Leaf morphoanatomy of ryegrass in the tree species understory in agroforestry systems

ABSTRACT The verification of changes that occur in the plant, due to the acclimatization to the shading, assists in the selection of forage species suitable for use in agroforestry systems. The aim of this study was to evaluate the leaf morphoanatomy of ryegrass (Lolium multiflorum Lam.) in the tree species understory in agroforestry systems. The experiment was conducted in Frederico Westphalen, RS, Brazil, between June and September 2012, in an experimental design of randomized blocks. The annual ryegrass was sown in three environments: full sunlight, understory of angico-vermelho (Parapiptadenia rigida Benth.), and canafístula (Peltophorum dubium Spr. Taubert), with three replications. Forest species were distributed in five lines, separated by 6.0 m. The following variables were evaluated: incident photosynthetically active radiation (RFAi), transmissivity of RFAi, specific leaf area, leaf mesophyll thickness, thickness of outer periclinal wall + cuticle, stomatal size, and stomatal density. The presence of forest species causes changes in the lighting conditions of the production environment of ryegrass and causes adjustments in the leaves of this species, which result in increased specific leaf area, decreased mesophyll and thickness of the outer periclinal wall + cuticle, as well as increased amount and size of the stomata. These adjustments result from the acclimation capacity of ryegrass, which, in low-light conditions, alter their morphology to capture more solar radiation and increase the photosynthetic area.