Seasonal changes in the contribution of root respiration to total soil respiration in a freshwater marsh in Sanjiang Plain, Northeast China

Separating the two major components of soil respiration, root respiration ( R r ) and heterotrophic respiration ( R h ), is an important step for understanding and modelling carbon cycling in organic soils. However, few partitioning studies exist regarding wetland ecosystems. For this study, we selected a freshwater marsh on Sanjiang Plain, Northeast China and used a trenching method to determine the contribution of R r to soil respiration during the two growing seasons in 2010 and 2011. The decomposition rate of dead roots ( R D ) was estimated to correct the soil respiration of the trenching plots. The soil respiration rates in the control plot increased from May (288–508 mg CO 2 m −2 h −1 ) to late June (1103 mg CO 2 m −2 h −1 in 2010) or early July (1278 mg CO 2 m −2 h −1 in 2011) and later decreased during the last growing season. The soil respiration rate in the trenching plot exhibited a similar pattern of seasonal change, but the rates were lower than in the control plot, except at the beginning of trenching. When considering the dead root decomposition in the trenching plots, the contributions of R r to total soil respiration in the two growing seasons were estimated to range from 22 to 77 % (2010) and 46 to 81 % (2011). The mean contribution of R D was approximately 12 % in the growing season of the first year (2010) and later decreased to approximately 6 % in the second year (2011). The contents of soil NH 4 + -N and NO 3 − -N were significantly greater in the trenching plots than in the control plots. The content of microbial biomass nitrogen tended to increase after trenching for the 0- to 30-cm soil depth. These results indicate that the microbial community may change in the second year, which may affect the estimation of the contribution of root respiration to total soil respiration.