Current issue: 54(3)
Under compilation: 54(4)
The eddy covariance technique is a novel micrometeorological method that enables the determination of the atmosphere-biosphere exchange rate of gases such as ozone and carbon dioxide on an ecosystem scale. This paper describes the technique and presents results from the first direct measurements of turbulent fluxes of O3, CO2 and H2O above a forest in Finland. The measurements were performed during 15 July-5 August 1994 above a Scots pine (Pinus sylvestris L.) stand near the Mekrijärvi research station in Eastern Finland.
The expected diurnal cycles were observed in the atmospheric fluxes of O3, CO2 and H2O. The data analysis includes interpretation of the O3 flux in terms of the dry deposition velocity and evaluation the dependency of the net CO2 flux on radiation. The eddy covariance method and the established measurement system has proved suitable for providing high-resolution data for studying ozone deposition to a forest as well as the net carbon balance and related physiological processes of an ecosystem.
Forest ecosystems may accumulate large amounts of nitrogen in the biomass and in the soil organic matter. However, there is increasing concern that deposition of inorganic nitrogen compounds from the atmosphere will lead to nitrogen saturation; excess nitrogen input does not increase production. The aim of this study was to determine the long-term changes caused by nitrogen input on accumulation of nitrogen in forest soils and in ground vegetation.
The fertilization experiments used in this study were established during 1958–1962. They were situated on 36- to 63-year-old Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) stands of different levels of fertility. The experiments received nitrogen fertilization 5–7 times over a 30-year period, and the total input of nitrogen was 596–926 kg/ha.
Nitrogen input increased the amount of organic matter in the humus layer and the nitrogen concentration in the organic matter. Furthermore, the total amount of nutrients (N, P, K, Ca and Mg) bound by the humus layer increased due to the increase in the amount of organic matter. However, nitrogen input decreased the biomass of ground vegetation. The nitrogen concentration of the plant material on the nitrogen-fertilized plots was higher than on the control plots, but the amount of nutrients bound by ground vegetation decreased owing to the drastic decrease in the biomass of mosses. Ground vegetation does not have the potential to accumulate nitrogen, because vegetation is dominated by slow-growing mosses and dwarf shrubs which do not benefit from nitrogen input.
The interactive effects of potassium deficit and foliar application with acid water (pH 5.5, 4.5, 4.0 and 3.0 given consecutively) on CO2 exchange rate of Pinus sylvestris L. seedlings was investigated in field conditions. No reduction of the CO2 exchange rate was observed in the seedlings supplied with sufficient potassium. Only the seedlings having the lowest needle K concentration (2.4 mgg-1) had an apparently low CO2 exchange rate before the applications with acid water. The CO2 exchange rate of most of the seedlings with low needle K concentration (3.9–6.0 mgg-1) decreased after the acid water application. The threshold acidity for the reduction varied between pH 4,0 and 3.0 depending on the needle K concentration. The reduction was more apparent at high irradiance. It was concluded that acid precipitation disturbs the CO2 exchange only in conditions of mineral nutrient deficit.
The PDF includes an abstract in Finnish.
A comparison study concerning the effects of acid rain on Scots pine (Pinus sylvestris L.) seedlings has been performed. Two different X-ray fluorescence methods, PIXE and IXRF, were employed to produce multielement analyses of the samples. Seedlings were treated for 3 months with watering of pH=7 or pH=3 liquids on the needles and on the roots. One year and two years old needles of the seedlings were inspected for changes in photosynthetic rate as well as for changes in elemental concentrations.
Twelve elements from Si to Zn were compared in the samples. The PIXE results show that the amounts of most of these elements in the needles of the seedlings grown in sand increase, when treated with acid water. This growth is clearer when the roots are treated with acid water. The elemental concentrations of the needles in the seedlings grown in soil on the other hand decrease slightly.
Monitoring of heavy metal accumulation in plants has been used to reflect the deposition of heavy metals in terrestrial ecosystems. In some cases, the accumulation rates in plants are linearly correlated to deposition measured as bulk precipitation collected in funnel samplers. It is uncertain, however, how large the contribution due to adsorption/impaction of small particles is to this relationship. The need for design of enlightening experiments on deposition rates in different vegetation types and their relation to immission and bulk precipitation data is discussed.