Hierarchical analysis of switchgrass morphology

Switchgrass (Panicum virgatum L.) has potential as a biomass crop in North America. Our objective was to determine effects of cultivar and location on morphological traits that influence biomass in switchgrass. Six cultivars with origins from 37 degrees N, 88 degrees W (Cave-In-Rock and Shawnee) to 46 degrees N, 100 degrees W (Dacotah) were evaluated in 1-yr-old swards at Bristol and South Shore, SD; in 3-yr-old swards at Brookings, SD, and Arlington, WI; and in 15-yr-old swards at Pierre, SD, for biomass; tillers m(-2); reproductive tiller proportions by count and weight, weight tiller(-1); phytomers tiller(-1); leaf, stem, and inflorescence components of tiller weight; and sheath and stem components of phytomer weight. Biomass production was related to region of cultivar origin [e.g., Shawnee produced two times more than Dacotah (6.2 Mg ha(-1))]. Tiller density was highest for Dacotah (1090 tillers m(-2)) and lowest for Cave-In-Rock (520 tillers m(-2)). Reproductive tiller fractions by count were plastic and higher at Arlington (0.81) than Brookings (0.08). Weights per reproductive tiller ranged from 0.7 g (Dacotah) to 3.4 g (Cave-In-Rock). Phytomers per tiller was not plastic (5.2 for Dacotah to 7.4 for Cave-In-Rock). Internode weight exhibited a basipetal increase and was highly plastic. Cultivars responded similarly to location effects on tillers m(-2), weight tiller', and biomass production. Cultivar differences for biomass production were attributed to variation at tiller (phytomers tiller(-1)) and phytomer (weight phytomer(-1)) levels.