The utility of optical remote sensing for characterizing changes in the photosynthetic efficiency of Norway maple saplings following transplantation

Following outplanting, trees undergo a period of stress, referred to as transplant shock. Tree mortality rates are known to increase during this period, so monitoring the effects of transplant shock is key to improving the future survival rates of outplanted trees. Leaf reflectance spectra, measured by field spectrometry, can be used to derive reflectance indices that are related to a number of biophysical parameters, including photosynthetic efficiency and leaf chlorophyll content. Field spectrometry has the advantage of being non-invasive and relatively cheap and is therefore a suitable candidate for monitoring the effects of transplant shock. The objective of this study was to assess the applicability of passive remote sensing as a tool to measure the reduction, and the subsequent recovery, of photosynthetic efficiency during the weeks following transplantation. Spectral reflectance, gas exchange, and chlorophyll fluorescence measurements of Norway maple (Acer platanoides L.) saplings were collected over an 8 week period, following transplantation from a glasshouse to an outdoor environment. Very low photosynthetic rates were measured in the weeks after outplanting followed by gradual increases, with stabilization occurring in the later stages of the experimental period. Spectral data were collected on newly planted saplings in both clear and cloudy conditions, and the relationships between spectral reflectance indices, photosynthetic light-use efficiency (LUE), and the quantum yield of photosystem II, estimated using the fluorescence parameter Delta F/F'(m), were explored. The photochemical reflectance index (PRI) was weakly to moderately correlated with LUE (coefficient of determination (R-2) = 0.22, p <0.05), Delta F/F'(m) (R-2 = 0.34, p <0.05), and the photosynthetic photon flux density (R-2 = 0.30, p <0.05). Several chlorophyll-based spectral indices were moderately correlated with LUE, including ND 705 (R-2 = 0.45, p <0.05). As with LUE, there was a marked trend in PRI values over the study period, but no trend was observed in ND 705. The study demonstrates that hyperspectral remote sensing has the potential to be a useful tool in the detection and monitoring of the dynamic effects of transplant shock.