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Abstract

The response of soil respiration to varying environmental factors was studied in four Picea abies stands (47-, 87-, 111- and 146-year old) during the 1998 growing season. While within-site Variations of soil CO₂ efflux (up to 1.6 mu mol CO₂ m(-2) s(-1)) were larger than their diurnal variability (<0.25 mu mol CO₂ m(-2) s(-1)), spatial variations within a site were smaller than seasonal changes in soil respiration rates (up to 4.4 mu mol CO₂ m(-2) s(-1)). Highest within-site variability of soil efflux was generally found during the summer months when maximum flux rates of 4-6 mu mol CO₂ m(-2) s(-1) were reached (coefficient of variation 40%). Soil temperatures (in the O-f and O-h layers, and A(h) horizon) showed a pronounced seasonal course, in contrast to soil moisture. An exponential equation best described the relationships between soil temperature in the Of layer and soil CO₂ efflux (r(2) between 0.75 and 0.81). However, an Arrhenius type equation always resulted in lower r(2) values (0.52-0.71). The Q(10) values ranged between 2.39 (146-year old stand) and 3.22 (87-year old stand), averaging 2.72 for the P. abies stands within the watershed. The removal of litter and organic layers generally affected soil CO₂ efflux negatively. In three of the four P. abies stands (47-, 87-, 146-year old stands), soil respiration rates were reduced by 10-20% after removal of the L and O-f layer, and by 30-40% after removal of the L and most of the O-f and O-h layers. Thus, mineral soil respiration seemed to contribute a major fraction to the total soil CO₂ flux (> 60%). Trenching shallow fine roots during collar insertion and mechanical inhibition of root in-growth during the following months allowed fine root respiration to be separated from microbial respiration only in times of highest root growth. Microbial respiration seemed to dominate the respiratory CO₂ loss from the forest floor (>70%). The comparison of the annual soil CO₂ efflux in the 47-year old P. abies stand (about 710 g C m(-2) yr(-1)) with annual litterfall and root net primary productivity estimates supported this conclusion. (C) 2000 Elsevier Science Ltd. All rights reserved. [References: 51]