A multichannel automated chamber system for continuous measurement of forest soil CO2 efflux

摘要

We developed a fast-response multi-chamber system for measuring soil-surface CO2 efflux (F.). The chambers (90 x 90 x 50 cm, L x W x H) had lids that opened and closed automatically, and were connected in parallel to a single CO2 analyzer equipped with a 16-channel gas sampler. Between measurements the chamber lids were raised to allow precipitation and leaf litter to reach the enclosed soil surface. When a chamber was closed, it was ventilated with well-buffered ambient air (125 1 min(-1)) that entered by an inlet on one chamber sidewall and exited through a large vent on the opposite sidewall. The pressure difference between the inside and outside of the chamber was less than 0.22 Pa. Two additional mixing fans maintained an air speed of 0.3 +/- 0.1 in s(-1) at 20 cm above the soil surface. Air was withdrawn continuously from the inlets and outlets of each chamber, and fed sequentially to an infrared CO2 analyzer. With this system, we measured F-c in a 40-year-old temperate Pinus densiflora Sieb. & Zucc. forest from February 8 to May 30, 2001. Mean F, increased steadily from 0.9 mumol m(-2) s(-1) at the beginning of February to 4.6 mumol m(-2) s(-1) by the end of May. There was a statistically significant correlation between F-c and surface soil temperature (r = 0.896; P < 0.0001), and the Q(10) value was 2.8. Spatial variation of F-c was higher in the non-growing season than in the growing season. Measurements were not interrupted by either rain or snow.