Leaf Area and Competition for Light between Plant Species using Direct Sunlight Transmission

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Abstract
A technique based on the relationship between leaf area index (LAI) and the transmittance of direct sunlight was developed for the in situ study of competition for light between plant species. Field studies were conducted in 1984 and 1985 using monocultures and mixtures of rapeseed (Brassica napus L.), wild mustard (Sinapis arvensis L. # SINAR), and common lambsquarters (Chenopodium album L. # CHEAL). LAI estimated nondestructively by this method agreed closely with LAI determined by conventional destructive techniques. Light measurements at several heights in the canopy were used to determine the vertical distribution of canopy leaf area. Combining this information with species heights allowed the separation of the canopy LAI into individual species LAI, from which light competition could be estimated by calculating the sunlit LAI of each species. The technique permits many detailed measurements in the same canopy throughout the growing season. The light sensor required is not costly and is simple to operate and to maintain.