Research was conducted in 1998 and 1999 to characterize common lambsquarters photosynthesis and seed production as influenced by biotic (crop environment) and abiotic (climate) factors. Treatments were common lambsquarters in soybean, in corn, and in common lambsquarters monoculture. Common lambsquarters net photosynthesis was variable among treatments and differed between years. In 1998, early-season common lambsquarters net photosynthesis did not differ in soybean, corn, or common lambsquarters monoculture. In 1999, early-season common lambsquarters net photosynthesis was greater in corn than in soybean, but did not differ from that of common lambsquarters in monoculture. By midseason in both years, common lambsquarters net photosynthesis was less in soybean than in corn or in common lambsquarters monoculture. By late season in both years, common lambsquarters net photosynthesis was greater in common lambsquarters monoculture than in soybean or corn. Common lambsquarters seed production per plant was greater in common lambsquarters monoculture than in soybean or corn. Common lambsquarters seed production was variable among plants and between years. Practical applications of models to predict weed fitness that are based on photosynthetic capacity will be limited until variability in net photosynthesis and in seed production are better understood.
Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; corn, Zea mays L. ‘Dekalb DK493SR’; soybean, Glycine max L. Merr., ‘Asgrow AG2101RR’.