YIELD COMPONENTS AND FLUORIDE ACCUMULATIO N IN STANDARDIZED GRASS CULTURES AS INFLUENCED BY METHODOLOGICAL VARIATIONS AND ENVIRONMENTAL-FACTORS

Standardized grass cultures of varying seeding densities and sward dia meters were exposed in two trials for two and four weeks, respectively , under open field conditions as well as in a small greenhouse and in a wind tunnel. Among the yield components studied, number of leaves pe r plant and specific longitudinal leaf weight were most responsive to light intensity which declined in the order 'open field' > 'greenhouse ' > 'wind tunnel'. Increasing seeding density and sward diameter showe d a tendency to enhance the effects of reduced irradiation. Increasing the wind speed in the wind tunnel resulted in a reduction of leaf len gth, which was otherwise enhanced due to insufficient irradiation. Ave rage fluoride contents of 189 and 275 mug/g dry matter were analyzed i n grass cultures after continuous exposure to 1.10 mug HF/m3 in the gr eenhouse and 1.35 mug HF/m3 in the wind tunnel, respectively. Fluoride uptake into the grass depended on the position within the enlarged sw ards and the exposure to the wind direction, presumably due to altered deposition fluxes. As a result it is suggested to discontinue the use of clean-air chambers or filtered-air greenhouses as control treatmen ts for the exposures of grass cultures, since altered light conditions and deposition fluxes in these environments are likely to cause consi derable bias. As an alternative the utilization of unshaded open-top c hambers with high air exchange rates or field exposure systems is sugg ested.