Fortnightly soil respiration data from Climoor fieldsite in Clocaenog Forest 1999 - 2015

Soil respiration has been measured fortnightly using different methods over the years, reflecting advances in technology and instrumentation over the time period. It has always been measured over the same area of soil in the plots however, over collars installed in December 1999.

Three opaque soil collars (20 cm diameter) per plot were installed 5-10 cm into the soil (cut by sharp knife) and with a 3-13 cm edge above the soil surface, including both heterotrophic respiration from soil microorganisms as well as autotrophic respiration from roots within the measured soil respiration. Any above-ground plant growth within the collars was removed on a regular basis. Following installation, the vegetation surrounding the collars was not visually affected (i.e. there was no dieback of vegetation), suggesting limited or no disturbance to the plants. However, in summer 2013, bigger soil collars were installed over one of the 3 long-term collars for automated soil respiration measurements. The automated equipment requires space around the soil collar and vegetation had to be tied away. Even though no vegetation was cut, the soil around these soil respiration collars is visibly drier than in the remaining two collars per plot potentially affecting the measured soil respiration. The three measurements taken within each plot were averaged to give one measurement per plot.

Measurements were taken with static chambers and a gas syringe between 1999 and 2000. Between 2001 and 2008, measurements were taken using a portable infra-red gas analyser (EGM-2, PP Systems, CIRAS-2) linked to a soil respiration chamber (closed chamber system (not vented), volume of headspace 1171 cm3, SRC-1, PP Systems). Measurements were taken by placing the chamber on the collar and the build-up of CO2 within the system was monitored by an infra-red gas analyser and the rates of soil respiration were determined from this. To avoid an excessive build-up of CO2 concentration, which could result in suppression of soil respiration, the time the chamber was placed on the collar was kept to a minimum of 40-120 seconds (timing was extended during cold weather, when rates were particularly low). After 2008, soil respiration measurements were taken using a LI-8100 Analyser with a 10cm survey chamber (vented closed system chamber, 8100-102, LI-COR Biosciences, Cambridge, UK). Measurements were taken over the same collars as previously. Due to a fault in the Licor soil respiration chamber and long repair time, soil respiration measurements were taken with an infra-red gas analyser (EGM4, PP Systems) linked to a SRC-1 soil respiration chamber (system similar to the on described above but updated technology) from 2014 onwards. Sampling time was 120 seconds.

Field (raw) data is converted into a CO2 flux expressed in mg CO2-C m-2 hr-1. Conversions from the different machines are as follows:

Units of raw from CIRAS-2: g CO2 m-2 hr-1
Units of raw from LICOR 8100: µmol m-2 s-1

To convert g CO2 m-2 hr-1 to mg CO2-C m-2 hr-1, multiply by 0.272727, then multiply by 1000. To convert µmol m-2 s-1 to mg CO2-C m-2 hr-1, divide by 1000000*3600*44.0096*0.272727*1000 (calculations use the ideal gas law to convert units).