The Interactive Effects of Atmospheric Carbon Dioxide and Light on Stem Elongation in Seedlings of Four Species

Four species, Sinapis alba L., Medicago sativa L., Gypsophila paniculata L. and Picea abies (L.) Karsten, were grown in three light regimes: darkness, low light (25 μmol m −2 s −1 for 10 min d −1 ) and high light (120 μmol m −2 s −1 for 12 h  d −1 ) and four levels of carbon dioxide: 0, 350, 700 and 1400±50 μl l −1 . Germination was not affected by any of the treatments. The effects of carbon dioxide on stem elongation were identical in low and high light: stem length increased at a decreasing rate with level of carbon dioxide in all species. Level of carbon dioxide also affected stem elongation in complete darkness, but the pattern was more complex and varied among species. Total weight did not vary with level of carbon dioxide to any significant extent in either darkness or low light, but increased with level of carbon dioxide at high light in all four species. Due to the absence of any effect of carbon dioxide on growth in darkness and low light, we suggest the effects of carbon dioxide on stem elongation are independent of effects on growth and may be due to a direct interaction with developmental processes. In contrast, level of carbon dioxide had little effect on allocation patterns in the dark and low light experiments, but had marked effects in high light. Therefore, the effect of carbon dioxide on allocation was probably due to the effects of carbon dioxide on growth rather than to any direct interaction between carbon dioxide and development. An understanding of the mechanisms by which carbon dioxide affects development may help us understand the often variable effects of carbon dioxide upon plants.