The application of Fourier Transform Infra-Red spectrometry to assess the impact of changes in Photosynthetic Photon Flux on cell wall components and turf quality of different cultivars of <i>Cynodon</i> grasses

The impact of decreased Photosynthetic Photon Flux (PPF) on the biomass and quality of Cynodon turf grasses are of considerable interest to the turf community, however there is little available data regarding its effect upon cell walls. Fourier Transform Infra-Red (FTIR)-based Partial Least Squares Regression (PLSR) models are useful for assessing the cell wall composition of a multitude of samples in a high-throughput manner. Such models were generated to predict cell wall components, water and extractive non-cell wall content of Cynodon grass biomass to determine if different levels of PPF imposed by woven polyester cloth influenced the cell wall composition of six cultivars of C. dactylon and two hybrid cultivars of C. dactylon × C. transvaalensis. The trial ran over seven weeks, and cell wall composition was assessed at three time points, week two (short period), week five (medium period) and week seven (long period). Cultivar had the strongest influence on cell wall composition in the short period, while at the end of the long period, reduced PPF was the more influential factor affecting the composition of the cell wall. At the final experimental time point, turf quality was negatively correlated with reduced PPF (50% and 70% reduction), total lignin and Acid Insoluble Lignin (AIL) and positively correlated with higher PPF (30% and 0% reduction) carbohydrates and Acid Soluble Lignin (ASL). It is proposed that the defense response pathway was preferred over the typical shade avoidance responses due to the weekly clipping regime confounding the response to reductions in PPF, leading to higher percentages of lignin, ash and lower carbohydrate content in the cell wall of Cynodon grasses.