Towards a global arctic-alpine model for Near-infrared reflectance spectroscopy (NIRS) predictions of foliar nitrogen, phosphorus and carbon content

Abstract

Near-infrared spectroscopy (NIRS) is a high-throughput technology with potential to infer nitrogen (N), phosphorus (P) and carbon (C) content of all vascular plants based on empirical calibrations with chemical analysis, but is currently limited to the sample populations upon which it is based. Here we provide a first step towards a global arctic-alpine NIRS model of foliar N, P and C content. We found calibration models to perform well (R 2 validation = 0.94 and RMSEP = 0.20% for N, R 2 validation = 0.76 and RMSEP = 0.05% for P and R 2 validation = 0.82 and RMSEP = 1.16% for C), integrating 97 species, nine functional groups, three levels of phenology, a range of habitats and two biogeographic regions (the Alps and Fennoscandia). Furthermore, when applied for predicting foliar N, P and C content in samples from a new biogeographic region (Svalbard), our arctic-alpine NIRS model performed well. The precision of the resulting NIRS method meet international requirements, indicating one NIRS measurement scan of a foliar sample will predict its N, P and C content with precision according to standard method performance. The modelling scripts for the prediction of foliar N, P and C content using NIRS along with the calibration models upon which the predictions are based are provided. The modelling scripts can be applied in other labs, and can easily be expanded with data from new biogeographic regions of interest, building the global arctic-alpine model.

One leaf for all: Chemical traits of single leaves measured at the leaf surface using Near infrared-reflectance spectroscopy (NIRS)

“…Near infra-red reflectance spectroscopy (NIRS) has recently been found to provide cost-efficient and accurate measures of leaf chemical traits independent of species, phenology, ecological context and region (Serbin et al ; Petisco et al 2005; Serbin et al 2014; Smis et al 2014; Couture et al 2016; Murguzur et al 2019). Such cost-efficient measures open avenues for incorporating leaf chemical traits in large-scale ecological studies.…”

“…And although cost-efficient, the process-time for milling is still a constraint (Couture et al 2016). Here we ask if arctic-alpine calibration models for NIRS-based measures of chemical traits (Smis et al 2014; Murguzur et al 2019), models that are based on NIRS-spectra from dried, milled and tableted leaves, can be applied to NIRS-spectra of single, whole leaves and still provide accurate measures of chemical content.…”

“…It is therefore a great challenge to assess the actual accuracy of NIRS based measures. Still, NIRS calibration models for a range of chemical constituents perform well, and are not inferior to chemical analysis in terms of accuracy (Smis et al 2014; Murguzur et al 2019). The arctic-alpine NIRS calibration models are developed for measures of foliar Nitrogen, Phosphorus, Carbon (Murguzur et al 2019), and Silicon content (Smis et al 2014).…”

“…Still, NIRS calibration models for a range of chemical constituents perform well, and are not inferior to chemical analysis in terms of accuracy (Smis et al 2014; Murguzur et al 2019). The arctic-alpine NIRS calibration models are developed for measures of foliar Nitrogen, Phosphorus, Carbon (Murguzur et al 2019), and Silicon content (Smis et al 2014). We chose these models for this particular study because they provide accurate measures of chemical traits for a range of growth forms and species, at a range of phenological stages in both arctic and alpine environments.…”

“…Hence, they can potentially provide robust measures of chemical content of single leaves from any species in these environments. Furthermore, there is potential to build on these arctic-alpine NIRS calibration models to become global (Murguzur et al 2019), making them relevant to a range of other environments.…”