Katja Klančnik

Use of a modified Allium test with nanoTiO2

Extensive production and wide application of TiO(2) nanoparticles has stimulated research on its potential biological effects on different groups of organisms but the interaction of TiO(2) nanoparticles with higher plants remains poorly understood. We have studied the effect of TiO(2) nanoparticles on Allium cepa using a modification of the conventional Allium test with nanoparticles suspended in distilled water as opposed to growth medium. Nanoparticulate TiO(2) was found to have low toxic potential and the mitotic index was among the most sensitive measures of the effect of nano-TiO(2). We conclude that modified Allium test is suitable to provide comparative data on the biological potential of a variety of nanoparticles and could be used in a tiered approach to nanotoxicity testing.

Silicified structures affect leaf optical properties in grasses and sedge.

Silicon (Si) is an important structural element that can accumulate at high concentrations in grasses and sedges, and therefore Si structures might affect the optical properties of the leaves. To better understand the role of Si in light/leaf interactions in species rich in Si, we examined the total Si and silica phytoliths, the biochemical and morphological leaf properties, and the reflectance and transmittance spectra in grasses (Phragmites australis, Phalaris arundinacea, Molinia caerulea, Deschampsia cespitosa) and sedge (Carex elata). We show that these grasses contain >1% phytoliths per dry mass, while the sedge contains only 0.4%. The data reveal the variable leaf structures of these species and significant differences in the amount of Si and phytoliths between developing and mature leaves within each species and between grasses and sedge, with little difference seen among the grass species. Redundancy analysis shows the significant roles of the different near-surface silicified leaf structures (e.g., prickle hairs, cuticle, epidermis), phytoliths and Si contents, which explain the majority of the reflectance and transmittance spectra variability. The amount of explained variance differs between mature and developing leaves. The transmittance spectra are also significantly affected by chlorophyll a content and calcium levels in the leaf tissue.

Leaf optical properties are affected by the location and type of deposited biominerals

This study aimed to relate the properties of incrusted plant tissues and structures as well as biomineral concentrations and localization with leaf reflectance and transmittance spectra from 280nm to 880nm in the grasses Phragmites australis, Phalaris arundinacea, Molinia caerulea and Deschampsia cespitosa, and the sedge Carex elata. Redundancy analysis revealed that prickle-hair length on adaxial surface and thickness of lower epidermis exerted significant effects in P. australis; prickle-hair density at abaxial leaf surface and thickness of epidermis on adaxial leaf surface in P. arundinacea; thickness of epidermis on adaxial leaf in D. cespitosa; prickle-hair density on adaxial leaf surface and thickness of cuticle in M. caerulea; and prickle-hair density on adaxial leaf surface and cuticle thickness of the lower side in C. elata. Micro-PIXE and LEXRF elemental localization analysis show that all of these structures and tissues are encrusted by Si and/or by Ca. Reflectance spectra were significantly affected by the Ca concentrations, while Si and Mg concentrations and the Ca concentrations significantly affected transmittance spectra. High concentrations of Mg were detected in epidermal vacuoles of P. arundinacea, M. caerulea and D. cespitosa. Al co-localises with Si in the cuticle, epidermis and/or prickle hairs.

Spectral Signatures of Conifer Needles Mainly Depend on Their Physical Traits

ABSTRACT The aim of this study was to determine the traits that define the optical properties of the needles of four coniferous species: Picea abies, Picea omorika, Abies alba and Pinus sylvestris. The analysis included measurements of the needles for their morphological and anatomical aspects, reflectances at the upper and lower needle surfaces through their 280–880-nm spectra, and biochemical traits. The needles of these species differed significantly in the majority of morphological and anatomical traits, with the most pronounced differences seen for the thickness of the cuticle and epidermis, the needle width and thickness, the width of the central cylinder, and the position and density of the stomata. The reflectance spectra of the upper needle surface were very similar, while for the reflectance of the lower needle surface, P. omorika reflected light the most efficiently, followed by A. alba. The biochemical properties indicated significant differences in the amounts of UV-absorbing compounds, which were highest in P. sylvestris, and relatively low in A. alba and P. abies. The upper needle surface reflectance spectra were significantly affected by thickness of the cuticle, by pore width and by total mesophyll thickness, which explained 24%, 12% and 4% of the variability, respectively. The needle traits that explained the reflectance spectra variability of the lower needle surface were the hypoderm (28%), needle thickness (4%), density of stomata (28%), length of the outer pores (9%), and amount of UV-A-absorbing compounds (7%). Our data show that the needle reflectance spectra are primarily affected by the physical structure of the needles, and little by the needle biochemistry. This calls into question the methodologies for determination of the biochemical status of conifers based on their reflectance spectra.

Do Reflectance Spectra of Different Plant Stands in Wetland Indicate Species Properties

This contribution discusses the relationships between reflectance spectra obtained by field spectroscopy and properties of the leaves of the species that form a stand and the relation between reflectance spectra and stand characteristics. We thus investigate the reliability of conclusions made at the species levels on the basis of the reflectance spectra of the stands. We studied monospecific and mixed stands that thrive in habitats along a hydrological gradient in the intermittent Lake Cerknica. The reflectance spectra differed significantly at the stand and leaf levels; however, although the shape of the reflectance spectra of a monospecific stand with Phalaris arundinacea was similar to the shape of the leaf spectra, this was not the case for mixed stands. The leaf morphological and biochemical properties that explain most of the variability of the spectra differed for graminoids and different dicotyledons. This study shows that based on the reflectance spectra, the species properties for monospecific stands can be deduced, while for mixed stands, such deductions can be misleading.

The quality and quantity of light in the water column are altered by the optical properties of natant plant species

Floating-leaved rhizophytes and pleustophytes are the first barrier to Sun’s rays and significantly affect the light regime of the water column. To evaluate these effects on light attenuation, the reflectance and transmittance spectra variability were examined according to the leaf traits within three plant groups: (1) seed plants with green abaxial surfaces; (2) seed plants with red abaxial surfaces; and (3) ferns with trichomes. Specific leaf area (SLA), chlorophyll a and b, and UV-B and UV-A-absorbing substances differed between these three groups. The ‘spectral signatures’ of floating-leaved seed plants are similar to those of terrestrial seed plants, with a peak in the green region and a pronounced ‘red edge’. Ferns transmitted more light along the whole spectrum compared to other species. Most reflectance and transmittance spectra variability of the first group was explained by SLA. In the second group, 36% of the reflectance spectra variability was explained by tissue density and carotenoids, and 48% of the transmittance spectra variability by carotenoids, anthocyanins and SLA. In ferns, the reflectance spectra variability was mainly explained by chlorophylls, and partly by trichome length and mesophyll thickness, with the transmittance spectra variability significantly affected by chlorophyll b.

Optical properties of halophyte leaves are affected by the presence of salt on the leaf surface

Abstract Halophytes have developed a variety of adaptations to cope with excessive salt and other environmental constraints. These have resulted in altered leaf traits that affect the leaf optical properties and energy balance. In halophytes, there is often salt on the leaf surface due to salt aerosols and salt excretion from glandular cells. After examining the effects of the natural salt deposition on the leaf surface on the leaf light reflectance and transmittance, we defined the relationship between different leaf traits and the leaf optical properties in four halophytes (Atriplex prostrata, Atriplex portulacoides, Crithmum maritimum, and Limonium angustifolium). They differed significantly in the amount of naturally deposited salt on their leaves (range, 0.50–7.55 mg cm−2) and in the majority of the measured leaf traits. Differences were most pronounced for epidermal layer thickness, dry mass per leaf volume, and amount of UV-absorbing compounds. For the leaf optical properties, the salt on the leaf surface significantly reduced transmittance of UV, violet, and blue wavelengths. Redundancy analysis indicated that leaf upper epidermis thickness and leaf surface salt explained 58% and 7%, respectively, of the variability of the measured reflectance spectra. Leaf surface salt was particularly important for short wavelengths, explaining 35% of the reflectance variability in the UV region, and 20% in the violet and blue regions. The majority of the transmittance spectra variability was explained by leaf pigment content. These data reveal that leaf surface salt can function as a UV screen, to filter out potentially damaging short-wave radiation.