Functional Plant Species Traits That Shape Canopy Light Interception and Agronomic Performance of Perennial Forage Grasses Cultivated in Monoculture and Association

ABSTRACT Functional traits of plants control a series of agronomic and ecological responses that are related to plant productivity. The botanical proportion and productive performance of forage grass species associations are underpinned by shifts in plant traits and associated resource (especially light) partitioning. However, most studies involving associations of forage species are to pastures in temperate climates. Studies in tropical conditions and environments are practically nonexistent. Therefore, in an experimental study, three perennial tropical forage grass species, Andropogon gayanus cv. Planaltina (andropogon grass), Panicum maximum cv. Massai (massai grass) and Brachiaria brizantha cv. BRS Piatã (piata grass), were cultivated in monoculture and in association (the three species in equal proportions based on the number of viable seeds). Among the monocultures, piata grass presented the greatest herbage mass, but in the association, massai grass did. The performance of the association was mainly shaped by competition for light, with massai grass present in greater proportion and showing greater productive performance than the remaining grass species. Foliage angle, leaf elongation rate per tiller, number of leaves per tiller and canopy leaf area index are functional traits that shape the dynamics of the competition for light, botanical proportion and productive performance of grass species in the association. This study provides new insights into the functional traits that control the agronomic and ecological responses that shape competition for light in a tropical perennial grass mixture and that should be considered when selecting grass species for new associations.