The 1993 (SP005) sampling grid was expanded to 183 sites providing a more comprehensive sampling grid. Because of potential edge effects problems, all sample locations were moved at least 20 meters from the closest road or clearing. Changes from the original location are given in entity 2. CO2 is measured over a period of 41 weeks in soils collected from all of the REU synoptic sample sites in the summer of 1994. Soils were weighted at the same time that respiration was assayed and moisture content was maintained at the same level throughout the series. The time period represented by this data is 15 September 1994 to 12 July 1995. In the initial stages, CO2 concentrations were assayed every week, after 15 weeks, the incubation period was extended to 2 weeks. After the incubation vessels were assayed, the headspace was flushed with lab air and the moisture was adjusted with sterile deionized water. Results show that there was a very high correlation between respiration rates during the 1st and 3rd weeks (r = 0.96) suggesting that the two week incubation period we us as an indicator of initial concentrations of labile carbon is valid. There was also a high correlation between rates observed within the first week and rates observed after 41 weeks (r = 0.85) suggesting that the initial rates provide a good relative guide to rates observed after 10 months. In addition, respiration rates after 41 weeks were 80% of those observed during the first week.
Robert P. Griffiths
To determine how climate change and forest disturbance influences soil nitrogen and carbon cycling. Because of the broad geographical representation of these sites, all climate zones as influenced by slope, aspect and elevation, are represented as well as differing vegetation types, and disturbance histories. At the present time, we represent different climate zones primarily by elevation. As the climate models are perfected, soils data can be evaluated in terms of annual mean temperatures and precipitation. This is an extension of the 1994 REU study of the synoptic Andrews sampling grid study reported as SP006. As a part of that study, we conducted respiration rate studies on sieved soils using a 2-week incubation period. We have used this as an indicator of labile carbon in these soils. We wanted to determine how representative this procedure is in determining labile carbon over longer time periods (e.g. will the patterns of relative respiration remain the same) and to determine how long it would take for rates to diminish with time.