Abstract
Miscanthus hybrids are leading candidates for bioenergy feedstocks in mid to high latitudes of North America and Eurasia, due to high productivity associated with the C4 photosynthetic pathway and their tolerance of cooler conditions. However, as C4 plants, they may lack tolerance of chilling conditions (0-10 °C) and frost, particularly when compared with candidate C3 crops at high latitudes. In higher latitudes, cold tolerance is particularly important if the feedstock is to utilize fully the long, early-season days of May and June. Here, leaf gas exchange and fluorescence are used to assess chilling tolerance of photosynthesis in five Miscanthus hybrids bred for cold tolerance, a complex Saccharum hybrid (energycane), and an upland sugarcane variety with some chilling tolerance. The chilling treatment consisted of transferring warm-grown plants (25/20 °C day/night growth temperatures) to chilling (12/5 °C) conditions for 1 week, followed by assessing recovery after return to warm temperatures. Chilling tolerance was also evaluated in outdoor, spring-grown Miscanthus genotypes before and after a cold front that was punctuated by a frost event. Miscanthus×giganteus was found to be the most chilling-tolerant genotype based on its ability to maintain a high net CO2 assimilation rate (A) during chilling, and recover A to a greater degree following a return to warm conditions. This was associated with increasing its capacity for short-term dark-reversible photoprotective processes (ΦREG) and the proportion of open photosystem II reaction centres (qL) while minimizing photoinactivation (ΦNF). Similarly, in the field, M.×giganteus exhibited a significantly greater A and pre-dawn F v/F m after the cold front compared with the other chilling-sensitive Miscanthus hybrids.
Highlights
Hybrids of the C4 grass species Miscanthus sacchariflorus and M. sinensis are leading candidates for second-generation bioenergy feedstocks of cool-temperate climates (Deuter, 2000; Heaton et al, 2010; Zub and Brancourt-Hulmel, 2010; Jones, 2011)
Leaf gas exchange and fluorescence are used to assess chilling tolerance of photosynthesis in five Miscanthus hybrids bred for cold tolerance, a complex Saccharum hybrid, and an upland sugarcane variety with some chilling tolerance
Relative to other cultivated C4 species, Miscanthus hybrids exhibit higher net CO2 assimilation rates (A) at cool temperatures (10–18 °C), and produce a canopy with a leaf area index >1 well before other C4 crops of the temperate zone (Beale and Long, 1995; Beale et al, 1996; Dohleman and Long, 2009; Dohleman et al, 2009). This ability to produce an early-season canopy is critical for the success of Miscanthus varieties in higher latitudes, because it allows them to exploit the long photoperiods of May and June
Summary
Hybrids of the C4 grass species Miscanthus sacchariflorus and M. sinensis are leading candidates for second-generation bioenergy feedstocks of cool-temperate climates (Deuter, 2000; Heaton et al, 2010; Zub and Brancourt-Hulmel, 2010; Jones, 2011). Relative to other cultivated C4 species, Miscanthus hybrids exhibit higher net CO2 assimilation rates (A) at cool temperatures (10–18 °C), and produce a canopy with a leaf area index >1 well before other C4 crops of the temperate zone (Beale and Long, 1995; Beale et al, 1996; Dohleman and Long, 2009; Dohleman et al, 2009). This ability to produce an early-season canopy is critical for the success of Miscanthus varieties in higher latitudes, because it allows them to exploit the long photoperiods of May and June. In addition to placing a low ceiling on photosynthetic capacity, a Rubisco limitation may restrict photochemical quenching and predispose C4 species to photoinhibition in chilly conditions (Kubien et al, 2003; Kubien and Sage, 2004a; Long and Spence, 2013)
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