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Aims: Soil priming affects soil N transformation and plant N availability, but few studies have investigated these interactions to date. Methods: To address this, we reviewed the literature for studies quantifying soil priming, soil N transformation and plant N uptake. Results: Gross N mineralization was strongly controlled by soil priming in studies with plants, while abiotic factors had a minor influence on gross N mineralization. In contrast, soil priming was negatively related to gross N mineralization and had a low explanatory power in incubation studies where substrates are added as surrogates for root exudates. These results indicate that plants support increased N mineralization and that this is not adequately reflected in incubation studies. Additionally, we observed a positive relationship between soil priming and the % of Norg-derived N uptake as well as total N uptake, which demonstrates that priming enhances the availability of N that was previously organically bound and that at least part of the N mineralized during priming was available for plant uptake. Conclusion: Our results show that the effect of roots and rhizodeposition leads to a number of processes supporting N mineralization and availability through priming that are not well reflected in incubation studies. To fully capture the interactions between plant roots and their associated microbiota, we recommend focusing research on systems with plants. Additionally, the strong correlation between C and N transformation should be considered in biogeochemical modelling. [ABSTRACT FROM AUTHOR]

Aims: Microbial turnover processes are typically restricted by low substrate availability in the subsoil. We hypothesized that SOM decomposition increases with plant density and decreases with N fertilization: We expected a greater rate of C allocation to the rhizosphere in the topsoil than in the subsoil treatments. Methods: In order to simulate different degrees of rhizodeposition, wheat was planted in pots at four different densities. The plants were continuously labeled with 13C-depleted CO2. Soil CO2 efflux was partitioned for root- and SOM-derived CO2. Moreover, we determined the enzyme kinetics by measuring catalytic efficiency and enzyme stoichiometry in both topsoil and subsoil. Results: Shoot biomass and the shoot to root ratio were significantly higher for plants grown in the topsoil compared with the subsoil, which demonstrated higher relative C allocation to root biomass in the subsoil treatment. Despite the similar size of the rhizosphere, root-derived CO2 was always higher in the topsoil compared with the subsoil treatment, indicating enhanced root exudation. Effect sizes of all enzyme activities showed stronger magnitudes for the subsoil treatments. This was in line with a two-times increase of the effect size of SOM decomposition in the subsoil relative to topsoil. Conclusions: Overall, the plants in the subsoil treatments allocated more C to root biomass, less C to shoot biomass, and substantially less C to root exudates. However, the effect sizes of both SOM decomposition and enzyme activities were higher in the subsoil than in the topsoil, reflecting a stronger sensitivity to C inputs. [ABSTRACT FROM AUTHOR]