Hyperspectral VNIR-spectroscopy and imagery as a tool for monitoring herbicide damage in wilding conifers

Abstract

Wilding conifers, the naturally regenerated scions of exotic conifer species, are a major ecological and economic issue in New Zealand. Hyperspectral imagery could provide a useful means of monitoring the efficacy of wilding control measures but little research has examined this possibility. Data were collected from an experiment, that included thirty-nine young Pinus contorta (Douglas) trees allocated to a control and two herbicide treatments (triclopyr butoxyethyl ester and diquat dibromide monohydrate). The objectives of this research were to examine the temporal impacts of herbicide on needle discolouration, spectral properties and tree physiology and to develop models to predict photosynthetic parameters from hyperspectral data. In accordance with obvious discolouration on the first day after treatment, values of net photosynthesis rate (A), electron transport rate (ETR), stomatal conductance (G) and optimal quantum yield of photosystem II (F v /F m) declined rapidly for plants treated with diquat. Discolouration following application of triclopyr was not evident before the second week, and values of A, ETR, G and F v /F m declined slower than those of diquat. Of the tested narrow-band spectral indices calculated from needle spectra photochemical reflectance index (PRI) exhibited the strongest correlation with the four photosynthetic parameters and R 2 values between PRI and A, F v / F m , ETR and G were, respectively, 0.53, 0.46, 0.68 and 0.29. Models that used raw spectra as inputs showed that sparse partial least squares (SPLS) outperformed the three other approaches tested (PLS, Support Vector Machines, Elastic Net) and R 2 values using this approach for A, F v /F m , ETR and G were, respectively, 0.64, 0.62, 0.65 and 0.42.

Using hyperspectral plant traits linked to photosynthetic efficiency to assess N and P partition

“…The availability of P has an impact on many important aspects of photosynthesis (Marschner, 1995;Taiz et al, 2015) and, as shown in our study, P has been found to be significantly and positively related to both Vcmax and Jmax (Bown et al, 2007). Given that photosynthetic rate is also positively related to both PRI (Gamon et al, 2016;Ripullone et al, 2011;Scholten et al, 2019;Wong and Gamon, 2015a, b) and SIF (Frankenberg et al, 2011;Guanter et al, 2014;Smith et al, 2018) it follows that these traits were positively related to P when data was restricted to the P limiting range.…”

Monitoring biochemical limitations to photosynthesis in N and P-limited radiata pine using plant functional traits quantified from hyperspectral imagery

“…Research has widely demonstrated the utility of PRI for predicting light use efficiency (Garbulsky et al 2011;Peñuelas et al 2011) and key photosynthetic parameters under a range of stresses including severe drought conditions (Ripullone et al 2011), cold winter temperatures (Gamon et al 2016;Wong and Gamon 2015a, b) and herbicide damage (Scholten et al 2019). The relationship found here between PRI and photosynthetic capacity is consistent with Scholten et al (2019) and has a strong theoretical basis as PRI can track plant photosynthetic activity through its intimate link with the dissipation of excess energy by nonphotochemical quenching (NPQ) via the xanthophyll cycle. The xanthophyll cycle is activated during periods of excess excitation energy in the leaf and through this process violaxanthin is de-epoxidized to zeaxanthin.…”

“…PRI provides a linkage with the efficiency of photosystem II through characterising variation in xanthophyll pigments and as such quantifies changes in non-photochemical quenching and light use efficiency (Gamon et al 1997). This index has been successfully used to predict photosynthetic rate (Drolet et al 2008;Fuentes et al 2006;Gamon et al 1997;Guo and Trotter 2004;Hilker et al 2008;Middleton et al 2009;Nichol et al 2000;Penuelas et al 1995;Stylinski et al 2000) and the photosynthetic response of plants subject to a range of stresses (Dobrowski et al 2005;Hernández-Clemente et al 2011;Scholten et al 2019;Suárez et al 2008) and is responsive to seasonal changes in pigments (Gitelson et al 2017). PRI can be readily used to scale photosynthesis to the canopy level as recently launched satellite based hyperspectral imagers (e.g.…”

Near-Infrared Hyperspectral Imaging Pipelines for Pasture Seed Quality Evaluation: An Overview

“…Applications in plant-based industries include fruit, grain and seed quality, particularly pathogen infestation and varietal purity, as well as chemical composition. The list of applications continues to grow rapidly [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37].…”