Recently fixed carbon fuels microbial activity several meters below the soil surface

[摘要] The deep soil, >1  m, harbors a substantial shareof the global microbial biomass. Currently, it is not known whethermicrobial activity several meters below the surface is fueled by recentlyfixed carbon or by old carbon that persisted in soil for several hundredyears. Understanding the carbon source of microbial activity in deep soil isimportant to identify the drivers of biotic processes in the critical zone.Therefore, we explored carbon cycling in soils in three climate zones (arid,mediterranean, and humid) of the Coastal Cordillera of Chile down to a depthof 6 m, using carbon isotopes. Specifically, we determined the 13 C :  12 C ratio ( δ 13 C) of soil and roots and the 14 C :  12 C ratio ( Δ 14 C) of soil organic carbon andCO 2 –C respired by microorganisms. We found that the Δ 14 Cof the respired CO 2 –C was significantly higher than that of the soilorganic carbon in all soils. Further, we found that the δ 13 C ofthe soil organic carbon changed only in the upper decimeters (by less than 6 ‰). Our results show that microbial activity severalmeters below the soil surface is mostly fueled by recently fixed carbon thatis on average much younger than the total soil organic carbon present in therespective soil depth increments, in all three climate zones. Further, ourresults indicate that most decomposition that leads to enrichment of 13 C occurs in the upper decimeters of the soils, which is possibly dueto stabilization of organic carbon in the deep soil. In conclusion, ourstudy demonstrates that microbial processes in the deep soil several metersbelow the surface are closely tied to input of recently fixed carbon.

[学科分类] 大气科学