Abstract
The research objective was to use proximal spectroscopy in visible and near infrared (VNIR) spectra to determine the total leaf nitrogen (TN) content and the above-ground biomass of Miscanthus × giganteus (MxG) grown in the open-roof greenhouse experiment on soil contaminated with cadmium and mercury (100 mg Cd/kg soil; 20 mg Hg/kg soil), in dependence of different soil amendments in four treatments (I-soil without amendment; II-sludge; III-mycorrhizae; IV-MxG ash). Leaf reflectance was acquired using a field spectroradiometer (350–1050 nm) at the end of the vegetation period between 2018 and 2019 (n = 24). TN content was determined using the dry combustion method, while biomass was weighted immediately after the harvest. In terms of the treatment effect, sludge showed the greatest contribution in TN content. Regarding the biomass quantity, MxG ash revealed the best results as soil amendment. Applying the partial least squares regression, complete correlation and low root mean squared error (RMSE) were obtained between predicted and measured values for the validation dataset of TN content (R2 = 0.87, RMSE = 0.139%), while a strong correlation was calculated for biomass (R2 = 0.53, RMSE = 0.833 t/ha). As an additional tool with analytical methods, proximal spectroscopy is suitable to integrate the optical and physiological properties of MxG, and to assess nutrient stress in crop grown on contaminated soils.
Highlights
Many soils are known to be contaminated with heavy metals due to industrialization [1]
By measuring the reflection of plant tissue in the visible and near-infrared (VNIR) regions of the electromagnetic spectrum, it is possible to determine physiological and biochemical processes in the cell, such as the decrease of green quantity and photosynthesis or the decline of nutrient absorption and transportation in a crop grown on soils contaminated with heavy metals, even before the appearance changes [29]
The research objective was to use proximal visible and near infrared (VNIR) spectroscopy to determine leaf N content and the above-ground biomass yield of Miscanthus grown in the open-roof greenhouse experiment on soil contaminated with cadmium and mercury in dependence of different soil amendments
Summary
Many soils are known to be contaminated with heavy metals due to industrialization [1]. The most common symptoms of mercury contamination are inhibition of photosynthesis and potassium intake, retardation of seedling and root growth, yield reduction, impairment of plant transport systems and water uptake, and leaf chlorosis [15,16,17] For this reason, plants have developed various mechanisms to control the entry and transport of metals within their organs. By measuring the reflection of plant tissue in the visible and near-infrared (VNIR) regions of the electromagnetic spectrum, it is possible to determine physiological and biochemical processes in the cell, such as the decrease of green quantity and photosynthesis or the decline of nutrient absorption and transportation in a crop grown on soils contaminated with heavy metals, even before the appearance changes [29]. The specific goals were (a) to determine the influence of soil contamination with cadmium and mercury on TN content in MxG leaf, above-ground biomass yield and leaf reflection; (b) to discriminate between experiment treatments based on hyperspectral leaf reflection; and (c) to develop a calibration model to estimate leaf TN content and the yield of aboveground MxG biomass based on leaf reflection using a linear algorithm
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