The recent interest on the potential of biofuels (Koonin, 2006; Ragauskas et al., 2006; U.S.DOE, 2006) to supply energy security, reduce carbon dioxide emissions and support agriculture, demands that the most productive, efficient and environmentally responsible cropping systems are used (Heaton et al., 2008). At present ethanol constitutes 99% of the biofuels in the United States and it is mainly derived from maize (Zea mays L.) (Farrell et al., 2006). Although the use of maize-derived ethanol is expected to increase, cellulosic ethanol will be needed in order to meet the longer-term renewable energy mandate (U.S.DOE, 2006). In addition, when harvesting biomass crops nearly all aboveground plant components can be used for cellulosic ethanol production which can enable much larger quantities of biofuel production compared with grain-derived ethanol (Lewandowski et al., 2000). Miscanthus×giganteus, Greef et Deux. Hodkinson et Renvoize, (Hodkinson & Renvoize, 2001), hereinafter referred to as M.×giganteus, is a C4 perennial grass with high yield potential (Heaton et al., 2004, 2008), efficient conversion of radiation to biomass (Beale & Long, 1997), efficient use of nitrogen (N) and water (Beale & Long, 1995), which has been extensively researched in Europe (Lewandowski et al., 2000). However, at the moment M.×giganteus is not commercially produced at large scale in the United States, being limited mostly to experimental plots. Thus, there is a need for the development and parameterization of process-based crop models that can provide reliable predictions of carbon assimilation, growth and yield. Further, it is currently an unimproved crop with significant opportunities for yield improvement via selection, breeding and genetic engineering. A semimechanistic model would provide a framework in which to evaluate potential traits for improvement, ahead of a lengthy breeding program.
Previous semimechanistic models based on light conversion efficiency and temperature thresholds for leaf growth have been shown effective for simulating M.×giganteus yields (Clifton-Brown et al., 2000, 2004; Price et al., 2004). These models strongly depend on a parameter which describes the efficiency of the crop in converting radiation to biomass (radiation use efficiency, RUE). Although in these models RUE has been treated as a constant, Clifton-Brown et al. (2000, 2004) reported that the value of ec for M.×giganteus ranged from 2.4 to 4.2 g MJ−1 PAR. These authors recognized that the model depends strongly on RUE and that a more mechanistic model would be more appropriate (Clifton-Brown et al., 2001). These models are appealing due to their simplicity but by their design they cannot provide insights into the physiological basis of RUE variation, or growth and the physiology of water use (Demetriades-Shah et al., 1992; Reddy, 1995; Loomis & Amthor, 1999).
WIMOVAC is a generic plant production model, based on the key physiological and micrometeorological processes underlying plant production (Humphries & Long, 1995). Here, we describe the model as adapted to the specific crop, M.×giganteus. The model was parameterized from laboratory physiological measurements and shown to effectively predict diurnal photosynthesis in the field. Biomass partitioning was parameterized from measurements made at one site in England. Finally, we demonstrate the ability of the model to predict biomass accumulation and yield for the same genotype at sites distinct from that used for parameterization.