Exploring Genetic and Environmental Drivers of Variation in Wheat Growth and Carbon Metabolism

Abstract

Business-as-usual agricultural performance is failing to keep up with the demand for crops in a growing global population. At the same time, climate change is increasing the frequency and severity of extreme weather events that disrupt agriculture. In Chapter 1, we underscore the importance of plant physiology in enhancing crop performance, particularly focusing on carbon assimilation and the efficiency with which that carbon is converted to biomass. There is untapped potential to enhance crop yields through improvements this efficiency closer to its theoretical maximum. Because much less is known about respiration than photosynthesis with regards to the mechanisms controlling rates, this thesis focuses on respiration as a trait of interest that could boost yield potential. However, measuring respiration was traditionally slow - yet, using high-throughput measurement techniques, it becomes more viable to explore the relationship between respiration and other growth traits on the larger scale necessary. This thesis therefore explores respiration across various plant tissue types and aims to relate Rdark with carbohydrate status of leaves and associated transport costs; biomass allocation and the contributions of shoot- and root-respiration to whole-plant properties; and relative growth rates across a range of environmental conditions across 8 wheat genotypes. Chapter 2 explores the influence of different light environments and growth temperatures on respiration and starch levels in wheat flag leaves. We found that starch levels are significantly affected by the two environmental variables we manipulated, with reduced-irradiance treatments showing lower starch accumulation and degradation rates. However, respiration rates showed little thermal acclimation. Importantly, the export costs in a mature flag leaf were non-linear and point to substrate-dependent rates of export in wheat leaves. Chapter 3 extends the analysis to the whole shoot and root systems to correlate growth and respiration at the whole-plant level. Heat treatments generally negatively impact growth rate in DNA #1704, a heat-intolerant genotype, but commercially high-performing genotypes show more resilience. Contrary to prior findings, warmer days had some limited exidence of exhibiting greater acclimation than warmer nights. In Chapter 4, eight wheat genotypes are assessed in field settings, revealing variation in leaf respiration and aboveground relative growth rate across environments and developmental stages. Importantly, the ranking of Rdark showed some consistency across sites. Lastly, Chapter 5 discusses the implications of these findings for improving crop yield, emphasizing the need for high-throughput physiological measurements and advanced digital phenotyping in the field. Overall, understanding respiration and its response to changing climates is essential for enhancing crop productivity. Show more