Opuntia basilaris

Abstract: Measurements of internal gas phase CO(2) concentration, stomatal resistance, and acid content were made in Crassulacean acid metabolism plants growing under natural conditions. High CO(2) concentrations, sometimes in excess of 2%, were observed during the day in a range of taxonomically widely separated plants (Opuntia ficus-indica L., Opuntia basilaris Engelm. and Bigel., Agave desertii Engelm., Yucca schidigera Roezl. ex Ortiges, Ananas comosus [L.] Merr., Aloe vera L., Cattleya sp. and Phalanopsis sp.) and below ambient air concentrations were observed at night.Stomatal resistance was always high when CO(2) concentration was high and experiments in which attempts were made to manipulate internal CO(2) concentrations gave data consistent with stomatal behavior in Crassulacean acid metabolism being controlled by internal CO(2) concentration. Exogenous CO(2) applied in darkness at a concentration similar to those observed in the light caused stomatal resistance to increase.In pads of Opuntia basilaris Engelm. and Bigel. subjected to severe water stress internal gas phase CO(2) concentrations exhibited fluctuations opposite in phase to fluctuations in acid content. Stomatal resistance remained high and the opening response to low CO(2) concentration was almost entirely eliminated.

Abstract: Acid metabolism and gas exchange studies were conducted in situ on the cactus Opuntia basilaris Engelm. and Bigel. A pattern of significant seasonal variation was evident. The pattern was controlled by rainfall, which significantly influenced plant water potentials, total gas transfer resistances, and nocturnal organic acid synthesis. In winter and early spring, when plant water stress was mild, stomatal and mesophyll resistances remained low, permitting enhanced nocturnal assimilation of 14CO2. The day/night accumulation of acidity was large during these seasons. In summer and fall, plant water stress was moderate, although soil water stress was severe. The nocturnal assimilation of 14CO2 was very low during these seasons, even in stems with open stomata, indicating large mesophyll resistances restricting exogenous gas incorporation. The day/night accumulation of acidity was reduced, and a low level of acid metabolism persisted throughout this period. The rapid response to a midsummer rainfall emphasizes the importance of plant water potential as a parameter controlling over-all metabolic activity. The seasonal variations of acid metabolism and gas exchange significantly influenced the efficiency of water use and carbon dioxide assimilation. Periods of maximal efficiency followed rainfall throughout the course of the year.

Abstract: An immediate, marked response to small amounts of rainfall occurs in Opuntia basilaris, despite previous drought conditions. The effect of rainfall is upon plant water potential, which is the single most important parameter influencing stomatal opening, C02 assimilation, and organic acid synthesis. Nocturnal stomatal opening is initiated following rainfall, and stomata remain open during the daytime. Decreasing stomatal and mesophyll resistances correlate with increasing rates of nocturnal assimilation of 14CO2. Photosynthetic rates of 14CO2 assimilation are low, despite high plant water potentials and low stomatal diffusion resistances. The decreased mesophyll resistances and increased rates of nocturnal 14CO2 assimilation correlate with the increases of nocturnal efficiency of water use and CO2 assimilation. The diurnal efficiency of water use and CO2 assimilation is lower than the nocturnal gas exchange efficiency values.

Abstract: Measurements of acid metabolism and gas exchange were carried out four times during a year to assess the relative importance of temperature and the accompanying seasonal change to the carbon metabolism of Opuntia basilaris Engelm. & Bigel. plants growing in situ under irrigated and natural (control) conditions. Our experiments showed that this cactus did not change its pattern of carbon assimilation when continuously irrigated under field conditions. Non-irrigated cacti had maximum acid accumulation after periods of precipitation. Maximum acid accumulation in irrigated cacti occurred when there was a large difference between day/night temperatures (i.e., 16°C), and when nighttime temperatures were moderate (14C). Irrigated cacti had greater duration of stomatal opening and lower resistance to 14CO2 uptake. When temperatures were low, daytime stomatal resistance to 14CO2 uptake decreased (to 20-40 s cm-1), but never to the level of the nocturnal resistances (5-10 s cm-1). During periods of drought, nonirrigated cycti changed to a pattern in which organic acids fluctuated. Irrigated cacti continued to have 14CO2 uptake when nighttime temperatures were as high as 33°C. 13C/12C isotope composition ratios, determined after two years of irrigation, were near -12‰ in irrigated and non-irrigated plants. Therefore, under conditions of continual irrigation, seasonal and temperature changes affected the degree of dark CO2 fixation and acid metabolism, but these cacti did not change from CAM to CO2 fixation in the light.