Does Bienertia cycloptera with the single-cell system of C(4) photosynthesis exhibit a seasonal pattern of delta (13)C values in nature similar to co-existing C (4) Chenopodiaceae having the dual-cell (Kranz) system?

Family Chenopodiaceae is an intriguing lineage, having the largest number of C(4) species among dicots, including a number of anatomical variants of Kranz anatomy and three single-cell C(4) functioning species. In some previous studies, during the culture of Bienertia cycloptera Bunge ex Boiss., carbon isotope values (delta(13)C values) of leaves deviated from C(4) to C(3)-C(4) intermediate type, raising questions as to its mode of photosynthesis during growth in natural environments. This species usually co-occurs with several Kranz type C(4) annuals. The development of B. cycloptera morphologically and delta(13)C values derived from plant samples (cotyledons, leaves, bracts, shoots) were analyzed over a complete growing season in a salt flat in north central Iran, along with eight Kranz type C(4) species and one C(3) species. For a number of species, plants were greenhouse-grown from seeds collected from the site, in order to examine leaf anatomy and C(4) biochemical subtype. Among the nine C(4) species, the cotyledons of B. cycloptera, and of the Suaeda spp. have the same respective forms of C(4) anatomy occurring in leaves, while cotyledons of members of tribe Caroxyloneae lack Kranz anatomy, which is reflected in the delta(13)C values found in plants grown in the natural habitat. The nine C(4) species had average seasonal delta(13)C values of -13.9 per thousand (with a range between species from -11.3 to -15.9 per thousand). The measurements of delta(13)C values over a complete growing season show that B. cycloptera performs C(4) photosynthesis during its life cycle in nature, similar to Kranz type species, with a seasonal average delta(13)C value of -15.2 per thousand.

Induction of crassulacean acid metabolism in Mesembryanthemum crystallinum increases reproductive success under conditions of drought and salinity stress.

Mesembryanthemum crystallinum L., an inducible crassulacean acid metabolism (CAM) plant, was grown for approximately 5 weeks following germination in well-watered, non-saline soil in a controlled-environment chamber. During this time, plants were characterized by C3 photosynthetic carbon metabolism. After the initial 5 weeks, CAM was induced by a combination of high soil salinity and reduced soil water content. One group of plants was allowed to engage in CAM by being continuously exposed to normal CO2-containing air (about 350-400 ppm). A second group of plants was deprived of ambient CO2 each night (12 h dark period) until completion of their life cycle, thereby minimizing potential carbon gain via dark CO2 fixation. The capacity to express CAM under conditions of drought and salinity stress markedly improved reproductive success: plants kept in normal CO2-containing air produced about 10 times more seeds than plants kept in CO2-free air during dark periods. Seeds from plants deprived of ambient CO2 overnight had more negative δ13C values than seeds from plants kept in normal air.

Crassulacean acid metabolism in Kalanchoë species collected in various climatic zones of Madagascar: a survey by δ13C analysis.

The carbon isotope compositions of samples of Kalanchoë species collected at the natural stands in Madagascar were determined. The results suggest that all species of the genus Kalanchoë are capable of crassulacean acid metabolism. The observed δ13C values cover the whole range from -10 to -30‰. This high diversity of the δ13C values was found among the species of the genus as well as, in certain cases, within a single species. This suggest that the CAM patterns in Kalanchoë are generally very flexible. The δ13C values show a clear correlation with the climate of the habitats from where the samples derived. Values indicative of CO2 fixation taking place exclusively during the night were found in the dry regions of Madagascar, whereas δ13C values indicative of mixed CO2 fixation during night and day or of CO2 fixation entirely during the day are distributed in the humid zones.

δ13C values of CO2 from soil respiration on sites with crops of C3 and C4 type of photosynthesis.

Based on the differential discrimination between 13CO2 and 12CO2 during photosynthetic CO2 fixation by C3 and C4 plants, the relative contribution of organic soil material of varying age can be checked by measuring the δ13C value of CO2 evolved during soil respiration.The CO2 from a soil cropped only with C3 plants for at least 7 years showed a δ13C value very close to that of C3 plant tissue. Correspondingly, a soil bearing the C4 plant maize for at least 6 years had a δ13C value for the respiratory CO2 quite near to that of a typical C4 plant. A soil cropped with maize in the year of study only showed intermediate δ13C values, with a tendency towards C4. With soil standardised for cultivation and cropping, a quantification of the part that fresh organic matter and especially the last year plant residues play in soil respiration, can be achieved.

Biomass production of C3- and C4-plant species in pure and mixed culture with different water supply.

Pure and mixed cultures of the dicotyledons Atriplex hortensis L. (C3 plant) and Amaranthus retroflexus L (C4) on the one hand and of the grasses Avena sativa L (C3) and Panicum miliaceum L. (C4) on the other hand were maintained in a standard soil with different ground water tables. After 12 weeks the length, dry weight and nitrogen-content of the aboveground and belowground parts of the plants, and in addition the carbon-and ash-content and the δ13C value of the aboveground parts were determined. It turned out that the length and the dry weight of the shoots of the C3 species showed on increasing tendency with increased water supply, while the values of the C4 species were drastically diminished at the highest water level only. The roots showed in most cases an increased length and dry weight at drier conditions, more pronounced in the C4 than in the C3 species. The nitrogen content of the shoots was mostly higher in the shoots of the C3 plants and in the roots of the C4 plants; it changed in a non-regular manner with variations in water supply. Since the carbon content did not change markedly, the C/N ratio was variable. There was a slight tendency for a higher carbon content and mostly also for a higher C/N-ratio in the shoots of C4 plants. The δ13C values of both C3 as C4 plants were in general not at all influenced by the water supply; they were fixed genetically. The ash content of the analyzed species did not show a clear relationship to the type of photosynthetic CO2-fixation or to the water regime.The influence of light intensity was studied with mixed cultures of all four plant species, again with different water supply. There was a strong effect of light intensity on the competitive behaviour of the C3 and C4 plants under modified water conditions. The wild C3 plant Atriplex hortensis was most successful under conditions of relatively low light intensity and high water availability, while the cultivated 'artificial' species Avena sativa showed much less differences between full-light grown and shadow plants. The C4 plant Amaranthus retroflexus is most successful under competitive conditions at high water stress in full light. The C4 grass Panicum miliaceum showed maximum shoot growth in light, but was successful under competitive conditions especially also with good water supply. The light intensity had no effect on the δ13C values. - There was no indication that the soil-type as such has a distinct influence on the success of C3 or C4 plants in mixed cultures.