Free Air CO2 Enrichment Rings Research Articles

Elevated carbon dioxide increases soil nitrogen and phosphorus availability in a phosphorus-limited Eucalyptus woodland.

Free-air CO2 enrichment (FACE) experiments have demonstrated increased plant productivity in response to elevated (e)CO2, with the magnitude of responses related to soil nutrient status. Whilst understanding nutrient constraints on productivity responses to eCO2 is crucial for predicting carbon uptake and storage, very little is known about how eCO2 affects nutrient cycling in phosphorus (P)-limited ecosystems. Our study investigates eCO2 effects on soil N and P dynamics at the EucFACE experiment in Western Sydney over an 18-month period. Three ambient and three eCO2 (+150 ppm) FACE rings were installed in a P-limited, mature Cumberland Plain Eucalyptus woodland. Levels of plant accessible nutrients, evaluated using ion exchange resins, were increased under eCO2, compared to ambient, for nitrate (+93%), ammonium (+12%) and phosphate (+54%). There was a strong seasonality to responses, particularly for phosphate, resulting in a relatively greater stimulation in available P, compared to N, under eCO2 in spring and summer. eCO2 was also associated with faster nutrient turnover rates in the first six months of the experiment, with higher N (+175%) and P (+211%) mineralization rates compared to ambient rings, although this difference did not persist. Seasonally dependant effects of eCO2 were seen for concentrations of dissolved organic carbon in soil solution (+31%), and there was also a reduction in bulk soil pH (-0.18 units) observed under eCO2. These results demonstrate that CO2 fertilization increases nutrient availability - particularly for phosphate - in P-limited soils, likely via increased plant belowground investment in labile carbon and associated enhancement of microbial turnover of organic matter and mobilization of chemically bound P. Early evidence suggests that there is the potential for the observed increases in P availability to support increased ecosystem C-accumulation under future predicted CO2 concentrations.

Influence of Global Atmospheric Change on the Feeding Behavior and Growth Performance of a Mammalian Herbivore, Microtus ochrogaster

Global atmospheric change is influencing the quality of plants as a resource for herbivores. We investigated the impacts of elevated carbon dioxide (CO2) and ozone (O3) on the phytochemistry of two forbs, Solidago canadensis and Taraxacum officinale, and the subsequent feeding behavior and growth performance of weanling prairie voles (Microtus ochrogaster) feeding on those plants. Plants for the chemical analyses and feeding trials were harvested from the understory of control (ambient air), elevated CO2 (560 µl CO2 l−1), and elevated O3 (ambient × 1.5) rings at the Aspen FACE (Free Air CO2 Enrichment) site near Rhinelander, Wisconsin. We assigned individual voles to receive plants from only one FACE ring and recorded plant consumption and weanling body mass for seven days. Elevated CO2 and O3 altered the foliar chemistry of both forbs, but only female weanling voles on the O3 diet showed negative responses to these changes. Elevated CO2 increased the fiber fractions of both plant species, whereas O3 fumigation elicited strong responses among many phytochemical components, most notably increasing the carbon-to-nitrogen ratio by 40% and decreasing N by 26%. Consumption did not differ between plant species or among fumigation treatments. Male voles were unaffected by the fumigation treatments, whereas female voles grew 36% less than controls when fed O3-grown plants. These results demonstrate that global atmospheric change has the potential to affect the performance of a mammalian herbivore through changes in plant chemistry.

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.

Independent, Interactive, and Species-Specific Responses of Leaf Litter Decomposition to Elevated CO2 and O3 in a Northern Hardwood Forest

The future capacity of forest ecosystems to sequester atmospheric carbon is likely to be influenced by CO2-mediated shifts in nutrient cycling through changes in litter chemistry, and by interactions with pollutants like O3. We evaluated the independent and interactive effects of elevated CO2 (560 l ll )1 ) and O3 (55 nl l l )1 )o n leaf litter decomposition in trembling aspen (Populus tremuloides) and paper birch (Betula papyrifera) at the Aspen free air CO2 enrichment (FACE) site (Wisconsin, USA). Fumigation treatments consisted of replicated ambient, +CO2, +O3, and +CO2 +O 3 FACE rings. We followed mass loss and litter chemistry over 23 months, using reciprocally transplanted litterbags to separate substrate quality from environment effects. Aspen decayed more slowly than birch across all treatment conditions, and changes in decomposition dynamics of both species were driven by shifts in substrate quality rather than by fumigation environment. Aspen litter produced under elevated CO2 decayed more slowly than litter produced under ambient CO2, and this effect was exacerbated by elevated O3. Similarly, birch litter produced under elevated CO2 also decayed more slowly than litter produced under ambient CO2. In contrast to results for aspen, however, elevated O3 accelerated birch decay under ambient CO2, but decelerated decay under enriched CO2. Changes in decomposition rates (k-values) were due to CO2- and O3-mediated shifts in litter quality, particularly levels of carbohydrates, nitrogen, and tannins. These results suggest that in early-successional forests of the future, elevated concentrations of CO2 will likely reduce leaf litter decomposition, although the magnitude of effect will vary among species and in response to interactions with tropospheric O3.

Elevated atmospheric CO2: a nurse plant substitute for oak seedlings establishing in old fields

AbstractIt has been hypothesized that elevated levels of atmospheric CO2 (eCO2) may facilitate the encroachment of woody plants into grasslands by reducing water stress. In east‐central Minnesota, sandy soils frequently create drought conditions for plants, and water limitation inhibits the establishment of oaks into old fields situated on these soils. Some have argued that eCO2 should slow secondary succession by favoring fast‐growing early successional species. However, if oak encroachment into old fields is being inhibited by water stress, then eCO2 could accelerate old‐field succession in this region. The purpose of this study was to test the hypothesis that eCO2 will increase the establishment success of oak seedlings in an old field environment. The study was conducted with CO2 levels controlled by free air CO2 enrichment (FACE). In May 1999, four oak (Quercus ellipsoidalis) acorns were planted in each of 24 plots in each of six experimental FACE rings (n= 576), three of which received elevated levels (550 ppm) of CO2. Half the plots in each ring were weeded during the first three summers of the experiment. In summer 2000, water input was manipulated during a 3.5‐week period, during which half the plots received regular watering while the other half received no water. Summer 2001 was dry, receiving 35% less rainfall than the mean level. Under hot and dry conditions, eCO2 increased soil water levels in unweeded plots and enhanced oak establishment (survival and growth) in weeded plots. In 2006, after the eighth growing season following planting, survival was five times greater under elevated than ambient CO2. The results showed that under hot and dry conditions, eCO2 can act like a nurse plant for tree seedlings growing in bare and unshaded areas, increasing seedling survival and growth, and thereby expanding the establishment window for trees encroaching into a grassland environment.

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.

Effects of elevated CO2 on fine root dynamics in a Mojave Desert community: a FACE study

AbstractFine roots (≤1 mm diameter) are critical in plant water and nutrient absorption, and it is important to understand how rising atmospheric CO2 will affect them as part of terrestrial ecosystem responses to global change. This study's objective was to determine the effects of elevated CO2 on production, mortality, and standing crops of fine root length over 2 years in a free‐air CO2 enrichment (FACE) facility in the Mojave Desert of southern Nevada, USA. Three replicate 25 m diameter FACE rings were maintained at ambient (∼370 μmol mol−1) and elevated CO2 (∼550 μmol mol−1) atmospheric concentrations. Twenty‐eight minirhizotron tubes were placed in each ring to sample three microsite locations: evergreen Larrea shrubs, drought‐deciduous Ambrosia shrubs, and along systematic community transects (primarily in shrub interspaces which account for ∼85% of the area). Seasonal dynamics were similar for ambient and elevated CO2: fine root production peaked in April–June, with peak standing crop occurring about 1 month later, and peak mortality occurring during the hot summer months, with higher values for all three measures in a wet year compared with a dry year. Fine root standing crop, production, and mortality were not significantly different between treatments except standing crop along community transects, where fine root length was significantly lower in elevated CO2. Fine root turnover (annual cumulative mortality/mean standing crop) ranged from 2.33 to 3.17 year−1, and was not significantly different among CO2 treatments, except for community transect tubes where it was significantly lower for elevated CO2. There were no differences in fine root responses to CO2 between evergreen (Larrea) and drought‐deciduous (Ambrosia) shrubs. Combined with observations of increased leaf‐level water‐use efficiency and lack of soil moisture differences, these results suggest that under elevated CO2 conditions, reduced root systems (compared with ambient CO2) appear sufficient to provide resources for modest aboveground production increases across the community, but in more fertile shrub microsites, fine root systems of comparable size with those in ambient CO2 were required to support the greater aboveground production increases. For community transects, development of the difference in fine root standing crops occurred primarily through lower stimulation of fine root production in the elevated CO2 treatment during periods of high water availability.

An Idea of Concentration Gradient FACE (Free Air CO2 Enrichment) and a Preliminary Experiment of Its Control Using a Neural Network

In existing FACE (Free Air CO2 Enrichment) systems, efforts have been made to maintain the CO2 concentration within a FACE ring at the setpoint value. Therefore, effects of only one elevated CO2 concentration on plants and/or ecosystems can be examined with one ring. The basic idea of the present study was, instead of controlling the CO2 concentrations within a ring at a constant value, to create and maintain a constant CO2 concentration gradient within a ring. In this way, examinations of the effects of different CO2 concentrations on plants and/or ecosystems would be realized using one ring. An artificial neural network was applied to control the CO2 gradient within a ring of a stretched hexagon with ten CO2 emitting tubes. The results of the experiments showed that when the wind speed was more than the detectable range by the anemometer (about 30 cm s-1), a concentration gradient was in most cases observed, though not completely the same as the target gradient. When the wind speed was less than the detectable value, the CO2 concentrations within a ring rose far above the target values and the gradient was not created.

Carbon isotope discrimination by Sorghum bicolor under CO2 enrichment and drought

Summary Sorghum bicolor was exposed to free‐air CO2 enrichment (FACE) and drought at the Maricopa Agricultural Center, AZ, USA, in summer 1998. We predicted that bundle sheath leakiness (Φ) would be insensitive to FACE under well‐irrigated (wet) conditions, but would be lower in FACE compared with control‐CO2 treatments when irrigation was withheld (dry). Leaf and air δ13C values and leaf pi/pa from gas exchange were measured to estimate carbon isotope discrimination (Δ) and F. Midday leaf water potential (Ψ) and photosynthetic rate were simultaneously measured to evaluate the influence of plant water status on Φ and the association between Φ and carbon gain. Irrigation treatments affected Ψ, pi/pa, Δ and Φ in control CO2 and FACE rings. Differences in leaf Δ between wet‐ and dry‐treatment plots resulted from changes in Φ and to stomatal influences on pi/pa. FACE had very little effect on Ψ, Δ and Φ in wet‐treatment plots. However, Φ and Δ in dry plots were higher in control than in FACE rings. FACE ameliorated the effects of drought on bundle sheath leakiness and Δ by reducing transpiration, prolonging soil water availability and enhancing plant water status. Direct effects of CO2 enrichment on C4 photosynthetic metabolism in Sorghum apparently are minimal and indirect effects depend on soil water supply.

A field fumigation system for elevated carbon dioxide exposure in chaparral shrubs

1. Modifications and improvements in the hardware and software of a free‐air CO2 enrichment (FACE) system are described. The modifications were undertaken to minimize the amount of structure required and to improve software control of CO2 set points. 2. A new low‐cost CO2 flow controller which provides increased reliability is described. 3. Analysis of system performance during a 79‐day evaluation period of operation (13 h day–1) showed that for 1 min averages, the system is capable of maintaining a 550 p.p.m. ± 10% CO2 set point during 78% of the operating time and a 550 p.p.m. ± 20% set point during 95% of the operating time. Ten‐minute averages were within ± 10% and 20% during 87% and 96% of the operating time, respectively. 4. Continuous measurements of the spatial variation in CO2 concentration inside the FACE ring over an 18‐day period showed that of the total 16‐m diameter treatment area, the central 11‐m diameter portion remains within the 550 p.p.m. ± 10% set point. 5. Daily course gas‐exchange measurements in matched individuals of the chaparral shrub Adenostoma fasciculatum just prior to and following a 6‐week fumigation period at 550 p.p.m. CO2 in the FACE treatment ring showed the FACE plants with reduced photosynthetic rates and higher (less stressful) water potentials compared with control A. fasciculatum plants measured at the same times and conditions, indicating the responsiveness of this species to elevated CO2 conditions.

Free Air CO2 Enrichment of potato (Solanum tuberosum L.): development, growth and yield

AbstractA FACE (Free Air CO2 Enrichment) experiment was carried out on Potato (Solanum tuberosum L., cv. Primura) in 1995 in Italy. Three FACE rings were used to fumigate circular field plots of 8 m diameter while two rings were used as controls at ambient CO2 concentrations. Four CO2 exposure levels were used in the rings (ambient, 460, 560 and 660 μmol mol–1). Phenology and crop development, canopy surface temperature, above‐ and below‐ground biomass were monitored during the growing season. Crop phenology was affected by elevated CO2, as the date of flowering was progressively anticipated in the 660, 560, 460 μmol mol–1 treatments. Crop development was not affected significantly as plant height, leaf area and the number of leaves per plant were the same in the four treatments. Elevated atmospheric CO2 levels had, instead, a significant effect on the accumulation of total nonstructural carbohydrates (TNC = soluble sugars + starch) in the leaves during a sunny day. Specific leaf area was decreased under elevated CO2 with a response that paralleled that of TNC concentrations. This reflected the occurrence of a progressive increase of photosynthetic rates and carbon assimilation in plants exposed to increasingly higher levels of atmospheric CO2. Tuber growth and final tuber yield were also stimulated by rising CO2 levels. When calculated by regression of tuber yield vs. the imposed levels of CO2concentration, yield stimulation was as large as 10% every 100 μmol mol–1 increase, which translated into over 40% enhancement in yield under 660 μmol mol–1. This was related to a higher number of tubers rather than greater mean tuber mass or size. Leaf senescence was accelerated under elevated CO2 and a linear relationship was found between atmospheric CO2 levels and leaf reflectance measured at 0.55 μm wavelength. We conclude that significant CO2 stimulation of yield has to be expected for potato under future climate scenarios, and that crop phenology will be affected as well.