Modern agriculture’s goal of improving crop resource acquisition efficiency relies on the intricate relationship between the root system and the soil. Root and rhizosphere traits play a critical role in the efficient use of nutrients and water, especially under dynamic environments. This review emphasizes a holistic perspective, challenging the conventional separation of nutrient and water uptake processes and the necessity for an integrated approach. Anticipating climate change-induced increase in the likelihood of extreme weather events that result in fluctuations in soil moisture and nutrient availability, the study explores the adaptive potential of root and rhizosphere traits to mitigate stress. We emphasize the significance of root and rhizosphere characteristics that enable crops to rapidly respond to varying resource availabilities (i.e. the presence of water and mobile nutrients in the root zone) and their accessibility (i.e. the possibility to transport resources to the root surface). These traits encompass for example root hairs, mucilage and extracellular polymeric substance (EPS) exudation, rhizosheath formation and the expression of nutrient and water transporters. Moreover, we recognize the challenge of balancing carbon investments, especially under stress, where optimized traits must consider carbon-efficient strategies. To advance our understanding, the review calls for well-designed field experiments, recognizing the limitations of controlled environments. Non-destructive methods such as mini rhizotron assessments and in-situ stable isotope techniques, in combination with destructive approaches such as root exudation analysis, are proposed for assessing root and rhizosphere traits. The integration of modeling, experimentation, and plant breeding is essential for developing resilient crop genotypes capable of adapting to evolving resource limitation.

Nitrogen availability in the rhizosphere relies on root‐microorganism interactions, where root exudates trigger soil organic matter (SOM) decomposition through the rhizosphere priming effect (RPE). Though microbial necromass contribute significantly to organically bound soil nitrogen (N), the role of RPEs in regulating necromass recycling and plant nitrogen acquisition has received limited attention. We used ¹⁵N natural abundance as a proxy for necromass‐N since necromass is enriched in ¹⁵N compared to other soil‐N forms. We combined studies using the same experimental design for continuous ¹³CO₂ labelling of various plant species and the same soil type, but considering top‐ and subsoil. RPE were quantified as difference in SOM‐decomposition between planted and unplanted soils. Results showed higher plant N uptake as RPEs increased. The positive relationship between ¹⁵N‐enrichment of shoots and roots and RPEs indicated an enhanced necromass‐N turnover by RPE. Moreover, our data revealed that RPEs were saturated with increasing carbon (C) input via rhizodeposition in topsoil. In subsoil, RPEs increased linearly within a small range of C input indicating a strong effect of root‐released C on decomposition rates in deeper soil horizons. Overall, this study confirmed the functional importance of rhizosphere C input for plant N acquisition through enhanced necromass turnover by RPEs.

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 N_org-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.

Background and aims: While nitrogen (N) derived from soil organic matter significantly sustains agricultural plants, the complexities of organic N utilization pathways remain poorly understood. Knowledge gaps persist regarding diverse organic N pools, the microbial processes in N mineralization, and how plants shape the N-mineralizing microbial community through root exudation. Results: To address these gaps, we propose an integrated conceptual framework that explores the intricate interplay of soil, plant, and microbiome dynamics within the context of soil carbon (C) cycling. Emphasizing plant effects on gross depolymerization and deamination of organic N—a crucial yet often overlooked aspect—we aim to enhance our understanding of plant N utilization pathways. In this context, we suggest considering the linkages between root and hyphal exudation, followed by rhizosphere priming effects which in turn control N mobilization. Based on the relation between exudation and N turnover, we identify microbial necromass as a potentially important organic N source for plants. Furthermore, we propose applying root economic theory to gain insights into the diverse strategies employed by plants in accessing soil organic N. Stable isotope tracers and functional microbiome analytics provide tools to decipher the complex network of the pathways of organic N utilization. Conclusions: The envisioned holistic framework for organic N utilization pathways, intricately connects plants, soil, and microorganisms. This lays the groundwork for sustainable agricultural practices, potentially reducing N losses.