- Title
- Unravelling cell wall composition in C₄ grasses by application of Fourier transform infrared spectroscopy
- Creator
- Brown, Christopher
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2024
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- C₄ grasses are ubiquitous across the world and have grown in their importance to mankind since evolving almost 30 million years ago. They constitute a significant proportion of staple food crops globally, providing calories for millions of people living in emerging economies. Furthermore, they provide feed for animals that humans depend upon and more recently have been flagged as potential sources of feed stock for the biofuels industry. The key to their success is the potential energy stored within their cells. The cell wall of C4 grasses is of particular interest in livestock forage and biofuel industries as its composition determines the digestibility of the biomass and is vital to releasing the potential energy stored within. Many established methods for analysis of cell walls and determination of digestibility require substantial resources, including time, often an obstacle limiting rapid assessment in both research and industrial settings. Chemometric methods using Fourier transform infrared (FTIR) spectroscopy is an approach that has been increasingly applied to biomass compositional analysis, requiring fewer resources and providing the basis for accelerated high throughput assessment, once suitable models have been established. The overall aim of this study was to demonstrate successful application of FTIR spectroscopy towards unravelling differences in cell wall components, influenced by genetic diversity within the species or external environmental factors, of three unrelated C₄ grasses. These grasses are adapted to different environments, provide value to mankind in different ways, are genetically unrelated and successful application of FTIR based predictive models would demonstrate the broad utility of the technology to researchers working on other C₄ grasses. The work presented herein aimed to develop FTIR-based predictive models using the partial least squares regression approach to assess cell wall composition and digestibility, of three C₄ grass species in three separate studies. The first study encompassed 183 accessions of Setaria italica, and as a proof of concept, predictive models were established to determine cell wall composition with R2 values of at least 0.87. Predicted values were able to successfully differentiate cultivars into separate classifications based upon their cell wall composition. The second study utilising the grass species Cynodon dactylon, was a more extensive trial investigating the response of eight different Cynodon spp. varieties grown under different shade conditions over two months. Models developed for this trial generated predictions with R2 values over 0.9 for all cell wall components with the exception of arabinan, galactan and mannan, which had R2 values no less than 0.8. The cell wall response to shade stress was not initially detectable but accumulated over the course of the experiment with notable differences in cell wall composition ultimately evident in all cultivars grown under 50 and 70% shade treatments. Not only were models able to detect changes in cell wall composition as a consequence of the shade treatments, but they also highlighted that shade, in combination with regular clipping, increased lignin content in the cell wall, whereas typically, a decrease in lignin has been reported as part of the shade response. The final study focused on Cenchrus ciliaris, sought to assess differences in leaf and stem composition at different strata levels of yet a larger scale trial with four different tissues analysed over two harvesting periods from 228 different accessions. Modelling both leaf and stem tissues together produced less accurate predictions compared to previous single leaf or stem tissue models, but all components measured were still able to achieve R2 values over 0.8. This trial also measured Neutral Digestible Fibre (NDF) and indigestible neutral detergent fibre (iNDF) both of which modelled well, achieving R2 scores over 0.9. By relating iNDF as a measure of digestibility with cell wall components it was found that digestibility was closely linked with xylan content in all tissue types assayed, but also strongly linked to lignin, predominantly in stem material. By increasing the efficiency of cell wall analysis using FTIR spectroscopy and facilitating larger-scale trials, the scope of research projects aimed at developing new varieties and cultivars of C₄ grasses can be substantially increased. Furthermore, a deeper understanding of how different stressors affect biomass and cell wall composition and the implications of these relationships can contribute to effective forage and feedstock management.
- Subject
- cell wall; FTIR; Fourier transform; C₄ grasses; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1511431
- Identifier
- uon:56495
- Rights
- Copyright 2024 Christopher Brown
- Language
- eng
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