Coupled N and P cycling as driven by microbial taxa and interactions.

The coupled cycling of nitrogen (N) and phosphorus (P) is fundamental to ecosystem functioning, yet the specific microbial taxa and their interactions underlying N-P coupling and decoupling remain poorly understood. Based on a natural laboratory in Yunnan with both coupled and decoupled N-P cycling, we explored bacterial, fungal, and phoD-harboring communities using amplicon sequencing and their relationships with N and P cycling variables. We uncovered 14 phyla and 68 genera both correlated with N and P cycling variables, identified as coupled taxa. Among them, 5 coupled phyla (Nitrospirota, WPS-2, Mortierellomycota, Fungi_phy_Incertae_sedis, and Rozellomycota) and 24 coupled genera (Candidatus Koribacter, Candidatus Solibacter, A21b, etc.) were also enriched in sites where N and P dynamics change synchronously (coupled sites), indicating a key role of these coupled taxa in promoting N-P coupling. The 11 phyla and 48 genera correlated with either N- or P-cycling variables were grouped as decoupled taxa. Moreover, the networks composed of coupled taxa (coupled networks) displayed a greater ratio of positive to negative interactions than those composed of decoupled taxa (decoupled networks). Literature confirms that potential keystone genera (WPS-2, Acidibacter, TK10, etc.) from the coupled network positively interacted with each other to facilitate N-P coupling while potential keystone genera (an unclassified Subgroup_17 genus, etc.) from the decoupled network negatively interact with members to enhance N-P decoupling. These findings suggest that coupled taxa, individually and by synergistically interacting, could enhance N-P coupling whereas decoupled taxa, individually and by antagonistically interacting, might facilitate N-P decoupling. Overall, by uncovering key microbial taxa and interactions underpinning N-P coupling, our study provides a foundation for managing nutrient cycling in forest ecosystems under environmental change.