C₃ Photosynthesis and Crassulacean Acid Metabolism in a Kansas Rock Outcrop Succulent, Talinum calycinum Engelm. (Portulacaceae)

Abstract

The potential for Crassulacean acid metabolism (CAM) was investigated in the sandstone outcrop succulent Talinum calycinum in central Kansas. Field studies revealed CAM-like diurnal acid fluctuations in these plants. These fluctuations persisted under all moisture and temperature regimes in the laboratory. Despite this CAM-like acid metabolism, simultaneous gravimetric determinations of day-and nighttime transpiration rates indicated the presence of a C3 gas exchange pattern. Subsequent analyses of diurnal CO2 and H20 exchange patterns under wellwatered conditions and after 3, 5, and 7 days of drought confirmed these findings, though low rates of nocturnal CO2 uptake were observed on the fifth night after continuous drought. Finally, the 5'3C/'2C value of this succulent, -27.8%o, emphasizes the insignificance of any nocturnal C02 uptake in the lifelong accumulation of carbon in this species. Thus, it is proposed that T. calycinum is a C3 plant with some CAM charcteristics, including the ability to re-fix respiratory CO2 at night under all moisture regimes, potentially resulting in a conservation of carbon, and occasionally to fix atmospheric CO2 at night. These findings may prove to be common among rock outcrop succulents.

Correlation between CAM-Cycling and Photosynthetic Gas Exchange in Five Species of Talinum (Portulacaceae)

“…ther evidence in support of this is found in the negative results confirm the occurrence of CAM-cycling correlation between malic acid fluctuations and net daytime in T. calycinum (10,14), T. parviflorum (10), and T. teretifolium (I13) and demonstrate, for the first time, this phenomenon in T. calcaricum and T. mengesii. This overall physiological similarity among the species is not surprising given their high degree of morphological similarity.…”

“…In certain species, e.g. Talinum calycinum and Sedum nuttallianum, CAM-cycling may be less important as a precursor for CAM-idling because CAM activity is substantially reduced during severe drought stress (12,14). Instead, as initially hypothesized by Cockburn (2), CAM-cycling may effect an increase in the WUE of plants by increasing daytime CQ in the leaves, as a result of the decarboxylation of malic acid, thus reducing stomatal conductance and transpiration.…”

“…Correlations among malic acid accumulation, CO2 assimilation, transpiration, and WUE were examined in 69 plants of five species of Talinum (Portulacaceae). Photosynthesis was examined previously in T. calycinum, which exhibited C3 gas exchange in addition to overnight malic acid accumulation (10,14). Carbon metabolism has not been investigated in the other four species of Talinum, except for reports of acid fluctuations in Talinum teretifolium (13) and Talinum parviflorum (10 …”

Compensation Point and Isotopic Characteristics of C3/C4 Intermediates and Hybrids in Panicum

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ABSTRACT 16,19,[24][25][26][27]Isotope analysis of plant matter provides a powerful method of studying photosynthetic modes. In addition to the well known separation of C3 plants from C4 and CAM plants based on stable carbon isotope ratios (17), oxygen and hydrogen isotope ratios ofcellulose and cellulose nitrate, respectively, also are influenced by photosynthetic mode (20,(22)(23)(24)(25).

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Crassulacean Acid Metabolism in the Gesneriaceae

“…Not all CAM species are found in arid environments; in fact, many occur in xeric microenvironments of mesic regions, such as rock outcrops (Martin and Zee, 1983), and others are tropical epiphytes that periodically become drought stressed (Winter et al, 1983;Sinclair, 1984;Ting et al, 1985). The CAM pathway of photosynthesis occurs in tropical epiphytes of the Bromeliaceae (McWilliams, 1970;Medina and Troughton, 1974), Orchidaceae (Knauft and Arditti, 1969;McWilliams, 1970;Neales and Hew, 1975;Sinclair, 1984), Cactaceae (Wiehler, 1982), Rubiaceae (Winter et al, 1983), and the Piperaceae (Sternberg, Deniro and Ting 1984;Sipes and Ting, 1985).…”