Nocturnal CO2 Uptake Research Articles

Influence of Applied NaCl on Crassulacean Acid Metabolism and Ionic Levels in a Cactus, Cereus validus

To determine possible physiological responses to salinity, seedlings of Cereus validus Haworth, a cactus from Salinas Grandes, Argentina, were treated with up to 600 millimolar NaCl for up to 16 days when they were about 9 months old and 100 millimeters tall. Salt stress decreased stem biomass, e.g. it was 19.7 grams for controls and 11.4 grams for plants treated with 400 millimolar NaCl for 14 days. Nocturnal CO(2) uptake in these obligate Crassulacean acid metabolism (CAM) plants was inhibited 67% upon treatment with 400 millimolar NaCl for 14 days (controls, 181 millimoles CO(2) per square meter), while nocturnal accumulation of malate was inhibited 49% (controls, 230 millimoles malate per square meter). The larger accumulation of malate as compared to uptake of atmospheric CO(2) suggests that internal CO(2) recycling occurred during the dark period. Such recycling was lower in the controls ( approximately 20%) than in the NaCl-treated plants ( approximately 50%). The nocturnal increase in malate and titratable acidity depended on the total daily photosynthetically active radiation available; measurements suggest a quantum requirment of 26 photons per malate. As NaCl in the medium was increased to 600 millimolar in daily increments of 50 millimolar, Na and Cl concentrations in the roots increased from about 7 to 100 millimolar, but K concentration in the cell sap remained near 26 millimolar. Concomitantly, concentrations of Na and Cl in the shoots increased from 8 to 17 millimolar and from 1 to 7 millimolar, respectively, while the K concentration increased about 16 to 60 millimolar. In plants maintained for 14 days at 500 millimolar NaCl, the root levels of Na and Cl increased to 260 millimolar, the shoot levels were about 60 millimolar, and the stem bases began to become necrotic. Such Na retention in the roots together with the special possibilities of carbon reutilization given by CAM are apparently survival mechanisms for the temporarily saline conditions experienced in its natural habitat.

Influence of Photoperiod and Leaf Age on Crassulacean Acid Metabolism in Portulacaria afra (L.) Jacq.

The possibility that Crassulacean acid metabolism (CAM) is subject to long day photoperiodic control in Portulacaria afra (L.) Jacq., a facultative CAM plant, was studied. Periodic measurements of (14)CO(2) uptake, stomatal resistance, and titratable acidity were made on plants exposed to long and short day photoperiods. Results indicates that waterstressed P. afra had primarily nocturnal CO(2) uptake, daytime stomatal closure, and a large diurnal acid fluctuation in either photoperiod. Mature leaf tissue from nonstressed plants under long days exhibited a moderate diurnal acid fluctuation and midday stomatal closure. Under short days, there was a reduced diurnal acid fluctuation in mature leaf tissue. Young leaf tissue taken from nonstressed plants did not utilize the CAM pathway under either photoperiod as indicated by daytime CO(2) uptake, lack of diurnal acid fluctuation, and incomplete daytime stomatal closure.The induction of CAM in P. afra appears to be related to the water status of the plant and the age of the leaf tissue. The photosynthetic metabolism of mature leaves may be partly under the control of water stress and of photoperiod, where CAM is favored under long days.

Physiological responses of Opuntia ficus‐indica to growth temperature

The influences of various day/night air temperatures on net CO2 uptake and nocturnal acid accumulation were determined for Opuntia ficus‐indica, complementing previous studies on the water relations and responses to photosynthetically active radiation (PAR) for this widely cultivated cactus. As for other Crassulacean acid metabolism (CAM) plants, net nocturnal CO2 uptake had a relatively low optimal temperature, ranging from 11°C for plants grown at day/night air temperatures of 10°C/0°C to 23°C at 45°C/35°C. Stomatal opening, which occurred essentially only at night and was measured by changes in water vapor conductance, progressively decreased as the measurement temperature was raised. The CO2 residual conductance, which describes chlorenchyma properties, had a temperature optimum a few degrees higher than the optimum for net CO2 uptake at all growth temperatures. Nocturnal CO2 uptake and acid accumulation summed over the whole night were maximal for growth temperatures near 25°C/15°C, CO2 uptake decreasing more rapidly than acid accumulation as the growth temperature was raised. At day/night air temperatures that led to substantial nocturnal acid accumulation (25°C/15°C.). 90% saturation of acid accumulation required a higher total daily PAR than at non‐optimal growth temperatures (10°C/0°C and 35°C/25°C). Also, the optimal temperature of net CO2 uptake shifted downward when the plants were under drought conditions at all three growth temperatures tested, possibly reflecting an increased fractional importance of respiration at the higher temperatures during drought. Thus, water status, ambient PAR, and growth temperatures must all be considered when predicting the temperature response of gas exchange for O. ficus‐indica and presumably for other CAM plants.

CO2 exchange of CAM exhibiting succulents in the southern Namib desert in relation to microclimate and water stress

The responses of CO2 exchange and overnight malate accumulation of leaf and stem succulent CAM-plants to water stress and the particular climatic conditions of fog and föhn in the southern Namib desert have been investigated. In most of the investigated CAM plants a long term water stress gradually attenuated any uptake of external CO2 and led to CO2 release throughout day and night. No CAM-idling was observed. Rainfall or irrigation immediately restored daytime CO2 uptake while the recovery of the nocturnal CO2 uptake was delayed. Dawn peak of photosynthesis was only found in well watered plants but was markedly reduced by the short term water stress of a föhn-storm. Morning fog with its higher diffuse light intensity compared with clear days increased photosynthetic CO2 uptake considerably. Even in well watered plants nocturnal CO2 uptake and malate accumulation were strongly affected by föhn indicating that the water vapour pressure deficit during the night determines the degree of acidification.

Limited photosynthetic plasticity in Sedum pulchellum Michx.

Carbon dioxide exchange pattern, carboxylating enzyme specific activity and titratable acidity were measureed for field collected individuals of Sedum pulchellum Michx., a winter annual of xeric cedar glade communities in central Tennessee. Evidence of a weak-CAM mode of photosynthesis was found on 4 of 27 sampling dates during a three year period. Three of these dates occurred during 1978, the driest study season, and nocturnal CO2 uptake contributed a maximum of 10% of the plants daily CO2 uptake. Weak CAM in the field was associated with elevated phosphoenol-pyruvate (PEP) carboxylase activity and, to a lesser degree, with decreased ribulose bisphosphate (RuBP) carboxylase activity. In contrast, carboxylating enzyme specific activities of the sympatric, obligate CAM species Opuntia compressa, a dominant perennial of the cedar glades, were highly stable.Weak CAM was also induced in S. pulchellum upon water stress in the laboratory. Again, weak CAM was associated with elevated PEP carboxylase and decreased RuBP carboxylase activities and represented a relatively minor CO2 uptake contribution. The potential ecological significance of this limited photosynthetic flexibility in S. puchellum is not obvious but it may play an important role in successful yearly reproduction in this annual species at a time when water stress is frequent.

Crassulacean Acid Metabolism in Orchids under Water Stress

The effect of water stress on the Crassulacean acid metabolism of tropical orchids was examined. Imposition of water stress in young and adult thick-leaved orchids caused a reduction in the titratable acidity (TA) of the leaves. The reduction in TA of orchids under water stress was correlated with a decrease in nocturnal CO2 uptake. The relative contribution of night and day CO2 assimilation in these orchids varied with water availability. Under severe water stress, CO2 assimilation was greatly reduced and exclusively nocturnal. Rewatering restored both CO2 assimilation and TA.

Shifts in the optimal temperature for nocturnal CO2 uptake caused by changes in growth temperature for cacti and agaves

When the day/night air temperatures were raised from 10°C/10°C to 30°C/30°C, the optimal tempearture for nocturnal CO2 uptake by six species of cacti and three species of agave shifted from an average of 12°C to an average of 20°C. The maximum rate of CO2 uptake was higher for Agave americana at the higher ambient temperature, lower for A. deserti, and much lower for A. utahensis, consistent with the relative mean temperatures of their native habitats. For the cactus Coryphantha vivipara, which had the greatest temperature shift observed (13°C), the halftime was 8 days for the upward shift and 4 days for the downward shift. The halftimes for the comparable shifts averaged 1.6 days for three other species of cacti and less than 1 day for two agave species. The shifts in the optimal temperature for nocturnal CO2 uptake were in response to changes in nighttime temperature, at least for C. vivipara, and reflected temperature responses of both the stomates and the chlorenchyma.

Crassulacean Acid Metabolism in the Epiphyte Tillandsia usneoides L. (Spanish Moss)

Patterns of CO(2) exchange in Spanish moss under various experimental conditions were measured using an infrared gas analysis system. Plants were collected from a study site in North Carolina and placed in a gas exchange chamber for several days of continuous measurements. No substantial seasonal effects on CO(2) exchange were observed. High rates of nocturnal CO(2) uptake were observed under day/night temperature regimes of 25/10, 25/15, 25/20, 30/20, and 35/20 C; however, daytime temperatures of 40 C eliminated nighttime CO(2) uptake and a nighttime temperature of 5 C eliminated nocturnal CO(2) uptake, regardless of day temperature. Constant chamber conditions also inhibited nocturnal CO(2) uptake. Constant high relative humidity (RH) slightly stimulated CO(2) uptake while low nighttime RH reduced nocturnal CO(2) uptake.Reductions in daytime irradiance to approximately 25% full sunlight had no effect on CO(2) exchange. Continuous darkness resulted in continuous CO(2) loss by the plants, but a CO(2) exchange pattern similar to normal day/night conditions was observed under constant illumination. High tissue water content inhibited CO(2) uptake. Wetting of the tissue at any time of day or night resulted in net CO(2) loss. Abrupt increases in temperature or decreases in RH resulted in sharp decreases in net CO(2) uptake.The results indicate that Spanish moss is tolerant of a wide range of temperatures, irradiances, and water contents. They also indicate that high nighttime RH is a prerequisite for high rates of CO(2) uptake.