Maria Niklińska

THE DYNAMICS OF CHEMICAL ELEMENTS IN FOREST LITTER

Litter bags with natural mixed litter were incubated until =60-70% mass loss in two oak-hornbeam and two pine-beech forest stands in southern Poland. At the same stands the input of chemical elements with throughfall was followed. Decomposition con- stants k for the oak-hornbeam litters were -0.57 and -0.55, and for the pine-beech litters -0.30 and -0.27. Chemical elements (except for Cu and Mn) revealed similar relative mobility in the four litters. On average the elements could be ordered by decreasing mobility as follows: K > Mg > Ca > S > Cu > Na > Mn = N > Cd > Pb = Zn > Fe. Instead of the two presupposed factors controlling litter decomposition, biological and chemical, three factors were specified: (1) biological, dominating the decay of organic matter and the dynamics of N, Ca, Mg, Mn, and S; (2) physical, dominated by leaching and atmospheric deposition, and controlling the dynamics of organic matter, K, Na, Pb, Cd, and Zn; and (3) chemical, determining the dynamics of Fe, Zn, Pb, and Cd through the fixation of metal ions to humic substances. Potassium was the only element that decreased in concentration in all litters, while the concentrations of N, Na, Fe, Zn, Pb, and Cd increased in all litters. S, Ca, Mg, and Mn concentrations revealed different patterns in different litters, presumably due to the differences in initial concentrations and soil acidity. No clear trend was found for Cu. In all litter types, Fe, Zn, Pb, and Cd significantly increased in absolute amounts at the end of litter-bag incubation. In all four stands the input with throughfall was high enough to explain the increases in amount of elements, with the exception of Fe in the oak-hornbeam litters.

Effect of temperature on humus respiration rate and nitrogen mineralization: Implications for global climate change

Respiration and nitrogen mineralization rates of humus samples from 7 Scots pine stands located along a climatic transect across the European continent from the Pyrenees (42°40′) to northern Sweden (66°08′) were measured for 14 weeks under laboratory conditions at temperatures from 5 °C to 25 °C. The average Q10 values for the respiration rate ranged from about 1.0 at the highest temperature to more than 5 at 10 °C to 15 °C in the northernmost samples. In samples from more northern sites, respiration rates remained approximately constant during the whole incubation period; in the southern end of the transect, rates decreased over time. Respiration rate was positively correlated with incubation temperature, soil pH and C∶N ratio, and negatively with soil total N. Regressions using all these variables explained approximately 71% of the total variability in the respiration rate. There was no clear relation between the nitrogen mineralization rate and incubation temperature. Below 15 °C the N-mineralization rate did not respond to increasing temperature; at higher temperatures, significant increases were found for samples from some sites. A regression model including incubation temperature, pH, Ntot and C∶N explained 73% of the total variability in N mineralization. The estimated increase in annual soil respiration rates due to predicted global warming at the high latitudes of the Northern Hemisphere ranged from approximately 0.07×1015 to 0.13×1015 g CO2 at 2 °C and 4 °C temperature increase scenarios, respectively. Both values are greater than the current annual net carbon storage in northern forests, suggesting a switch of these ecosystems from net sinks to net sources of carbon with global warming.

Decreased Energetic Reserves, Morphological Changes and Accumulation of Metals in Carabid Beetles (Poecilus cupreus L.) Exposed to Zinc- or Cadmium-contaminated Food

The prime objective of the study was to find out whether contamination of food with metals affects body size, energetic reserves and developmental instability in ground beetles (Poecilus cupreus L.: Carabidae). The transfer of Cadmium (Cd) and Zinc (Zn) from medium (nominal concentrations in the medium: 0, 40, 160, 640 or 800 mg kg−1 for Cd and 0, 400, 1600 or 6400 mg kg−1 for Zn) to housefly larvae to beetles was also studied. Feeding the beetles throughout their entire lifetime with Cd-contaminated housefly pupae resulted in a significant decrease in body caloric value and the size of the elytrae, tibiae and rear femora. Although body mass also decreased with increasing Cd concentration, this effect was non-significant due to large variance in all treatments. Similar trends were also found in beetles fed pupae contaminated with Zn, but the effect on body mass and caloric value was non-significant. Zn exerted significant effects only on the size of the elytrae, middle and rear tibiae, and front and rear femora. No effect on fluctuating asymmetry (FA) was found in Cd- or Zn-treated beetles. The results indicate that ground beetles exposed to metal-contaminated food have lower amounts of energy available, which may be reflected in lower energetic reserves and changed body growth. However, the metals do not cause developmental instability in the carabids studied, at least not in the first generation. The concentrations of Zn were efficiently regulated in carabids, resulting in only minor differences between the beetles exposed to different Zn treatments. In contrast, Cd accumulated both in the housefly and the beetles, and the concentrations increased significantly with increasing medium contamination level.

Effect of heavy metals on coelomocytes of the earthworm Allolobophora chlorotica

Earthworms are sensitive bioindicators of soil pollution. The aim of present investigations was to study the effects of heavy metals on earthworms and on their coelomocytes involved in the defence reactions. Adult individuals of Allolobophora chlorotica collected in Krakow (K) soil were kept in the laboratory either in the K soil, or were transferred to unpolluted soil from the rural area Sierbowice (S) or to the heavily polluted (Zn>Pb>Cd>Cu) soil from the industrial area, Bukowno (B). They were kept there at 22 °C for up to 8 weeks. Cocoons and juveniles appeared in S and K soil samples. The number and activity of the coelomocytes of worms maintained in S and K soils were unaffected despite some accumulation of heavy metals in the earthworm tissues. In contrast, in the B soil samples, bioaccumulation of metals was strongest, high mortality of adults was recorded, body mass was reduced, and reproduction completely inhibited. Coelomocytes retrieved from the B soil survivors exhibited significant impairment of pinocytosis and plastic adherence. Perhaps impairment of immune functions contributed to the poor survival under conditions of heavily polluted B soil samples.

Microbial community structure and functioning along metal pollution gradients.

Toxic effects of heavy metals on soil microorganisms have been confirmed in a number of laboratory studies. However, most real-field studies do not allow for strong general conclusions due to a range of problems, such as pseudoreplication and confounding factors, which are almost impossible to control for with the most commonly used polluted versus unpolluted or random sampling designs. Effects of metal contamination on soil microbial community traits were measured along 2 pollution gradients in southern Poland. Employing an experimental regression design, using 2 separate gradients, the authors aimed to control for effects of soil properties and beta-diversity of microbial communities. General microbial activity was measured as soil basal respiration rate and substrate-induced respiration, while microbial functional and structural diversity were analyzed with community-level physiological profiles and phospholipid fatty acid patterns, respectively. Metal concentrations were normalized to their toxicity and integrated in a toxicity index (TI). Microbial activity (basal and substrate-induced respiration) decreased in both gradients with increasing TI. Community-level physiological profiles for fungi correlated positively with TI, but no impact of TI on the community-level physiological profiles of bacteria was observed. The phospholipid fatty acids a:15 and i:17 were positively correlated with TI, whereas 16:1ω9 and 18:2ω9 were negatively correlated with TI. The use of 2 gradients (Olkusz and Miasteczko Śląskie) allowed the authors to reveal a clear effect of pollution on general microbial structure and activities, even though they were not able to control completely for all confounding factors. Soil pH, organic matter content, and nutrient level appeared to be at least as important as TI in determining microbial community structure and activities.

The effect of different tree species on the chemical and microbial properties of reclaimed mine soils

The chemical and microbial properties of afforested mine soils are likely to depend on the species composition of the introduced vegetation. This study compared the chemical and microbial properties of organic horizons and the uppermost mineral layers in mine soils under pure pine (Pinus sylvestris), birch (Betula pendula), larch (Larix decidua), alder (Alnus glutinosa), and mixed pine–alder and birch–alder forest stands. The studied properties included soil pH, content of organic C (Corg) and total N (Nt), microbial biomass (Cmic), basal respiration, nitrogen mineralization rate (Min-N), and the activities of dehydrogenase, acid phosphomonoesterase, and urease. Near-infrared spectroscopy (NIR) was used to detect differences in the chemical composition of soil organic matter under the studied forest stands. There were significant differences in Corg and Nt contents between stands in both O and mineral soil horizons and also in the chemical composition of the accumulated organic matter, as indicated by NIR spectra differences. Alder was associated with the largest Corg and Nt accumulation but also with a significant decrease of pH in the mineral soil. Microbial biomass, respiration, the percentage of Corg present as Cmic, Min-N, and dehydrogenase activity were the highest under the birch stand, indicating a positive effect of birch on soil microflora. Admixture of alder to coniferous stand increased basal respiration, Min-N, and activities of dehydrogenase and acid phosphomonoesterase as compared with the pure pine stand. In the O horizon, soil pH and Nt content had the most important effects on all microbial properties. In this horizon, the activities of urease and acid phosphomonoesterase did not depend on microbial biomass. In the mineral layer, however, the amount of accumulated C and microbial biomass were of primary importance for the enzyme activities.

Microbial community composition and functions are resilient to metal pollution along two forest soil gradients

Despite the global importance of forests, it is virtually unknown how their soil microbial communities adapt at the phylogenetic and functional level to long-term metal pollution. Studying 12 sites located along two distinct gradients of metal pollution in Southern Poland revealed that functional potential and diversity (assessed using GeoChip 4.2) were highly similar across the gradients despite drastically diverging metal contamination levels. Metal pollution level did, however, significantly impact bacterial community structure (as shown by MiSeq Illumina sequencing of 16S rRNA genes), but not bacterial taxon richness and community composition. Metal pollution caused changes in the relative abundance of specific bacterial taxa, including Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Planctomycetes and Proteobacteria. Also, a group of metal-resistance genes showed significant correlations with metal concentrations in soil. Our study showed that microbial communities are resilient to metal pollution; despite differences in community structure, no clear impact of metal pollution levels on overall functional diversity was observed. While screens of phylogenetic marker genes, such as 16S rRNA genes, provide only limited insight into resilience mechanisms, analysis of specific functional genes, e.g. involved in metal resistance, appears to be a more promising strategy.

Effect of heavy metals and mineral nutrients on forest litter respiration rate.

Two hypotheses were tested: (1) heavy metals such as Zn, Pb and Cd can suppress the respiration rate of forest litter at low-moderate pollution levels, and (2) mineral nutrients such as K, Ca and Mg can counteract the toxicity of heavy metals when applied onto the polluted litter. In a completely randomised design, three doses of heavy metals were used: Cd-10, 50, 250; Pb-100, 500, 2500; Zn-200, 1000, 5000 microg/g dwt litter, respectively. For Ca, Mg and K, the doses corresponded to 100, 500 and 2500 microg/g. A significant decrease in cumulated CO2 evolution after 4 weeks of incubation was found for the litter samples treated with medium doses of Zn, Cd/Ca, Cd/Mg, Pb/Ca, Pb/Mg, Pb/K, Zn/Mg, Zn/Ca, Zn/K and for all the highest-dose treatments. The largest drop in respiration rate in both the medium and the highest doses was caused by additions of Zn either alone or in combination with K, Ca or Mg. The additions of mineral nutrients were found to decrease the litter respiration rate below the value measured for the respective heavy metal alone in the case of Cd/Ca, Cd/Mg, Pb/Ca, Pb/Mg and Pb/K in the medium-dose treatments, and for Cd/Ca, Cd/Mg, Cd/K, Pb/Ca and Pb/Mg in the highest-dose treatments. In all other cases, additions of the mineral nutrients did not influence the respiration rate significantly when compared to the effect of the respective heavy metal.

Soil fertility and plant diversity enhance microbial performance in metal-polluted soils

This study examined the effects of soil physicochemical properties (including heavy metal pollution) and vegetation parameters on soil basal respiration, microbial biomass, and the activity and functional richness of culturable soil bacteria and fungi. In a zinc and lead mining area (S Poland), 49 sites were selected to represent all common plant communities and comprise the areas diverse soil types. Numerous variables describing habitat properties were reduced by PCA to 7 independent factors, mainly representing subsoil type (metal-rich mining waste vs. sand), soil fertility (exchangeable Ca, Mg and K, total C and N, organic C), plant species richness, phosphorus content, water-soluble heavy metals (Zn, Cd and Pb), clay content and plant functional diversity (based on graminoids, legumes and non-leguminous forbs). Multiple regression analysis including these factors explained much of the variation in most microbial parameters; in the case of microbial respiration and biomass, it was 86% and 71%, respectively. The activity of soil microbes was positively affected mainly by soil fertility and, apparently, by the presence of mining waste in the subsoil. The mining waste contained vast amounts of trace metals (total Zn, Cd and Pb), but it promoted microbial performance due to its inherently high content of macronutrients (total Ca, Mg, K and C). Plant species richness had a relatively strong positive effect on all microbial parameters, except for the fungal component. In contrast, plant functional diversity was practically negligible in its effect on microbes. Other explanatory variables had only a minor positive effect (clay content) or no significant influence (phosphorus content) on microbial communities. The main conclusion from this study is that high nutrient availability and plant species richness positively affected the soil microbes and that this apparently counteracted the toxic effects of metal contamination.

Effects of temperature and soil pollution on the presence of bacteria, coelomocytes and brown bodies in coelomic fluid of Dendrobaena veneta

Adult Dendrobaena veneta (Annelida; Oligochaete; Lumbricidae), were kept for 2-4 weeks at either 22 °C or 10 °C in control (C) heavy metal-free commercial soil, or in relatively unpolluted Krakow (K) urban soil, or in heavily polluted (Zn>Pb>Cd) Bukowno (B) industrial soil. At the end of exposures, the numbers of coelomocytes, brown bodies, and bacterial content was measured in coelomic fluid, while heavy metal accumulation was recorded in the animal tissues. The most drastic changes, with high mortality of animals (30 %), were recorded in D. veneta kept for 4 weeks at 22 °C in heavily polluted B soil samples; the number of free coelomocytes in the surviving worms in this treatment group was decreased, whilst the numbers of brown bodies and of bacteria (both free in coelomic fluid and entrapped in the brown bodies) were significantly increased. These changes were absent in earthworms exposed to B soil at 10 °C, as well as at both temperatures in relatively uncontaminated K soil.