Analysis of the Differential Response of Five Annuals to Elevated CO2 during Growth

Abstract

In order to investigate the effects, without competition, of CO2 on germination, growth, physiological response, and reproduction, we focussed on co—occurring species that are prominent members of an annual community in Illinois. Five species of old field annual plants—Abutilon theophrasti (C3), Amaranthus retroflexus (C4), Ambrosia artemisiifolia (C3), Chenopodium album (C3), and Setaria faberii (C4)–were grown for their entire life cycle as individuals at CO2 concentration of 350 @mL/L, 500 @mL/L, and 700@mL/L. Emergence time, growth rate, shoot water status, photosynthesis, conductance, flowering time, nitrogen content, and biomass and reproductive biomass were measured. There was no detectable effect of enhanced CO2 on timing of emergence in any of the species. Amaranthus relative growth rate (RGR) was always higher at 700 @mL/L CO2 than at 350 @mL/L. In both Abutilon and Ambrosia, RGR was greater at 700 @mL/L than at 350 @mL/L during the first half of the experimental period, but during the second half of the period the reverse was true. Shoot water potential significantly increased (became less negative) with increasing CO2 in Amaranthus and Setaria. Similar but statistically nonsignificant trends were found in Chenopodium and Abutilon. Overall rate of photosynthesis increased with CO2 but there were no significant effects, at the species level, of CO2 on photosynthetic rates. Stomatal conductance decreased with increased CO2 at both high and low light levels in C3 species but only at high light levels in C4 species. In all species, intercellular CO2 increased with external CO2. Amaranthus flowered significantly earlier at 700 @mL/L than at 350 @mL/L, and Setaria flowered significantly later at 700 @mL/L than at either of the other CO2 levels. Both Abutilon and Ambrosia showed a trend towards earlier flowering but this was not statistically significant. Of the morphological characters measured at the final harvest only specific leaf area (SLA) showed a consistent response to CO2, decreasing with increasing CO2. Significant CO2 x species interactions were also found for leaf area, leaf biomass, biomass of reproductive parts, and seed biomass indicating species—specific responses for these characters. The proportion of nitrogen declined with increasing CO2: there was also a significant CO2 x species interaction caused by the different rates of decline in proportion of nitrogen among the species. The response of most characters had a significant species x CO2 interaction. However, this was not simply caused by the C3/C4 dichotomy. Reproductive biomass (seed, fruits, and flowers) increased with increasing CO2 in Amaranthus (C4) and in Chenopodium and Ambrosia (both C3), but there was no change in Setaria (C4), and Abutilon (C3) showed a peak a 500 @mL/L. Species of the same community differed in their response to CO2, and these differences may help explain the outcome of competitive interactions among these species above ambient CO2 levels.

Can elevated CO2 modify regeneration from seed banks of floating freshwater marshes subjected to rising sea-level?

“…Our findings differ somewhat from germination studies of non-wetland species, which generally conclude that germination is little affected by elevated CO 2 (Garbutt et al, 1990;Huxman et al, 1998;Steinger et al, 2000;Poorter & Navas, 2003). In these terrestrial studies, a lack of germination density response to elevated CO 2 has been attributed partly to the fact that the CO 2 levels of terrestrial soils are higher than in the atmosphere (Bazzaz, 1979).…”

“…For example, C 3 brackish marsh species such as Schoenoplectus americanus increase in biomass when subjected to elevated CO 2 levels (Curtis et al, 1989(Curtis et al, , 1990Ziska et al, 1990;Rasse et al, 2003). While most studies find that terrestrial C 3 species grow faster under elevated CO 2 , the growth response of C 3 seedlings to elevated CO 2 can be negative (Garbutt et al, 1990), or positive for C 4 species (Wand et al, 1999).…”

Acquisition and allocation of carbon and nitrogen by Danthonia richardsonii in response to restricted nitrogen supply and CO2 enrichment

“…2a) was not statistically different at high CO 2 , although the small, non-statistically significant increases, especially at high-N would have contributed to the CO 2 effect on dry weight accumulation. A CO 2 effect on RGR is generally observed only very early in growth, if it is detected at all (Garbutt, Williams & Bazzaz 1990;Watson & Graves 1993;Baxter et al 1994a;Stulen et al 1994). Relative growth rate normally declines with increasing plant dry weight (Evans 1993) as growth moves out of the exponential phase.…”

Decrease in Phosphoribulokinase Activity by Antisense RNA in Transgenic Tobacco. Relationship between Photosynthesis, Growth, and Allocation at Different Nitrogen Levels1

“…At the level of the whole plant, increased SLA could potentially attenuate the effect of decreased photosynthesis and is associated with changes in the aerial environment, e.g. light and CO 2 , which affect the rate of photosynthesis (Bjorkman, 1981;Garbutt et al, 1990). However, leaf area per se was unchanged, the increase in SLA reflecting a Figure 6.…”