Redox control on rhizosphere priming in wetlands

Abstract

Rhizosphere priming describes a positive or negative change in the rate of soil organic matter decomposition caused by root activity and represents an important terrestrial soil–climate feedback. Few studies have investigated rhizosphere priming in wetlands, despite their disproportionate role in the global soil carbon budget. Here we present a literature analysis to show that both positive and negative rhizosphere priming can be much stronger in wetland than upland ecosystems. We argue that differences in plant–soil microbial interactions between dominantly oxic and anoxic soil environments induce the different degrees of rhizosphere priming effects. A conceptual framework is proposed in which wetland plants control soil redox status by acting as sources of both electron donors and acceptors, thereby influencing soil carbon stability through interactions with microbial communities. We identify key uncertainties in the mechanistic and quantitative understanding of wetland rhizosphere priming and demonstrate how priming could govern wetland soil carbon dynamics and ecosystem stability in response to climate change. Rhizosphere priming effects are stronger in wetland soils than in upland soils due to the greater variation in the redox condition in the rhizosphere, according to a data analysis of existing observations.