Statistical analyses of inter-annual variations in the vertical profile of atmospheric CO2 mixing ratio and carbon budget in a cool-temperate deciduous forest in Japan

Using the 1994-2002 Continuous data of CO2 mixing ratio, CO2 flux and meteorological parameters observed at the Takayama site located in a cool-temperate deciduous forest in central Japan, various statistical analyses are performed to examine inter-annual variations of annual mean height-dependent vertical CO2 mixing ratio differences; these are then compared to annually integrated carbon budget components estimated from the flux measurement. The mixing ratio measurements are made at 27 and 18 in (located above the canopy), and 8.8 and 5.8 m (located inside the canopy) on a tower Situated at the site. Relative to 27 m, the annual mean mixing ratios in the lower layers show a significant positive correlation (> 90 or > 95% confidence level) with the annually integrated soil respiration, while a significant negative correlation (> 95% confidence level) between the 18- and 27-m mixing ratio difference for the daytime data and the annually integrated gross primary production is obtained. Significant long-term trends (> 95% confidence level) of the annual mean vertical mixing ratio differences are found, with an increasing trend for the daytime and nighttime data at the lower levels inside the canopy and a decreasing trend for the daytime data near the canopy height. Seasonal analysis shows that the increase in trend occurs mostly in mid-Summer Of the growing season, while the decrease in trend occurs in laic spring. It is therefore Suggested that the inter-annual variation and the long-term trend of the vertical CO2 mixing ratio difference obtained from high-precision mixing ratio measurements on a tower in a forest Could provide Lis with useful information on the carbon budget components. (c) 2005 Elsevier B.V. All rights reserved.