Growth and thinning effects during a rotation period of hybrid aspen in southern Sweden

Hybrid aspen is an interesting tree species for wood production in northern Europe. In this study we examined growth dynamics over the whole rotation period. Height and diameter development, as well as annual growth of stem volume and stem biomass, were repeatedly recorded in 14 planted and 2 root sucker stands, aged up to 26 years, in southern Sweden. A main aim was to study the productivity level for hybrid aspen forestry with an expected rotation period of about 25 years. The study verified earlier prognoses, showing a mean annual increment (MAI) of 19.5 m³ of stem wood ha^?1 yr^?1 after 25 years. This corresponds to a dry weight of stem biomass of 7.2 tons dry matter (DM) ha^?1 yr^?1. Maximum MAI was still not reached after 25 years, although the growth curve was flattening out. If branch biomass is included, MAI is estimated to about 9 tons DM ha^?1 yr^?1 and further improvements in growth is expected by using the best genotypically selected clones available. Results from three different thinning regimens showed that thinning intensity provided significantly larger diameter growth, while no significant yield effects were seen among the thinning regimens.     

Effects of harvesting date and storage on the amounts of polyacetylenes in carrots, Daucus carota

The amounts of three main polyacetylenes in carrots; falcarinol, falcarindiol, and falcarindiol-3-acetate, were determined by HPLC, during three seasons, in carrots harvested several times per season and at different locations in Sweden. The amounts of falcarindiol first decreased from a relatively high level and then increased later in the harvest season. The amounts of falcarindiol-3-acetate showed similar variations, whereas the amounts of falcarinol did not exhibit any significant variation during the harvest season. During storage the amount of polyacetylenes leveled off, increasing in samples initially low and decreasing in samples initially high in polyacetylenes. The amounts of all polyacetylenes varied significantly due to external factors and between stored and fresh samples. This variation opens up possibilities to achieve a chemical composition of polyacetylenes at harvest that minimizes the risk of bitter off-taste and maximizes the positive health effects reported in connection with polyacetylenes in carrots.     

A comparison of linear and exponential regression for estimating diffusive CH4 fluxes by closed-chambers in peatlands

The closed-chamber method is the most common approach to determine CH₄ fluxes in peatlands. The concentration change in the chamber is monitored over time, and the flux is usually calculated by the slope of a linear regression function. Theoretically, the gas exchange cannot be constant over time but has to decrease, when the concentration gradient between chamber headspace and soil air decreases. In this study, we test whether we can detect this non-linearity in the concentration change during the chamber closure with six air samples. We expect generally a low concentration gradient on dry sites (hummocks) and thus the occurrence of exponential concentration changes in the chamber due to a quick equilibrium of gas concentrations between peat and chamber headspace. On wet (flarks) and sedge-covered sites (lawns), we expect a high gradient and near-linear concentration changes in the chamber. To evaluate these model assumptions, we calculate both linear and exponential regressions for a test data set (n = 597) from a Finnish mire. We use the Akaike Information Criterion with small sample second order bias correction to select the best-fitted model. 13.6%, 19.2% and 9.8% of measurements on hummocks, lawns and flarks, respectively, were best fitted with an exponential regression model. A flux estimation derived from the slope of the exponential function at the beginning of the chamber closure can be significantly higher than using the slope of the linear regression function. Non-linear concentration-over-time curves occurred mostly during periods of changing water table. This could be due to either natural processes or chamber artefacts, e.g. initial pressure fluctuations during chamber deployment. To be able to exclude either natural processes or artefacts as cause of non-linearity, further information, e.g. CH₄ concentration profile measurements in the peat, would be needed. If this is not available, the range of uncertainty can be substantial. We suggest to use the range between the slopes of the exponential regression at the beginning and at the end of the closure time as an estimate of the overall uncertainty.     

Fate of heavy metals in a strongly acidic shooting‐range soil: small‐scale metal distribution and its relation to preferential water flow

To assess the mobility of Pb and associated metals in a highly contaminated shooting range soil (Losone, Ticino, Switzerland), we investigated the spatial distribution of the metals and their relation to preferential water flow paths. A 2.2 m² plot located 40 m behind the stop butt was irrigated with a solution containing bromide and Brilliant Blue, a slightly sorbing dye. A soil profile 50 cm in width was sampled down to 80 cm with a spatial resolution of 2.5 cm, resulting in 626 samples. Concentrations of elements (12 ≤ Z ≤ 92) were determined by energy‐dispersive Xray fluorescence spectrometry, and Brilliant Blue concentrations were determined with a chromameter. In the acidic (pH 3), organic matter‐rich, well drained Dystric Cambisol, maximum concentrations of 80.9 g kg^‐1 Pb, 4.0 g kg^‐1 Sb, and 0.55 g kg^‐1 Cu were measured in the topsoil. Within 40 cm soil depth, however, Pb, Sb, and Cu approached background concentrations of 23 mg kg^‐1, 0.4 mg kg^‐1, and 9.4 mg kg^‐1, respectively. The even horizontal distribution and the steep gradient along soil depth indicate tight metal binding in the topsoil, and a fairly homogeneous transport front. In contrast, water flow through the profile was highly heterogeneous. In the uppermost 20 cm, preferential flow was initiated by heterogeneous infiltration at the soil surface, but had no influence on metal distribution. Below 20 cm, however, preferential flow originated from larger tree roots, and metal concentrations were significantly elevated along these macropores. Spatial distributions of Pb, Sb, and Cu were similar, suggesting that all three metals are strongly retained in the topsoil and transported along preferential water flow paths in the subsoil.     

Heterogeneity of bacterial populations and pesticide degradation potentials in the unsaturated zone of loamy and sandy soils

Soil microbial processes play an important role in relation to pesticide pollution of groundwater, and may be strongly influenced by hydrological and geochemical properties. The consequences of such heterogeneous environments on bacterial biomass, enzymatic activities, carbon utilisation patterns, and pesticide mineralisation potentials in the unsaturated zone of a sandy loam and a coarse sandy soil profile were studied. In sandy loam soil profiles the number of bacteria decreased from 10⁹ cells g^-1 in the surface layers to about 10⁷ cells g^-1 at 1.5-5 m depth. Simultaneously, the hydrolysis of fluorescein diacetate and arylsulfatase activity decreased to below the detection limit at about 1.5 m depth, and carbon utilisation patterns showed that bacterial populations from surface soil were significantly different from those from 4 m depth. Bacterial biomass and activity in macropore soil tended to be slightly higher than in matrix soil, and the carbon utilisation patterns of bacterial populations extracted from macropore soil and from matrix soil seemed to be different. Maximally 3% of ¹⁴C-labelled mecoprop and isoproturon was mineralised in soil from the 1-1.5 m depth, and less than 1.5% was mineralised in soil from the 3.5-4 m depth. The macropore soil tended to have a higher degradation potential than the matrix soil. The total number of bacteria in the coarse sandy soil profile decreased from about 10⁸ in the plough layer to 10⁷ cells g^-1 at 0.4-2 m. The enzymatic activities and the degradation potentials of ¹⁴C-labelled mecoprop and isoproturon were significantly correlated (r² >0.79) and showed a distinct decrease at about 0.4 m. In addition to the depth variability, a horizontal heterogeneity in this soil was observed as horizons or compartments that differed in colour, i.e. with different chemical composition and concentrations of Fe and organic matter. Counts of viable bacteria and measurements of fluorescein diacetate hydrolysis and arylsulfatase activity confirmed a high variability of microbial biomass and activity in the sandy soil profile.     

Irrigation of Landfill Leachates in Energy Forests — A Technique to Recover Nutrients from Municipal Solid Wastes

From an ecological point of view it is important to close nutrient cycles by recirculating mineral nutrients from the urban society back to agriculture and forestry, and thereby obtaining a sustainable resource utilisation. A part of this cycle is illustrated by irrigation of bioreactor landfill leachates on short rotation forests. This paper presents a budget for nutrients and heavy metals, beginning with the leachates and ending with the harvested tree fraction. The hypotheses were: The applied minerals deliver nutrients to the trees. The nutrient content in the accumulating biomass corresponds to the amount of mineral nutrients applied. The concentrations of heavy metals in the trees will remain low. The uptake of elements in birch was for P 35%, Ca 1. 2%, Cd 64%, Cu 10%, Mn 19%, Ni 0. 11%, and for Zn 26% of the supplied amounts. It was concluded that nutrients, with some exceptions, are supplied in sufficient amounts from the irrigated leachates to achieve optimal biomass growth, that the amounts of ions immobilised by the plants were significantly lower compared to the applied amounts, and that the concentrations of heavy metals are not increasing in the trees after irrigation. The overall conclusion is that a leachate irrigation system is efficient if the available vegetated land area is large enough for effective nutrient uptake, but the nutrient ratio may need to be balanced to meet the needs of the plants.     

Changes in volatile compounds of carrots (Daucus carota L.) during refrigerated and frozen storage

Carrots (Daucus carota L.) of cv. Bolero and cv. Carlo were processed into shreds and stored for up to 4 months at -24 degrees C (frozen storage), or the roots were stored for up to 4 months at 1 degrees C (refrigerated storage) followed by processing into shreds. Volatiles from the carrot shreds were collected by dynamic headspace technique and analyzed by GC-FID, GC-MS, GC-MS/MS, and GC-O to determine the volatile composition and aroma active components of carrots stored under different temperature conditions. A total of 52 compounds were quantified, of which mono- and sesquiterpenes accounted for approximately 99% of the total volatile mass. Major volatile compounds were (-)-alpha-pinene, beta-myrcene, (-)-limonene, (+)-limonene, (+)-sabinene, gamma-terpinene, p-cymene, terpinolene, beta-caryophyllene, alpha-humulene, and (E)- and (Z)-gamma-bisabolene. A considerable increase in the concentration of mono- and sesquiterpenes was observed during refrigerated storage, whereas the concentration of terpenoids was around the same level during frozen storage. GC-O revealed that the major volatiles together with (+)-alpha-pinene, (-)-beta-pinene, (+)-beta-pinene, 6-methyl-5-hepten-2-one, (-)-beta-bisabolene, beta-ionone, and myristicin had an odor sensation, which included notes of "carrot top", "terpene-like", "green", "earthy", "fruity", "citrus-like", "spicy", "woody", and "sweet".