Photosynthetic down-regulation over long-term CO enrichment in leaves of sour orange (Citrus aurantium) trees.

•  Understanding how trees are affected by a long-term increase in atmospheric CO is crucial to understanding the future impact of global climate change. Measurements of photosynthetic characteristics were made in sour orange trees (Citrus aurantium) growing under an enhanced CO atmosphere and N-replete soil for 14 yr to determine whether photosynthetic down-regulation had occurred. •  Photosynthesis, A : C gas exchange relationships and Rubisco activity and content were measured throughout the 14th year of the experiment.

Light and assimilation number in a small desert, recharged-groundwater pond.

Measurements of irradiance, chlorophyll a concentration, respiration, and net and gross photosynthesis were carried out in a small desert pond containing recharged-groundwater from the Flushing Meadows water reclamation project at Phoenix, Arizona. Over the 6-month period May-October, chl. a concentration averaged 119 mg m; and gross primary productivity in terms of the mean daily carbon fixation rate was 8.

An analytical study of three characteristic forms of light-forced primary production in aquatic ecosystems.

Primary production in aquatic ecosystems is largely a function of irradiance, with photosynthetic response to light ranging from "light saturation" through "asymptotic inhibition" to "complete inhibition". Equations describing these three basic types of response have been solved to yield instantaneous integral photosynthesis as a function of irradiance, chlorophyll a concentration, light extinction coefficient, and photosynthetic capacity of the phytoplankton at optimum irradiance. These results were used to calculate diurnal trends of instantaneous integral photosynthesis for several different latitudes and seasons and finally day-rate integrals of photosynthesis as a function of time of year at several latitudes.