPAD reading’s threshold value by at least 5% to adjust for applying N fertilizer within the rice cropping system by mid-century.

Fertilizer-derived nitrogen use of two varieties of single-crop paddy rice: a free-air carbon dioxide enrichment study using polymer-coated 15N-labeled urea

ABSTRACT Atmospheric concentrations of carbon dioxide (CO2) have steadily increased over recent decades. The fertilization effect of elevated CO2 concentrations (E-[CO2]) is known to increase the biomass production and also the nitrogen (N) demand of paddy rice, which affects the rice N use efficiency. This study was conducted to elucidate the fertilizer-derived N use of paddy rice (Oryza sativa L.) for two varieties, japonica cv. Koshihikari and indica cv. Takanari, with and without E-[CO2] using a free-air CO2 enrichment (FACE) facility in central Japan. To quantify the fate of fertilizer-derived N directly, polymer-coated 15N-labeled urea was used with a one-shot application rate of 80 kg N ha–1 incorporated into the plowed layer at the basal fertilization before transplanting of rice seedlings. The biomass, total N concentrations, and 15N abundance in each part of the rice plants were measured at the panicle initiation, heading, and maturing stages. The total N content and 15N abundance in the soil were measured at the maturing stage to evaluate the N balance of the rice–soil system. While E-[CO2] significantly increased the whole plant biomass and the total N content in panicles, it did not increase the total N and the fertilizer-derived N content in the whole plant. The recovery efficiency (fertilizer-derived N in the whole plant to applied N, RE) ranged between 64.9% and 68.7%, and the agronomic efficiency (fertilizer-derived N in panicles to applied N, AE) ranged between 37.8% and 43.8%. The effect of CO2 on RE and AE was not significant. The REs, higher in Koshihikari, and the AEs, higher in Takanari indicated that Takanari preferentially allocated fertilizer-derived N to panicles. The REs, 69% at the maximum in this study, implies an upper limit of use efficiency of N fertilizer, even for polymer-coated (controlled-release) fertilizer. E-[CO2] significantly increased the rice N uptake from sources other than fertilizer, of which mineralization was the most-likely source. Monitoring of soil fertility and appropriate fertilization management are, therefore, necessary for sustainable rice production avoiding long-term decline in soil N fertility.

Response of rice growth and leaf physiology to elevated CO2 concentrations: A meta-analysis of 20-year FACE studies

The Free Air CO2 Enrichment (FACE) facility enables the study of plant responses to climate change under open field conditions. This meta-analysis was conducted to quantitatively assess the effects of elevated CO2 concentration ([CO2]) on 47 variables describing rice growth physiology and whether CO2 effects were influenced by cultivar, plant growth stage, nitrogen application rate or temperature. On average, elevated [CO2] increased root and shoot biomass by 28% and 19%, respectively. Among shoot organs, the [CO2]-induced increase in leaf biomass was only 9%, significantly smaller than a 24% increase in stems or a 25% increase in panicles. The higher biomass for FACE rice was consistent with the stimulation in plant height (4%), maximum tiller number (11%), leaf area index (9%) and light-saturated photosynthetic rate (Asat, 22%). When compared within rice groups, hybrid rice showed the greatest CO2 response in growth and leaf physiological variables. Elevated [CO2] increased plant biomass and Asat at each rice growth stage, but the increment tended to decline with the advancement of rice growth and development. The increase in aboveground biomass at elevated [CO2] was enhanced by a higher nitrogen supply but reduced with a temperature elevation of 1–2 °C. Rice growth benefited more from elevated [CO2] in Chinese FACE studies than in Japanese FACE studies, which may result from the different cultivars and nitrogen application rates used in the two countries. Combined with a previous meta-analysis of the rice yield response to FACE, the [CO2] level predicted in the middle of this century will improve rice productivity by stimulating leaf photosynthesis. However, the effects of CO2 on the photosynthetic rate and rice growth tend to shrink over the plant life cycle. Selecting heat-resistant, high-yield hybrid rice cultivars with large sink capacity, supplemented with appropriate nitrogen input, will maximize the CO2 fertilizer effect in the future.

Response of Yield, CH4, and N2O Emissions from Paddy Fields to Long-term Elevated CO2 Concentrations

Elevated atmospheric CO2 concentrations([CO2]e) are the main driving force of global climate change, which directly and indirectly affect carbon and nitrogen cycling in the paddy ecosystems. Therefore, understanding the response of rice yield and greenhouse gas emissions to long-term(more than 10 years)[CO2]e from paddy fields is of great significance for food security and future climate change assessment. In this study, strongly and weakly responsive cultivars were used as the experimental materials. Based on a free-air CO2 enrichment(FACE) platform continuously run for 14 years, two treatments of different[CO2] were set:a control(i.e., normal[CO2] and[CO2]a) and a 200 μmol·mol-1 higher than[CO2]a condition, ([CO2]e). CH4 and N2O emissions from the rice paddy fields were monitored in situ by static transparent chamber-gas chromatography, and grain yields were also obtained. The results showed that compared with the[CO2]a treatment, long-term[CO2]e increased grain yields of the strongly and weakly responsive cultivars by 29%-31%(P<0.05) and 12%-14%(P>0.05), and CH4 emissions of the strongly and weakly responsive cultivars were reduced by 21%-59% and 11%-54%, respectively. Furthermore, N2O emissions from the strongly and weakly responsive cultivars were significantly reduced by 70%(P<0.05) and 40%(P<0.05), respectively. The short- and long-term responses of grain yields and CH4 emissions from rice paddy fields to[CO2]e were significantly different. Specifically, with the increase in the duration of[CO2]e, the increases in rice yields and CH4 emissions significantly decreased, while the N2O emissions showed no significant changes. Therefore, under long-term[CO2]e conditions, the strongly responsive cultivar has a high potential to reduce greenhouse gas emission and increase grain yields.

Elevated CO2 levels alleviated toxicity of ZnO nanoparticles to rice and soil bacteria

Rising CO2 levels will change the behavior and toxicity of soil contaminants. However, it remains unclear whether elevated CO2 levels will change the nanoparticle dissolution or their biological effects in soil. In this study, we used a free-air CO2 enrichment system to examine the effects of elevated CO2 on phytotoxicity and bacterial toxicity of zinc oxide nanoparticles (nZnO) in a paddy soil system. The elevated CO2 changed the nZnO diffraction in soil, slightly increasing its dissolution but remarkably improving its bioavailability. Elevated CO2 did not change Zn accumulation in rice, but still alleviated the adverse effects of nZnO on rice growth, although grain protein, K and P decreased. Moreover, nZnO alone significantly decreased the number of observed soil bacterial species and altered the community organization, while elevated CO2 moderated such changes. Overall, these results increase our understanding of plant response and microbial variation in nanoparticle-contaminated soil under elevated-CO2 conditions. It is necessary to pay attention to soil pollution while facing climate change.

Forest stand and canopy development unaltered by 12years of CO2 enrichment.

Canopy structure—the size and distribution of tree crowns and the spatial and temporal distribution of leaves within them—exerts dominant control over primary productivity, transpiration and energy exchange. Stand structure—the spatial arrangement of trees in the forest (height, basal area and spacing)—has a strong influence on forest growth, allocation and resource use. Forest response to elevated atmospheric CO2 is likely to be dependent on the canopy and stand structure. Here, we investigated elevated CO2 effects on the forest structure of a Liquidambar styraciflua L. stand in a free-air CO2 enrichment experiment, considering leaves, tree crowns, forest canopy and stand structure. During the 12-year experiment, the trees increased in height by 5 m and basal area increased by 37%. Basal area distribution among trees shifted from a relatively narrow distribution to a much broader one, but there was little evidence of a CO2 effect on height growth or basal area distribution. The differentiation into crown classes over time led to an increase in the number of unproductive intermediate and suppressed trees and to a greater concentration of stand basal area in the largest trees. A whole-tree harvest at the end of the experiment permitted detailed analysis of canopy structure. There was little effect of CO2 enrichment on the relative leaf area distribution within tree crowns and there was little change from 1998 to 2009. Leaf characteristics (leaf mass per unit area and nitrogen content) varied with crown depth; any effects of elevated CO2 were much smaller than the variation within the crown and were consistent throughout the crown. In this young, even-aged, monoculture plantation forest, there was little evidence that elevated CO2 accelerated tree and stand development, and there were remarkably small changes in canopy structure. Questions remain as to whether a more diverse, mixed species forest would respond similarly.

Effect of Elevated CO2 on N2O Emissions from Different Rice Cultivars in Rice Fields

Using the free air CO2 enrichment (FACE) platform, an in-situ field experiment was conducted to explore the impacts of elevated CO2 mole fraction (x[CO2]) on N2O emissions from strongly and weakly responsive rice cultivars. Under elevated x[CO2], grain yield of the strongly responsive rice cultivars increased significantly, by more than 30%, whereas the weakly responsive cultivars showed a growth rate of 10%-15%. The four treatments comprised A-W (normal x[CO2]+weakly responsive cultivar), F-W (elevated x[CO2]+weakly responsive cultivar), A-S (normal x[CO2]+strongly responsive cultivar), and F-S (elevated x[CO2]+strongly responsive cultivar). Compared to the normal x[CO2] treatments (A-S and A-W), when the strongly and weakly responsive cultivars were exposed to elevated x[CO2](F-S and F-W), N2O emissions decreased by 52.54% (P<0.05) and 38.40% (P<0.05), rice yield increased by 22.96% (P<0.05) and 12.11% (P>0.05), and N2O emission intensity decreased by 61.68% (P<0.05) and 45.13% (P<0.05), respectively. Moreover, N2O emissions of all treatments were significantly positively correlated with NH4+-N content (P<0.05), whereas not correlated with NO2--N content. Soil temperature is an important factor affecting the N2O emissions of the strongly responsive cultivar in rice fields under elevated x[CO2] conditions. Through comprehensive consideration of climate conditions, in the future, priority should be given to planting the strongly responsive cultivar, ensuring high rice yield and significant reduction in N2O emissions.

Monitoring physiological and chemical response of lichen in free air CO2 enrichment (FACE) station

The elevation of CO2 will bring forth several effects on the plant’s growth especially the physiological traits and chemical responses. However, there is lacking knowledge on how the elevation on CO2 will affect lichen physiology and chemical response. Therefore, this study aims to study the physiological changes in lichen in FACE Station and to analyze the chemical profile changes of lichen in FACE Station. This study has been conducted in FACE Station at Jengka, Pahang. A total of 20 sampling trees have been selected and epiphytic lichen have been collected from the selected trees. In this study, there are three (3) sampling and experimental approaches;’) Sample collection from control and FACE station; 2) Analyzing sample in the laboratory (physiological and chemical response) and 3) statistical analysis (Mann-Whitney U test) will be used for testing the relationship between parameters and sampling areas. This study has found only three species of foliicolous lichen from both stations namely a) Byssoloma subdiscordans, b) Eugeniella micrommata and c) Sporopodium flavescens. For the photosynthetic cell efficiency test, the FV/FM ratio shows a significant difference for both stations where all of the three species from FACE Station have lower cell efficiency compare to the Control Station. At the other hand, for the membrane cell integrity analysis, no significant changes were found for the three species from both stations. In term of chemical response, there is no any significant difference on the secondary metabolite from any sample taken from both stations. This study urges that there is slight difference in term of lichen physiology from Face Station and Control Station. This proves that lichen responded towards CO2 elevation and effect their growth simultaneously. In bigger perspective, climate change and global warming will be affecting lichen diversity and growth.

Is photosynthetic enhancement sustained through three years of elevated CO2 exposure in 175-year-old Quercus robur?

Current carbon cycle models attribute rising atmospheric CO2 as the major driver of the increased terrestrial carbon sink, but with substantial uncertainties. The photosynthetic response of trees to elevated atmospheric CO2 is a necessary step, but not the only one, for sustaining the terrestrial carbon uptake, but can vary diurnally, seasonally and with duration of CO2 exposure. Hence, we sought to quantify the photosynthetic response of the canopy-dominant species, Quercus robur, in a mature deciduous forest to elevated CO2 (eCO2) (+150 μmol mol−1 CO2) over the first 3 years of a long-term free air CO2 enrichment facility at the Birmingham Institute of Forest Research in central England (BIFoR FACE). Over 3000 measurements of leaf gas exchange and related biochemical parameters were conducted in the upper canopy to assess the diurnal and seasonal responses of photosynthesis during the 2nd and 3rd year of eCO2 exposure. Measurements of photosynthetic capacity via biochemical parameters, derived from CO2 response curves, (Vcmax and Jmax) together with leaf nitrogen concentrations from the pre-treatment year to the 3rd year of eCO2 exposure, were examined. We hypothesized an initial enhancement in light-saturated net photosynthetic rates (Asat) with CO2 enrichment of ≈37% based on theory but also expected photosynthetic capacity would fall over the duration of the study. Over the 3-year period, Asat of upper-canopy leaves was 33 ± 8% higher (mean and standard error) in trees grown in eCO2 compared with ambient CO2 (aCO2), and photosynthetic enhancement decreased with decreasing light. There were no significant effects of CO2 treatment on Vcmax or Jmax, nor leaf nitrogen. Our results suggest that mature Q. robur may exhibit a sustained, positive response to eCO2 without photosynthetic downregulation, suggesting that, with adequate nutrients, there will be sustained enhancement in C assimilated by these mature trees. Further research will be required to understand the location and role of the additionally assimilated carbon.

Does a Large Ear Type Wheat Variety Benefit More From Elevated CO2 Than That From Small Multiple Ear-Type in the Quantum Efficiency of PSII Photochemistry?

Recently, several reports have suggested that the growth and grain yield of wheat are significantly influenced by high atmospheric carbon dioxide concentration (CO2) because of it photosynthesis enhancing effects. Moreover, it has been proposed that plants with large carbon sink size will benefit more from CO2 enrichment than those with small carbon sink size. However, this hypothesis is yet to be test in winter wheat plant. Therefore, the aim of this study was to examine the effect of elevated CO2 (eCO2) conditions on the quantum efficiency of photosystem II (PSII) photochemistry in large ear-type (cv. Shanhan 8675; greater ear C sink strength) and small multiple ear-type (cv. Early premium; greater vegetative C source strength) winter wheat varieties. The experiment was conducted in a free air CO2 enrichment (FACE) facility, and three de-excitation pathways of the primary reaction of PSII of flag leaf at the anthesis stage were evaluated under two CO2 concentrations (ambient [CO2], ∼415 μmol⋅mol–1, elevated [CO2], ∼550 μmol⋅mol–1) using a non-destructive technique of modulated chlorophyll fluorescence. Additionally, the grain yield of the two varieties was determined at maturity. Although elevated CO2 increased the quantum efficiency of PSII photochemistry (ΦPSII) of Shanhan 8675 (SH8675) flag leaves at the anthesis stage, the grain number per ear and 1,000-kernel weight were not significantly affected. In contrast, the ΦPSII of early premium (ZYM) flag leaves was significantly lower than that of SH8675 flag leaves at the anthesis stage, which was caused by an increase in the regulatory non-photochemical energy dissipation quantum (ΦNPQ) of PSII, suggesting that light energy absorbed by PSII in ZYM flag leaf was largely dissipated as thermal energy. The findings of our study showed that although SH8675 flag leaves exhibited higher C sink strength and quantum efficiency of PSII photochemistry at the anthesis stage, these factors alone do not ensure improved grain yield under eCO2 conditions.

Promise and pitfalls of modeling grassland soil moisture in a free-air CO2 enrichment experiment (BioCON) using the SHAW model

Free-air carbon dioxide (CO2) enrichment (FACE) experiments provide an opportunity to test models of heat and water flow under novel, controlled situations and eventually allow use of these models for hypothesis evaluation. This study assesses whether the United States Department of Agriculture SHAW (Simultaneous Heat and Water) numerical model of vertical one-dimensional soil water flow across the soil-plant-atmosphere continuum is able to adequately represent and explain the effects of increasing atmospheric CO2 on soil moisture dynamics in temperate grasslands. Observations in a FACE experiment, the BioCON (Biodiversity, CO2, and Nitrogen) experiment, in Minnesota, USA, were compared with results of vertical soil moisture distribution. Three scenarios represented by different plots were assessed: bare, vegetated with ambient CO2, and similarly vegetated with high CO2. From the simulations, the bare plot soil was generally the wettest, followed by a drier high-CO2 vegetated plot, and the ambient CO2 plot was the driest. The SHAW simulations adequately reproduced the expected behavior and showed that vegetation and atmospheric CO2 concentration significantly affected soil moisture dynamics. The differences in modeled soil moisture amongst the plots were largely due to transpiration, which was low with high CO2. However, the modeled soil moisture only modestly reproduced the observations. Thus, while SHAW is able to replicate and help broadly explain soil moisture dynamics in a FACE experiment, its application for point- and time-specific simulations of soil moisture needs further scrutiny. The typical design of a FACE experiment makes the experimental observations challenging to model with a one-dimensional distributed model. In addition, FACE instrumentation and monitoring will need improvement in order to be a useful platform for robust model testing. Only after this can we recommend that models such as SHAW are adequate for process interpretation of datasets from FACE experiments or for hypothesis testing.