Effects of light intensity on growth, anatomy and forage quality of two tropical grasses (Brachiaria brizantha and Panicum maximum var. trichoglume)

Abstract

Effects of light intensity on growth, histology and anatomy, and nutritive value were studied in seedlings of two shade tolerant species: Brachiaria brizantha and Panicum maximum var. trichoglume. They were studied under greenhouse conditions in pots with sandy soil and sufficient N and cut after a growth period of 8 weeks. High light intensity stimulated growth, tillering and yield per tiller and increased stem proportion. It greatly increased number of sclerenchyma cells, their wall thickness in all organs and the content of cell wall constituents. High light intensity also reduced concentrations of total N, NO3-N and ash appreciably. It reduced digestibility of cell wall constituents in leaf blades but increased it in leaf sheaths and stem, especially in Panicum. Variation in sclerenchyma tissue could be associated with variation in percentage of cell wall constituents, but not with variation in cell wall digestibility. The result of these effects of light intensity on composition of organs was a higher digestibility of organic matter of the whole crop at lower light intensity. Brachiaria was more tolerant to shade than Panicum with regard to growth, N-concentration and digestibility, but it accumulated more nitrate. It was suggested that light intensity may affect forage quality little under low nitrogen supply in the tropics, but effects may be larger at ample nitrogen supply. Individual species may partly divert from this general pattern.