The seasonal pattern of CO2 exchange of Festuca rubra L. in a montane meadow community in Northern Germany

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Abstract
Completely climatized cuvettes were used to follow the CO2 gas exchange of red fescue (Festuca rubra L.), growing on a fertilized and an unfertilized plot, during a growing season from May through October. Objective of the study was to determine the effect of environmental factors on the seasonal CO2 gas exchange. Gas exchange rates were calculated on the basis of leaf dry weight, surface area and chlorophyll content. Photosynthetic rates differed between the fertilized and unfertilized plants when based on leaf dry weight or leaf surface area but were similar when based on chlorophyll. Multiple regression analysis was used to related photosynthetic rates to radiation, temperature, water vapor concentration difference, chlorophyll content and time. A cubic regression equation based on daily radiation alone explained 85% of the variation for the fertilized plants and 87% of the variation for the unfertilized plants. During the growing season the unfertilized plants had a continual decline in their photosynthetic rates. The fertilized plants had high photosynthetic rates in the spring and in the fall. Light response curves indicated greater photosynthetic rates at light saturation as well as in the light limited portion of the light response curve for the fertilized plants. Photosynthetic rates of the fertilized plants were generally depressed during periods of warm temperature and high light intensity in June and July. Photosynthetic rates declined at temperatures above 24°C. The decline was greater for the more mesomorphic fertilized plants. A similar response was noted to increasing water vapor difference, although it was difficult to separate from the temperature effect. Maximum photosynthetic rates were found between 14°C and 22°C, although there was considerable variation in the maximum rates. The effects of cutting (mowing) on the gas exchange were difficult to determine due to the interaction of the environmental factors. Chlorophyll content showed significant correlation with photosynthetic rates.