The response of plants to elevated CO2

Summary Communities, consisting of six co-occurring, disturbed site annuals, were subjected to CO₂ unenriched (300 ppm) and to CO₂ enriched (450 and 600 ppm) atmospheres at different levels of light and nutrient availability. In general, total community production increased with CO₂ enrichment to 450 ppm, but a further increase in CO₂ to 600 ppm had little or no effect. The response of community production to CO₂ level was not affected by nutrient availability but was affected by light level.Of the six species, four display C₃ metabolism. The proportion of total community production contributed by these species increased as a result of CO₂ enrichment, and was dependent upon both light and nutrient availability. The relative success of some species, particularly in terms of reproduction (total seed biomass), was significantly altered by CO₂ concentration depending on the level of nutrients. There were not only changes in reproductive success (seed biomass) and shoot biomass but also changes in the proportion of biomass allocated to seed.These experiments demonstrate that CO₂ enrichment does affect annual plant communities both in terms of productivity and species composition and that the affect of CO₂ on such system may depend upon other resources such as light and nutrients.     

Seed germination in relation to salt concentration in three populations of Prosopis farcta

Summary Prosopis farcta (Banks et Sol.) Eig., is a widespread perennial shrub in a variety of habitats over a large geographic area in the Middle East. In iraq it occurs in non-saline deserts of the west and saline agricultural lands of the Mesopotamian Plain. The species is economically important as fuel for a sizable segment of the population in rural areas. Seeds were collected in three environmentally distinct habitats, with regard to annual precipitation and soil salt content. The seeds were germinated in various concentrations of sodium chloride and their germination, seedling radicle growth, and dark respiration studied. The results indicate that the three populations differend in their response to NaCl with the northern population being generally more sensitive than the other two populations. The three populations represent salt ecotypes of this very widely distributed shrub. The salt ecotypes seem to be of somewhat recent origin and apparently have been further spread by improper agricultural land-use which created vast saline areas.     

In situ measurements of carbon dioxide gradients in a soil-plant-atmosphere system

Summary In order to more fully understand carbon dioxide dynamics in a soil-plant-atmosphere system, an in situ sampling technique has been developed to measure carbon dioxide concentration within the soil profile as well as in the atmosphere. Gas samples are automatically pumped in sequence from six porous collectors within the soil profile and five aboveground inlets through an infrared gas analyzer. Field measurements in a first year field, indicated that carbon dioxide concentrations reached a maximum value (1800 ppm) in the deepest soil sampling site (-180 cm). Temporal and spatial variations of carbon dioxide concentration were related to the development of root and vegetation structure as well as the position of the groundwater table.Supported, in part, by a grant from the Graduate Research Board. We acknowledge, with thanks, the competent assistance of Frank W. Schwartz.     

Elevated CO2 differentially alters the responses of coocurring birch and maple seedlings to a moisture gradient

Summary To determine the effects of elevated CO₂ and soil moisture status on growth and niche characteristics of birch and maple seedlings, gray birch (Betula populifolia) and red maple (Acer rubrum) were experimentally raised along a soil moisture gradient ranging from extreme drought to flooded conditions at both ambient and elevated atmospheric CO₂ levels. The magnitude of growth enhancement due to CO₂ was largely contingent on soil moisture conditions, but differently so for maple than for birch seedlings. Red maple showed greatest CO₂ enhancements under moderately moist soil conditions, whereas gray birch showed greatest enhancements under moderately dry soil conditions. Additionally, CO₂ had a relatively greater ameliorating effect in flooded conditions for red maple than for gray birch, whereas the reverse pattern was true for these species under extreme drought conditions. For both species, elevated CO₂ resulted in a reduction in niche breadths on the moisture gradient; 5% for gray birch and 23% for red maple. Species niche overlap (proportional overall) was also lower at elevated CO₂ (0.98 to: 0.88: 11%). This study highlights the utility of of experiments crossing CO₂ levels with gradients of other resources as effective tools for elucidating the potential consequences of elevated CO₂ on species distributions and potential interactions in natural communities.     

Cost of reproduction as reduced growth in genotypes of two congeneric species with contrasting life histories

Summary We examined the effect of reproduction on growth in 33 genotypes of Plantago major and 14 genotypes of P. rugelii. These two herbaceous perennials have contrasting life histories; P. major reproduces at a smaller size, and allocates a larger proportion of its biomass to reproduction, than P. rugelii. The effect of reproduction on frowth was determined experimentally using photoperiod manipulations to control level of reproduction. The difference in growth between reproductive treatments was divided by the difference in capsule weight to produce a measure of reproductive cost per g of capsule for genotypes of the two species. In both species there was substantial variation among genotypes in the effect of reproduction on growth. Much of this variation could be correlated with differences among genotypes in the extent of reproductive investment and plant size. Cost in terms of reduction in growth per g of capsule increased with reproductive investment in P. rugelii, and with plant size in P. major. We suggest the differences between species in timing and extent of reproduction are related to the differences between species in effect of reproduction on growth. Plantago rugelii may reproduce to a lesser extent than P. major because cost per g of capsule in terms of reduced vegetative biomass, increases with reproductive output in the former species, but not in the latter. Similarly, P. major may reproduce earlier than P. rugelii because cost per g of capsule increases with plant size in P. major, but not in P. rugelii.     

Genetic insertion and exposure of a reporter epitope in the ferrichrome-iron receptor of Escherichia coli K-12.

The ferrichrome-iron receptor of Escherichia coli K-12 is FhuA (M(r), 78,992), the first component of an energy-dependent, high-affinity iron uptake pathway. FhuA is also the cognate receptor for bacteriophages T5, T1, phi 80, and UC-1, for colicin M and microcin 25, and for albomycin. To probe the topological organization of FhuA which enables recognition of these different ligands, we generated a library of 16 insertion mutations within the fhuA gene. Each insertion spliced a 13-amino-acid antigenic determinant (the C3 epitope of poliovirus) at a different position within FhuA. Immunoblotting of outer membranes with anti-FhuA and anti-C3 antibodies indicated that 15 of 16 FhuA.C3 proteins were present in the outer membrane in amounts similar to that observed for plasmid-encoded wild-type FhuA. One chimeric protein with the C3 epitope inserted after amino acid 440 of FhuA was present in the outer membrane in greatly reduced amounts. Strains overexpressing FhuA.C3 proteins were subjected to flow cytometric analysis using anti-FhuA monoclonal antibodies. Such analysis showed that (i) the chimeric proteins were properly localized and (ii) the wild-type FhuA protein structure had not been grossly altered by insertion of the C3 epitope. Twelve of sixteen strains expressing FhuA.C3 proteins were proficient in ferrichrome transport and remained sensitive to FhuA-specific phages. Three FhuA.C3 proteins, with insertions after amino acid 321, 405, or 417 of FhuA, were detected at the cell surface by flow cytometry using anti-C3 antibodies. These three chimeric proteins were all biologically active. We conclude that amino acids 321, 405, and 417 are surface accessible in wild-type FhuA.     

Adjuvant therapy with γ‐tocopherol‐induce apoptosis in HT‐29 colon cancer via cyclin‐dependent cell cycle arrest mechanism

Resistance to chemotherapy with 5‐fluorouracil (5‐FU) in patients with colorectal cancer (CRC) is the major obstacle to reach the maximum efficiency of CRC treatment. Combination therapy has emerged as a novel anticancer strategy. The present study evaluates the cotreatment of γ‐tocopherol and 5‐FU in enhancing the efficacy of chemotherapy against HT‐29 colon cancer cells. Cytotoxic effect of this combination was examined using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay and a synergistic effect was evaluated by a combination index technique. Nuclear morphology was studied via 4′,6‐diamidino‐2‐phenylindole staining and flow cytometric assays were conducted to identify molecular mechanisms of apoptosis and cell cycle progression. We investigated the expression of Cyclin D1, Cyclin E, Bax, and Bcl‐2 by a quantitative real‐time polymerase chain reaction. The IC₅₀ values for 5‐FU and γ‐tocopherol were 21.8 ± 2.5 and 14.4 ± 2.6 μM, respectively, and also this combination therapeutic increased the percentage of apoptotic cells from 35% ± 2% to 40% ± 4% (P < .05). Furthermore, incubation HT‐29 colon cells with combined concentrations of two drugs caused significant accumulation of cells in the subGsubG1 phase. Our results presented the combination therapy with 5‐FU and γ‐tocopherol as a novel therapeutic approach, which can enhance the efficacy of chemotherapy.     

Chilling-Induced Photoinhibition in Two Oak Species: Are Evergreen Leaves Inherently Better Protected Than Deciduous Leaves?

We compared the sensitivity to cold stress, in terms of photosynthetic capacity and changes in chlorophyll fluorescence of photosystem 2 (PS2), of an evergreen and a deciduous oak species, which co-occur in the southeastern United States. We predicted that the evergreen species, Quercus virginiana, which must endure winter, is likely to have an inherently greater capacity for energy dissipation and to be less susceptible to chilling stress than the deciduous species, Quercus michauxii. Short-term cold stress in both species lead to greater than 50 % reduction in maximum photosynthetic rates, 60-70 % reduction in electron transport, and irreversible quenching of PS2 fluorescence. The kinetics of recovery in the dark after exposure to 1 h high irradiance (1000 μmol m^-2 s^-1) and chilling (5 °C) showed that the evergreen Q. virginiana exhibited more protective q_E and less irreversible quenching (q_I) than the deciduous Q. michauxii. The large q_E which we observed in Q. virginiana suggests that the capacity for photoprotection at low temperatures is not induced by a long-term acclimation to cold but preexists in evergreen leaves. This capacity may contribute to the ability of this species to maintain leaves during the winter. This revised version was published online in June 2006 with corrections to the Cover Date.     

The density dependence of plant responses to elevated CO2

1 Stands of the annual Brassica kaber were grown at a range of six densities in both ambient and elevated CO₂ environments, and measurements of shoot growth were made from seedling emergence through to reproduction.
2 Early in stand development (21 days following emergence), CO₂ enhancement (β) for above-ground biomass was highly density-dependent, ranging from 1.41 at the lowest density (20 plants m−2) to 0.59 at the highest density (652 plants m−2).
3 As stands matured and total biomass exceeded a relatively low threshold level (<10.0 g m^{−2; c.}  20% of final yield), the density-dependence of β disappeared. Above this shoot biomass threshold, β-values remained remarkably stable (β = 0.34) across a broad range of stand biomass, independent of a stand's initial density or age.
4 Average stand-level reproductive β-values at a final harvest were very similar to biomass values (β = 0.38) and, as with biomass values at later stages, showed no apparent density-dependence.
5 These results highlight the importance of considering density and the time-course of stand development simultaneously when assessing the potential for CO₂-induced growth enhancements in plants.