Stomata1 resistance, photosynthesis and water relations in mountain birch in the subarctic

The role of water in regulating stomata1 aperture and carbon assimilation of mountain birch (Betzda pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman) was studied in the Swedish Subarctic. Stomata exhibited a clear response to changes in humidity and water potential. High evaporative demand caused stomata1 closure at midday. The diurnal curve of net photosynthesis, measured on a warm day in early July, had two peaks, and photosynthetic rate was reduced by 2530 % at midday