Soil respiration rates and their relating micro environmental factors were measured in September in 1999 and 2000 to clarify the controlling factors of soil respiration rates in a cool temperate broad leaved deciduous forest. The study site was located on a southwestern slope of Mt. Norikura at about 1,400m asl. The site contained an experimental area of one hectare, subdivided into 100 sub plots, each 10 m by 10 m in size. The rate of soil respiration was measured by the closed chamber method. The micro environmental factors examined included temperature (air, soil), soil water contents, CO
2 concentration, biomass (tree, understory vegetation), soil nitrogen and carbon contents, thickness of soil layers, and topographic conditions. Results of multiple regression analysis were as follows: 1) Rate of soil respiration was strongly affected by topographic conditions, being 5 12% higher at the summit of the hill and 2.5% lower at the bottom of the valley, compared with the average. 2) Multiple regression analysis of 2 year data using the stepwise method clarified that
V
SR=27.94 X
ts-0.58 X
CO2+3.26 X
a+17.89 X
l-1.74 X
w+118.44 (R
2=0.707)
where V
SR is the soil respiration rate, X
ts the soil temperature at -10cm, X
CO2 the CO
2 concentration at 0 cm, X
a the relative altitude, X
l the thickness of litter layers and X
w the soil water content. 3) The measured soil respiration rate was high in 1999 (408.2mgCO
2m
-2h
-1 on average) and low in 2000 (354.0mgCO
2m
-2h
-1 on average), reflecting previous rainfall. The soil water contents in 1999 and 2000 were 33.6% and 20.8%, respectively. Environmental factors in 1999 were still unstable after plenty of rainfall. The high moisture content in 1999 seemed to conceal the effects of other micro-environmental factors.
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