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° N, 88° W (Cave‐In‐Rock and Shawnee) to 46° N, 100° 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 −1 , and biomass production. Cultivar differences for biomass production were attributed to variation at tiller (phytomers tiller −1 ) and phytomer (weight phytomer −1 ) levels.