Lignification and Tannin Localization During the Development of Birdsfoot Trefoil Stems

Abstract

ABSTRACTStem dry matter accumulation is correlated with a decline in digestibility in both birdsfoot trefoil (Lotus corniculatus L. [BFT]) and alfalfa (Medicago sativa L.), and the shear force required to harvest mature BFT stems can inhibit BFT grazing by ruminants. Decline in digestibility and increase in shear force are both correlated with increase in stem lignin content. Alfalfa stem development has been well documented, and our objective was to analyze stem development, lignification and tannin in BFT stems using alfalfa as a benchmark. The sixth internode from the base of ten BFT and two alfalfa control plants was sampled from 3 to 15 wk of stem regrowth in midsummer. Lignification occurred primarily in stem secondary xylem and was apparent in the xylary ring of Internode 6 by 5 wk of regrowth. The xylary ring reached maximum thickness by 7.5 wk of regrowth in both BFT and alfalfa but developed at a more rapid rate and to a greater thickness in BFT. Flowering in BFT began at 5.5 wk of regrowth, and full bloom was reached by 6.5 wk of regrowth. The number of cells containing tannin remained constant with stem development, which would decrease stem tannin concentration with internode maturation. Internode 6 of BFT is located 60 to 120 mm from the base of stems, within the recommended cutting height of 75 mm, with sufficient leaves and branches at subtending nodes to support shoot regrowth. These data relate growth and lignification in lower stems of BFT to grazing management recommendations.