Chamber effects and responses of trees in the experiment using open top chambers

Chamber effects are unintentional concomitants of experiments using open-top field chambers (OTCs). Cylindrical OTCs were used in a mountain Norway spruce stand. Chamber effects were investigated as well comparing samples in OTCs with ambient air and samples not enclosed in OTCs (control). The OTCs were 2.5 m in diameter at the base, 6.0 m high and the volume was 20 m(3). The iron frames were covered by transparent 0.2 mm PVC film. Changes of growth conditions as follows: Transmission of the chambers covered by a new clear film was 91 +/- 2% of the solar photosynthetically active radiation (84 +/- 4% at the end of the growing season). Mean air temperatures inside OTCs were 1.3 degrees C higher than outside OTCs on sunny days. Inside there were decreases in relative humidity during the sunny hours by as much as 10%. Responses of the trees as follows: Continual increase of chlorophyll content (a + b) tvas recorded during the cultivation of the trees in the OTCs in comparison with the control (76%). A similar situation was observed for the carotenoids content. We recorded seasonal increases of F-v/F-max values and the t(1/2) parameter in the OTCs in comparison with the control treatment. At the beginning of the seasons (1993 and 1994) stem respiration was greater in the control than in the OTC (70% and 85% of the control) but at the end of the seasons the situation was opposite (115% and 230% of the control). No differences were found in the development of apical shoots. Differences were found only in length increases of whorl branches, in the season 1994 (p=0.01). The length increase in the OTCs was greater by 38%.