Articles containing the keyword 'light intensity'

The effect of photon flux density on bud dormancy release in two-year-old seedlings of Norway spruce (Picea abies (L.) H. Karst.) was examined. The seedlings were first chilled for 0–21 weeks under natural conditions and then forced in a warm greenhouse either in low (15 μEm^-2s^-1) or in high (300 μEm^-2s^-1) photon flux density. Occurrence of bud burst was observed in the forcing conditions, and the observations were used for estimating the cumulative frequency distribution of the chilling requirement for growth competence. The estimated distribution had greater variance in the low photon flux density than in the high photon flux density forcing. This finding suggests that unnaturally low photon flux densities during forcing may yield overestimates of the genetic within-population variation in the chilling requirement for growth competence.

The PDF includes an abstract in Finnish.

• Höyhtyä, E-mail: rh@mm.unknown
• Hänninen, E-mail: hh@mm.unknown

The aim of the present paper was to study the annual production of Pleurozium schreberi (Brid.) Mitt., Hylocomnium splendens (Hedw.) B.S.G and Dicranum polysetum Sw. as a function of light available for photosynthesis. The productivity of the above moss species is studied using the harvested quadrats method in Norway spruce (Picea abies) stands of the Myrtillus site type representing different stand density classes (basal area from 0 to 34 m2/ha) in Southern Finland.

The annual production of each species in different stands was correlated with the amount of light available for photosynthesis i.e. with the photosynthetic production. Functions for the dependence of productivity on light conditions were produced for each species. The individual functions and their ecological significance is discussed. The adaptation of each species to low light intensity is evident since no meaningful addition to production takes place when the photosynthetic light ratio reaches values greater than 0.3–0.4. In other words, the level of photosynthesis which is 30–40% of that possible in the open, provides sufficient supply of carbohydrates or the basic functions of the moss species studied. Pleurozium schreberi and Dicranum polysetum seem to have greater light requirements than Hylocomnium splendens.

The PDF includes a summary in Finnish.

• Kellomäki, E-mail: sk@mm.unknown
• Hari, E-mail: ph@mm.unknown
• Väisänen, E-mail: ev@mm.unknown

The photosynthetic rate of Pleurosium schreberi (Willd.), Hylocomnium splendens (Hedw.) and Dicranum undulatum (Sw.) grown in plastic containers was monitored with infrared gas analyser in open air under natural weather conditions. It proved that the photosynthetic rate of wet moss cushions was satisfactorily predicted by temperature and light intensity. In dry moss cushions this kind of model gave too high an estimate for photosynthetic rate. Water requirements of each moss species were found to be moderate, and water content of moss cushions limited photosynthetic rate only under serious water deficiency.

The PDF includes a summary in Finnish.

• Kellomäki, E-mail: sk@mm.unknown
• Hari, E-mail: ph@mm.unknown

Light intensity inside the canopy varies considerably both in space and time. A new apparatus was developed which is disturbed as little as possible by the above-mentioned variation. The construction is based on the linear relationships between light intensity (measured using silicon diodes) and photosynthesis. This procedure permits linear operations (summing and integration) to be carried out on the output of the diodes without any loss of accuracy. There are five diodes in each assimilation chamber. A model, in which the independent variables include ligth, measured with the present equipment, and temperature, fits the photosynthetic rates well even inside the canopy.

The PDF includes a summary in Finnish.

• Hari, E-mail: ph@mm.unknown
• Huhtamaa, E-mail: mh@mm.unknown
• Pelkonen, E-mail: pp@mm.unknown
• Pohjonen, E-mail: vp@mm.unknown
• Salminen, E-mail: rs@mm.unknown