Asymmetric responses of roots and hyphae to inorganic and organic nutrient additions: a global meta-analysis

Background and Aims Fine roots and mycorrhizal hyphae represent two critical pathways for plants to acquire nutrients. Nevertheless, the mechanisms by which roots and hyphae respond to variations in inorganic and organic nutrients remain inadequately understood. Methods We conducted a meta-analysis on the effects of nitrogen, phosphorus, nitrogen-phosphorus combination and organic nutrient additions on root length (RL), root biomass (RB), root colonization (RC), hyphal length (HL), and hyphal biomass (HB) based on 738 root-hyphae observation pairs. Results We found that RB and RL increased by 27%-34% and 31%-36%, respectively, following nitrogen and/or phosphorus additions, whereas HL increased by 26% and RC decreased by 20%. The effect sizes of organic nutrient addition on hyphae were two to three times greater than those observed for fine roots. The impact of nitrogen addition on HL, RB and RC significantly decreased with increasing experiment duration, amount of nitrogen addition and/or soil total phosphorus, conversely, its effect on HL and RL significantly intensified with soil total organic carbon. The effects of nitrogen and organic nutrient additions on RB exhibited significant positive and negative correlations, respectively, with their effects on HL in ectomycorrhizal hosts. No significant relationships were detected for arbuscular mycorrhizal hosts. Conclusion Our results demonstrate that plants preferentially employ root-dependent acquisition strategies under high inorganic nutrients but rely more on hypha-dependent strategies under abundant organic nutrients. This study underscores the necessity of integrating both roots and hyphae within current nutrient acquisition frameworks to evaluate the effects of global changes on carbon and nitrogen cycling.