Optimising Miscanthus - a clean energy biofuel to reach Net Zero targets

This thesis examines how the early development of Miscanthus, a perennial grass widely promoted for bioenergy, can be improved to support net-zero climate targets. Miscanthus has attracted significant attention because it produces large amounts of biomass, requires relatively low inputs, and can grow on land that is less suitable for food crops. These characteristics make it a strong candidate for sustainable energy production and carbon mitigation. However, despite this potential, large-scale deployment remains limited. A central reason for this gap between potential and practice is the difficulty of establishing the crop successfully in the field, particularly during the earliest stages of growth. The research begins from the observation that most existing studies and models focus on mature biomass yield, while underestimating the importance of early development. In perennial systems such as Miscanthus, early growth is not a temporary phase that can be corrected later; instead, it sets the trajectory for the entire lifespan of the crop. Poor establishment can lead to reduced plant density, uneven stands, and delayed or reduced yields for many years. In contrast, strong early development increases the likelihood of achieving stable and productive systems. This thesis therefore reframes establishment as a critical developmental stage, arguing that the success of Miscanthus depends less on its theoretical yield potential and more on its ability to establish reliably under real-world conditions. To explore how early development might be improved, the thesis investigates the role of biological interventions, including plant growth regulators (PGR) and biostimulants (BS). These inputs are designed to influence plant growth, for example by affecting internal plant signals, improving stress tolerance, or enhancing nutrient uptake. A review of existing research shows that while these approaches are widely studied, the evidence base is fragmented. Most studies are carried out under controlled conditions, focus on short-term outcomes, and rely on planting methods that are not representative of current large-scale practices. As a result, they provide limited insight into how these treatments perform in real field environments. The experimental work in this thesis addresses some of these limitations by focusing on seed-derived, plug-based systems, which are increasingly important for large-scale planting. The results show that early development can be influenced. Some PGR and BS treatments improved early plant height, biomass accumulation, and aspects of photosynthetic performance during establishment. This confirms that young Miscanthus plants are responsive during this period, and that it is possible to guide their development to some extent. However, the results also show clear limits to this influence. Improvements observed under controlled conditions often became weaker or disappeared after plants were transferred to field environments. Factors such as soil quality, water availability, and temperature may have had a stronger effect on plant performance than the treatments applied earlier. In addition, early improvements were rarely maintained over time. Gains in growth or plant function during the early stage did not consistently translate into better performance across a full growing season. The research also revealed that responses to these treatments were often variable. A treatment that worked well in one situation or environment could have little or no effect in another, and sometimes even reduced performance. These differences are not simply experimental inconsistencies but reflect the complexity of plant systems. The effectiveness of PGR and BS depends on several interacting factors, including plant type, environmental conditions, and application rate. Some treatments were only effective within a narrow range, meaning that careful and precise use is essential. These findings have important implications for the role of Miscanthus in net-zero strategies. For the crop to contribute meaningfully to climate mitigation, it must be grown successfully at scale, often on land with less favourable conditions. This requires moving beyond short-term controlled experiments and focusing on long-term, field-based approaches that reflect real growing environments. It also highlights the importance of seed- and plug-based systems, which are more suitable for large-scale deployment but present additional challenges during early growth. From a practical perspective, PGR and BS should be used carefully and strategically. They are most effective during the early stages of growth, particularly in controlled plug production systems. However, they should not be viewed as solutions that can overcome poor site conditions or guarantee success. Instead, they should be used alongside other management practices, including appropriate plant selection, soil preparation, and site-specific management. Overall, this thesis shifts the focus of Miscanthus research from maximising yield in mature plants to understanding the importance of early development. It shows that while biological interventions can influence early growth, their effects are limited, context dependent, and often short-lived. Recognising these constraints provides a more realistic foundation for improving Miscanthus establishment and supports the development of more reliable and scalable bioenergy systems.