Photosynthesis

About: Photosynthesis is a research topic. Over the lifetime, 19789 publications have been published within this topic receiving 895197 citations.

Photosynthetic Acclimation to Temperature in the Desert Shrub, Larrea divaricata: I. Carbon Dioxide Exchange Characteristics of Intact Leaves.

Abstract: Larrea divaricata, a desert evergreen shrub, has a remarkable ability to adjust its photosynthetic temperature response characteristics to changing temperature conditions. In its native habitat on the floor of Death Valley, California, plants of this C(3) species when provided with adequate water are able to maintain a relatively high and constant photosynthetic activity throughout the year even though the mean daily maximum temperature varies by nearly 30 C from winter to summer. The temperature dependence of light-saturated net photosynthesis varies in concert with these seasonal temperature changes whereas the photosynthetic rate at the respective optimum temperatures shows little change.Experiments on plants of the same age, grown at day/night temperatures of 20/15, 35/25, and 45/33 C with the same conditions of day length and other environmental factors, showed a similar photosynthetic acclimation response as observed in nature. An analysis was made of a number of factors that potentially can contribute to the observed changes in the temperature dependence of net CO(2) uptake at normal CO(2) and O(2) levels. These included stomatal conductance, respiration, O(2) inhibition of photosynthesis, and nonstomatal limitations of CO(2) diffusive transport. None of these factors, separately or taken together, can account for the observed acclimation responses. Measurements under high saturating CO(2) concentrations provide additional evidence that the observed adaptive responses are primarily the result of changes in intrinsic characteristics of the photosynthetic machinery at the cellular or subcellular levels. Two apparently separate effects of the growth temperature regime can be distinguished: one involves an increased capacity for photosynthesis at low, rate-limiting temperatures with decreased growth temperature, and the other an increased thermal stability of key components of the photosynthetic apparatus with increased growth temperature.

Vertical separation of light and available nutrients as a factor causing replacement of green algae by blue-green algae in the plankton of a stratified lake

Abstract: (1) A change from the green alga, Dictyosphaerium pulchellum to the blue-green algae Microcystis aeruginosa and Anabaena spiroides occurred in the plankton of Mt Bold reservoir, South Australia, during November and December 1978. (2) The reservoir was 30-34 m deep, thermally stratified with water mixed to 6-7 m, and a euphotic zone of less than 2.7 m. Measurements of photosynthesis and light penetration showed that photosynthesis was restricted probably to the upper 2.5 m. (3) Growth experiments with eight cultured species, and the natural phytoplankton assemblage, showed that during this change there was a decline of the potential of the water for algal growth to undetectable levels at a depth of 8 m. This could be restored by the combined addition of nitrogen, phosphorus and Fe-EDTA. (4) Continuous measurement of concentration of chlorophyll a in the water column demonstrated that the blue-green algal community was able to migrate to a depth of 12 m despite substantial density barriers. (5) In situ growth experiments, using dialysis bags, showed that populations which were artificially circulated between 0.2 and 10 m, were able to grow, whereas those maintained at a single depth (0-2 m or 10 m) were not. (6) The ability of blue-green algae to overcome successfully this spatial separation between light and nutrients was proposed as the probable cause of the change from green to blue-green algae.

Photosynthetic Acclimation and Nitrogen Partitioning Within a Lucerne Canopy. I. Canopy Characteristics

Abstract: Acclimation by the photosynthetic system to the gradient in irradiance through a leaf canopy was investigated with a plot of lucerne (Medicago sativa L. cv. Aurora). The aims were to determine the extent to which acclimation occurred in a natural canopy and to quantify the changes in the partitioning of nitrogen within the leaf that are associated with acclimation. The canopy grew up around light sensors placed at 10 cm height increments which logged the irradiance at 1 min intervals for the 4 days that preceded sampling. Photosynthetic capacity was measured with leaf disc oxygen electrodes and the chlorophyll, soluble protein and nitrogen contents of the leaves were determined. Daily irradiance declined exponentially down through the canopy. Nitrogen content and photosynthetic capacity both declined down through the canopy. Photosynthetic acclimation by the lower leaves was evident from the lower chlorophyll a/b ratios and reduced photosynthetic capacity per unit chlorophyll. The lower photosynthetic capacity per unit of chlorophyll was offset by an increased proportion of leaf nitrogen present in the thylakoids. Consequently, the photosynthetic capacity per unit leaf nitrogen was nearly independent of irradiance. Based on a comparison of the response of many species to different irradiances during growth, it is generally the case that the proportion of thylakoid nitrogen increases for leaves grown under lower irradiance so as to maintain a constant ratio of photosynthetic capacity to total leaf nitrogen. However, the ratio of photosynthetic capacity to total leaf nitrogen varies widely between species.

Interactions between Senescence and Leaf Orientation Determine in Situ Patterns of Photosynthesis and Photoinhibition in Field-Grown Rice

Abstract: Photosynthesis and photoinhibition in field-grown rice (Oryza sativa L.) were examined in relation to leaf age and orientation. Two varieties (IR72 and IR65598-112-2 [BSI206]) were grown in the field in the Philippines during the dry season under highly irrigated, well-fertilized conditions. Flag leaves were examined 60 and 100 d after transplanting. Because of the upright nature of 60-d-old rice leaves, patterns of photosynthesis were determined by solar movements: light falling on the exposed surface in the morning, a low incident angle of irradiance at midday, and light striking the opposite side of the leaf blade in the afternoon. There was an early morning burst of CO2 assimilation and high levels of saturation of photosystem II electron transfer as incident irradiance reached a maximum level. However, by midday the photochemical efficiency increased again almost to maximum. Leaves that were 100 d old possessed a more horizontal orientation and were found to suffer greater levels of photoinhibition than younger leaves, and this was accompanied by increases in the de-epoxidation state of the xanthophyll cycle. Older leaves had significantly lower chlorophyll content but only slightly diminished photosynthesis capacity.