VARIATION IN GROWTH-STIMULATION BY ELEVATED CARBON-DIOXIDE IN SEEDLINGS OF SOME C-3 CROP AND WEED SPECIES

Seven C-3 crop and three C-3 weed species were grown from seed at 360 and at 700 cm(3) m(-3) carbon dioxide concentrations in a controlled e nvironment chamber to compare dry mass, relative growth rate (RGR), ne t assimilation rate (NAR), leaf area ratio (LAR) and photosynthetic ac climation at ambient and elevated carbon dioxide. The dry mass at the final harvest at elevated carbon dioxide relative to that at ambient c arbon dioxide was highly correlated with the RGR at the lower carbon d ioxide concentration. This relationship could be quite common, because it does not require that species differ in the response of RGR or pho tosynthesis to elevated carbon dioxide, and holds even when species di ffer moderately in these responses. RGR was also measured for a limite d period at the end of the experiment to determine relationships with leaf gas exchange measured at this time. Relative increases in RGR at elevated carbon dioxide at this time were more highly correlated with the relative increase in NAR at elevated carbon dioxide than with the response of LAR. The amount of acclimation of photosynthesis was a goo d predictor of the relative increase in NAR at elevated carbon dioxide , and the longterm increase in photosynthesis in the growth environmen t. No differences between crops and weeds or between cool and warm cli mate species were found in the responses of growth or photosynthetic a cclimation to elevated carbon dioxide.