Hanne Suokanerva

Long-term effects of elevated UV-B radiation on photosynthesis and ultrastructure of Eriophorum russeolum and Warnstorfia exannulata

The depletion of stratospheric ozone above the Arctic regions may increase the amount of UV-B radiation to which the northern ecosystems are exposed. In this paper, we examine the hypothesis that supplemental UV-B radiation may affect the growth rate and photosynthesis of boreal peatland plants and could thereby affect the carbon uptake of these ecosystems. In this study, we report the effects of 3-year exposure to elevated UV-B radiation (46% above ambient) on the photosynthetic performance and ultrastructure of a boreal sedge Eriophorum russeolum and a moss Warnstorfia exannulata. The experiment was conducted on a natural fen ecosystem at Sodankylä in northern Finland. The effects of UV-B radiation on the light response of E. russeolum CO(2) assimilation and the maximal photochemical efficiency of photosystem II in a dark-adapted state (F(v)/F(m)) were measured in the field. In addition, the effect of supplemental UV-B radiation on organelles of photosynthetic cells was studied by electron microscopy. The UV-B treatment had no effect on the CO(2) assimilation rate of either species, nor did it affect the structure of the cell organelles. On chlorophyll fluorescence, the UV-B exposure had only a temporary effect during the third exposure year. Our results suggested that in a natural ecosystem, even long-term exposure to reasonably elevated UV-B radiation levels does not affect the photosynthesis of peatland plants.

Seasonal acclimation of the moss Polytrichum juniperinum Hedw. to natural and enhanced ultraviolet radiation

Short- and long-term changes in the methanol-extractable UV-absorbing compounds and biomass of the pioneer moss Polytrichum juniperinum in response to natural and enhanced UV radiation were studied. Under natural conditions, the compounds were found to fluctuate seasonally. In summer these compounds correlated negatively with irradiation. The concentration was low in July after a period of simultaneous heat, drought and high irradiation. Transient positive correlation between daily concentration and UV was seen in June. The concentration increased towards autumn and was relatively high under snow. Two enhanced UV experiments were performed. Seasonality in the compounds was again observed, with negative correlations with irradiation. During the first weeks, a transient inhibition of compound production was observed after the daily UV-B treatment. After six years of modulated UV-treatment in situ, photosynthesizing biomass decreased under UV-B and increased under UV-A. A larger variation in the UV-absorbing compounds was observed under UV-B treatment.

SNORTEX (Snow Reflectance Transition Experiment): Remote sensing measurement of the dynamic properties of the boreal snow-forest in support to climate and weather forecast: Report of IOP-2008

Large discrepancies are observed between snow albedo in Numerical Weather Prediction (NWP) models and from satellite observations in the case of high vegetation. Knowledge of the Bidirectional Reflectance Distribution Function (BRDF) of snow-forest system is required to solve the problem. The 3-years SNORTEX (Snow Reflectance Transition Experiment) campaign acquires from 2008 in situ measurements of snow and forest properties in support to the development of modelling tools and to validate coarse resolution satellite products (POLDER, MODIS, MERIS, METOP). The measurement scheme and some first example results are presented from the Intensive Observing Period (IOP) of 2008, which can be decomposed into airborne and ground operations. Multi-temporal BRDF at a metric resolution were acquired from OSIRIS (airPOLDER) onboard a helicopter and from ground with FigiFiGo spectrogoniometer. The same helicopter embarked a pair of UV sensors, pyranometers and a wide-optics camera. Ground component includes exhaustive snow measurements.

Reflectance spectroradiometer measurement system in 30 meter mast for validating satellite images

Reflectance spectroscopy is a well established field of research, evolved from simple laboratory instruments into a satellite-oriented global environment research tool. However, due to the effect of the atmosphere and the large area coverage of satellite images, reflectances extracted from satellite data or ground based spectra are not correlating properly. In order to improve the comparability of satellite-borne and ground-based reflectance observations, we have constructed a reflectance spectrometer measurement assembled to a 30 meter mast. With this construction we are able to average reflectance spectra from up to 400 m2 area in the ground and up to 180 m2 area in the level of tree tops, respectively. A primary function of our measurement system is the correction of satellite images from atmospheric effects. This paper presents the measurement system for validating satellite images, constructed to Arctic Research Centre in Sodankylauml. The operative measurements in the system started at the summer of 2006.

Different response of two reindeer forage plants to enhanced UV-B radiation: modification of the phenolic composition

The long-term effects of enhanced UV-B radiation on the content and composition of leaf phenolics in Epilobiumangustifolium L. and Eriophorumrusseolum Fries ex Hartman were studied in northern Finland (68°N) using two UV-B enhancement experiments, both simulating UV-BCIE radiation and corresponding to a 20% loss of ozone layer. High proportions of hydrolyzable tannins (69%) and condensed tannins (66%) characterized both Epilobium and Eriophorum leaves, respectively. No UV treatment effect was detected in the content or composition of Epilobium leaf soluble phenolics, whereas significant UV effects were detected in Eriophorum leaves in a developmental-specific manner. At the end of the growing season, the proportion of total soluble phenolics was higher in leaves exposed to enhanced UV-A and UV-B radiation than in the control leaves, but the phenolic composition was not significantly modified. This study introduces a new example on plants’ phenolic response to UV radiation being species-specific and detectable only at certain developmental stages. Possible consequences of increased phenolic content in forage plants for selection and digestibility by reindeer are, however, not yet known.

Decreased frost hardiness of Vaccinium vitis-idaea in reponse to UV-A radiation

The aim of this study was to investigate plant frost hardiness responses to ultraviolet (UV) radiation, since the few results reported are largely contradictory. It was hypothesized that functional adaptation of life forms could explain these contradictions. Dwarf shrubs and tree seedlings, representing both evergreen and deciduous forms, were tested (Vaccinium vitis-idaea, Vaccinium myrtillus, Pinus sylvestris, Betula pubescens and its red form f. rubra). The research was performed in Sodankylä, Northern Finland (67°N), with enhanced UV-B- and UV-A-radiation treatments between 2002 and 2009. Plant frost hardiness was determined using the freeze-induced electrolyte leakage method in early autumn, during the onset of the frost hardening process. Additional physiological variables (malondialdehyde, glutathione, total phenols, C and N contents) were analyzed in V. vitis-idaea to explain the possible responses. These variables did not respond significantly to UV-radiation treatments, but explained the frost hardiness well (r² = 0.678). The main finding was that frost hardiness decreased in the evergreen shrub V. vitis-idaea, particularly with enhanced UV-A radiation. No significant responses were observed with the other plants. Therefore, this study does not support the idea that enhanced UV radiation could increase plant frost hardiness.

Validation of microwave emission models by simulating AMSR-E brightness temperature data from ground-based observations

For several applications, spaceborne microwave measurements are used to get large scale information of snow- covered terrain. Emission models for soil, vegetation and snow are needed in extraction of snow parameters from satellite measurements. In this paper space-observed brightness temperature of snow-covered terrain is simulated from in situ measurements using HUT snow model, rough bare soil reflectivity model and boreal forest emission model. The results are compared with AMSR-E data. Correlations of time series between simulated and measured brightness temperatures were best on the highest frequencies being better than 0.7 on frequencies above 18 GHz.

Reflectance Properties of Snow and Forest Canopy: Impact on Snow Retrieval Algorithms

Field spectroscopy is an effective means to determine the reflectance of different terrain surfaces for the development and validation of monitoring systems using Earth Observation data. The objective of this investigation is to examine the variability of snow and forest canopy reflectance in the boreal forest area in order to improve the existing snow mapping algorithms, such as the reflectance model-based snow covered area (SCA) SCAmod snow mapping method by the Finnish Environment Institute (SYKE). The field experiments were conducted by using two identical spectroradiometers. One instrument was in portable use and the other was installed to a 30-meter mast in order to obtain the forest canopy reflectances. We present here the obtained reflectance variability for dry snow and the simulated results for scene reflectance above the tree cover obtained by the comparison of mast-based spectrometer measurements with linear spectral mixing of ground-based reflectances. The results show that the field spectrometer observations are feasible for the assessment of the variability of reflectance and validation of satellite based mapping.

Comparison of MODIS surface reflectance with mast-based spectrometer observations using CORINE20001and cover database

In this work we compared the MODIS surface reflectance observations with the spectrometer measurements made from the 30 m high mast set up at Sodankyla. Combining MODIS data from wider area around the mast location with the information of land cover types found in high resolution (25 m*25 m) CORINE2000 database we were able to retrieve the reflectance of coniferous forests, which is the land cover type around the tower. As a result we found a good co-variation between the reflectance values of MODIS and the mast-based spectrometer although there was a consistent low bias in MODIS values. The effect of aerosol content in the atmosphere on the biases between two instruments was studied and a significant correlation was found between the biases and the AOD values.