Effects of interaction between mycorrhizal dominance and tree diversity on plant productivity or carbon storage

Although previous studies have observed that mycorrhizal dominance can modulate the relationships between tree diversity and productivity/carbon storage, it remains unclear how the interaction effects between mycorrhizal dominance and tree diversity influence tree productivity or carbon storage. Thus, we leveraged nationwide forest inventory networks comprising 5,215 plots in China and 27,467 plots in USA to investigate the interaction effects between mycorrhizal associations and tree diversity on tree productivity/carbon storage. Our results revealed divergent climate-contingent interactions in China: tree diversity effects on tree carbon storage attenuated with increasing EcM fungal dominance in temperate zones but amplified in subtropical regions. Conversely, EcM dominance impacts diminished under higher tree diversity in temperate ecosystems, whereas subtropical systems exhibited positive synergies between tree diversity and mycorrhizal mediation. USA forests exhibited a reversed pattern: tree diversity effects on tree productivity intensified with rising EcM dominance in temperate forests but weakened in subtropical systems. Similarly, EcM dominance impacts positively scaled with tree diversity in temperate zones, whereas subtropical EcM effects declined amid richer tree communities. These results reveal that the effects of mycorrhizal-diversity interactions on ecosystem functioning are climate-regulated and demonstrate significant intercontinental variations, highlighting the critical role of the "climate-mycorrhizal-diversity" triad in governing ecosystem functions.