Butler, Holly and Martin, Frank and McAinsh, Martin (2016) Optimising nutrient use efficiency in crop production. PhD thesis, Lancaster University.
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Abstract
Food security for a growing population presents a significant challenge for crop production, with increasing pressures upon agriculutral productivity. There is a vast need to improve crop yield and quality using an efficient approach that does not present negative environmental impacts. A novel interrogation technique that is able to provide information of the overall health of a plant, would be extremely beneficial in an agriculutral, as well as research, setting. This information could be utilised to better understand the mechanisms of plant functions, including stress responses. Vibrational spectroscopy encompasses a range of techniques that are able to derive chemically specific information from a biological sample in a rapid, nondestructive and cost-effective manner. Fourier-transform infrared (FTIR) spectroscopy and Raman spectroscopy are two such approaches and have been readily implemented across biological samples. However, their applications in the field of plant science have been relatively underexploited. This is largely associated with the presence of water and fluorescent metabolites found in plant tissues. The application of attenuated total reflectance (ATR)-FTIR and spontaneous Raman spectroscopy for in vivo plant monitoring to elucidate spectral alterations indicative of healthy plant growth in a non-destructive manner. These approaches are able to characterise the biochemical signature of leaves at distinct developmental stages, and correspond to known biological processes within the leaf such as cell wall expansion. This information is useful prior to monitoring studies as normal leaf growth could be considered background variance. No significant local or systemic effects manifest as a consequence of interrogation with these techniques, establishing this as a non-destructive approach for plant system investigations. Raman microspectroscopy as a tool for monitoring nutrient uptake at the leaf surface is also considered, alongside complementary ion probe and elemental analysis. Such a technique is useful in the agrochemical production of foliar fertilisers, where the efficiency of specific formulae can be rapidly compared. This can also further the current understanding of nutrient transport into plant tissues, as well as translocation. Agriculturally relevant levels of calcium were applied to the leaf surface and uptake was successfully illustrated at concentrations as low as 15 mM using Raman microspectroscopy. Ion probe analysis also complemented these findings, with elemental analysis unable to detect this subtle uptake of nutrients. This assay is now being implemented in agrochemical practise as a fertiliser screening method. Deficiencies in essential nutrients such as calcium are detrimental to crop yield and thus are a potential target for improving crop production. A range of spectroscopic methods, including the use of synchrotron radiation, were utilised to presymptomatically detect these deficiencies prior to their onset in live samples. Coupled with multivariate analysis, these techniques discriminate between deficient and control samples with high sensitivity and specificity, without extensive sample preparation that traditional analytical techniques require. These results suggest that Raman and ATRFTIR spectroscopic approaches could highly valuable in the field, where plant health and nutrient status could be assessed rapidly in situ. Here it is shown that these issues can be overcome and that qualitative spectral measurements can be obtained from plant samples. Due to the non-destructive nature of these approaches, they can be applied for a wider range of crop screening investigations, including the efficiency of nutrient uptake, as well as distinguishing nutrient deficiencies presymptomatically. As such, these spectroscopic methods may be implemented to unearth further details regarding nutrient use efficiency during crop production.