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CROP PHYSIOLOGY & METABOLISM

Tropospheric Ozone and Interspecific Competition between Yellow Nutsedge and Pima Cotton

^a Dep. of Botany and Plant Sci. and Air Pollution Research Center, Univ. of California, Riverside, CA, and Kearney Agricultural Center, 9240 S. Riverbend Ave., Parlier, CA 93648
^b Statewide Integrated Pest Management Program, Univ. of California, Kearney Agricultural Center, 9240 S. Riverbend Ave., Parlier, CA 93648

^* Corresponding author (david{at}uckac.edu)

Plant competition may be altered by ongoing climate change, including rising tropospheric O₃. This may depend less on the O₃ tolerance of isolated species than on O₃ effects on the mechanisms of competition. To explore this possibility, we investigate the growth and gas exchange responses of a crop–weed system in partial additive competition in open-top chambers (OTCs). Yellow nutsedge (Cyperus esculentus L.) and Pima cotton (Gossypium barbadense L.) were grown in pots in ratios of 0:1, 1:1, 2:1, and 3:1, plus 1:0 to contrast with 0:1. O₃ concentrations (12-h means) were 12.8 nL L^–1 (low O₃, LO3), 79.9 nL L^–1 (medium O₃, MO3), and 122.7 nL L^–1 (high O₃, HO3). Cotton was more sensitive than nutsedge to O₃ (reduction at HO3: 75 vs. 20% in shoot growth, 33 vs. 20% in assimilation). Cotton was inhibited by O₃ and by competition and the interaction was significant for leaf properties of cotton and tuber production in nutsedge. A coefficient of competition (slope of inverse cotton shoot biomass vs. nutsedge density) was significantly increased at HO3. The species were mutually inhibitory to similar extents. Root respiration declined with O₃ in nutsedge but increased in cotton, though both species reduced allocation below-ground. Nutsedge tuber production increased inconsistently with O₃. Rising tropospheric O₃ may decrease the current C₄ advantage of nutsedge in water use efficiency (WUE) and stomatal avoidance of O₃, but appears likely to increase the competitiveness of nutsedge with respect to cotton.

Abbreviations: HO3, high O₃ concentration • LAR, leaf area ratio (total leaf area/total shoot dry weight) • LO3, low O₃ concentration • LWR, leaf weight ratio (total leaf dry weight/total shoot dry weight) • MO3, medium O₃ concentration • OTC, open-top chamber • R_r, fine root respiration • SJV, San Joaquin Valley • SLW, specific leaf weight (total leaf dry weight/total leaf area) • WUE, water use efficiency