No abstract

Growth temp. effects on anatomy and digestibility of leaf and stem of tropical and temperate forage species (Cynodon dactylon, Panicum maximum var. trichoglume, P. laxum, Lolium perenne and Medicago sativa), representing a range of anatomical types, was evaluated. Plants were grown in controlled-environment greenhouses at day/night temp. of 32/26 or 22/16 degrees C. Tissues of defined development stage were sampled for analysis of proportion of cell types, cell wall thickness, staining properties and digestion, using transverse sections on microscope slides immersed in rumen fluid. Leaf and stem harvested from whole plant tops was analysed for OM digestibility (OMD), cell wall digestibility (DCW), lignin, cell wall and insoluble ash. Temp. had little consistent effect on the proportion of different cell types, or the thickness of cell walls, cell wall content or insoluble ash. The digestion of the walls of sclerenchyma, bundle sheath and xylem cells was lower in tissues grown at the higher temp., especially for leaf. High temp. decreased OMD by an average of 6.6 percentage units for leaf and 12.4 percentage units for stem in the grasses, and by 2.6 percentage units for both tissues in M. sativa. The decrease in OMD and DCW with high temp. (excluding stem of M. sativa) was correlated with increase in lignin concn. High temp. appeared to increase the intensity of lignification of the existing lignified cells rather than increase the proportion of cells becoming lignified. Staining intensity was an insensitive indicator of this change in lignification. (Abstract retrieved from CAB Abstracts by CABI’s permission)

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.

For part 1, not numbered, see Abst. 4271, Vol. 37. 2. Digestibility of forages grown at different in-tensities of light, temperatures and amounts of N fertilizer was estimated with wethers. The different factors affected chemical composition more than digestibility. Greater intensity of light increased digestibility and higher temperature decreased it. N fertilizer increased it but not significantly. Digesti-bility was less during stem formation. For prediction of digestibility in vivo by different chemical procedures, true digestibility in vitro estimated from digestibility of cell walls was the most accurate.-T. W. (Abstract retrieved from CAB Abstracts by CABI’s permission)

In a cooperative experiment, yield and herbage quality of timothy was measured during the uninterrupted growth of the 1st cut at 6 lat. (51-69 deg N). Rate of production was greatest at Tromso (69 deg N), apparently because of the long day and rapid reproductive development. Digestibility of OM declined faster at higher lat. because stem development proceeded faster and less leaf DM was produced. At the same morphological stage, digestibility of the whole crop was better at higher lat. because of the better digestibility of the cell walls from the stems. It was concluded that rate of lignification could not keep pace with the rapid rate of stem development. (Abstract retrieved from CAB Abstracts by CABI’s permission)