Miscanthus × Giganteus Senescence Is Affected By Stand Age.

Despite the many advantages of Miscanthus × giganteus as a biomass crop, first-year winter losses have been problematic, especially during early European trials. Concomitantly, first-year M. × giganteus exhibited a delayed senescence, remaining bright green until a killing frost. In contrast, senescence proceeded normally and survival rates were much improved in subsequent years. An anecdotal explanation for these correlated observations was that delayed or absent first-year senescence led to decreased nutrient availability to the perennating rhizome. However, no trials ever considered multiple stand-ages of M. × giganteus in a single design, and only assessed senescence based on greenness ratings. To investigate these phenomena further, we established a chronoseries of first-, second- and third-year M. × giganteus. Senescence timing was determined by measuring photosynthetic parameters and leaf [N] from late summer through a killing frost. We found that photosystem II efficiencies and photosynthetic rates were up to 4 times greater in first-year plants than third-year plants during the late fall when senescence should be occurring. Additionally, leaf [N] was up to 2.4 times greater in first-year plants than third-year by the end of the growing season. These observations support the theory that while older plants are dismantling the photosynthetic apparatus in preparation for autumnal senescence and nutrient translocation, younger plants are not. Consequently, in first-year plants, the nutrients stored in leaf proteins are lost after a killing frost resulting in a higher winter loss potential.