1975. The occurrence of functional non-chlorophyllous guard cells in Paphiopedilrrm spp. Can. J . Bot. 53: 1-7. Hypostomatous lady slipper orchids, Paphiopedilum spp., were found to have nonchlorophyllous epidermal cells, including guard cells. The lack of chlorophyll within the guard cells was demonstrated by fluorescence microscopy. A "normal" chlorophyllous mesophyll was present. The leaf resistances of intact leaves were about 5-10 s cm-I in the light and were greater than 100 s cm-I in the dark, indicating light opening and dark closure of the stomata. A CO2-dependent stomatal response (i.e., a tendency to close at elevated CO2 levels) was demonstrated, as was a C02-independent light response (i.e., greater opening in blue light than in red). This provides direct evidence to support the idea that guard cell chlorophyll is not necessary for stomatal functioning. NELSON, S. D., et J. M. MAYO. 1975. The occurrence of functional non-chlorophyllous guard cells inPaphiopedilum spp. Can. J. Bot. 53: 1-7. Des orchidCes hypostomatiques du genre Paphiopedilum ont des cellules epidermiques nonchlorophylliennes, y compris les cellules de garde. L'absence de chlorophylle dans les cellules de garde a kt6 d8montrCe par microscopie en fluorescence. I1 y a un mesophylle chlorophyllien "normal." La resistance foliaire des feuilles intactes est d'environ 5-10 s cm-I B la lumikre et est superieure a 100 s cm-I ? iI'obscuritC, ce qui montre que les stomates s'ouvrent a la lumibre et se ferment i l'obscuritk. Une riponse stomatique like au C02 (tendance B se fermer aux concentrations ilevees de CO2) a t t e demontree, ainsi qu'une rCponse B la lumikre independante du CO2 (une ouverture plus grande en lumibre bleue qu'en lumibre rouge). Ces donnCes apportent des preuves directes que la chlorophylle des cellules de garde n'est pas nkcessaire au fonctionnement des stomates.[Traduit par le journal]

Relatively little work has been done to evaluate the effects of chronically high levels of carbon dioxide on growth and physiology of woody plants. In this study, seedlings of lodgepole pine (Pinuscontorta Dougl. var. latifoliaEngelm.) were grown for 5-month periods at 330, 1000, or 2000 μL CO2•L−1. Height growth; leaf area production; biomass of leaves, stems, and roots; and photosynthetic responses to changing light, moisture, and CO2 concentration were measured. Significant differences between treatments were found in mean seedling height on all measurement dates. Seedlings grown at 1000 μL CO2•L−1 were tallest, with seedlings grown in 2000 μL•L−1 intermediate between the control (330 μL•L−1) and 1000 μL•L−1 treatments. The same relationship was found in production of total leaf surface area. Increased leaf surface area yields a productive advantage to seedlings grown at concentrations of CO2 up to 2000 μL•L−1 even if no increase in net photosynthesis is assumed. Biomass of stems, roots, and secondary leaves was increased in both elevated CO2 conditions, with root biomass approximately 15 times greater in seedlings grown at 1000 μL•L−1 than in those grown at 330 μL•CO2•L−1. Stomatal resistances were essentially the same for all treatments, indicating no CO2-induced stomatal closure to at least 2000 μL•L−1. Photosynthetic Vmax (milligrams per square decimetre per hour) for light response curves varied with CO2 concentration. If results are extrapolated beyond a 5-month period and into field conditions, it appears that size of trees, interactions with competitors, and ecological role of the species might be altered.

The effect of water stress on the moss Dicranum polysetum Sw. was studied in the growth chamber, and water potential (ψ) was found to vary as much as 15 atm between the tip of the plant and areas 2 to 4 cm within the cushion, which suggests that very little water is transported from the base of the stem to its tip. With an infrared gas analyzer it was determined that photosynthesis ceases at −21 to −23 atm and the moss remains dormant until it is rewetted. Upon rewetting, there is a sharp burst of respiration that doubles the normal CO2 output. This burst reached its maximum level of 4 mg CO2 g−1 h−1 within 15 min and was of short duration. Full photosynthetic rate was restored in 8 h.

No abstract

Net CO2 assimilation and water relations of Dryas integrifolia from Devon Island, N. W. T., were studied under controlled-environment conditions. Maximum net CO2 assimilation rate for single leaves was 18.7 mg g−1h−1. The optimum leaf temperature for net CO2 assimilation was between 9 and 14 °C. Positive net CO2 assimilation occurred at −5 °C. Respiration and net CO2 assimilation decreased with the onset of dormancy. Dark respiration was generally equal to or greater than that of other arctic and alpine species. The mean leaf water potential of actively growing plants was −11.4 bars. Values higher than −7 bars were found only infrequently. Turgor pressure was maintained at high values (+6 to +10 bars) over a wide range of water potentials, suggesting osmotic adjustment to soil moisture deficit.