Contribution of root respiration to soil respiration in a C3/C4 mixed grassland

The spatial and temporal variations of soil respiration were studied from May 2004 to June 2005 in a C-3/C-4 mixed grassland of Japan. The linear regression relationship between soil respiration and root biomass was used to determine the contribution of root respiration to soil respiration. The highest soil respiration rate of 11(.)54 mu mol m(-2) s(-1) was found in August 2004 and the lowest soil respiration rate of 4.99 mu mol m(-2) s(-1) was found in April 2005. Within-site variation was smaller than seasonal change in soil respiration. Root biomass varied from 0-71 kg m(-2) in August 2004 to 1.02 in May 2005. Within-site variation in root biomass was larger than seasonal variation. Root respiration rate was highest in August, 2004 (5(.)7 mu mol m(-2) s(-1)) and lowest in October 2004(1(.)7 mu mol m(-2) s(-1)). Microbial respiration rate was highest in August 2004 (5(.)8 mu mol m(-2) s(-1)) and lowest in April 2005 (2(.)59 mu mol m(-2) s(-1)). We estimated that the contribution of root respiration to soil respiration ranged from 31% in October to 51% in August of 2004, and from 45% to 49% from April to June 2005.