Seasonal Carbohydrate Dynamics and Climatic Regulation of Senescence in the Perennial Grass, Miscanthus

Abstract

Miscanthus is a perennial energy grass predominantly used for combustion but there is increasing interest in fermenting the cell-wall carbohydrates or green-cutting for soluble sugars to produce bioethanol. Our aims were to: (1) quantify non-structural carbohydrates (NSC), (2) observe the timing of seasonal shifts in the stems and rhizome, and (3) identify developmental and/or climatic conditions that promoted carbohydrate remobilization from the stems to the rhizome during senescence. Two genotypes of Miscanthus sinensis, a Miscanthus sacchariflorus and a Miscanthus × giganteus were grown at replicated field sites in Aberystwyth, West Wales and Harpenden, South East England. NSC were quantified from the rhizome and aboveground organs and then correlated with climatic data collected from on-site weather stations. PAR and maximum daily temperatures were higher at Harpenden throughout the year, but daily minimum temperatures were lower. Senescence was accelerated at Harpenden. Carbohydrates were retained within the stems of nonflowering genotypes, at both sites, in winter and were still present after a frost event to −2°C. Rhizome starch concentrations were at least equal to the previous winter's levels (February 2011) by September. Lower daily minimum temperatures accelerate the rate of senescence and warmer daily maximum temperatures cannot counteract this effect. At current yields, M. × giganteus, could produce 0.7 t ha −1 of NSC in addition to ligno-cellulosic biomass in November but with concerted breeding efforts this could be targeted for improvement as has been achieved in other crops. Shifting harvests forward to November would not leave the rhizome depleted of carbohydrates.

Predicting future biomass yield in Miscanthus using the carbohydrate metabolic profile as a biomarker

“…Soluble sugars and starch were analysed as previously described (Purdy et al ., , ). Soluble sugar extraction: approximately 20 mg (actual weight recorded) of each cryomilled (6870 Freezer Mill, Spex, Sampleprep, Stanmore, UK) plant tissue sample was weighed into 2‐mL screwcap microcentrifuge tubes.…”

“…Sucrose is formed of a molecule each of glucose and fructose, and relationships between the hexoses and biomass traits had previously been observed (Purdy et al ., ). Unlike many C3 temperate grasses, C4 species such as Miscanthus do not accumulate fructans (Muguerza et al ., ) but instead accumulate starch as a transient form of storage carbohydrate (de Souza et al ., ; Purdy et al ., ).…”

“…The choice of nonstructural carbohydrates to profile was based on previously observed genotypic differences in abundance and partitioning in four genotypes (Purdy et al ., , ). Sucrose is the most abundant soluble sugar in Miscanthus, and owing to the close phylogenetic relationship between Miscanthus and sugarcane (Hodkinson et al ., ), it was an obvious candidate for study in diverse genotypes.…”

“…To grow, plants must accumulate structural mass, predominantly cellulose and the cell wall hemicellulose polysaccharides. Both starch and cellulose are polymers of glucose, and we hypothesized that rapidly growing genotypes of Miscanthus may be accumulating cellulose more rapidly at the expense of starch biosynthesis, thus explaining the negative relationship between starch and growth observed in our previous study and that of others (Rocher, ; Sulpice et al ., ; Purdy et al ., , ). Therefore, starch, cellulose and the hemicelluloses were also assayed to assess a potential role as yield biomarkers.…”

Impact of rhizome quality on Miscanthus establishment in claypan soil landscapes

“…Another factor that affects M. × giganteus winter survival is its ability to store or sequester a critical amount of metabolic reserve going into the first winter (Christian and Hasse, 2001;Purdy et al, 2015). This ability to store metabolites likely is influenced by the quality of the planted rhizome and the soil resource that supports the rhizome.…”