Environmental and Experimental Botany, Vol. 22, No. 2, pp. 143 to 154, 1982 0098-8472/82/020143-12 $03.00/0 Printed in Great Britain ~) 1982. Pergamon Press Ltd. EFFECTS OF MULTIPLE 0 3 EXPOSURES ON CARBOHYDRATE AND MINERAL CONTENTS OF LADINO CLOVER*t UDO BLUM~, GARY R. SMITH and ROGER C. FITES§ Botany Department, North Carolina State University, Raleigh, NC 27650, U.S.A. (Received 16 June 1980; in revised form 18 March 1981; infinal form 21 May 1981) BLUM U., SMITHG. R. and FITESR. C. The effects of multiple 03 exposures on carbohydrate and mineral contents of ladino clover. ENVIRONMENTALAND EXPERIMENTAL BOTANY 22, 1 4 3 - 1 5 4 . - - L a d i n o clover plants of various ages were exposed for 5 consecutive days for 6 hr/day to either carbon- filtered air or 0.1 ppm 0 3 during one of two growth periods (August or April). The plants were grown during June-August and during January~pril. Plants were harvested 1 week after receiving the final 0 3 exposure. Ozone reduced root, shoot and plant dry weights and total non- structural carbohydrate (TNC, mg/g). Root TNC was not modified by 03. When 03 induced reductions were expressed on a per cent basis, the reductions were identical for the two experimental growth periods. Plant size and TNC content were greater for plants grown during the January-April growth period whereas mineral content (% or ppm) was greater in plants from June to August. When mineral content was altered by 0 3 (and this varied with growth period), 0 3 increased mineral content except for reductions in plant Na (during June-August growth period) and shoot S (determined only for January-April growth period). The potential effects of multiple 0 3 exposures on forage quality and quantity are discussed. INTRODUCTION LADINO clover (Trifolium repens L. cv Tillman), a common forage legume grown alone or in combi- nation with grass, has a number of excellent characteristics: long growing season, perennial nature, rapid recovery after drought, high carbo- hydrate and mineral contents, and 20-30% pro- tein content, ls'6~ Ozone (O3) , an ubiquitous air pollutant, inhibits growth and nodulation, re- duces total plant nitrogen, and reduces the corn- petitive ability of clover grown in association with grasses. ~2'11'x2) In other species 0 3 has been shown to modify mineral, carbohydrate, and/or vitamin contentJ 15'18) Given the economic im- portance of this forage crop, it is important that the full impact of 0 3 on forage quality and quantity be elucidated and understood. This study was designed to determine the effects of multiple low level 0 3 exposures on carbohy- drate and mineral content of clover. Emphasis was placed on these constituents in as much as *Cooperative investigations of North Carolina Agricultural Research Service at Raleigh, the U.S. Department of Agriculture, Raleigh, NC 27650. tPaper No. 6466 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, North Carolina. :~Physiological Ecologist. §Plant Physiologist. Mention of trade or company names does not constitute a guarantee or warranty of the product by U.S. Department of Agriculture, or the North Carolina Agricultural Research Service and does not imply their approval to the exclusion of other products that may be suitable. 143