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Photosynthesis rates

ALGAE (various species) 22 pg/L, 7 days No effect on photosynthesis rate, chlorophyll content, or cell numbers (Plumley and Davis 1980)... [Pg.786]

These changes persisted for 6 hr. Twenty-one hr after ozone exposure, the ATP level and photosynthetic rate had returned to normal. Seventy two hr after ozonation, respiration rates were still increased but photosynthesis rates and total adenylate levels had returned to normal. The ATP content of the ozonated bean plants showed a secondary increase over control plants after 72 hr. [Pg.110]

Sublethal plant exposures to a number of phytotoxic air pollutants can cause the reversible suppression of one of life s most basic processes— photosynthesis. The possibility of plant growth suppression by atmospheric pollution is a concern of many people. We need to know if subnecrotic pollutant exposures that may occur in ambient air can repress photosynthesis rates sufficiently to cause significant retardation of plant growth. Some insight into the capability for short-term exposures to HF, CI2, O3, S029 NO2 and NO— applied singly and as dual pollutant mixtures— to suppress apparent photosynthesis rates of several important crop species is presented here. [Pg.115]

Given these restrictions, oat, barley and alfalfa canopies required treatments with more than 1 pphm HF, about 5 pphm O3 or CI2, 20 pphm SO2, and 40-60 pphm NO2 or NO before apparent photosynthesis rates were measurably depressed by the end of 2 hr of exposure. Above these apparent threshold values the 2-hr depressions induced were linearly related to pollutant concentrations applied up to those that caused visible foliar injury to the tissues. Foliar necrosis occurred to some plant tissues within the canopies exposed to approximately 15 pphm HF,... [Pg.119]

Table II includes supporting data for greater-than-additive inhibition of alfalfa apparent photosynthetic rates induced by SO2+NO2 mixtures. The enhanced effects were most marked at the lower concentrations applied, becoming less pronounced as pollutant levels were raised. At 50 pphm of each gas no synergism was evident. At this SO2 exposure concentration, sulfur dioxide appeared to regulate the observed plant responses. Significant amounts of inhibition resulted from the lowest bipollutant concentrations used (15 pphm of each gas) these concentrations were well below those required for the individual pollutants to measurably suppress apparent photosynthesis rates. At these exposure levels where no tissue necrosis occurred, the plants recovered completely within 2 hr after fumigation. The manner by which this inhibiting interaction occurred is not well understood. This pollutant combination is also known to act in a synergistic fashion to cause visible injury to plants, and further study of this mixture may be warranted. Table II includes supporting data for greater-than-additive inhibition of alfalfa apparent photosynthetic rates induced by SO2+NO2 mixtures. The enhanced effects were most marked at the lower concentrations applied, becoming less pronounced as pollutant levels were raised. At 50 pphm of each gas no synergism was evident. At this SO2 exposure concentration, sulfur dioxide appeared to regulate the observed plant responses. Significant amounts of inhibition resulted from the lowest bipollutant concentrations used (15 pphm of each gas) these concentrations were well below those required for the individual pollutants to measurably suppress apparent photosynthesis rates. At these exposure levels where no tissue necrosis occurred, the plants recovered completely within 2 hr after fumigation. The manner by which this inhibiting interaction occurred is not well understood. This pollutant combination is also known to act in a synergistic fashion to cause visible injury to plants, and further study of this mixture may be warranted.
Leaf maximum photosynthesis rate Single leaf maximum photosynthetic rate 29-40 gmol CO. nr2-sear1 Soja and Haunold, 1991... [Pg.328]

The C02-fixing pathways used by a specific biomass species will affect the efficiency of photosynthesis, so from a biomass energy standpoint, it is desirable to choose species that exhibit high photosynthesis rates to maximize the yields of biomass in the shortest possible time. Obviously, however, there are numerous factors that affect the efficiency of photosynthesis other than the... [Pg.65]

Thermotolerant genotypes have less depressed photosynthesis rates, with faster recovery after stress [46]. Maintenance of activity and increased transcription levels of antioxidant enzymes and nonenzymatic antioxidants, as well as photosynthesis are associated with variable... [Pg.202]

Figure 6 The light-saturation curve of photosynthesis Rates of oxygen evolution on a per Chi basis. Note the similar initial slopes and the different light-saturated rates between control and Chi A-less mutant. Figure 6 The light-saturation curve of photosynthesis Rates of oxygen evolution on a per Chi basis. Note the similar initial slopes and the different light-saturated rates between control and Chi A-less mutant.
In the natural environment, the light intensity to which the phytoplankton are exposed is not uniformly at the optimum value but it varies as a function of depth because of the natural turbidity present and as a function of time over the day. Thus, the phytoplankton in the lower layers are exposed to intensities below the optimum and those at the surface may be exposed to intensities above the optimum so that their growth rate would be inhibited. Figure 3b,c,d from Ryther (28) are plots of the photosynthesis rate normalized by the photosynthesis rate at the optimum or saturating light intensity vs. the light intensity, I, incident on the populations. Figure 3a is a plot of function... [Pg.149]

However, as pointed out by Sathyendranath and Platt (1994) and Sathyen-dranath etal. (1999), models that only consider mixed layer dynamics without taking into account changes in bio-optical properties of phytoplankton are probably insufficient to explain the occurrence of phytoplankton blooms in the Arabian Sea. Sathyendranath etal. (1999) provided evidence for significant seasonal changes in the parameters that describe the dependence of photosynthesis rate of phytoplankton on the amount of light available (P-I curves), viz. the assimilation number (PmB) and the initial slope of photosynthesis-light curve (aB), as well as in the specific absorption coefficient of phytoplankton (ac ). [Pg.173]

Any condition that lowers photosynthesis rates at a given PFD without a change in light absorphon results in a greater level of excess absorbed light. [Pg.253]

Fig. 13. Seasonal changes in the maximal capacity for photosynthetic oxygen evolution in the mesophytic herb Malva neglecta versus the evergreen sclerophytes Finca minor (Periwinkle) and Pinus ponderosa (Ponderosa pine). To express photosynthesis rates of Ponderosa pine on a leaf area basis, needles were aligned beside each other and taped together. Data from Verhoeven et al. (1999) and TN Rosenstiel, WW Adams III, B Demmig-Adams, unpublished... Fig. 13. Seasonal changes in the maximal capacity for photosynthetic oxygen evolution in the mesophytic herb Malva neglecta versus the evergreen sclerophytes Finca minor (Periwinkle) and Pinus ponderosa (Ponderosa pine). To express photosynthesis rates of Ponderosa pine on a leaf area basis, needles were aligned beside each other and taped together. Data from Verhoeven et al. (1999) and TN Rosenstiel, WW Adams III, B Demmig-Adams, unpublished...

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See also in sourсe #XX -- [ Pg.364 , Pg.416 , Pg.417 , Pg.420 ]




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Photosynthesis, maximum rate

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