CHAMBER EFFECTS AND RESPONSES OF TREES IN THE EXPERIMENT USING OPEN-TOP CHAMBERS

Chamber effects are unintentional concomitants of experiments using op en-top field chambers (OTCs). Cylindrical OTCs were used in a mountain Norway spruce stand. Chamber effects were investigated as well compar ing 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 grow ing season). Mean air temperatures inside OTCs were 1.3 degrees C high er than outside OTCs on sunny days. Inside there were decreases in rel ative humidity during the sunny hours by as much as 10%.Responses of t he trees as follows: Continual increase of chlorophyll content (a + b) tvas recorded during the cultivation of the trees in the OTCs in comp arison with the control (76%). A similar situation was observed for th e carotenoids content. We recorded seasonal increases of F-v/F-max val ues and the t(1/2) parameter in the OTCs in comparison with the contro l treatment. At the beginning of the seasons (1993 and 1994) stem resp iration 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 (11 5% and 230% of the control). No differences were found in the developm ent 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%.