Karl J. Johanson

Exudation-reabsorption in a mycorrhizal fungus, the dynamic interface for interaction with soil and soil microorganisms

Abstract The mycelium of Suillus bovinus slowly absorbed [U-14C]glucose and other tracers from droplets placed on the cords, translocated them to the peripheral hyphae and exuded them into fluid drops on the hyphal tips. The exudate was characterized by 1H NMR spectroscopy and by sugar and amino acid analysis. The exuded compounds were mainly carbohydrates and peptides. Acetic acid and oxalic acid were also present in the exudate along with a number of unidentified compounds. Released ions (K, Na, Cl, P, Mg and Ca) were identified by X-ray microanalysis. The mycelium was shown to reabsorb up to 65% of the exuded 14C compounds in 2 days. Glucose, mannitol, glutamic acid (pH 3.2), and Rb+ (as well as other mineral ions) were all readily absorbed by the mycelium, while oxalic acid at pH 4.2 and glutamic acid at pH 6.5 were not. Exudation of fluid droplets on the surface of the hydrophobic mycorrhizal fungus S. bovinus may represent an ecophysiologically important function of the extramatrical hyphae, which provides an interface for interaction with the immediate hyphal environment and its other microorganisms where the peripheral hyphae exchange their photosynthetically derived products for nutrients to be used later by the pine host. We hypothesize that actively absorbed carbohydrates from the root are translocated to the peripheral hyphae along a concentration gradient of sugars and polyols by means of active translocation and diffusion in cell elements and by acropetal water transport in the cord vessels.

Radiocesium in soil and plants in a forest in central Sweden

The distribution of 137Cs in the soil profile and in plants was studied in a forest located 35 km northwest of Uppsala. More than 85% of the total 137 Cs activity was found in the upper 5 cm of the soil profile, implying that nearly all 137 Cs activity is found in the raw humic layer that extends to a depth of about 10 cm in a normal Swedish coniferous forest. The 137Cs activity concentrations in some plants (birch, Scots pine, bilberry, lingonberry, and heather) are presented for the period from 1986 until 1991. Levels of 137 Cs activity in bilberry and lingonberry have decreased since 1986, but in the other plants, the level of activity seems to be relatively constant from 1986 to 1991. This means that the normal level of 137Cs activity found in heather is about 12000 Bg/kg (dry wt.).

Fractionation of caesium (137Cs) in coniferous forest soil in central Sweden

Sequential extraction procedure (SEP) was applied for fractionation of Chernobyl fallout 137Cs bound onto soils of a coniferous forest ecosystem located in central Sweden. Results of sequentially extracted 137Cs fractions demonstrated that 8% (mean value) of the total deposited 137Cs was water soluble (F1) and 13% was NH4OAc extractable (F2). Oxidation of F2 residuals by H2O2 led to a release of 15% of soil-bound 137Cs (F3). Acid digestion of F3 residuals showed a possibility of releasing an extra amount of soil-bound 137Cs, 22% of the total soil 137Cs inventory (F4). These two fractions (F3 and F4) include strongly bound 137Cs that seems to require longer biodegradation processes by soil microflora and microfauna before becoming available for uptake by plants and fungi. More than 37% of the total soil 137Cs inventory was bound onto soil residuals in a non-extractable form that includes slowly degradable organic matter and other soil residual compartments. The distribution coefficient (Kd) was rather low and shows an inverse relation with the increase of percentage of soil organic matter, which indicates a week binding of 137Cs onto forest soil. In contrast, chemical fractionation of soil bound 137Cs showed a substantial fraction of 137Cs was strongly bound onto soil as organically bound 137Cs. Apparently, the binding processes of radiocaesium onto forest soil seems to be time dependent.

Accumulation of 137Cs by fungal mycelium in forest ecosystems of Ukraine.

During 1996-1998, 16 fruit bodies of different species and 204 soil samples down to 10 cm in the close vicinity of the fruit body sites were collected in a coniferous forest in the Ovruch region of Ukraine. The soil samples were sliced into 1 or 2 cm layers and the fungal mycelium was prepared from each of the layers. The 137Cs activity concentration was determined in both soil and mycelium. The mean weight of fungal mycelium was 13.8 mg g(-1) of soil in the upper 4 cm and 7.3 mg g(-1) when measured for the upper 10 cm. At the sites of Paxillus involutus and Sarcodon imbricatus, the mycelium was rather homogeneously distributed in the upper 10 cm and at sites of Xerocomus subtomentosus and Cantharellus cibarius, the mycelium was distributed mostly in the upper layers. The highest 137Cs activity concentrations were found in the upper layers of the soil profile. The 137Cs activity concentrations were usually higher in the fruit bodies compared with the mycelium, with ratios ranging from 0.1 to 66 and a mean of 9.9. The percentage of the total inventory of 137Cs in the soil found in the fungal mycelium ranged from 0.1 to 50%, with a mean value of 15%.

Seasonal variation in the activity concentration of 137Cs in Swedish Roe-deer and in their daily intake

Abstract The seasonal variation of the activity concentration of 137 Cs in roe-deer ( Capreolus capreolus ) from the central part of Sweden was studied in order to test whether there is a relationship with any variation in the seasonal intake of 137 Cs from different plant species. Muscle samples of roe-deer were collected by local hunters in 1986 (June–Septemb er), 1987 and 1988. In 1986, samples were collected in the contaminated regions of central Sweden. In 1987, samples were collected in the Gavle Commune. In 1988, samples were collected from two study areas in central Sweden: Gavle and Harbo. The ground deposition in the Gavle area was 30 000–120 000 Bq m −2 , and in the Harbo area 35 000–45 0 00 Bq m −2 . The calculated daily intake of 137 Cs was based on knowledge of the feed composition taking into account the seasonal shift in diet for roe-deer and the activity concentrations of 137 Cs in the most important feed plants. Radiocesium in the plants which typically constitute roe-deer diet has been regularly measured in the Harbo region since the Chernobyl accident. In these plants, there was only a minor variation of 137 Cs content during these years and a mean 137 Cs activity concentration was therefore used in subsequent calculations. An increase in the activity concentration of 137 Cs in roe-deer was observed in August and September of 1986, 1987 and 1988. For example, the activity concentration of 137 Cs seemed to have increased in Gavle in 1988 from levels of 1000–3000 Bq kg −1 during January–July to 11 800 Bq kg −1 in August. The seasonal variation of the activity concentration of 137 Cs in roe-deer observed in Harbo in 1988 was similar to that seen in Gavle in 1988, with pronounced maximum values in August and September. The calculated daily intake of 137 Cs corresponds well to the activity concentrations of 137 Cs in roe-deer, except in April. Intake of fungal species seems to be an important cause of the maximum values of early autumn.

Model of the seasonal variations of fungi ingestion and 137Cs activity concentrations in roe deer

Abstract This paper presents experimental data on 137Cs activity concentrations in roe deer during 1989–1994 in Harbo, Sweden. The data indicate that 137Cs levels in roe deer are rather constant in the period outside the mushroom season and increase between 2.4 and 4.9 times in autumn and summer. A data set of rumen analyses obtained in the same area is used to estimate the 137Cs daily intakes by roe deer. The time dependence of the calculated daily intakes resembles the kinetics of the activity concentrations in roe deer and supports the hypothesis that the autumn increase of 137Cs concentrations in roe deer is due to the increase of the ingestion rate of mushrooms. A model of the seasonal variations of fungi ingestion and 137Cs activity concentrations in roe deer is presented. The model parameters were estimated from experimental data on 137Cs activity concentrations in roe deer meat and feeds in combination with data of rumen composition. The time when the maximum ingestion rate of mushrooms takes place and the maximum ingestion rate of mushrooms are the model parameters that influence mostly the model predictions. An independent estimation of the ingestion rates of mushrooms, made from experimental values of the rumen composition measured in 1990, was compared with values predicted by the model. An agreement, within a factor of 1.5, was observed.

Radiocaesium transfer to man from moose and roe deer in Sweden

Studies of radiocaesium in the forest ecosystems in Sweden resulted in aggregated transfer factors quantified for the transfer of 137Cs from soil to moose and roe deer. These aggregated transfer factors were 0.02 m2 kg-1 for moose and 0.05 m2 kg-1 for roe deer. There seems to be no decrease in the 137Cs activity concentrations in moose harvested in our research area and therefore we suggest the use of the physical half-life of 137Cs (30 years) as the effective ecological half-life. The time-integrated transfer of 137Cs from the Chernobyl fall-out to man by moose in Sweden was calculated and found to be 115 GBq, corresponding to 1500 man Sv for moose. The time-integrated transfer by roe deer to man was estimated to be between 25-48 GBq, corresponding to 327-620 man Sv for roe deer. The annual transfer of 137Cs to man by moose has varied between 2.0-2.7 GBq, corresponding to 27-34 man Sv. Depending on the group studied, the mean annual transfer of 137Cs can be calculated to be from about 250 to 43,000 Bq. For example, the mean annual transfer of 137Cs by moose to hunters and their families in Gävle commune, the most affected commune in Sweden, was estimated to be about 26,000 Bq, corresponding to 0.34 mSv.

Radiocaesium in fruitbodies and mycorrhizae in ectomycorrhizal fungi

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.

Activity concentrations of 137Cs in moose and their forage plants in mid-Sweden

Abstract The 137 Cs activity concentrations in moose and their principal fodder plants as well as the botanical composition of the rumen content in moose were studied in three areas of the country of Vasternorrland in Sweden. The mean 137 Cs activity concentration in moose muscle samples from the three areas with a ground deposition from 20 to 60 kBq m −2 varied between 540 and 915 Bq kg −1 . During the period July to October, three plant species — fireweed, birch and bilberry — constitute more than 70% of the rumen content. Estimation of the daily 137 Cs intake was performed based on the botanical analysis of rumen content and the 137 Cs activity concentrations found in samples of fodder plants. A mean F f of 0·19 day kg −1 was calculated. A mean aggregated transfer factor of 0·016 m 2 kg −1 was found for the three areas.

Influence of zeolite on the availability of radiocaesium in soil to plants.

Plant availability of radiocaesium is usually high immediately after incorporation in a soil. However, for some Swedish soils, e.g, peat soils, a high radiocaesium uptake in plants has also been observed during a second growth period after contamination. For these soils the reduction in the plant availability of the nuclide seems to be a slow process. In the last two years the mineral zeolite has become of interest and has been tested as a caesium binding agent in both animal and in soil-plant systems. The aim of this study was to evaluate the time dependency and the effect of zeolite on the plant availability of radiocaesium in a peat soil-plant system. The pot experiments designed for this purpose were carried out in a climate chamber, using winter wheat as the test crop. A significant reduction of the uptake of 134Cs was obtained in wheat when increasing amounts of zeolite were added. This reduction in plant uptake, up to a factor of 8, might depend on two factors. One is that zeolite has reduced the activity concentration of radiocaesium in the soil solution available to the plant roots. The other is that the potassium added with the natural zeolite increased the degree of dilution of caesium in the soil solution. Also, increasing equilibration time for caesium in soil before sowing brought about an effective reduction in the caesium uptake.