Physiological Characteristics of Photosynthesis and Respiration in Stems of Populus tremuloides Michx.

Abstract

The physiological responses of 6-to 8-year-old aspen (Populus tremuloides Michx.) stems to temperature, light, and CO2 concentration were investigated in the field throughout the year using infrared CO2 analysis. Light response studies showed that the rate of gross photosynthesis was linear from 0 to 400 ft-c (0 to 1.6 mw/cm2 of 400-700 nm) with light saturation being reached between 800 to 1400 ft-c (3.2 to 5.6 mw/cm2 of 400-700 nm). At this light intensity, the respiratory CO2 loss was reduced to 10 to 15% of dark rates. Net photosynthetic CO2 uptake was not observed even at intensities as high as 3400 ft-c (13.6 mw/cm2 of 400-700 nm). The light response curve was similar for both winter and summer stems.During summer months, the respiratory and photosynthetic rates of the aspen stem increased with temperature at a near constant rate between 5 and 35 C. For winter stems, the gross photosynthetic rate increased in a pattern similar to the dark respiratory rate as the temperature rose from 3 to 17 C. Below 0 C and above 17 C, however, the gross photosynthetic rate feD off in relation to the respiratory rate so that the per cent of CO2 reassimilated decreased from 75% to less than 50%. Measurable bark photosynthetic activity was not observed below -3 C.The gross photosynthetic rate of stems was not affected when the gas passing through the cuvette contained concentrations of CO2 ranging from 0 to 580 ,ul CO2/l air.Twigs and stems of living shrubs and trees have a greenish corticular layer just beneath the bark surface. The green pigment is Chl which is concentrated in photosynthetically active chloroplasts (17). Photosynthesis by the stem is termed corticular photosynthesis (20) or bark photosynthesis.Most species in which bark photosynthesis has been investigated were not capable of net photosynthesis, but stem photosynthesis did reduce substantially the respiratory loss of CO., from the stem (1, 8-10, 13, 16, 19 No fertilizer was added in 1973. The trees were watered every 1 to 3 days so that the soil moisture tension in each box was maintained between 0 and 100 centibars. Extensive use of the trees was started 1 year after the transplanting to allow for site adjustment. The boxed trees were healthy and vigorous as evident from the rates of shoot growth, the color and size of the leaves, and the width of the growth rings. Bud break occurred April 18 to 25, 1973; leaf fall, October 12 to 26, 1973. Bark slippage commenced in mid-April and ceased in October. Stem diameters were observed to increase from mid-May through mid-August.Photosynthetic and respiratory CO, exchange rates were measured using a 30-cm, water-cooled, acrylic plastic cuvette consisting of two halves that could be placed around the stem and sealed with no apparent injury to the stem (5). To reduce water, CO2, and heat gradients within the cuvette, an air recirculation system was used with the cooling coils submerged in water or a water-ethanol mixture depending on the operating temperature (5).An open system was used from June to Augus...

Diurnal and Seasonal Patterns of Photosynthesis and Respiration by Stems of Populus tremuloides Michx.

“…All on the Syracuse campus. The silvicultural treatment of these trees has been previously described (7). For clonal comparisons, trees representing three other clones were also planted in boxes at the same site and treated similarly to clone PH.…”

“…Climatological parameters measured were light intensity at the cuvette, temperatures on the north and south sides of the stem within, and on a stem adjacent to the cuvette (7). Stem temperatures in Figures 1 to 4 hr.…”

“…It appears that most of the CO2 used in bark photosynthesis comes from stem respiration rather than the atmosphere. Such an internal source of CO2 is suggested by the considerable higher concentration of CO2 inside the sapwood of the tree (1), the high diffusion resistance of the bark to gases (13,21), the lack of a response of aspen bark photosynthesis to outside CO2 concentrations as high as 580 ,tl C02/1 of air (7), and the low rate of incorporation of externally supplied "4CO2 into stem bark tissue (21). If the source of CO2 is internal rather than external, those factors affecting the respiratory rate such as temperature and stem ontogeny would also affect the amount of CO2 available for bark photosynthesis.…”

“…For the entire year, 28.7% of the respiratory CO2 loss was reduced by bark photosynthesis on a daytime basis. On a 24-hr basis, the amount of CO2 reassimilated is estimated to be 16 to 18% based on nocturnal respiratory studies, night temperatures of the 45 diurnal assays, and seasonally determined dark respiratory rate temperature curves (7).…”

Seasonal Acclimation of Stem Photosynthesis in Woody Legume Species from the Mojave and Sonoran Deserts of California

“…In this article we define stem P n as occumng in a stem with abundant epidermal stomata that has net C 0 2 accumulation from the atmosphere (Gibson, 1983;Osmond et al, 1987;Nilsen and Bao, 1990). In contrast, corticular P n (Strain and Johnson, 1963), earlier termed bark Pn (Pearson and Lawrence, 1958), occurs in stems without frequent epidermal stomata and there is no net carbon gain from the atmosphere (Foote and Scheadle, 1976;Coe and McGlaughlin, 1980;Han and Suzaki, 1981). The importance of both stem and corticular P n to canopy carbon gain has been documented in species from a diversity of habitats (Pearson and Lawrence, 1958;Strain and Johnson, 1963;Mooney and Strain, 1964;Adams and Strain, 1968;Foote and Scheadle, 1976;Coe and McGlaughlin, 1980;Han and Suzaki, 1981;Nilsen et al, 1989;Nilsen, 1992a).…”