Fourteen plant species from early-, mid-, and late-successional habitats were grown for a period of 25 to 50 days in each of two light environments, i.e. full sunlight and in deep shade. The rate of photosynthesis for newly formed leaves was measured as a function of light intensity for plants from each light environment. Photosynthetic flexibility, measured as the difference in response between sun- and shade-grown plants, was determined for each of 5 parameters including dark respiration, quantum yield, light compensation, half-saturating irradiance for photosynthesis, and the photosynthetic rate at 1,400 μE m s. We found photosynthetic flexibility to be high for early successional annuals, intermediate for midsuccessional species, and low for late successional species.

No abstract

SUMMARYThe energetic cost for a plant to produce reproductive structures is termed reproductive effort and is most frequently expressed as the ratio of reproductive biomass to total plant biomass. This expression may lead to an incorrect analysis of reproductive effort unless an account is taken of (a) the cost of producing male flowers or male flower parts, and (b) the photosynthetic contribution (reproductive assimilation) of reproductive structures to propagule production.An analysis was made of the carbon budget for reproduction in Ambrosia trifida L., based on measurements of CO2 flux, and the elaboration of seed by excised immature pollinated inflorescences in the absence of carbohydrate from the main stem. Reproductive assimilation accounted for 41 and 57 % respectively of the carbohydrate required to produce male and female inflorescences on intact plants. Individual flowers retain their ability to elaborate seed even after being removed frora the parent plant at the time of pollination.

Detached corn and sunflower leaves exposed to various concentrations of Cd, supplied as CdCU, exhibit reduced photosynthesis and transpiration. The reduction is dependent on the concentration of CdCU solution and generally becomes more pronounced with time. In sunflower, net photosynthesis and transpiration are completely inhibited within 45 min after the introduction of 18 mM Cd. Within two hours net photosynthesis is reduced to 40% and 70% of maximum after the introduction of 9 and 4.5 mM Cd respectively. In corn the trend of photosynthetic response to Cd is similar to that in sunflower except that the inhibition in corn is more pronounced at all treatment levels. A strong linear relationship between photosynthesis and transpiration inhibition is obtained in both species suggesting that Cd contamination induces stomatal closure.

No abstract