Articles containing the keyword 'irradiance'

The accompanying collective research report is the result of the research project in 1986–90 between the Finnish Academy and the former Soviet Academy of Sciences. The project was organized around common field work in Finland and in the former Soviet Union, and theoretical analyses of tree growth determining processes. Based on theoretical analyses, dynamic stand growth models were made and their parameters were determined utilizing the field results.

Annual cycle effects the tree growth. Our theoretical approach was based on adaptation to local climate conditions from Lapland to South Russia. The initiation of growth was described as a simple low and high temperature accumulation driven model. The model was linked with long-term temperature data.

Analysis of field measurements of CO₂ exchange showed that irradiance is the dominating factor causing variation in photosynthetic rate in natural conditions during summer. The penetration of irradiance into Scots pine (Pinus sylvestris L.) canopy is a complicated phenomenon. A moderately simple but balanced forest radiation regime sub-model was constructed.

The common field excursions in different geographical regions resulted in a lot of experimental data of regularities of woody structure. The water transport seems to be a good common factor to analyse these properties of tree structure. The produced theoretical and experimental material was utilized in the development of stand growth model that describes the growth and development of Scots pine stands in Finland and the former Soviet Union. The core of the model is carbon and nutrient balances. This means that carbon obtained in photosynthesis is consumed or growth and maintenance and nutrients are taken according to the metabolic need. Since the fundamental metabolic processes are the same in all locations, the same growth model structure can be applied in the large range of Scots pine. The model enables the analysis of geographical differences in the growth of Scots pine. The present approach enables utilization of structural and functional knowledge gained in places of intensive research, in the analysis of growth and development of any stand.

• Hari, E-mail: ph@mm.unknown
• Ross, E-mail: jr@mm.unknown
• Mecke, E-mail: ph@mm.unknown

The dependence of the rates of photosynthesis and transpiration are studied on the environmental factors and on the control of the plant metabolism with Scots pine (Pinus sylvestris L.) in the natural environment. The importance of the different environmental factors to the photosynthetic production are evaluated. In modelling the dependence of the rates of photosynthesis and transpiration on the environmental factors and on the control processes, a dynamic system analysis approach is applied. Irradiance, temperature and water are explored during the annual cycle. Field measurements of the CO₂ exchange and environmental factors over three years are used in the analysis of the rate of the photosynthesis. The effect of different environmental factors on photosynthetic production is evaluated by model estimations using weather data in a 20-year period.

The PDF includes a summary in Finnish.

• Korpilahti, E-mail: ek@mm.unknown

The problems caused by the temporal and spatial microvariation in irradiance during field measurements of photosynthesis are studied. It is concluded on the basis of variation analyses based on irradiance data measured in a Scots pine (Pinus sylvestris L.) stand that the microvariation should be measured by integrating it over the measurement time and space.

However, the curvlinearity of the light response of photosynthesis results in biased estimates when linear integration (mean irradiance) is used. The significance of the bias is examined using a simulation technique on irradiance material. Whether the actual integral of photosynthesis can be approximated with mathematical method is next studied. The method gave satisfactory results only for a low curvature response, but the latter method was applicable also to the high curvature response. However, both methods presuppose that the mean and variance are known. Measurement of the variance is based on integration of the second power.

A new method, where the nonlinearity problem is avoided, is presented to measure fluctuation of the irradiance. The method enables the shoot geometry to be taken into account and it is also applicable to transpiration studies.

The PDF includes a summary in Finnish.

• Smolander, E-mail: hs@mm.unknown