A Review of Modeled Water Use Efficiency of Highly Productive Perennial Grasses Useful for Bioenergy

Abstract

Whole plant productivity is obviously the ultimate product of leaf photosynthesis and this has led to numerous efforts to relate the two. However, often with perennial grasses, plant productivity is more sink-limited than source-limited, causing the linkage between the photosynthetic rate and productivity to be weak or nonexistent. This has led to a different approach, characterizing plant productivity in terms of the efficiency of intercepted light use in producing biomass, also called radiation use efficiency. Likewise, the efficiency of the use of water to produce plant biomass, or water use efficiency, has been the object of much interest. The use of a simulation model to quantify biomass, using radiation use efficiency in parallel with a daily water balance simulation, allows for the effective calculation of water use efficiency. In this project, the process of determining radiation use efficiency with field data is described, as well as example values for highly productive perennial grasses useful for feedstock for bioenergy. In addition, values of water use efficiency for these grasses are reported and compared with other perennial grasses and common cultivated crops.Water requirements for growing switchgrass and giant miscanthus are often an issue. Without adequate water, their biomass yields can be reduced by 45%-80% of total biomass yields [10,11]. Moreover, competition for water with other users makes maximizing water use efficiency vitally important. Again, process-based simulation models are valuable tools since they simulate the dynamics of crop water use based on evaporation of soil water, leaf transpiration, weather, and dynamics of plant communities. Quantifying Photosynthetic Performance via Two Approaches: Single Leaf Photosynthesis vs. Radiation Use Efficiency (RUE)There are many plant simulation models based on single leaf photosynthesis, which is then scaled up to the whole leaf canopy. Such models, such as ORYZA for rice (Oryza sativa L.) [12,13], are based on the assumption that photosynthesis is a major driver and determinant for whole plant productivity. However, frequently grass systems have been shown to be more sink-limited than source-limited. They often rely more on the processes of tiller production, leaf development, and leaf canopy orientation.Examples:

Warming Reduces Net Carbon Gain and Productivity in Medicago sativa L. and Festuca arundinacea

“…Previous studies on tall fescue have observed similar trends with festucoid species observed to have an optimum growth temperature between 20-27 • C [85,87,104,105]. The significant declines in biomass for tall fescue, despite little change in photosynthetic capacity, suggests that whole-plant productivity may be more sink-limited than source-limited [106], with productivity regulated by tiller production & leaf canopy orientation [107]. The significant decline in productivity for both species under warming may also be linked to the significant reduction we observed in C:N ratio, which suggests a decline in long term nitrogen use efficiency [108].…”

Plant Morphoecological Traits, Grass-Weed Interactions and Water Use Efficiencies of Grasses Used for Restoration of African Rangelands

“…Therefore, plant genotypes with high drought tolerance or WUE can contribute to yield increases and enhance rangeland restoration success. Moreover, competition for water with other users e.g., weeds, makes maximizing water use efficiency vitally important (Kiniry and Kim, 2020). This is because, arid and semiarid rangelands in Africa are infested with aggressive weeds e.g., Ipomoea kituensis that often engulfs emerging grass seedlings leading to poor establishment.…”