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Elevated atmospheric C[O.sub.2] and ozone ([O.sub.3]) may affect productivity of legumes in part by altering symbiotic [N.sub.2] fixation. To investigate this possibility, measurements of plant biomass, N levels and natural [sup.15]N abundance ([delta]sup.15]N) were used to examine the effects of elevated C[O.sub.2] and [O.sub.3] on N acquisition in field-grown peanut (Arachis hypogaea L.) using open-top chambers. Seasonal 12-h daily average C[O.sub.2] treatment concentrations were 376, 550, and 730 [micro]mol [mol.sup.-1] Carbon dioxide treatments were applied in reciprocal combinations with seasonal 12-h daily average [O.sub.3] concentrations of 21, 49, and 79 nmol [mol.sup.-1]. At mid-vegetative growth, elevated C[O.sub.2] significantly reduced leaf N concentrations by up to 44%, but not [delta][sup.15]N values. Elevated [O.sub.3] did not significantly affect N concentrations or [delta][sup.15]N values. At harvest, plant N concentrations were similar among treatments except for a 14% reduction in the highest-level C[O.sub.2]-[O.sub.3] treatment. Plant N accumulation varied in proportion with treatment effects on biomass production, which was increased with elevated C[O.sub.2] when averaged over the [O.sub.3] treatments and suppressed by high-level [O.sub.3] at ambient C[O.sub.2]. Elevated C[O.sub.2] reduced plant [delta][sup.15]N values in low- and mid-level [O.sub.3] treatments while mid- and high-level [O.sub.3] increased them at ambient C[O.sub.2]. The changes in [delta][sup.15]N values suggested that [N.sub.2] fixation activity was stimulated with elevated C[O.sub.2] and inhibited by elevated [O.sub.3]. Elevated C[O.sub.2] ameliorated detrimental [O.sub.3] effects to varying extents depending on the concentrations of the two gases. These results indicated that interactions between C[O.sub.2] and [O.sub.3] on plant physiology can alter N acquisition processes, with impacts on peanut productivity likely dependent in part on these changes.

Prior work showed that C[O.sub.2] enhancement ratios (ER) were similar for plants grown in open-top chambers (OTCs) whether grown in the ground or in insulated containers aboveground. Per plant comparisons were suspect since the ground-grown plants were cultivated in rows at normal densities making it difficult to separate the effects of plant competition from the variables of interest. Soybean [Glycine max (L.) Merr. cv. Essex] was grown in the ground and in aboveground containers in OTCs in ambient and elevated C[O.sub.2] at equal planting densities. The hypothesis was that at equal densities, container- and ground-grown plants would exhibit both equivalent ERs and equivalent per plant yields. Although the only differences in net photosynthetic rate ([A.sub.n]: [micro]mol [m.sup.-2] [s.sup.-1]) and conductance to water vapor ([g.sub.s]:mol [m.sup.-2] [s.sup.-1]) were due to C[O.sub.2] and container-and ground-grown plants had similar ERs (mean = 20%), per plant yields were still less in the container-grown plants at both levels of C[O.sub.2] (mean = -17%). Reproductive measures, except mass per seed, as well as total stem biomass were significantly reduced in the containers. High C[O.sub.2] increased seed oil concentration and the level of fatty acid saturation. The only observed environmental difference was higher daytime root zone temperatures in containers (2-6[degrees]C). The robust ERs suggest that neither above- nor belowground resource limitations was the cause of the yield discrepancies.

Many adverse effects of tropospheric [O.sub.3] on [C.sub.3] crop plants are ameliorated by elevated concentrations of atmospheric C[O.sub.2], but the extent of the interaction can vary, depending on the species, gas concentrations, and other experimental conditions. A 2-yr open-top field chamber experiment was conducted to examine this interaction in peanut (Arachis hypogaea L.) by testing the effects of [O.sub.3] and C[O.sub.2] mixtures on yield and seed quality. Treatments were ambient C[O.sub.2] (375 [micro]mol [mol.sup.-1]) and C[O.sub.2] additions of approximately 173 and 355 [micro]mol [mol.sup.-1] in combination with charcoal-filtered (CF) air (22 nmol [O.sub.3] [mol.sup.-1]), nonfiltered (NF) air (46 nmol [O.sub.3] [mol.sup.-1]), and NF air plus [O.sub.3] (75 nmol [O.sub.3] [mol.sup.-1]). At ambient C[O.sub.2], pod number was suppressed 16% in NF air and 44% in elevated [O.sub.3]. Pod and seed mass were not significantly affected in NF air but were lowered 33 to 37% in elevated [O.sub.3]. Elevated C[O.sub.2] increased yield parameters 7 to 17% for plants grown in CF air and restored yield in NF air and elevated [O.sub.3] treatments to control or higher levels. Gas treatment effects on peanut market grade characteristics were small. No treatment effects were observed on the protein and oil contents of seeds, but there were changes in fatty acid composition. Overall results indicate that increasing concentrations of tropospheric [O.sub.3] will suppress yield of [O.sub.3]-sensitive peanut cultivars, while elevated C[O.sub.2] will moderate this response. Elevated [O.sub.3] and C[O.sub.2] are not expected to have major effects on peanut seed composition and quality.

The effects of elevated C[O.sub.2] and ozone ([O.sub.3]) on net photosynthetic rate (A) and growth are generally antagonistic although plant responses are highly dependent on crop sensitivity to the individual gases and their concentrations. In this experiment, we evaluated the effects of various C[O.sub.2] and [O.sub.3] mixtures on leaf gas-exchange, harvest biomass, and leaf chemistry in peanut (Arachis hypogaea L.), an [O.sub.3]-sensitive species, using open-top field chambers. Treatments included ambient C[O.sub.2] (about 375 [micro]mol [mol.sup.-1]) and C[O.sub.2] enrichment of approximately 173 and 355 [micro]mol [mol.sup.-1] in combination with charcoal-filtered air (22 nmol [O.sub.3] [mol.sup.-1]), nonfiltered air (46 nmol [O.sub.3] [mol.sup.-1]), and nonfiltered air plus [O.sub.3] (75 nmol [O.sub.3] [mol.sup.-1]). Twice-ambient C[O.sub.2] in charcoal-filtered air increased A by 23% while decreasing seasonal stomatal conductance ([g.sub.s]) by 42%. Harvest biomass was increased 12 to 15% by elevated C[O.sub.2]. In ambient C[O.sub.2], nonfiltered air and added [O.sub.3] lowered A by 21% and 48%, respectively, while added [O.sub.3] reduced [g.sub.s] by 18%. Biomass was not significantly affected by nonfiltered air, but was 40% lower in the added [O.sub.3] treatment. Elevated C[O.sub.2] generally suppressed inhibitory effects of [O.sub.3] on A and harvest biomass. Leaf starch concentration was increased by elevated C[O.sub.2] and decreased by [O.sub.3]. Treatment effects on foliar N and total phenolic concentrations were minor. Increasing atmospheric C[O.sub.2] concentrations should attenuate detrimental effects of ambient [O.sub.3] and promote growth in peanut but its effectiveness declines with increasing [O.sub.3] concentrations.

In studies of C[O.sub.2]-enrichment effects on plants, the applicability of results derived from experiments using container-grown plants for predictions of future crop performance in a C[O.sub.2]-enriched atmosphere has been questioned. Concerns also have been expressed about plant growth studies with the air pollutant [O.sub.3] in pot-grown plants. Further, since elevated C[O.sub.2] and [O.sub.3] co-occur, studies are required with the combination of gases. In this 2-yr experiment, soybean [Glycine max (L.) Merr.] plants grown in large pots (15 and 21 L) and in the ground were exposed to mixtures of C[O.sub.2] and [O.sub.3] in open-top chambers. The C[O.sub.2] treatments were ambient and C[O.sub.2] enrichment of approximately 337 µmol [mol.sup.-1] added 24 h [d.sup.-1]. Ozone treatments were charcoal-filtered (CF) air (23 nmol [mol.sup.-1]) and approximately 1.5 times ambient [O.sub.3] levels (71 nmol [mol.sup.-1]) given 12 h [d.sup.-1]. Relative effects of elevated C[O.sub.2], and [O.sub.3] on aboveground biomass and seed yield were quite similar for plants grown in pots compared with plants grown in the ground. Elevated C[O.sub.2] increased total seed mass and [O.sub.3] suppressed it to similar magnitudes in both rooting environments. Elevated C[O.sub.2] also reduced the toxic effects of [O.sub.3]. Net photosynthesis (A) was similar while stomatal conductance ([g.sub.s],) was higher in pot-grown compared with ground-grown plants, possibly due to better soil moisture status. The results indicated that planting density and rooting environment affected plant morphology, but relative responses of seed yield to elevated C[O.sub.2] and [O.sub.3] were not fundamentally different between soybean plants grown in large pots and in the ground in open-top chambers., MOST STUDIES of elevated atmospheric C[O.sub.2] effects on agricultural and natural plant systems have shown that C[O.sub.2] enrichment stimulates plant growth (Ainsworth et al., 2002; Bazzaz, 1990; Cure and Acock, [...]

The heterotrimeric G-protein complex provides signal amplification and target specificity. The Arabidopsis (Arabidopsis thaliana) Gβ-subunit of this complex (AGB1) interacts with and modulates the activity of target cytoplasmic proteins. This specificity resides in the structure of the interface between AGB1 and its targets. Important surface residues of AGB1, which were deduced from a comparative evolutionary approach, were mutated to dissect AGBl-dependent physiological functions. Analysis of the capacity of these mutants to complement well-established phenotypes of Gβ-null mutants revealed AGB1 residues critical for specific AGB1-mediated biological processes, including growth architecture, pathogen resistance, stomata-mediated leaf-air gas exchange, and possibly photosynthesis. These findings provide promising new avenues to direct the finely tuned engineering of crop yield and traits. [ABSTRACT FROM AUTHOR]

Climate change factors such as elevated atmospheric carbon dioxide (CO2) and ozone (O3) can exert significant impacts on soil microbes and the ecosystem level processes they mediate. However, the underlying mechanisms by which soil microbes respond to these environmental changes remain poorly understood. The prevailing hypothesis, which states that CO2- or O3-induced changes in carbon (C) availability dominate microbial responses, is primarily based on results from nitrogen (N)-limiting forests and grasslands. It remains largely unexplored how soil microbes respond to elevated CO2 and O3 in N-rich or N-aggrading systems, which severely hinders our ability to predict the long-term soil C dynamics in agroecosystems. Using a long-term field study conducted in a no-till wheat-soybean rotation system with open-top chambers, we showed that elevated CO2 but not O3 had a potent influence on soil microbes. Elevated CO2 (1.56ambient) significantly increased, while O3 (1.46ambient) reduced, aboveground (and presumably belowground) plant residue C and N inputs to soil. However, only elevated CO2 significantly affected soil microbial biomass, activities (namely heterotrophic respiration) and community composition. The enhancement of microbial biomass and activities by elevated CO2 largely occurred in the third and fourth years of the experiment and coincided with increased soil N availability, likely due to CO2- stimulation of symbiotic N2 fixation in soybean. Fungal biomass and the fungi:bacteria ratio decreased under both ambient and elevated CO2 by the third year and also coincided with increased soil N availability; but they were significantly higher under elevated than ambient CO2. These results suggest that more attention should be directed towards assessing the impact of N availability on microbial activities and decomposition in projections of soil organic C balance in N-rich systems under future CO2 scenarios. [ABSTRACT FROM AUTHOR]

Elevated atmospheric CO2 and ozone (O3) may affect productivity of legumes in part by altering symbiotic N2 fixation. To investigate this possibility, measurements of plant biomass, N levels and natural 15N abundance (δ15N) were used to examine the effects of elevated 002 and O3 on N acquisition in field-grown peanut (Arachis hypogaea L.) using open-top chambers. Seasonal 12-h daily average CO2 treatment concentrations were 376, 550, and 730 μmol mol1. Carbon dioxide treatments were applied in reciprocal combinations with seasonal 12-h daily average O3 concentrations of 21, 49, and 79 nmol mol-1. At mid-vegetative growth, elevated 002 significantly reduced leaf N concentrations by up to 44%, but not δ15N values. Elevated O3 did not significantly affect N concentrations or δ15N values. At harvest, plant N concentrations were similar among treatments except for a 14% reduction in the highest-level 002-O3 treatment. Plant N accumulation varied in proportion with treatment effects on biomass production, which was increased with elevated 002 when averaged over the O3 treatments and suppressed by high-level O3 at ambient CO2. Elevated 002 reduced plant δ15N values in low- and mid-level O3 treatments while mid- and high-level O3 increased them at ambient CO2. The changes in ö15N values suggested that N2 fixation activity was stimulated with elevated CO2 and inhibited by elevated O3. Elevated CO2 ameliorated detrimental O3 effects to varying extents depending on the concentrations of the two gases. These results indicated that interactions between CO2 and O3 on plant physiology can alter N acquisition processes, with impacts on peanut productivity likely dependent in part on these changes. [ABSTRACT FROM AUTHOR]