Root exudates in wetland soils – compound diversity and priming effect

Root exudation plays a critical role in the biogeochemical functioning of wetlands, influencing nutrient cycling, shaping both plant-plant and plant-microbe interactions and affecting soil organic carbon (SOC) decomposition via priming effects. We showed that contrary to most observations in aerated upland soils, glucose inputs can induce strong negative priming effects on anoxic peat. This finding yields important implications for the stability of the vast organic carbon reserves in global wetland soils. However, root exudation dynamics are complex, and the biogeochemical implications of the hundreds of diverse compounds released from roots remain elusive.

Here we present 1) a meta-analysis compiling data on wetland plant root exudates, focusing on both fluxes and compound diversity, and 2) preliminary results from incubation experiments simulating the effects of a typical wetland plant exudate composite on SOC decomposition.

Our meta-analysis elucidates the challenges in cross-study comparison of quantitative root exudate data due to methodological heterogeneity as well as the strong effects of environmental, biological and chemical parameters influencing plant traits. We found organic acids to be the primary compound class released by wetland roots, and organic acids have been assessed by the majority of studies. By contrast, few studies assessed the compound classes of sugars, amino acids, and secondary compounds, representing important knowledge gaps in our understanding of wetland-plant-microbe interaction and C cycling. To understand the complex effects of diverse root exudates on wetland SOC cycling, our ongoing incubation experiments compare the priming effect of a wetland plant exudate composite with that of conventionally used single sugar inputs.