ABB LGR | Soil properties and substrate quality determine the priming of soil organic carbon during

Soil properties and substrate quality determine the priming of soil organic carbon during vegetation succession

Soil organic matter (SOM), the largest carbon (C) pool in terrestrial ecosystems, is extremely vulnerable to climate and human disturbances. Even a small change in SOM can greatly influence atmosphere CO2 concentration and C balance. Fresh organic matter (FOM), e.g., leaf litter and root exudate, contributes considerably to SOM formation, but can also modify SOC mineralization through the priming effect (PE). While many studies have shown that plant derived C entering the soil would increase with vegetation succession, the amount of soil C loss caused by PE remains unclear during succession, which causes great uncertainty in the prediction of SOC change throughout this process. Therefore, understanding the underlying mechanisms of PE is urgently needed. In fact, the development of vegetation succession is usually accompanied by changes in soil properties like nutrient availability, aggregate stability, pH, and microbial communities. But, how changes in these properties interact with extraneous FOM to regulate PE, which would further affect SOC dynamics, remains unknown.

Based on this, to fill research gap, a group of Chinese scientists conducted a field investigation in the Foping National Nature Reserve (33°33′-33°46′N, 107°40′-107°55′, 1075–1301 m a.s.l) in the south aspect of the Qinling Mountains, China (Fig.1a) to examine the pattern of SOC stock along with secondary succession ecosystems (cropland→shrubland→forest); then, using a laboratory incubation experiment, they explored the mechanism underlying SOC patterns with regard to PE. Specifically, they evaluated the patterns of PEs induced by ¹³C-labeled glucose (GLU) as well as LOM and ROM extracted from ¹³C-labeled maize leaf. Aiming to answer the following questions: (1) How would FOMs with different quality affect soil C mineralization by PE across vegetation succession? And (2) What are the driving factors in regulating PE among succession stages?

Fig.1 The location of study area (a) and the representative plots for each succession stage (b).

[δ¹³C measurement]: During incubation experiment, the authors collected gas samples from the flasks on days 1, 4, 7, 14, 27 and 43. As the fluxes of CO₂ from substrate treated soils were low and had no significant differences with CK soil after the sixth sampling, the incubation was stopped at day 43. Then, they measured the CO₂ concentration. To measure the δ¹³C of the gas sample, they flushed the headspace gas out of the flasks using CO₂-free air into pre-evacuated gas sampling bags. The δ¹³C of the gas samples were measured with a CO₂ Isotope Analyzer (912–0003, LGR, America).

[Results]:

Cumulative priming effect (PE) from different C substrate treatments, succession stages, and soil depths at the end of the incubation.

Linear regressions for testing the relationships between priming effect and soil properties for each substrate treatment and soil depth.

Structural equation modeling for examining the direct and indirect effects of soil properties on priming effect (PE) among succession stages.

Conceptual diagram illustrating the priming effect (PE) on soils along the secondary succession ecosystems.

[Conclusion]:

The authors concluded that the magnitude of PE depended not only on the added substrate type but also on soil types specifically associated with vegetation succession. FOM quality contributed to the PE differently. Specifically, GLU and LOM generally induced a higher PE than ROM by increasing the abundance of GN in soil. In contrast, ROM caused PE in soil by increasing the abundance of fungi. These results suggest that GLU, LOM, and ROM may induce PE through different mechanisms. In addition, after FOM addition, soils from the croplands exhibited higher PEs than those from the shrublands and forests. The differences in PE between the succession stages negatively correlated with MWD, TIN, and AP but positively correlated with soil pH and F/B. The results indicate soil properties and substrate quality determine the PE in soils from consecutive vegetation succession stages. PE might be one of the mechanisms underlying distinct soil C dynamics during the process of vegetation succession.