Ozone Impacts on Assimilation and Allocation to Reproductive Sinks in the Vegetatively Propagated C-4 Weed, Yellow Nutsedge

Crop production in many irrigated agricultural regions is challenged by both air pollution and weed pressure. Impacts of ozone (O-3) on C-4 plants have received little attention. Yet many important crops and weeds utilize the C-4 pathway, including yellow nutsedge (Cyperus esculentus L.). A previous study suggested that this species may respond to O-3 exposure with enhanced allocation of biomass below ground, including potentially to reproductive tubers, an apparent exception to the general weakening of belowground sink strength. This hypothesis was not supported by the current experiments, as exposure to 60 nL L-1 and 115 nL L-1 O-3 (12-h daylight mean O-3 concentration) reduced biomass allocation to tubers, relative to 4 nL L-1. Chlorophyll content, specific leaf weight, and carbon assimilation were reduced, while intercellular CO2 concentration increased, reducing water use efficiency. We conclude that (i) this C-4 species exhibits substantial sensitivity to ambient O-3; (ii) O-3-inhibition of allocation belowground is not limited to roots but also applies to tubers; and (iii) the O-3 component of global change will increase the competitiveness of nutsedge with respect to specific crops as shown previously, but will decrease tuber production and degrade water use efficiency of this challenging C-4 weed.