Cell wall degradability and anatomy of grass leaves.
The effect of two controlled, contrasting environments on the anatomy
and cell wall degradability of leaf laminae was examined in a range of
temperate and tropical grass species: Dactylis glomerata cv. S37,
Festuca arundinacea cv. S170, Lolium perenne cv. S24, Phleum pratense
cv. S48 (temperate); Bothriochloa barbinodis, Cenchrus ciliaris cv.
Biloela, Chloris gayana cv. Pioneer and Eragrostis curvula (tropical).
Environment I was cool and humid with a low light intensity and
adequate water supply; Environment II was hot and dry with a higher
light intensity and restricted water supply. Cell walls were isolated
from leaf laminae and their degradability determined using a commercial
fungal cellulase. The anatomy of the lamina of the eighth leaf on
the main stem was examined to determine the possible anatomical basis
for differences observed in cell wall degradability.
Differences in cell wall degradability were found between species
grown in the same environment, but there was no significant difference
between the tropical and temperate species when considered as two
separate groups. Environment had a significant but opposite effect on
the tropical and temperate species: the cell walls of all the tropical
grasses were more degradable in Environment II than in I, whereas in
the temperate species they were less degradable. It was concluded
that the low feeding value of tropical grasses is not caused by an
inherently low degradability of cell walls in the leaf laminae, nor
by the effects of a hot, dry environment on cell wall degradability.
Anatomical features which could have accounted for differences
between species in cell wall degradability included variation in the
lignification of the parenchyma sheath cells and epidermis and in the
size of girders, strands and marginal caps, as seen in transverse
section. The increase in cell wall degradability in tropical. species
in Environment II was due, at least in part, to an increase in the
proportion of sclerenchyma fibres which were degraded by cellulctse.
This type of sclerenchyma fibre had very thick walls and was only
found in the tropical species. The decrease in cell wall degradability
in temperate species could be accounted for by an increase in the
thickness of lignified cell walls, and an increase in the resistance
of epidermal and parenchyma sheath cell walls to degradation.