Partitioning soil respiration in two typical forests in semi-arid regions, North China

- Auto- (RA) and heterotrophic respiration (RH) exhibited significantly diurnal and seasonal variations.
- The contribution of RA to RT exhibited remarkable diurnal and seasonal variations.
- The seasonal variation of RA/RT presented a bimodal curve for AS and VN sites.
- RA is more sensitive to the variation of soil temperature than RH.
- Dormant season may have greater soil respiration potential than growing season in our study area.

This investigation examines the contributions of autotrophic respiration (RA) and heterotrophic respiration (RH) to total soil respiration (RT) in two typical forests (Armeniaca sibirica Lam. (AS) and Vitex negundo Linn. var. Heterophylla (VN)) in semi-arid region of North China. The soil respiration components' responses to changing temperatures were also examined. A similar pattern was identified in the diurnal variation of RT and RH; RA exhibited a different diurnal pattern with nighttime values being greater than daytime values. On the seasonal scale, the variations of RT, RH and RA exhibited a similar and strong single-peak pattern with values peaking in early August for both forest sites. The seasonal variations of RT, RA and RH were strongly affected by soil temperature and moisture, with soil temperature accounting for more variations in soil respiration components at both sites. The contributions of RA to RT (RA/RT ratio) exhibited remarkable diurnal and seasonal variations. Due to the lag time between photosynthesis and root respiration, diurnal variation of RA/RT was lower during the daytime than at night in both AS and VN sites. Meanwhile, under the influence of plant physiology, the seasonal variation of RA/RT presented a bimodal curve, with ratios peaking in April and August and bottoming out in October. In addition, due to having higher fine root biomass, VN had a significantly higher annual mean RA/RT ratio (24.44%) than AS (17.46%). Regardless of vegetation type, the responses of RT, RA and RH to soil temperature were more sensitive during the dormant season than during the growing season, with their Q10 ranked as RA > RT > RH. Our results indicate that RA is more sensitive to temperature variation than RH, and that the dormant season may have greater soil respiration potential than the growing season in our study areas in the context of increasing global temperatures. The response of RT, RA and RH to soil temperature showed greater sensitivity for VN than for AS during the annual time scale. We can infer that soil respiration under VN may be more sensitive to temperature variations under global warming scenarios.