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Background and aims: The main objectives of this study were to determine how the carbon age of fine root cellulose varies between stands, tree species, root diameter and soil depth. In addition, we also compared the carbon age of fine roots from soil cores of this study with reported values from the roots of the same diameter classes of ingrowth cores on the same sites. Methods: We used natural abundance of C to estimate root carbon age in four boreal Norway spruce and Scots pine stands in Finland and Estonia. Results: Age of fine root carbon was older in 1.5-2 mm diameter fine roots than in fine roots with <0.5 mm diameter, and tended to be older in mineral soil than in organic soil. Fine root carbon was older in the less fertile Finnish spruce stands (11-12 years) than in the more fertile Estonian stand (3 and 8 years), implying that roots may live longer in less fertile soil. We further observed that on one of our sites carbon in live fine roots with the 1.5-2 mm diameter was of similar C age (7-12 years) than in the ingrowth core roots despite the reported root age in the ingrowth cores - being not older than 2 years. Conclusions: From this result, we conclude that new live roots may in some cases use old carbon reserves for their cellulose formation. Future research should be oriented towards improving our understanding of possible internal redistribution and uptake of C in trees. [ABSTRACT FROM AUTHOR]

To test the reliability of the radiocarbon method for determining root age, we analyzed fine roots (originating from the years 1985-1993) from ingrowth cores with known maximum root age (1-6 years old). For this purpose, three Scots pine ( Pinus sylvestris L.) stands were selected from boreal forests in Finland. We analyzed root C age by the radiocarbon method and compared it with the above-mentioned known maximum fine root age. In general, ages determined by the two methods (root C age and ingrowth core root maximum age) were in agreement with each other for roots of small diameter (<0.5 mm). By contrast, in most of the samples of fine roots of larger diameter (1.5-2 mm), the C age of root samples of 1987-1989 exceeded the ingrowth core root maximum age by 1-10 years. This shows that these roots had received a large amount of older stored carbon from unknown sources in addition to atmospheric CO directly from photosynthesis. We conclude that the C signature of fine roots, especially those of larger diameter, may not always be indicative of root age, and that further studies are needed concerning the extent of possible root uptake of older carbon and its residence time in roots. [ABSTRACT FROM AUTHOR]

This study presents the latitudinal variation (from 60° 30' N to 68° 2' N latitude) of natural abundances of 15N in the foliage, humus and soils of boreal forests of Finland. Our results clearly showed that N concentration of the foliage did not change significantly with latitudes but their 15N values were significantly higher in higher latitude sites relative to that of the mid and lower latitude sites, indicating the different forms of N uptake at the higher latitudes compared to the lower latitudes. We assume that the higher foliage δ15N values of the higher latitudes trees might be due to either more openness of N cycle (greater proportional N losses) in these latitudes compared to the sites of southern latitudes (lower N losses) or the differences in their mycorrhizal associations. Regression analysis showed that the temperature was the main factor influencing the 15N natural abundance of humus and soil of all forest ecosystems, both before and after clear-cut, whereas rainfall was the main controlling factor to the foliage 15N. Possible reasons behind the increasing δ15N natural abundances of plants and soils with increasing latitudes are discussed in this paper. The clear-cut did not show any specific trend on the 15N fractionation in humus and soil, i.e. both 15N-enrichment and -depletion occurred after clear-cut. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the impact of various soil preparations on the foliage nitrogen (N) dynamics of boreal forests in Finland. Here, the authors focus on clear cutting method, a common silvicultural practice in the country. To provide a better seed bed conditions, site preparations such as ploughing, burning and fertilization has been applied. They conclude that the long-term effects of various soil management can be studied through atmospheric N deposition.