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 (RS) into heterotrophic (RH) and rhizospheric (RR) components across the growing season of 2009. We found that the temporal variation of RR and RH can be well explained by soil temperature (T5) at 5 cm depth using exponential equations for all forests. However, RR of 40-year-old and 48-year-old forests peaked in September, while their T5 peaks occurred in August. RR of 80-year-old and 143-year-old forests showed a similar pattern to T5. The contribution of RR to RS (RC) of 40-year-old and 48-year-old forests presented a second peak in September. Seasonal variation of RR may be accounted for by the different successional stages. Cumulative RH and RR during the growing season varied with forest age. The estimated RH 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 RR 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 RH. There was no significant relationship between RR and fine root biomass regardless of stand age. Measured apparent temperature sensitivity (Q10) of RH (3.93 ± 0.27) was significantly higher than that of RR (2.78 ± 0.73). Capillary porosity decreased as stand age increased and it was negatively correlated to cumulative RS. 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.