View of one branch filter (May 2004).
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The objective is to test the following hypotheses on silver birch, white birch, grey alder and bilberry:
Stratospheric ozone depletion is causing an increase in UV-B at ground level, especially at high latitudes. Recovery of ozone levels is expected to occur not before the second half of the current century. More importantly, UV irradiance varies with the seasons of the year, latitude and altitude, and with the position in a canopy and the bearing towards which the foliage is exposed. UV affects plant chemistry, especially concentrations and relative composition of phenolics. Plants also respond to 'normal' levels of UV-B when compared to reduced UV-B, in addition to responding to increased UV-B. Changes in phenolic plant metabolites can affect interactions with herbivores and pathogens. Similar effects can happen in the decomposition of dead plant materials, the litter. However, in different experiments with UV-B, effects in different directions have been observed. Decomposer microbes (fungi and bacteria) have been shown to be affected, but effects on soil fauna have been rarely studied. Soil fauna, which includes both species that consume litter and species that consume microbes, has been shown to affect litter decomposition, soil microbes, and chemistry and in turn plant growth. The litter can also affect soil biota and chemistry at a distance, because substances including phenolics are leached and transported by water.
We will study litter decomposition both in microcosms in controlled environment conditions and at five forest sites. Litter produced under different UV-B levels will be compared. Extensive chemical characterization of the litter before and during decomposition will be done, including flavonoids, phenolic acids, tannins, lignin, cellulose, hemicellulose, starch and sugars. Concentrations of mineral nutrients will also be measured, and a stable isotope of nitrogen will be used to trace the fate of nitrogen in litter. Effects on litter and, soil biota will be assessed.
Boreal forests, and the organic matter in boreal forest soils, are a major pool of organic carbon globally, and it is important to get information on the effects of normal UV levels on soil organic matter. On the long term the amount of organic matter in the soil is not only affected by the size of litter inputs of organic matter into the soil, but more directly by the balance between the inputs and decomposition.
We started the first field experiment in the spring of 2004. Branch filters were installed in birch and alder trees growing in an abandoned agricultural field near Jyv?skyl?. We have three treatments: 1) near ambient UV, 2) UV-B attenuation, and 3) attenuation of the whole solar UV band. The filters have equal and very high transmittance of visible light. The lower side is open for ventilation. Sampling of leaves for phenolic analyses was done in early July and two other samplings during the summer, and leaf litter was collected in the autumn.
Click on the thumbnails for bigger images.
View of one branch filter (May 2004).
Another view of one branch filter (May 2004).
A filter on a branch, now with leaves (June 2004).
Six filters (three treatments) on the south facing side of an alder tree (June 2004).
Author: Pedro J. Aphalo.