4.1.1.1 Main Features

To date, most of the information gained on the growth and physiology of Miscanthus has come from studies of Miscanthus x giganteus, which has been shown to reach a maximum aboveground yield of 46 t ha-1 under non-irrigated conditions [20] and 49 t ha-1 under irrigated conditions [21]. However, as detailed in Section 4.2.3 (Genetic Diversity for Biomass Production), the aboveground yield of Miscanthus can vary greatly depending on climatic and seasonal conditions, soil type, crop management and crop age.

The root system of Miscanthus x giganteus is composed of a coarse cluster of rhizomes from which a mass of fine roots grow [22,23]. These fine roots represent just under a third of the total belowground biomass and can reach a depth of 250 cm in sandy loams [22,23]. The rhizome biomass of M. x giganteus has been shown to reach a maximum of 23.8 tDM ha-1, by the end of summer, with this amount maintained until early winter [20].

Aboveground growth is triggered once temperatures reach 6 or 10°C with the emer­gence of stems from buds located just below the soil surface [24]. After stem emergence, tillering increases rapidly throughout May-July with up to 40 stems per plant recorded for M. x giganteus in the United Kingdom [25]. The number of productive shoots decreases over the course of the growing period, with the youngest tillers dying off. The oldest tillers continue to grow through to August-September and even October, depending on the climate and the time between emergence and flowering. The harvestable number of stems per plant varies between species, with M. sinensis silberspinne producing about 200 stems per plant or about five times as many stems as M. x giganteus (40 stems per plant) at three years of age [26].

Leaf area increases throughout the growing season to reach a peak at flowering, after which the canopy starts to senesce [27]. In Miscanthus x giganteus, the maximum leaf area index (LAI) obtained each season increases with crop age reaching about 7-8 m2 m-2 in summer for a three-year-old stand [28]. At the onset of plant senescence, all stems left standing gradually dry out during winter until February-March, when the crop is ready for harvest. The light extinction coefficient (k) through the leaf cover of the crop provides a measurement of the capacity of leaves to intercept light. The k-value for M. x giganteus has been recorded at 0.56 [27] and 0.68 [29] and for M. sinensis Goliath at 0.66 [30]. However, most of these values need to be validated, especially at the interspecific level.