Lichen Carpet Research Articles

10.1007/s11476-008-2002-x

The distribution of radioactive Cs and heavy metals (V, Cr, Mn, Co, Ni, Cu, Zn, Cd, Hg, and Pb) in the lichen-substrate system and in lichen tissues were examined using the example of Cladonia genera. The upper podetia-lower podetia-dead podetia-base-substrate system was sampled at 32 sites in Novosibirsk oblast and Altai administrative territory, 16 of which were selected for detailed studying of the trace element distribution in the upper and lower podetia using cold press and the modified Dexter technique. One in vivo and two in vitro experiments simulated the influence of metal-rich atmospheric fallouts on the lichen carpet. The lichen carpet was irrigated by solution of metal nitrates (Co, Cu, Zn, Cd, Hg, and Pb) in the former case and loaded in these solution during the latter experiment. The experiment performed in the laboratory conditions (in vitro) was aimed at studying the dynamics of metal accumulation in lichen constituents and their subsequent extraction with distilled water to monitor metal sorption on the podetium cell walls. The metal contents and the activity of radioactive Cs in the lichen samples, including lichen cell sap, as well as in the base and substrate, were determined by atomic-absorption and gamma spectroscopic methods. In terms of accumulation, the elements are subdivided into two groups. The lowest contents of Group-1 elements (137 Cs, Zn, Cd, Hg, and Pb) were found in the substrate, and the highest contents, detected at the base and dead podetium, are presumably of technogenic origin. The Group-2 elements (Cr, Mn, Co, Ni, and Cu) enrich the substrate. It was established that the elements are mainly accumulated in lichens in cell walls and the membrane. The lichen sap and water-soluble compounds of protoplasma contain less than 0.1% of the total element content in the tissue. Most Zn, Cd, Co, and Pb ions (about 80% of the total absorbed amount) migrated from experimental solution into lichen cells during the first 12 h.

Distribution of radioactive Cs and trace elements in the lichen-substrate system and in the lichen body

The distribution of radioactive Cs and heavy metals (V, Cr, Mn, Co, Ni, Cu, Zn, Cd, Hg, and Pb) in the lichen-substrate system and in lichen tissues were examined using the example of Cladonia genera. The upper podetia-lower podetia-dead podetia-base-substrate system was sampled at 32 sites in Novosibirsk oblast and Altai administrative territory, 16 of which were selected for detailed studying of the trace element distribution in the upper and lower podetia using cold press and the modified Dexter technique. One in vivo and two in vitro experiments simulated the influence of metal-rich atmospheric fallouts on the lichen carpet. The lichen carpet was irrigated by solution of metal nitrates (Co, Cu, Zn, Cd, Hg, and Pb) in the former case and loaded in these solution during the latter experiment. The experiment performed in the laboratory conditions (in vitro) was aimed at studying the dynamics of metal accumulation in lichen constituents and their subsequent extraction with distilled water to monitor metal sorption on the podetium cell walls. The metal contents and the activity of radioactive Cs in the lichen samples, including lichen cell sap, as well as in the base and substrate, were determined by atomic-absorption and gamma spectroscopic methods. In terms of accumulation, the elements are subdivided into two groups. The lowest contents of Group-1 elements (137 Cs, Zn, Cd, Hg, and Pb) were found in the substrate, and the highest contents, detected at the base and dead podetium, are presumably of technogenic origin. The Group-2 elements (Cr, Mn, Co, Ni, and Cu) enrich the substrate. It was established that the elements are mainly accumulated in lichens in cell walls and the membrane. The lichen sap and water-soluble compounds of protoplasma contain less than 0.1% of the total element content in the tissue. Most Zn, Cd, Co, and Pb ions (about 80% of the total absorbed amount) migrated from experimental solution into lichen cells during the first 12 h.

137Cs and 90Sr in live and dead reindeer lichens (genera Cladonia) from the “Kraton-3” underground nuclear explosion site

The contents of 137Cs and 90Sr have been determined in 29 samples of live and dead reindeer lichens (genera Cladonia) collected at the “Kraton-3” underground nuclear explosion site (65.9°N 112.3°E, event year – 1978) in Yakutia, Russia in 2002. The area contamination was within the range of 0.36–700 and 0.13–770 kBq m −2 for 137Cs and 90Sr, respectively. The dead organisms were on average much more contaminated than the live ones. Vertical fractionation of the live lichen carpet demonstrated maximal activity concentrations of both radionuclides in the lower older section of the plants, while for the dead lichens the maximal activity concentrations of 137Cs were detected in the upper part. The vertical distribution of 90Sr was more or less homogeneous in the cushions of dead lichens. Elevated levels of 137Cs and 90Sr activity concentrations were also detected in the re-establishing young lichens growing over the residua of some dead lichens.

Caribou‐induced changes in species dominance of lichen woodlands: an analysis ofplant remains

Plant communities in northern Quebec-Labrador, Canada have been severely grazed and trampled since the early 1980s by the increasingly large George River caribou herd (GRCH). To evaluate changes in species dominance associated with caribou disturbance, we compared past and present ground vegetation from 14 lichen woodlands. Plant remains from superficial organic horizons indicate that ground vegetation was largely dominated by lichens (especially Cladina) before the onset of caribou disturbance. In enlargments of aerial photos taken before 1975 (i.e., prior to maximum size of the GRCH), all sites were free of caribou trails and were dominated by a continuous lichen (Cladina) carpet. Principal components analysis showed that partial or complete destruction of the Cladina-dominated lichen carpet was the most striking change in ground vegetation. Severe trampling degraded superficial organic horizons, subsequently exposing mineral soil in heavily used sites. With reduced caribou activity in the 1990s, exposed ground was colonized by crustose lichens and Cladonia. Sites that faced severe grazing but light trampling were recolonized mainly by small podetia of Cladina stellaris sprouting from the lichen litter. However, patterns of post-caribou disturbance lichen succession differed from those of post-fire succession, because species from different successional stages are present at the same time in a stand and also because caribou can modify the successional trajectory at any time.

Growth performance of Cladina stellaris following caribou disturbance in subarctic Quebec

:Cladina stellaris is a dominant lichen species of old-growth lichen-spruce woodlands in subarctic Québec, where the continuous lichen carpet persists for several decades in the absence of disturbance. The lichen carpet is, however, vulnerable to caribou (Rangifer tarandus) disturbance under dry site conditions. Through grazing and trampling, large herds of migratory caribou reduce C. stellaris abundance and modify ground vegetation composition. Here, we have evaluated the age and growth performance of C. stellaris in relation to the recent activity of the George River Caribou Herd (GRCH). We measured the age, length, and growth rate of C. stellaris podetia in and near caribou trails in 15 lichen-spruce woodlands across the summer habitat. The age of lichens, used to evaluate the initial period of lichen recruitment following the decline of the GRCH, indicated that lichen recovery began in the early 1990s in heavily disturbed sites, whereas comparisons between the age structure of border and trail lichens also suggested that the southern part of the calving ground was still heavily used in the early 1990s. Length and growth rate of C. stellaris thallus were closely associated with severity of caribou disturbance, as inferred from the residual ground cover of terrestrial lichens. Growth performance of C. stellaris during the initial stage of lichen recovery varied according to the spatial use of the summer habitat by caribou, with better performance at the edge of the summer and winter habitats and reduced performance in the extensively used calving ground. The analysis of growth performance of C. stellaris provides new insights on lichen-spruce stand recovery associated with caribou disturbance.

Are phenolics leaching from the lichen Cladina stellaris sources of energy rather than allelopathic agents for soil microorganisms?

Lichen phenolics that are known to leach out from lichen thalli during rainfall episodes are considered to be allelopathic or antimicrobial agents. On the other hand, small organic molecules originating from aboveground vegetation generally constitute an important C source for the soil microbial community. We studied the effects of leaching lichen acids on soil microbial processes by chemically removing usnic (UA) and perlatolic acid (PA) from the extracellular space of mat-forming lichen, Cladina stellaris, a dominant component of the ground vegetation in boreal oligotrophic forests. Removal of UA and PA did not affect the intracellular contents of the lichen. We hypothesized that if lichen acids have an adverse effect on soil biota, microbial respiration would increase underneath chemically manipulated lichen mats. In turn, if these substances provide energy source for the microorganisms, microbial respiration would decline under lichens from which PA and UA has been removed. Microbial metabolic activity, qCO 2 was significantly lower under the lichens from which UA and PA had been removed, thus supporting the latter hypothesis. Removing UA and PA did not affect the amount of microbial C, N and P, or soil nutrient concentrations. Our results suggest that the microbial community in the soil under a lichen carpet is adapted to the presence of these lichen secondary metabolites and can utilize them as a C source. The approach of removing lichen substances from the system could be used as an effective research tool as it can overcome several problems that are often common in the studies on allelopathic interactions.

Vegetation Composition Determines Microbial Activities in a Boreal Forest Soil.

Abstract Forest soil ecology was studied in Fennoscandinavian dry Scots pine forests grazed by reindeer to varying extents (ungrazed, lichen-dominated-sites; grazed sites; and bryophyte-dominated sites). We hypothesized that the productivity parameters of the site (i.e., tree growth and soil nutrient concentrations), the vegetation composition, and the microbial activities are directly correlated. Since the productivity of the lichen-dominated ecosystem is low, microbial activities are assumed to be naturally low. Grazing was expected to decrease both the amount of Scots pine fine roots and the soil microbial activities. Several variables on the characteristics of the soil microbial community, Scots pine fine roots, soil nutrients, and tree growth were studied in relation to vegetation composition by using non-metric multidimensional scaling (NMDS). Basal respiration (Bas), metabolic quotient of the microbial community (qCO2), and pine fine root parameters increased toward the ungrazed, nutrient-poor, lichen-dominated sites, which were grouped at one end of the first axis in the NMDS ordination. Soil nutrient and tree growth parameters and thickness of the humus layer increased toward bryophyte-dominated sites, which were grouped at the other end of the first axis in the ordination. The grazed sites fell between them. These were characterized by lower Bas and qCO2 values and longer lag, compared to ungrazed lichen- or bryophyte-dominated sites, probably due to decreased carbon input and microclimatic change (the soil without lichen carpet is exposed to direct sunlight and wind). Microbial biomass (Cmic), fungal biomass (ergosterol concentration), and the specific growth rate (µCO2) were not related to vegetation ordination. The high fine root production is the most plausible explanation for the high microbial activities at nutrient-poor, lichen-dominated sites, which produce qualitatively poor and slowly decomposing litter, as fine roots secrete considerable amounts of organic substances. At bryophyte-dominated sites, the higher soil nutrient concentrations and the higher production of easily decomposable substrates are likely to maintain the microbial activities.

Radioanalytical studies of fallout 63Ni

Fallout of Nickel-63 ( T 1/2 = 100 a) produced in small amounts at nuclear weapon tests following the neutron activation of weapon construction material was investigated by studying carpets of lichen collected during 1961 to 1988 at the Lake Rogen district in central Sweden (62.3°N, 12.4°E). The maximal level of 63Ni in the lichen carpet, which occurred in 1964, was about 0.6 Bq kg −1, dry weight, and decreased to 0.1 Bq kg −1 in 1988. The deposition pattern for 63Ni was similar to other fallout radionuclides such as 137Cs, 90Sr and 239+240Pu. The concentrations of stable Ni were relatively constant at 0.5 to 1.0 μg g −1 throughout the years resulting in, for example, a specific activity ( 63Ni/stable Ni) of 0.5 Bq mg −1 in 1964 and 0.1 Bq mg −1 in 1988. The total area content of 63Ni was estimated to be 1.0 Bq m −2 and the activity ratio 63Ni/ 60Co was estimated to be 0.03 in 1966. The Chernobyl accident in April 1986 did not significantly increase the levels of 63Ni. For the measurement of these extremely low-levels of 63Ni, 200 g of dry material (about 1 kg fresh) were ashed and leached with aqua regia after hydroxides had been precipitated with ammonia, leaving Ni in the aqueous phase. Nickel was extracted as a dimethylglyoxime complex by chloroform and back-extracted with HCl. Finally, Ni was electroplated onto copper discs from an ammonium sulfate medium at high pH. The radiochemical yield was determined by atomic absorbtion spectrometry of stable Ni before and after electrodeposition. Nickel-63 on the discs was measured by using a windowless anticoincidence-shielded Geiger-Müller gas-flow counter. Using a counting time of 3000 minutes the minimum-detection level was 1 mBq.

99Tc in the sub-arctic food chain Lichen-Reindeer-man

The deposition, migration and annual variations of 99Tc fallout in carpets of lichen collected during the period 1956–1981 have been investigated. The transfer of 99Tc to reindeer and man has also been studied. Technetium showed a shorter mean residence time than 137Cs in the lichen carpet. The activity ratio 99Tc/ 137Cs was generally lower than the theoretical fission ratio of 1·43 × 10 −4. The maximum concentration of 99Tc in lichens occurred in 1967 (ca. 60 mBq kg −1) but in 1975 higher values were found than would have been predicted from fallout. The average depth integrated concentration of 99Tc at 62·3°N, 12·4° E in 1972 was 540 ± 100 mBq m −2. The studies of reindeer tissues show that technetium has a short mean residence time in the muscle tissues (ca. 5 days) and is not accumulated like 137Cs. The committed dose equivalent from 99Tc to the local Lapp population engaged in reindeer breeding is negligible.

Biophysical aspects of Am-241 and Pu-241 in the environment

Most of plutonium released by nuclear explosions is Pu-241 which decays to Am-241. We have studied the deposition of Pu-241 and Am-241 in lichens collected since 1958 in the central part of Sweden (62.3 degrees N, 12. 4 degrees E). Comparative studies with Pu-isotopes, Pu-239 + 240 and Pu-238 were also performed. In 1972 the total accumulated deposition of Pu-241 was 8 mCi/km2 of Pu-239 + 240 1 mCi/km2 and of Am-241 0.2 mCi/km2. About 80% of the Am-241 activity has been formed in situ from decay of Pu-241. The biological mean-residence time for all Pu-isotopes were about 6 years and for Am-241 4 years. The spatial distribution of Am-241 in the lichen carpet is quite different from that of Pu-241. The activity concentrations of Am-241 and Pu-241 have been studied in reindeer liver and bone. The average concentrations found were in liver 0.6 and 40 pCi/kg, in bone 0.2 and 6 pCi per kg for Am-241 and Pu-241 respectively. The activity content of Am-241 and Pu-241 in the Lapps due to their reindeer diet was estimated to be in liver 1.0 E-4 and 1.0 E-2 pCi/kg, in bone (3-9) E-5 and 1.0 E-2 pCi/kg for Am-241 and Pu-241 respectively. The estimated values for the fractions of ingested activity retained were in liver 7 E-6 and 14 E-6, in bone 20 E-6 for Am-241 and Pu-241 respectively. The fraction of ingested activity of Pu retained in reindeer liver is about 2-3 times higher than that of Am.

137 Cs in the reindeer lichen Cladonia alpestris: deposition, retention and internal distribution, 1961-1970.

Abstract The accumulation of the fallout radionuclide 137Cs has been studied in a large number of samples of the important reindeer lichen Cladonia alpestris, collected in the Lake Rogen area (62.3°N, 12.4°E) in central Sweden during the period 1961–1970. The maximum area-content of 137Cs in the lichen carpet occurred in 1965 and 1966, and amounted to 46–66 nCi/m2, which corresponds to a dry mass content of 34–52 nCi/kg, due to the special characteristics of the lichen carpet and of the locality itself. In September 1970 the 137Cs levels for the whole lichen carpet were 50–80 per cent of the values obtained in 1965. The vertical distribution of 137Cs has been studied during 1966–1970 and the results indicate the existence of a short-time internal cycling of the radionuclide in the lichen carpet, so that in dry periods certain amounts of 137Cs are forced up to the top regions of the carpet and in periods of high precipitation washed down to its lower layers. The concentration of 137Cs at various depths recorded in carefully field-fractionated samples of lichen, gelatinous matter, humus and soil collected in the “normal” years 1969 and 1970 follows the empirically found relation c = constant *exp(−1.6 z0.75), where c denotes the 137Cs concentration in dry matter (nCi/kg) at the dry mass depth z (kg/m2). For comparison with the 137Cs results, the vertical distribution of two other alkali metals, potassium and sodium have also been studied. According to increasing penetration of the lichen carpet, the elements can be arranged in the following sequence: 137Cs = K ≪ Na. The principal ways for elimination of 137Cs from undisturbed carpets of Cladonia alpestris are physical decay of the radionuclide and the continuous growth of the lichen plants, the latter combined with a continuous decomposition of older material.

Radiolead ( 210 Pb) and Stable Lead in the Lichen Cladonia alpestris

Lichens of the genus Cladonia, mainly C. alpestris, collected during 1882-1972 were analyzed for stable lead and 210Pb. The specific activity of 210Pb (210Pb/Pb ratio) indicates a constant value of about 2 mCi/kg up to 1940, and then decreased to 0.6 mCi/kg during 1950-1960. As the average annual 210Pb deposition is relatively constant, the decrease in the 210Pb/Pb ratio after 1940 indicates an increased deposition of stable lead after 1940. A single exponential variation of the 210Pb/Pb ratio, in respect to latitude, was found in lichens collected in 1964. Values for 210Pb and stable lead in C. alpestris, collected in central Sweden during 1961-1972, appear to be relatively constant and the average area content of 210Pb and stable lead in lichen carpets was 15 ± 2 nCi/m2 and 25 ± 5 mg/m2 respectively. The pattern of vertical distribution was converted to a model for the translocation of lead in lichens, which included the diffusion principle. The diffusion coefficient for lead in the top layer of the lichen carpet was estimated to be about (0.2 ± 0.1) x 10-6 cm2 x s-1. (Less)

Separation of palladium and platinum

Fallout of Nickel-63 (T1/2 = 100 a) produced in small amounts at nuclear weapon tests following the neutron activation of weapon construction material was investigated by studying carpets of lichen collected during 1961 to 1988 at the Lake Rogen district in central Sweden (62.3°N, 12.4°E). The maximal level of 63Ni in the lichen carpet, which occurred in 1964, was about 0.6 Bq kg−1, dry weight, and decreased to 0.1 Bq kg−1 in 1988. The deposition pattern for 63Ni was similar to other fallout radionuclides such as 137Cs, 90Sr and 239+240Pu. The concentrations of stable Ni were relatively constant at 0.5 to 1.0 μg g−1 throughout the years resulting in, for example, a specific activity (63Ni/stable Ni) of 0.5 Bq mg−1 in 1964 and 0.1 Bq mg−1 in 1988. The total area content of 63Ni was estimated to be 1.0 Bq m−2 and the activity ratio 63Ni/60Co was estimated to be 0.03 in 1966. The Chernobyl accident in April 1986 did not significantly increase the levels of 63Ni.For the measurement of these extremely low-levels of 63Ni, 200 g of dry material (about 1 kg fresh) were ashed and leached with aqua regia after hydroxides had been precipitated with ammonia, leaving Ni in the aqueous phase. Nickel was extracted as a dimethylglyoxime complex by chloroform and back-extracted with HCl. Finally, Ni was electroplated onto copper discs from an ammonium sulfate medium at high pH. The radiochemical yield was determined by atomic absorbtion spectrometry of stable Ni before and after electrodeposition. Nickel-63 on the discs was measured by using a windowless anticoincidence-shielded Geiger-Müller gas-flow counter. Using a counting time of 3000 minutes the minimum-detection level was 1 mBq.