Ivanka Nikolova’s research while affiliated with Swedish University of Agricultural Sciences and other places

We examined the long-term effects of a single application of potassium (K) fertilizer (100 kg K ha(-1)) in 1992 on (137)Cs uptake in a forest ecosystem in central Sweden. (137)Cs activity concentrations were determined in three low-growing perennial shrubs, heather (Calluna vulgaris), lingonberry (Vaccinium vitis-idaea) and bilberry (Vaccinium myrtillus), and in four wild fungal species (Cortinarius semisanguineus, Lactarius rufus, Rozites caperata and Suillus variegatus). Uptake of (137)Cs by plants and fungi growing on K-fertilized plots 17 years after application of the K fertilizer was significantly lower than in corresponding species growing in a non-fertilized control area. The (137)Cs activity concentration was 21-58% lower in fungal sporocarps and 40-61% lower in plants in the K-fertilized area compared with the control. Over the study period, this decrease in (137)Cs activity concentration was more consistent in plants than in fungi, although the effect was statistically significant and strongly pronounced in all species. The effect of K fertilization in reducing (137)Cs activity concentration in fungi and plants decreased over time but was still significant in 2009, 17 years after fertilization. This suggests that application of K fertilizer to forests is an appropriate and effective long-term measure to decrease radiocaesium accumulation in plants and fungi.

Soil samples were collected in various forest stands, located about 40 km north-west from Uppsala. The various stands were: (1) Clear cut area made in 1987, (2) Normal forest with 50–100 old Norway spruce and Scots pine and with a thick humic layer of about 10 cm; (3) Raised bog with 50-year-old Scots pine and Sphagnum moss layer over peat soil. (4) Rocky area with old Scots pine, growing on a shallow soil, mainly of organic origin. (5) Normal forest with nearly 100-year-old spruce and pine, growing a shallow humic layer over sandy soil. Soil blocks of about 20×20 cm and down to a depth of 10–15 cm were collected on each site. The soil samples were mechanically separated into various fractions: bulk, rhizosphere and soil–root interface. The results showed that was unevenly distributed between the three soil fractions. The highest activity concentrations — 3–4 times higher than in the other two fractions — as well as the highest organic content — usually more than 95% — were found in the soil–root interface fraction. Of the total activity in the soil, 18% as a mean value was found in the soil–root interface fraction. The results thus show that a substantial fraction of the in the soils in some way associated with the biological part of the soil, probably with the fungal component.

The experience of radiation accidents, the Chernobyl accident in the first place, has shown that the methodology used to develop and estimate the effectiveness of countermeasures to reduce negative consequences of accidental contamination of the environment by radionuclides does not meet the requirements of fast response in case of an emergency. In order to overcome this shortcoming, Geographic Information Systems (GIS) and computer systems for decision-making support in case of emergency are being actively developed [l]. An essential part of such systems are mathematical models of migration and transformation of radionuclides in the environment and their impact on man and components of terrestrial and aquatic ecosystems. The accuracy of prediction by these models in determining the effectiveness of decisions making is largely dependent on the accuracy of estimating input parameters [2]. In this context, it is important to create an expert system for estimation of input model parameters which would form a separate module in the decision-making system. Special emphasis should be put on those parameters to which the predictions are more sensitive. An important component in calculation of radiation dose is the estimation of the soil-plant transfer of radionuclides. For this purpose, the concentration ratio CR is normally used which is defined as the ratio of radionuclide concentrations in the plant and in the upper soil layer. The values of CR determined experimentally in different conditions for a particular plant can differ by a factor hundred or even thousand [3]. Accordingly, using a plant-average CR leads to a considerable uncertainty in prediction. For this reason, numerous attempts were made to develop methods for estimating site-specific values of CR. A great effort went into deriving empirical relations between the accumulation of radionuclides in plants and soil properties [4]. An essential drawback of purely empirical characteristics is that they are not generally valid. In order to be applied to soils different from those that they were obtained, characteristics should be justified based on information about mechanisms of sorption-desorption of radionuclides in soil and their soil-plant transfer.

Fruitbodies of Suillus variegatus and Lactarius rufus and, at a maximum distance of 50 cm, the corresponding mycorrhizae, were collected on a rocky area in a coniferous forest. The tuberculate mycorrhizae collected close to S. variegatus fruitbodies were identified by the RFLP pattern to be S. variegatus mycorrhizae. In contrast the smooth brown mycorrhizae collected close to fruitbodies of L. rufus were found to be of various species — L. rufus, but also Russula sp. The 137Cs activity concentrations in fruitbodies and the fungal part of the tuberculate mycorrhizae of S. variegatus were about the same. A local enrichment of 137Cs within fruit-bodies was studied by collecting fruitbodies growing in clusters. Between 13 and 64% of the mean ground 137Cs deposition of the cluster area (400 or 625 cm2) was found in the fruitbodies. This indicates that there might be an important fungal redistribution of 137Cs in the forest floor during the production of fruitbodies. The distribution of 137Cs within the fruitbodies was heterogenous. For example in Cortinarious armillatus, the 137Cs level in the cap was 2.7 times higher compared to in the stripe.

Following the Chernobyl accident in 1986, sporocarps of Suillus variegatus in Sweden showed a large amount of individual variation in concentration of 137Cs activity. Our aim was to determine the degrees to which this variability in sporocarp 137Cs levels could be explained by differences between (i) local populations, (ii) fungal genets and (iii) locations within genets. Five populations in a 100-yr-old Scots pine forest, located within a 1 km2 area, and two populations in Scots pine/Norway spruce forest, located 40 km northwest of Uppsala, were investigated. In total, 154 sporocarps were analysed to determine their 137Cs content. Of these, the genetic affiliations of 86 were successfully characterized using somatic incompatibility reactions. Twenty-six genets were found which, on average, consisted of 6·5 sporocarps. The genets averaged 7·5 m in size, measured as the length between the most distant sporocarps. The mean sporocarp 137Cs level was 67·1 ± 2·8 kBq kg-1 D.W. (range between 13·6 and 182). According to analyses of variance, within-population variation accounted for 60% of the total variation in 137Cs levels, while 40% was ascribed to variation among populations. Within a population, 137Cs levels did not generally differ significantly between genets. Plausible reasons for intraspecific variation in radiocaesium content in sporocarps are discussed.

This article presents the current status and characteristics of China's space programme before describing the country's future goals and the specific types of research and satellite production that will be undertaken to realize them. China's programme, although small, has achieved much in terms of economic and social benefits for its people (eg through land-surveying, communications, education, water conservation and earthquake prediction). This is a result of the emphasis place on applied-satellites, coordination of production, development and research and intensive ground testing. This emphasis will remain, along with the effort to ensure that new satellites are long-lived and stable in operation. However, a change from the previous policy of independence is signalled by a growing interest in international cooperation, including that with other developing countries like Brazil.