Using near infra red reflectance spectroscopy (NIRS) to quantify tissue composition in the seagrass Posidonia australis

•Near infrared reflectance spectroscopy (NIRS) provides a rapid tool to analyse aquatic plant tissue.•NIRS reduces the costs associated with chemical analyses.•NIRS models successfully predicted total phenols and nitrogen content in the seagrass Posidonia australis.•Large scale spatial patterns in the phenol and nitrogen content of P. australis were quantified using NIRS.

Plant tissues display high levels of intra-specific variation in composition that strongly affects important ecosystem processes such as rates of herbivory, disease, and decomposition. Near infrared reflectance spectroscopy (NIRS) provides a rapid method to analyse tissue content with the potential for lower costs than conventional chemical analyses, and facilitating the high sample replication required to quantify spatial or temporal patterns in tissue variation. This study aims to determine the effectiveness of NIRS to quantify the ecologically important traits of total phenols, total nitrogen and total carbon in the seagrass Posidonia australis. Robust NIRS models were successfully developed for total phenols and nitrogen content, and used to quantify broad scale geographic patterns of intra-specific variation in these traits across 12 populations of P. australis. Given that only 90 out of 360 samples were required for the chemical analyses used to produce calibrations, NIRS facilitated this research by increasing sample size and reducing time and cost per sample.