PHOTOSYNTHESIS, GROWTH AND NUTRIENT CHANGES IN NONNODULATED PHASEOLUS-VULGARIS GROWN UNDER ATMOSPHERIC AND ELEVATED CARBON-DIOXIDE CONDITIONS

The response of Phaseolus vulgaris L. cv. Contender grown under contro lled environment at either ambient or elevated (360 and 700 mu mol mol (-1), respectively) CO2 concentrations ([CO2]), was monitored from 10 days after germination (DAG) until the onset of senescence. Elevated C O2 had a pronounced effect on total plant height (TPH), leaf area (LA) , leaf dry weight (LD), total plant biomass (TB) accumulation and spec ific leaf area (SLA). All of these were significantly increased under elevated carbon dioxide with the exception of SLA which was significan tly reduced. Other than high initial growth rates in CO2-enriched plan ts, relative growth rates remained relatively unchanged throughout the growth period. While the trends in growth parameters were dearly diff erent between [CO2], some physiological processes were largely transie nt, in particular, net assimilation rate (NAR) and foliar nutrient con centrations of N, Mg and Cu. CO2 enrichment significantly increased NA R, but from 20 DAG, a steady decline to almost similar levels to those measured in plants grown under ambient CO2 occurred. A similar trend was observed for leaf N content where the loss of leaf nitrogen in CO2 -enriched plants after 20 DAG, was significantly greater than that obs erved for ambient-CO2 plants. Under enhanced CO2, the foliar concentra tions of K and Mn were increased significantly whilst P, Ca, Fe and Zn were reduced significantly. Changes in Mg and Cu concentrations were insignificant. In addition, high CO2 grown plants exhibited a pronounc ed leaf discoloration or chlorosis, coupled with a significant reducti on in leaf longevity.