Microbial processes in relation to carbon, nitrogen and temperature regimes in litter and a sandy mineral soil from a central Siberian Pinus sylvestris L. forest

The coniferous forests of Siberia contain a significant fraction of the wor ld's terrestrial C. We have assessed organic matter storage and potential m etabolic activities in one of these forest stands by determining C and N po ols, microbial properties and C and N mineralization at different temperatu res in litter and a sandy mineral soil (a Pergelic Cryochrept) from a 215-y old forest of Pinus sylvestris L. Relationships between CO2-C production i n the laboratory and field were also assessed. The site was near Zotino in central Siberia at 61 degrees N, 89 degrees E and has an average air temper ature of ca. -4 degrees C and an annual precipitation of ca. 620 mm; it is subject to water deficits during summer and to recurrent fires. Results wer e evaluated by comparisons with data from other coniferous forests, includi ng those with sandy or sandy loam soils at three temperate sites under Pinu s radiata D. Don in New Zealand. The very acid (pH 4.1) litter (ca. 3 cm de pth) from the Zotino site contained (to 50 cm depth of mineral soil) ca. 41 % of the total C (2.8 kg m(-2)), 34% of the total N (86 g m(-2)) and about 50% of the microbial biomass and respiratory and net N-mineralizing activit y. The low values in the mineral soil were, except for total N which was lo west at this Zotino site, generally similar to those in two young coastal s ands under P. radiata in New Zealand. Rates of C and net N mineralization i n the Zotino mineral soil declined proportionately more between 13.5 and 5. 5 degrees C than between 25 and 13.5 degrees C. Use of temperature relation ships suggested that less than half of the CO2-C produced from the soil pro file in the field under well-watered conditions during summer would have or iginated from microbial respiration. In litter and in mineral soil, ratios of microbial C and N-to-total C and N, microbial C-to-microbial N, rates of CO2-C and net mineral-N production on a total C and N basis, and metabolic quotients (qCO(2) values) were all similar to at least some of the values found for the temperate pine-forest soils. Our results strongly suggest tha t soil organic matter content is low at this Zotino site, not because of di stinctive metabolic potentials of the microbial populations, but because of environmental constraints on ecosystem processes. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.