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Understorey plant species diversity significantly increases with the age of a Scots pine stand. • Biomass of mosses decreases by a quarter, while biomass of herbs increases several times. • Total understorey's carbon stock increases over three times. The highest amount of carbon is accumulated in understorey species like Vaccinium myrtillus and Dicranum polysetum. • The growing proportion of vascular plants in the understorey biomass results in an increase in the understorey C/N ratio. AbstractThe purpose of this study was to examine how the age of a stand of post-agricultural Scots pine forests affects the species composition, biomass and the carbon stock of the forest understorey. The community structure and species composition were studied in 75 plots (100 m 2 in size), the amount of biomass, organic carbon and total nitrogen were analysed in 75 subplots (1/16 m 2 in size). The plots were located in 21 plantations with the stand age of 41-60, 61-80 and over 80-years. Results show that the understorey species diversity increased with the increasing age of Scots pine stands, and the structure and species composition of secondary forests (although managed for timber production) became similar to the fresh pine forest of the European temperate region (Leucobryo-Pinetum community). Despite the increasing species diversity, however, only six understorey vascular and moss species played an important role in the biomass accumulation and C sequestration. Due to the differences in the dominant species composition, the total amount of understorey biomass significantly differed among the forest stands. The mean moss biomass ranged from 3046 kg ha -1 in 41-60-year-old stands, trough 2686 kg ha -1 in 61-80-yearold stands to 2273 kg ha -1 in over 80-year-old stands, and the mean understorey vascular plant biomass amounted to 2 kg ha -1 , 1924 kg ha -1 and 3508 kg ha -1 , respectively. The concentration of organic C varied considerably between species; it was the highest in Vaccinium myrtillus (50.6%) and in Dicranum polysetum (49.5%). The total mass of C was nearly 800 kg ha -1 in the youngest forests, in the subsequent age series it was two times higher and 3.5 times higher in the oldest ones. Differences in the species composition and in the C/N ratio in different species (generally higher for vascular plants and lower for mosses) were expressed in an increase in the understorey C/N ratio, which was 39.5, 46.6 and 48.6, respectively.

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During the research, cumulative properties of conifer needles P. armandii, P. banksiana, P. mugo, P. nigra, P. sylvestris and P. wallichiana in reference to Cu, Ni, Mn, Fe, Zn and Cd were analysed, and the factors which have an impact on the chemical composition of the bark of those species were identified. During the study, the age of needles and the content of the examined components in soil was taken into consideration. The content of metals in the needles varied, depending on a species and the age of the coniferous needles. In most cases, a higher level of content of those metals was determined in 2 years old needles, except for Cu and Zn (P. banksiana) as well as Zn (P. nigra), in which case, higher concentration of metals in 1 year old needles was determined. The obtained results indicate that the heavy metals' concentration in the samples of needles was relatively low, except for Ni (P. armandii, P. sylvestris, P. wallchiana) and Cd (P. armandii, P. banksiana), which showed higher levels. Among the examined elements, Mn was accumulated in the largest volume in the needles of P. banksiana, Fe and Cu in the needles of P. wallchiana, Ni in the needles of P. sylvestris, Zn in the needles of P. nigra and Cd in the needles of P. armandii. The bark samples represented a clearly acidic reaction, with pH levels from 3.7 (P. sylvestris) to 4.9 (P. armandii). The highest quantities of Mn, Fe, Cu and Cd were accumulated by the bark of P. armandii, Ni in the bark of P. sylvestris and Cu in the bark of P. mugo.

The paper concerns the bioaccumulation of zinc, nickel, iron and manganese in leaves and roots of selected macrophytes from the Krzynia Reservoir (northern Poland). The research was conducted within the area of 10 stations situated in the littoral zone of the reservoir. Samples of surface waters, bottom sediments and plants were taken in summer. Heavy metal content was determined by the atomic absorption spectrometry method (ASA). The concentration of heavy metals in the waters of Krzynia Reservoir was low and noinfluence of anthropogenic factors was found. Concentration of heavy metals in the examined bottom sediments was low and remained within the limits of the geochemical background for Zn and Fe. In the case of Ni and Mn it sporadically exceeded the level of the geochemical background. The tested plants mainly accumulated heavy metals in roots, with the exception of nickel which appeared in larger quantities in leaves. The relationships among the content of the determined elements in the organs of macrophytes was identical for the tested species and could be arranged into the following sequences: Mn>Fe>Ni>Zn in leaves and Fe>Mn>Zn>Ni in roots. Statistically significant differences were found in the content of Mn in leaves and Zn and Fe in the roots of Typha latifolia L. and Iris pseudacorus L. By accumulating substantial quantities of heavy metals in their organs, macrophytes constitute an effective protective barrier for the waters and bottom sediments.

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Abstract:The paper presents the results of study on heavy metals in needles of Pinus sylvestris in selected pine forests in Słowiński National Park. It was evidenced that heavy metal contents (Zn, Cu, Mn and Fe) in needles of Pinus sylvestris varied depending on the metal, the age of the needles and the humidity of a forest complex. Variation coeffi cients of such metals remained at the level of: 13-30% (Zn), 3-6% (Cu), 13-34% (Mn) and 12-30% (Fe) depending on the age of the needles. In the case of Zn, Mn and Fe higher concentrations of researched metal were found in the 2-year-old needles than in 1 year old needles, and in the case of Cu in 1 year old needles than in 2-year-old needles. The increase of zinc concentration found in 1-year-old needles after rainfall sums was (Bw, r = 0.67, p < 0.05, n = 24) and (Bśw, r = 0.39, p < 0.05, n = 24) in 2-year-old needles. The content of the above mentioned metals in needles of dry coniferous forests (Bs), fresh coniferous forests (Bśw) and humid coniferous forests (Bw) of the ground cover constitute the following decreasing series: Mn(323.8) > Fe(103.4) > Zn(65.5) > Cu(5.9).

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