GCB Bioenergy

Chilling temperatures (0–15°C) inhibit photosynthesis in most C₄ grasses, yet photosynthesis is chilling tolerant in the ‘Illinois’ clone of the C₄ grass Miscanthus x giganteus, a candidate cellulosic bioenergy crop. M. x giganteus is a hybrid between Miscanthus sacchariflorus and Miscanthus sinensis; therefore chilling‐tolerant parent lines might produce hybrids superior to the current clone. Recently a collection of M. sacchariflorus from Siberia, the apparent low temperature limit of natural distribution,became available, which may be a source for chilling tolerance. The collection was screened for chilling tolerance of photosynthesis by measuring dark‐adapted maximum quantum yield of PSII photochemistry (F_v/F_m) on plants in the field in cool weather. Superior accessions were selected for further phenotyping: plants were grown at 25°C, transferred to 10°C (chilling) for 15 days, and returned to 25°C for 7 days (recovery). Two experiments assessed: (a) light‐saturated net photosynthetic rate (A_sat) and operating quantum yield of PSII photochemistry (Φ_PSII), (b) response of net leaf CO₂ uptake (A) to intercellular [CO₂] (c_i). Three accessions showed superior chilling tolerance: RU2012‐069 and RU2012‐114 achieved A_sat up to double that of M. x giganteus prior to and during chilling, due to increased c_i ‐ saturated photosynthesis (V_max). RU2012‐069 and RU2012‐114 also maintained greater levels of Φ_PSII during chilling, indicating reduced photodamage. Additionally, accession RU2012‐112 maintained a stable A_sat throughout the 15‐day chilling period, while A_sat continuously declined in other accessions; this suggests RU2012‐112 could outperform others in lengthy chilling periods. Plants were returned to 25°C after the chilling period; M. x giganteus showed the weakest recovery after 1 day, but a strong recovery after 1 week. This study has therefore identified important genetic resources for the synthesis of improved lines of M. x giganteus, which could facilitate the displacement of fossil fuels by cellulosic bioenergy.