Temperature drives the coordination between above-ground nutrient conservation and below-ground nutrient acquisition in alpine coniferous forests

Above-ground nutrient conservation via resorption processes and below-ground nutrient acquisition from soils are two important mechanisms for plants to maintain nutrition and ecosystem functions. However, the mechanism by which plants coordinate these two nutrient strategies, especially for ectomycorrhizal (ECM)-dominated conifers in alpine forests, remains unclear.We investigated the relationships between above-ground nutrient conservation and below-ground nutrient acquisition and their environmental drivers by measuring leaf nutrient (i.e. nitrogen [N] and phosphorous [P]) resorption efficiency, resource foraging- and uptake-related root morphological (root diameter [RD], specific root length [SRL]/area [SRA]) and physiological (root tissue density [RTD], root N and P concentration) traits, mycorrhizal colonization rate (MCR), rhizosphere effect on soil N and P cycling, and environmental factors of 40 ECM coniferous populations on the eastern Tibetan Plateau, China.Our results showed that with increasing leaf nutrient (N and P) resorption efficiency, conifers shifted from depending on the 'outsourcing' strategy by mycorrhizal fungi (high MCR) to relying on the 'do-it-yourself' strategy of root mining (high rhizosphere effect on N- and P-mining-related enzyme activities) rather than on root foraging (high SRL and SRA) and preferred more conservative roots (high RTD and low root N and P concentrations). Temperature was the main factor driving a negative relationship of ECM fungi foraging, root uptake and a positive relationship of root mining with leaf nutrient resorption, while precipitation resulted in a decoupled relationship between root foraging and leaf nutrient resorption.Our findings demonstrate temperature-driven and diverse collaborations (e.g. trade-off or synergy) between below-ground nutrient acquisition and above-ground nutrient conservation strategies in alpine ECM conifers and highlight that the preference for below-ground nutrient acquisition strategies could influence the above-ground nutrient utilization strategy. This is insightful for a holistic understanding of the adaptation and responses of alpine forests to climatic change.Read the free Plain Language Summary for this article on the Journal blog.