Exudate components exert different influences on microbially mediated C losses in simulated rhizosphere soils of a spruce plantation

Root exudates play a vital role in driving ecosystem carbon (C) cycling; however, few studies have examined the degree to which a specific exudate component affects soil C loss. The objective was to examine the impacts of different exudate components on microbially-mediated C decomposition and their underlying mechanisms. In a well-controlled simulated rhizosphere system, we added exudate chemicals (glucose, glycine and oxalic acid) to spruce (Picea asperata) plantation soils over a 35-day period. The total C contents, net N mineralization rates, microbial communities and extracellular enzymes were measured. The three exudate components induced different C losses by different mechanisms. Oxalic acid promoted net C loss by accelerating microbial mineralization of soil organic matter (SOM). In contrast, glucose resulted in a net C accumulation, which challenged the assumption that glucose serves as a co-metabolite in driving SOM decomposition to lose C. Glycine increased the total C content via negative priming effects. Exudate-induced rhizosphere priming effects are not entirely dependent on the energy properties of root exudates. Different exudates may affect SOM decomposition differently, thus the component-specialized rhizosphere processes induced by individual exudate components on soil C dynamics should be integrated into forest C cycle-climate feedbacks under environmental changes.