Percentage of Tissue Types in Tropical and Temperate Grass Leaf Blades and Degradation of Tissues by Rumen Microorganisms

Tropical and temperate grasses were investigated for the amounts and the relative ease of degradation of tis. sue types in leaf blades to relate microanatomy to digestibility. Leaf blades of five tropical and six temperate grasses, grown in different locations but harvested at four weeks of summer regrowth, were examined by light microscopy for cross sectional percentages of total vascular tissue, lignified vascular tissue, phloem, epidermis, sclerenchyma, and mesophyll. Leaf blades of four of the tropical grasses and the six temperate species were evaluated for in vitro degradation of tissue types by tureen microorganisms using scanning electron microscopy. Bermudagrasses, Cynodon dactylon (L.) Pers. possessed about 36% total vascular tissue with 27% of the leaf blade section composed of parenchymal bundle sheaths; totals of vascular tissue for the other grasses were lower, ranging from 11.0% to 22.1%. The parenchymal bundle sheaths, which occupied > 50% of the area for total vascular tissue in tropical grasses but < 50% in all temperate species, were more rigid and usually digested at a slower rate in the tropical grasses. In all grasses, mesophyll and phloem were degraded before the other tissues but were degraded more rapidly in the temperate species. Leaf blades of tropical grasses had an average of 22 percentage units less of the easily digested tissue (mesophyll and phloem) and 25 percentage units more of the slowly digested tissues (epidermis and parenchymal bundle sheath) than temperate species. Except for the bermudagrasses, the percentages of lignified tissue were higher in temperate species. Differences in the ease of degradation were apparent between similar tissues of different grass types, species, and cultivars. Results indicated that leaf blade microanatomy and inherent characteristics of cell walls affect digestibility by rumen microorganisms.