Rhizospheric and heterotrophic respiration of a warm-temperate oak chronosequence in China

Plot trenching and root decomposition experiments were conducted in a warm-temperate oak chronosequence (40-year-old, 48-year-old, 80-year-old, and 143-year-old) in China. We partitioned total soil surface CO2 efflux (R-S) into heterotrophic (R-H) and rhizospheric (R-R) components across the growing season of 2009. We found that the temporal variation of R-R and R-H can be well explained by soil temperature (T-5) at 5 cm depth using exponential equations for all forests. However, R-R of 40-year-old and 48-year-old forests peaked in September, while their T-5 peaks occurred in August. R-R of 80-year-old and 143-year-old forests showed a similar pattern to T-5. The contribution of R-R to R-S (RC) of 40-year-old and 48-year-old forests presented a second peak in September. Seasonal variation of R-R may be accounted for by the different successional stages. Cumulative R-H and R-R during the growing season varied with forest age. The estimated R-H values for 40-year-old, 48-year-old, 80-year-old and 143-year-old forests averaged 431.72, 452.02, 484.62 and 678.93 g C m(-2), respectively, while the corresponding values of R-R averaged 191.94, 206.51, 321.13 and 153.03 g C m(-2). The estimated RC increased from 30.78% in the 40-year-old forest to 39.85% in the 80-year-old forest and then declined to 18.39% in the 143-year-old forest. We found soil organic carbon (SOC), especially the light fraction organic carbon (LFOC), stock at 0-10 cm soil depth correlated well with R-H. There was no significant relationship between R-R and fine root biomass regardless of stand age. Measured apparent temperature sensitivity (Q(10)) of R-H (3.93 +/- 0.27) was significantly higher than that of R-R (2.78 +/- 0.73). Capillary porosity decreased as stand age increased and it was negatively correlated to cumulative R-S. Our results emphasize the importance of partitioning soil respiration in evaluating the stand age effect on soil respiration and its significance to future model construction. (C) 2010 Elsevier Ltd. All rights reserved.