Elevational shifts in nutrient strategies of Abies fabri: From morphological foraging to enzymatic mining

In alpine conifer forests, nutrient acquisition is shaped by nitrogen (N), phosphorus (P) and cold soils, but the elevational adjustment of nutrient-acquisition traits in Abies fabri is still poorly known. Along the Gongga Mountain transect (2,800-3,400 m), soil inorganic N declined markedly with elevation, whereas available phosphorus, defined here as Bray-1 extractable P, did not differ significantly among elevations. Forests at 2,800, 3,100 and 3,400 m were sampled for soil nutrients, leaf N:P, foliar N and P fractions, root morphology, root exudation, mycorrhizal colonisation, root enzyme activities and non-structural carbohydrates (NSC) to test how leaf nutrient status was linked to belowground acquisition traits. The trait pattern did not follow a directional available-P gradient. With elevation, foliar N allocation shifted from Rubisco towards cell-wall pools, while foliar P shifted towards metabolic and nucleic-acid pools. Fine roots showed a more conservative morphology, with lower specific root length (SRL) and specific root area (SRA), whereas fine-root acid phosphatase (APase) and N-assimilating enzyme activities increased. With the high-elevation decline in leaf N:P, A. fabri responses reflected N-P stoichiometric context, internal nutrient allocation and root-trait coordination rather than a simple soil-P availability gradient.