Divergent root phosphorus-acquisition strategies of woody plants in the Qinling Mountains transition zone of China

Transition zones, characterized by pronounced environmental gradients and complex landscape elements, create selective pressures that drive plants to exhibit divergent resource-acquisition strategies (particularly for phosphorus [P]) to mitigate soil nutrient heterogeneity and interspecific competition. Nevertheless, the mechanisms underpinning the expression of root P strategies across multidimensional environmental conditions remain poorly resolved. In the Qinling Mountains, China's largest subtropical-warm temperate transition zone, we examined root P-acquisition traits of dominant woody species alongside associated environmental factors across 18 elevational sites spanning two slopes (north vs south) with contrasting climatic and vegetation characteristics. With increasing elevation, increased specific root length (SRL) and root nitrogen concentration coupled with decreased mycorrhizal colonization on the south slope drove a strategic shift from symbiosis between roots and mycorrhizal fungi (both arbuscular mycorrhizal and ectomycorrhizal species) towards a root morphological foraging strategy (high SRL) for plant-available soil P. Conversely, the north slope exhibited inverse root trait coordination: enhanced mycorrhizal colonization and root diameter but reduced phosphatase activity and SRL, triggering a transition from P mining to P scavenging. The difference in rhizosheath phosphatase activity between slopes reflects plants' divergent preferences for mineralizing the soil organic phosphorus pool: phosphodiesterase dominance at low-elevation south slope versus elevated phosphomonoesterase, phosphodiesterase and phytase activity on the north slope. Variation in P-acquisition strategies was jointly impacted by soil properties (pH, temperature, nutrient availability) and climate (humidity and temperature) on the south slope but primarily climate-mediated on the north slope. Synthesis. Collectively, these findings demonstrate that plants in transition zones dynamically reconfigured P-acquisition strategies through coordination of root and mycorrhizal trade-offs and preferential mineralization of organic phosphorus in response to multidimensional environmental filters. This variation of P-acquisition strategies between north and south slopes, triggered by the interplay of climate and soil properties, fundamentally structured P utilization patterns and drove niche differentiation in plant communities in transition zones.