The interaction between CO2 and plant nutrition: comments on a paper by Coleman,McConnaughay and Bazzaz

Effects of CO₂ on plants are often confounded with effects of nutrition. Coleman et al. (1993) showed that nitrogen concentrations in plants grown under different CO₂ levels did not differ if plants of equal sizes were compared but varied at equal times and equal sizes for different levels of nitrogen additions. I will suggest why this must occur under the conditions of the experiment. I will also suggest why nitrogen productivity should be used to interpret experimental results rather than the dubious nitrogen use efficiency.