Anatomical characters and digestibility of leaves of Panicum and other grass genera with C₃ and different types of C₄ photosynthetic pathway

Abstract

The relation between leaf anatomical structure and some nutritive quality attributes was investigated in a range of grasses of different photosynthetic pathway. The species sample comprised 12 Panicum species and 12 species from other grass genera. Dry matter digestibility (DMD), and cell wall and lignin content were determined on dried, ground samples of leaf blade.Leaves grown outdoors were smaller and had higher specific leaf weight than those from the glasshouse, but leaves from the two environments did not differ in anatomical characteristics or DMD.Anatomical differences between the leaf structural groups were consistently expressed, with C3 species having higher proportions of mesophyll (53-67%) and lower proportions of bundle sheath (5-20%) and vascular tissue (3-9%) than the C4 groups (28-47%, 12-33%and 6-12%, respectively). Within the C4 groups the 'classical' NADP-ME type had a lower mean proportion of 'Kranz' bundle sheath (14.9%) and vascular tissue (7.1%) than the 'classical' PCK and NAD-ME leaf-structural types (average values 24.3 and 9.3%, respectively). Conversely, species of the latter two C4 groups usually showed lower proportions of mesophyll and epidermal cells than those of the NADP-ME group. Leaf morphology was not consistently related to leaf-structural group, except that the C3 species in the sample usually had a smaller midrib relative to the cross-sectional area of the blade than the C4 species.The C3 group, with the notable exception of Panicum rivulare, generally had a lower cell wall content (37-49%) and higher DMD (67-74%) than the C4 groups (49-67% and 53-67%, respectively).The quantitative anatomical differences between C3 and C4 grasses accounted for a significant part of the generally higher DMD of C3 grasses (but exceptions can occur).