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PubMed1997

Effect of elevated carbon dioxide concentration and root restriction on net photosynthesis, water relations and foliar carbohydrate status of loblolly pine seedlings.

To determine the effects of CO(2)-enriched air and root restriction on photosynthetic capacity, we measured net photosynthetic rates of 1-year-old loblolly pine seedlings grown in 0.6-, 3.8- or 18.9-liter pots in ambient (360 micro mol mol(-1)) or 2x ambient CO(2) (720 micro mol mol(-1)) concentration for 23 weeks. We also measured needle carbohydrate concentration and water relations to determine whether feedback inhibition or water stress was responsible for any decreases in net photosynthesis. Across all treatments, carbon dioxide enrichment increased net photosynthesis by approximately 60 to 70%. Net photosynthetic rates of seedlings in the smallest pots decreased over time with the reduction occurring first in the ambient CO(2) treatment and then in the 2x ambient CO(2) treatment. Needle starch concentrations of seedlings grown in the smallest pots were two to three times greater in the 2x ambient CO(2) treatment than in the ambient CO(2) treatment, but decreased net photosynthesis was not associated with increased starch or sugar concentrations. The reduction in net photosynthesis of seedlings in small pots was correlated with decreased needle water potentials, indicating that seedlings in the small pots had restricted root systems and were unable to supply sufficient water to the shoots. We conclude that the decrease in net photosynthesis of seedlings in small pots was not the result of CO(2) enrichment or an accumulation of carbohydrates causing feedback inhibition, but was caused by water stress.

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PubMed1997

Seasonal air and soil temperature effects on photosynthesis in red spruce (Picea rubens) saplings.

Net photosynthesis and stomatal conductance were measured in ten red spruce (Picea rubens Sarg.) saplings, growing near Ithaca, New York, throughout the early spring and late-fall growing periods. Gas exchange and daily minimum and maximum soil and air temperatures were also measured. Linear regression analysis showed that rates of net photosynthesis were positively correlated with both minimum daily soil and air temperatures but that minimum soil temperature was a better predictor of net photosynthesis. Moreover, net photosynthesis was more sensitive to changes in soil temperature than to changes in air temperature, and photosynthesis was approximately twice as sensitive to temperature changes during the fall than during the spring.

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PubMed1999

Variation in net photosynthesis, stomatal characteristics, leaf area and whole-plant phytomass production among ten provenances of neem (Azadirachta indica).

Variation in net photosynthesis, CO(2) exchange parameters, stomatal characteristics, leaf area and seedling dry weight were investigated among 10 provenances of neem (Azadirachta indica A. Juss.). Significant provenance variation was established for net photosynthesis (8.14 to 15.13 &mgr;mol m(-2) s(-1)), stomatal conductance (0.37 to 0.59 mol m(-2) s(-1)), stomatal density (145 to 204 mm(-2)), and total guard cell length (2681 to 3873 &mgr;m). Net photosynthesis was positively correlated with whole-plant dry weight and leaf area. Stomatal density was positively correlated with net photosynthesis, whole-plant dry weight, and leaf area. Total guard cell length was positively correlated with all of these traits. Information on six traits was used in a cluster analysis to construct a dendrogram to assess phenetic relationships among the provenances. With a few exceptions, the dendrogram revealed three major clusters grouped according to rainfall distribution. The study indicated that whole-plant phytomass production of neem seedlings was associated with photosynthesis and stomatal characteristics during the early stages of growth.

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PubMed1999

Canopy photosynthesis of sugar maple (Acer saccharum): comparing big-leaf and multilayer extrapolations of leaf-level measurements.

A comparison is made between a big-leaf model (i.e., without details of the canopy profile) and two multilayer models (i.e., with details of the canopy profile) to estimate daily canopy photosynthesis of a sugar maple (Acer saccharum Marsh.) stand. The first multilayer model uses the distribution of leaf area by leaf mass per unit area (LMA) classes, the observed relationships between the parameters of a photosynthesis-irradiance curve and LMA, and the relationship between relative irradiance and LMA to estimate canopy photosynthesis. When compared with this model, the big-leaf model underestimates daily canopy photosynthesis by 26% because of an assumed proportionality between photosynthetic capacity and relative irradiance, a proportionality that is inconsistent with our data. The bias induced by this assumption is reduced when the big-leaf model is compared with the second multilayer model which, in addition to the assumptions made for the first multilayer model, accounts for the sunlit and shaded fractions of leaf area. The residual bias is almost eliminated when the big-leaf model is run using a weekly averaged irradiance. It is likely, however, that this is the result of a compensating bias that, in this particular case, compensates for the initial bias introduced by the proportionality assumption. It is also shown that canopy photosynthesis can be represented by spatially inexplicit multilayer models that use leaf mass per area as a covariable to describe leaf characteristics and environment. Such models represent an interesting alternative to the biased big-leaf approach.

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PubMed1986

Stomatal and nonstomatal limitations to net photosynthesis in Pinus taeda L. under different environmental conditions.

Net photosynthesis, transpiration and stomatal conductance of two-year-old Pinus taeda L. seedlings were compared under various environmental conditions. Responses to air temperature, irradiance, ambient CO(2) concentration, absolute humidity deficit and xylem pressure potential were examined. The seedlings exhibited little response to a wide range of absolute humidity deficits (7 to 16 g m(-3)) and temperatures (20 to 35 degrees C), but were sensitive to changes in water deficit, irradiance and CO(2) concentration. Net photosynthesis and stomatal conductance were linearly related under all of the environmental conditions measured. However, the gas phase limitation to photosynthesis was generally small (20 to 30%). It was concluded that although the stomatal response was closely coupled to changes in photosynthesis, internal limitations, rather than the rate of gaseous diffusion of CO(2), were primarily responsible for limiting photosynthesis.

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PubMed1990

Photosynthesis patterns during the establishment year within two Populus clones with contrasting morphology and phenology.

Diurnal and seasonal photosynthesis patterns were studied in poplar clones Populus tristis Fisch. x P. balsamfera L. cv. Tristis #1 (NC 5260) and Populus x euramericana (Dode) Guiner cv. Eugenei (NC 5326, Carolina poplar) during their first season in the field in a short rotation, intensive culture plantation. Photosynthetic rates were low in immature leaves; increased basipetally on the shoot and peaked in leaves that had recently reached full expansion; and thereafter declined in lower-crown leaves in both clones. Photosynthesis was associated with leaf age and stomatal conductance in immature leaves; adaxial photosynthetic photon flux density (PPFD) and leaf temperature in recently mature leaves; and leaf age and adaxial PPFD in lower-crown leaves. Diurnal photosynthesis patterns within trees were highly variable due to differential light interception among leaves. Results of clonal comparisons of photosynthetic rates were dependent on which leaves were pooled for comparison and how photosynthesis was expressed. Compared to Eugenei, Tristis produced smaller leaves which had higher unit-area photosynthesis rates. The more indeterminate Eugenei outgrew Tristis principally because it more fully utilized the growing season for leaf area production. Photosynthetic production integrated over the growing season was closely related to dry matter production in both clones.

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PubMed1991

Net photosynthesis and leaf conductance of loblolly pine seedlings in 2 and 21% oxygen as influenced by irradiance, temperature and provenance.

Carbon dioxide assimilation and transpiration by secondary needles of two-year-old loblolly pines (Pinus taeda L.) were measured at 2 and 21% (ambient) oxygen. Measurements were made with a Georgia provenance at irradiances (photosynthetic photon flux density) of 150, 300, 700 and 1200 micromol m(-2) s(-1) and a constant temperature of 25 degrees C, and at temperatures of 15, 25 and 35 degrees C and a constant irradiance of 1200 micromol m(-2) s(-1). Measurements were made with provenances from North Carolina, Florida, Arkansas, and Georgia at 25 degrees C and an irradiance of 1200 micromol m(-2) s(-1). There was no significant interaction between the effects of irradiance and oxygen on either net photosynthesis or leaf conductance. Taking all irradiances together, photosynthesis was 16% less and leaf conductance 28% less in 2% oxygen than in 21% oxygen. There was a significant interaction between the effects of temperature and oxygen concentration on both net assimilation and leaf conductance. Net photosynthesis at 21% oxygen relative to that at 2% was significantly reduced at 25 and 35 degrees C, but not at 15 degrees C, whereas leaf conductance at 21% oxygen relative to that at 2% was significantly increased at 15 and 25 degrees C, but not at 35 degrees C. In the provenance study, net photosynthesis was 11% higher and leaf conductance 36% lower in 2% oxygen than in 21% oxygen. There was no significant interaction between the effects of provenance and oxygen on either net photosynthesis or leaf conductance.

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PubMed1993

Acclimation of Photosynthesis and Dark Respiration of a Submersed Angiosperm beneath Ice in a Temperate Lake.

Ceratophyllum demersum L. remained physiologically active beneath ice of a southeastern Michigan lake. The effect of seasonally low photosynthetic photon flux density (PPFD) and cold but nonfreezing temperature on whole-plant physiology was studied. Net photosynthesis was measured at six temperatures and 12 PPFDs. Net photosynthesis, soluble protein concentration, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) protein concentration, and Rubisco activity of winter plants were 32, 31, 33, and 70% lower, respectively, than those of plants collected in the summer. Optimum temperatures for net photosynthesis of winter and summer plants were 5 and 30[deg]C, respectively. Dark respiration of winter plants was up to 313% greater than that of summer plants. Reduced Rubisco activity and increased dark respiration interacted to reduce net photosynthesis. Interaction of reduced net photosynthesis and increased dark respiration increased CO2 and light compensation points and the light saturation point of winter plants. Growth of C. demersum was limited by the ambient phosphorus concentration of lake water during summer. Apical stem segments of winter-collected plants had 54 and 35% more phosphorus and nitrogen, respectively, than summer-collected plants. Physiologically active perennation beneath ice enabled C. demersum to accumulate phosphorus during the winter when it was most abundant. Partial uncoupling of phosphorus acquisition from utilization may reduce phosphorus limitation upon growth during the summer when phosphorus concentration is seasonally the lowest.

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PubMed1994

Effects of Growth Temperature on the Responses of Ribulose-1,5-Biphosphate Carboxylase, Electron Transport Components, and Sucrose Synthesis Enzymes to Leaf Nitrogen in Rice, and Their Relationships to Photosynthesis.

Effects of growth temperature on the photosynthetic gas-exchange rates and their underlying biochemical properties were examined in young, fully expanded leaves of rice (Oryza sativa L.). The plants were grown hydroponically under day/night temperature regimes of 18/15[deg]C, 23/18[deg]C, and 30/23[deg]C and all photosynthetic measurements were made at a leaf temperature of 25[deg]C and an irradiance of 1800 [mu]mol quanta m-2 s-1. Growth temperature affected the photosynthetic CO2 response curve. The relative ratio of the initial slope to the CO2-saturated photosynthesis increased with rising growth temperature. This was caused mainly by an increase in CO2-limited photosynthesis for a given leaf nitrogen content with rising growth temperature. However, there was no difference in ribulose-1,5-bisphosphate carboxylase (Rubisco) content at any given leaf nitrogen content among temperature treatments. In addition, the activation state and catalytic turnover rate of Rubisco were not affected by growth temperature. The increase in CO2-limited photosynthesis with rising growth temperature was the result of an increase in the CO2 transfer conductance between the intercellular airspaces and the carboxylation sites. The amounts of total chlorophyll and light-harvesting chlorophyll a/b protein II increased for the same leaf nitrogen content with rising growth temperature, but the amounts of cytochrome f and coupling factor 1 and the activities of cytosolic fructose-1,6-bisphosphatase and sucrose-phosphate synthase were the same between plants grown at 23/18[deg]C and those grown at 30/23[deg]C. Similarly, CO2-saturated photosynthesis was not different for the same leaf nitrogen content between these treatments. For the 18/15[deg]C-grown plants, a slight decrease in the amounts of cytochrome f and coupling factor 1 and an increase in the activities of cytosolic fructose-1,6-bisphosphatase and sucrose-phosphate synthase were found, but these were not reflected in CO2-saturated photosynthesis.

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PubMed1994

Effects of a Short-Term Shift to Low Temperature and of Long-Term Cold Hardening on Photosynthesis and Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase and Sucrose Phosphate Synthase Activity in Leaves of Winter Rye (Secale cereale L.).

The effect of a short-term (hours) shift to low temperature (5[deg]C) and long-term (months) cold hardening on photosynthesis and carbon metabolism was studied in winter rye (Secale cereale L. cv Musketeer). Cold-hardened plants grown at 5[deg]C exhibited 25% higher in situ CO2 exchange rates than nonhardened plants grown at 24[deg]C. Cold-hardened plants maintained these high rates throughout the day, in contrast to nonhardened plants, which showed a gradual decline in photosynthesis after 3 h. Associated with the increase in photosynthetic capacity following cold hardening was an increase in ribulose-1,5-bisphosphate carboxylase/oxygenase and sucrose phosphate synthase activity and 3- to 4-fold increases in the pools of associated metabolites. Leaves of nonhardened plants shifted overnight to 5[deg]C required 9 h in the light at 5[deg]C before maximum rates of photosynthesis were reached. The gradual increase in photosynthesis in leaves shifted to 5[deg]C was correlated with a sharp decline in the 3-phosphoglycerate/triose phosphate ratio and by an increase in the ribulose bisphosphate/3-phosphoglycerate ratio, indicating the gradual easing of aninorganic phosphate-mediated feedback inhibition on photo-synthesis. We suggest that the strong recovery of photosynthesis in winter rye following cold hardening indicates that the buildup of photosynthetic enzymes, as well as those involved in sucrose synthesis, is an adaptive response that enables these plants to maximize the production of sugars that have both cryoprotective and storage functions that are critical to the performance of these cultivars during over-wintering.

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PubMed1995

C4 Photosynthesis (The Effects of Leaf Development on the CO2-Concentrating Mechanism and Photorespiration in Maize).

The effect of O2 on photosynthesis was determined in maize (Zea mays) leaves at different developmental stages. The optimum level of O2 for maximum photosynthetic rates was lower in young and senescing tissues (2-5 kPa) than in mature tissue (9 kPa). Inhibition of photosynthesis by suboptimal levels of O2 may be due to a requirement for functional mitochondria or to cyclic/pseudocyclic photophosphorylation in chloroplasts; inhibition by supraoptimal levels of O2 is considered to be due to photorespiration. Analysis of a range of developmental stages (along the leaf blade and at different leaf ages and positions) showed that the degree of inhibition of photosynthesis by supraoptimal levels of O2 increased rapidly once the ribulose-1,5-bisphosphate carboxylase/oxygenase and chlorophyll contents were below a critical level and was similar to that of C3 plants. Tissue having a high sensitivity of photosynthesis to O2 may be less effective in concentrating CO2 in the bundle sheath cells due either to limited function of the C4 cycle or to higher bundle sheath conductance to CO2. An analysis based on the kinetic properties of ribulose-1,5-bisphosphate carboxylase/oxygenase was used to predict the maximum CO2 level concentrated in bundle sheath cells at a given degree of inhibition of photosynthesis by supraoptimal levels of O2.

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PubMed1997

Regulation and Localization of Key Enzymes during the Induction of Kranz-Less, C4-Type Photosynthesis in Hydrilla verticillata.

Kranz-less, C4-type photosynthesis was induced in the submersed monocot Hydrilla verticillata (L.f.) Royle. During a 12-d induction period the CO2 compensation point and O2 inhibition of photosynthesis declined linearly. Phosphoenolpyruvate carboxylase (PEPC) activity increased 16-fold, with the major increase occurring within 3 d. Asparagine and alanine aminotransferases were also induced rapidly. Pyruvate orthophosphate dikinase (PPDK) and NADP-malic enzyme (ME) activities increased 10-fold but slowly over 15 d. Total ribulose-1,5-bisphosphate carboxylase/oxygenase activity did not increase, and its activation declined from 82 to 50%. Western blots for PEPC, PPDK, and NADP-ME indicated that increased protein levels were involved in their induction. The H. verticillata NADP-ME polypeptide was larger (90 kD) than the maize C4 enzyme (62 kD). PEPC and PPDK exhibited up-regulation in the light. Subcellular fractionation of C4-type leaves showed that PEPC was cytosolic, whereas PPDK and NADP-ME were located in the chloroplasts. The O2 inhibition of photosynthesis was doubled when C4-type but not C3-type leaves were exposed to diethyl oxalacetate, a PEPC inhibitor. The data are consistent with a C4-cycle concentrating CO2 in H. verticillata chloroplasts and indicate that Kranz anatomy is not obligatory for C4-type photosynthesis. H. verticillata predates modern terrestrial C4 monocots; therefore, this inducible CO2-concentrating mechanism may represent an ancient form of C4 photosynthesis.

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PubMed1999

Restrictions to carbon dioxide conductance and photosynthesis in spinach leaves recovering from salt stress

Salt accumulation in spinach (Spinacia oleracea L.) leaves first inhibits photosynthesis by decreasing stomatal and mesophyll conductances to CO2 diffusion and then impairs ribulose-1, 5-bisphosphate carboxylase/oxygenase (S. Delfine, A. Alvino, M. Zacchini, F. Loreto [1998] Aust J Plant Physiol 25: 395-402). We measured gas exchange and fluorescence in spinach recovering from salt accumulation. When a 21-d salt accumulation was reversed by 2 weeks of salt-free irrigation (rewatering), stomatal and mesophyll conductances and photosynthesis partially recovered. For the first time, to our knowledge, it is shown that a reduction of mesophyll conductance can be reversed and that this may influence photosynthesis. Photosynthesis and conductances did not recover when salt drainage was restricted and Na content in the leaves was greater than 3% of the dry matter. Incomplete recovery of photosynthesis in rewatered and control leaves may be attributed to an age-related reduction of conductances. Biochemical properties were not affected by the 21-d salt accumulation. However, ribulose-1, 5-bisphosphate carboxylase/oxygenase activity and content were reduced by a 36- to 50-d salt accumulation. Photochemical efficiency was reduced only in 50-d salt-stressed leaves because of a decrease in the fraction of open photosystem II centers. A reduction in chlorophyll content and an increase in the chlorophyll a/b ratio were observed in 43- and 50-d salt-stressed leaves. Low chlorophyll affects light absorptance but is unlikely to change light partitioning between photosystems.

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PubMed1967

Photosynthesis, Transpiration, Leaf Temperature, and Stomatal Activity of Cotton Plants under Varying Water Potentials.

Cotton plants, Gossypium hirsutum L. were grown in a growth room under incident radiation levels of 65, 35, and 17 Langleys per hour to determine the effects of vapor pressure deficits (VPD's) of 2, 9, and 17 mm Hg at high soil water potential, and the effects of decreasing soil water potential and reirrigation on transpiration, leaf temperature, stomatal activity, photosynthesis, and respiration at a VPD of 9 mm Hg.Transpiration was positively correlated with radiation level, air VPD and soil water potential. Reirrigation following stress led to slow recovery, which may be related to root damage occurring during stress. Leaf water potential decreased with, but not as fast as, soil water potential.Leaf temperature was usually positively correlated with light intensity and negatively correlated with transpiration, air VPD, and soil water. At high soil water, leaf temperatures ranged from a fraction of 1 to a few degrees above ambient, except at medium and low light and a VPD of 19 mm Hg when they were slightly below ambient, probably because of increased transpirational cooling. During low soil water leaf temperatures as high as 3.4 degrees above ambient were recorded. Reirrigation reduced leaf temperature before appreciably increasing transpiration. The upper leaf surface tended to be warmer than the lower at the beginning of the day and when soil water was adequate; otherwise there was little difference or the lower surface was warmer. This pattern seemed to reflect transpiration cooling and leaf position effects.Although stomata were more numerous in the lower than the upper epidermis, most of the time a greater percentage of the upper were open. With sufficient soil water present, stomata opened with light and closed with darkness. Fewer stomata opened under low than high light intensity and under even moderate, as compared with high soil water. It required several days following reirrigation for stomata to regain original activity levels.Apparent photosynthesis of cotton leaves occasionally oscillated with variable amplitude and frequency. When soil water was adequate, photosynthesis was nearly proportional to light intensity, with some indication of higher rates at higher VPD's. As soil water decreased, photosynthesis first increased and then markedly decreased. Following reirrigation, photosynthesis rapidly recovered.Respiration was slowed moderately by decreasing soil water but increased before watering. Respiration slowed with increasing leaf age only on leaves that were previously under high light intensity.

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PubMed1967

Kinetics of the Daily Rate of Photosynthesis at Low Temperatures for two Conifers.

The daily course of photosynthesis at low temperatures in 2 coniferous species, Pinus ponderosa Laws., and Pseudotsuga menziesii (Mirb.) Franco, were studied using controlled environment facilities. After having been grown at a 23 degrees day, and 19 degrees night for a year, seedlings were acclimatized for 4 months to either a 3 degrees , 7 degrees or 11 degrees day all under 1200 ft-c of light and followed by a 16-hour night at 3 degrees . Measurement of photosynthesis at 1200 ft-c revealed 3 separate responses. First, the rapidity at which the plants attained their maximum photosynthesis when the lights were turned on depended upon the species, the current temperature, and the previous temperature condition to which the plants had become acclimatized. The warmer the day temperature the sooner the daily maximum was reached. Second, fluctuations in the rate of photosynthesis during the day varied with the species and the day temperature. Photosynthesis in both fir and pine kept at an 11 degrees day and pines kept at a 7 degrees day attained a daily peak rate followed by a decline. This decline occurred even though temperature and light were kept constant, the CO(2) level was returned to 320 ppm from 290 ppm, and the plants were kept well watered. At a 3 degrees day neither species showed this decline. Third, a plant transferred to another temperature acquired a new stable daily photosynthetic pattern. The number of days required for stabilization depended upon the previous temperature history of the plant. The adjustment rate was faster when the temperature was raised than when it was lowered.

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PubMed1971

Recovery of photosynthesis in sunflower after a period of low leaf water potential.

Photosynthesis was studied in sunflower plants subjected to 1 to 2 days of desiccation and then permitted to recover. The leaf water potential to which leaves returned after rewatering was dependent on the severity of desiccation and the evaporative conditions. Under moderately evaporative conditions, leaf water potential returned to predesiccation levels after 3 to 5 hours when desiccation was slight. Leaf water potentials remained below predesiccation levels for several days after rewatering when leaf water potentials decreased to -13 to -19 bars during desiccation. Leaf water potential showed no sign of recovery when leaf water potentials decreased to -20 bars or below during desiccation. The lack of full recovery of leaf water potential was attributable to increased resistance to water transport in the roots and stem. The resistance ultimately became large enough to result in death of the leaves because net water loss continued even after the soil had been rewatered.Measurements of photosynthesis were made at high light intensities, where stomatal aperture often affects photosynthesis, and at low light intensities, where the photochemical activity of the leaves limits photosynthesis. Providing leaf water potentials remained above -12 bars during the desiccation period and returned to predesiccation levels during recovery, photosynthesis under both low and high light paralleled the recovery in leaf water potential after rewatering. After desiccation to leaf water potentials below -12 bars, recovery was incomplete under high light and could be attributed to lack of full stomatal opening. Lack of full opening persisted for 3 days and showed no sign of eventual recovery even though leaf water potentials recovered fully. Under low light, however, recovery in photochemical activity was complete within 15 hours after desiccation to leaf water potentials as low as -17 bars.

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PubMed1973

The effect on net photosynthesis of pedigree selection for low and high rates of photorespiration in tobacco.

A normal appearing plant with a low rate of photorespiration (ratio of (14)CO(2) released light/dark = 1.6) was found in an unselected tobacco (Nicotiana tabacum) cultivar. The plant was self-pollinated, and further selections were made on several successive generations. Excised leaves from the progeny of the selections were examined for photorespiration and net CO(2) assimilation in normal air during photosynthesis. Similar measurements were made of plants derived from selfed parents with high rates of photorespiration (ratio of (14)CO(2) released light/dark = 3.0 or greater). Efficient photosynthetic plants (greater than 22.0 mg of CO(2) dm(-2) hr(-1)) with low rates of photorespiration produced a larger proportion of efficient progeny (about 25%) than did selfing inefficient plants (about 6%), but this proportion did not increase in successive generations.Wide variations in photorespiration and photosynthesis were observed within populations of normal appearing plants grown in the same greenhouse environment. Several plants had photosynthetic rates as great as 25 mg of CO(2) dm(-2) hr(-1) coupled with light/dark ratios below 2.0.The characteristics of two representative contrasting plants were studied more extensively and were fairly constant, irrespective of leaf position on the stalk, leaf size, or time of sampling within approximately a 2-week period. One plant with a mean light/dark ratio of 1.7 showed a mean net photosynthesis of 23.4 mg of CO(2) dm(-2) hr(-1), while an inefficient plant with a light/dark ratio of 3.7 had an average photosynthetic rate of only 17.0 mg CO(2) dm(-2) hr(-1). The dark respiration was similar in these plants. Thus decreasing the photorespiratory rate by about one-half increased net photosynthesis by 38%. The results suggest that diminishing photorespiration, in an otherwise suitable genetic background, will result in large increases in net photosynthesis and plant productivity.

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PubMed1974

Endogenous rhythmic activity of photosynthesis, transpiration, dark respiration, and carbon dioxide compensation point of peanut leaves.

At 14-hour day length, 25 C leaf temperature, 9 mm Hg vapor-pressure deficit, and 1.17 joules cm(-2) min(-1) irradiance, the diurnal change in daily photosynthesis of the cultivated peanut (Arachis hypogaea L.) is a result of an endogenously controlled circadian rhythm in net photosynthesis which peaks near noon and troughs near midnight. By resetting the day-night light regime, the rhythm rephased in continuous light. The free-running rhythm approximates 26 hours. Both transpiration and dark respiration show similar rhythmicity, with transpiration closely in phase with the rhythm in photosynthesis. The rhythm in carbon dioxide compensation point is approximately 12 hours out of phase, peaking at midnight and troughing at midday. Endogenous changes in stomatal aperture seemed to be the major control of the rhythm in photosynthesis. The activity of ribulose-1,5-diphosphate carboxylase increased during the normal photoperiod, leveling off after 12 hours; however, the activity was not correlated with the rhythmic change in photosynthesis.

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