
%0 Journal Article
%A Wong, SC 
%A Osmond, CB 
%T Elevated Atmosphere Partial Pressure of CO<sub>2</sub> and Plant Growth. III. Interactions Between <I>Triticum aestivum</I> (C<sub>3</sub>) and <I>Echinochloa frumentacea</I> (C<sub>4</sub>) During Growth in Mixed Culture Under Different CO<sub>2</sub>, N Nutrition and Irradiance Treatments, With Emphasis on Below-Ground Responses Estimated Using the &#948;<sup>13</sup>C Value of Root Biomass
%J Functional Plant Biology
%D 1991/04/01
%V 18
%N 2
%P 137-152
%K 
%R https://doi.org/10.1071/PP9910137
%U https://www.publish.csiro.au/paper/PP9910137 
%X Wheat (Triticum aestivum L.), a C3 species, and Japanese millet (Echinochloa frumentacea Link), a C4 species, were grown in pots in monoculture and mixed culture (2 C3 : 1 C4 and 1 C3:2 C4) at two ambient partial pressures of CO2 (320 and 640 &#956;bar), two photosynthetic photon flux densities (PPFDs) (daily maximum 2000 and 500 µmol m-2 s-1) and two levels of nitrogen nutrition (12 mM and 2 mM NO3-). Growth of shoots of both components in mixed culture was measured by physical separation, and the proportions of root biomass due to each component were calculated from &#948;13C value of total root biomass. In air (320 &#956;bar CO2) at high PPFD and with high root zone-N, the shoot biomass of C3 and C4 components at the first harvest (28 days) was in proportion to the sowing ratio. However, by the second harvest (36 days) the C4 component predominated in both mixtures. Under the same conditions, but with low PPFD, C3 plants predominated at the first harvest but C4 plants had over- taken them by the time of the second harvest.      Elevated atmospheric CO2 (640 &#956;bar) stimulated shoot growth of Triticum in 15 of 16 treatment combinations and the stimulation was greatest in plants provided with low NO3-. Root growth of the C3 plants was generally stimulated by elevated CO2, but was only occasionally sensitive to the presence of C4 plants in mixed culture. However, growth of the C4 plants was often sensitive to the presence of C3 plants in mixed culture. In mixed cultures, elevated CO2 plants stimulated growth of C4 plants at high PPFD, high-N and in all low-N treatments but this was insufficient to offset a marked decline in shoot growth with increasing proportion of C3 plants in mixed cultures. The unexpected stimulation of growth of C4 plants by elevated CO2 was correlated with more negative &#948;13C values of C4 root biomass, suggesting a partial failure of the CO2 concentrating mechanism of C4 photosynthesis in Echinochloa under low-N. These experiments show that for these species nitrogen was more important than light or elevated pCO2 in determining the extent of competitive interactions in mixed culture. 
