Some physiological effects of atrazine on Douglas-fir seedlings

Graduation date: 1969This study was undertaken to ascertain some of the physiological\ud effects of the herbicide atrazine on Douglas-fir seedlings.\ud Photosynthetic and respirational rates were measured on seedlings\ud grown in a controlled environment chamber. Height and dry weight\ud increases, shoot/root ratios and percent total nitrogen were obtained\ud from treated and control seedlings growing on field plots.\ud Treatment of Douglas-fir seedlings with subtoxic levels of\ud atrazine caused an initial repression of photosynthesis and respiration,\ud with a subsequent recovery. Seedlings grown in sand and\ud treated with one fourth pound per acre (0.275 ppmw) had rates of\ud both physiological functions which exceeded the controls significantly\ud 36 days after chemical application. Application of one half pound per\ud acre (0.55 ppmw) supressed both photosynthesis and respiration to a\ud great extent, with full recovery occurring only after 36 days.\ud Seedlings grown on forest soils had similar, but less pronounced,\ud responses when treated with much higher concentrations of\ud herbicide. Eight pounds per acre (11.6 ppmw) inhibited photosynthesis\ud for a few days with recovery complete after nine days.\ud Neither photosynthesis nor respiration were markedly altered by\ud lower application rates of atrazine.\ud Atrazine slightly inhibited height growth and dry weight increase\ud the year of application in field plots where seedlings were grown\ud under weed-free conditions. The year following treatment the seedlings\ud exhibited increased growth which compensated for the inhibition\ud noted the first year. The shoot-/root ratios were not altered by atrazine\ud either year. Percent total nitrogen was increased by the application\ud of the herbicide the year of treatment but there were no significant\ud differences the second year