Evaluation of factors controlling net photosynthetic rate in Scots pine seedlings under field conditions without water stress

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Abstract
The ecological importance of different factors generating variation in the photosynthetic rate of a pine seedling (Pinus sylvestris) under nonstressing conditions are evaluated. The data consists of 1,300 observations of the photosynthetic rate and environmental factors possibly affecting photosynthesis. Statistical analysis of the data gave the following results: 1. light solely explained about 90% of the variance of photosynthetic rate during a day, 2. light and temperature together explained about 94% of it and 3. the other factors studied (leakage from the cuvette, different spectral sensitivity of photosynthesis and the monitoring apparatus, high transpiration rate, circadian rhythm and inhibition of photosynthesis by carbohydrates) were not found to be significant from the ecological point of view, since they explain less than 0.5% of the variance.