Microhistological Estimation of Grass Leaf Blade Percentages in Pastures and Diets

Abstract

Herbivores select plant parts to maximize the quality of their diets. However, there are few procedures available to quantify the relative consumption of leaf blades. In this study, we initially identified epidermal features that were specific of the blade in 4 grasses: Kleingrass (Panicum coloratum L.), tall wheatgrass (Thinopyrum ponticum [Podp.] Barkw. Dewey), tall fescue (Festuca arundinacea Schreb.), and salt grass (Distichlis scoparia L.). Then, we quantified the percentage of fragments with the blade epidermal feature for each species, evaluating whether they varied with plant maturity. We also evaluated whether those percentages were affected by digestion to determine if the procedure we propose could be used in diet analysis. Finally, by linear regression, we analyzed whether the relationships between the actual blade dry mass percentages (y) and those estimated by microanalysis (x) were 1:1 in mixes of different plant parts of the individual species as well as in mixed vegetation samples. Digestion affected the percentage of identifiable blade fragments of each species; but, after correction by digestion, all the estimates were accurate (a = 0 and b = 1 in all the regression equations) and precise (r2 > 0.90). Results indicate that epidermal features specific to blades would make it possible to estimate by microanalysis the percentage of this plant part for each species in vegetation samples from pastures composed of few species and also in the diets of herbivores grazing them. Although the proposed procedure was tested in simple systems, it could also be used to estimate the percentage of blades of the dominant species in the diets of herbivores grazing more complex systems.