A Conceptual Framework on the Fate of Rhizodeposits in Forming Mineral-Associated Organic Matter or Encapsulating Into Microaggreagtes

Rhizodeposition, as transported from photosynthates and exudated in soils via fine roots, is the pivot linking above- and belowground carbon (C) cycling pathways. Meanwhile, rhizodeposit C serves as “currency” for plant nutrient acquisition because of its critical roles in priming soil microorganisms, maintaining plant-mycorrhizal symbionts, and elongating plant roots. Therefore, a conceptual framework integrating knowledge on the biogeochemical fate of rhizodeposit C can help understand plant nutrient economics and soil C sink function. However, it still remains a great challenge to efficiently delineate the dynamics of rhizodeposit C in soils. In the framework, we present the possible stabilization pathways of rhizodeposit C via formation of mineral-associated organic matter (MAOM) or encapsulation by microaggregates. We further propose that continuous and pulse 13CO2 labeling are powerful techniques to track the fate of rhizodeposit C and to quantify how much C could eventually be sequestrated in soils as the component of MAOM or microaggregates. This framework would provide future research possibilities to better optimize plant C allocation and productivity and preserve soil C stocks.