Temperature drives the coordination between aboveground nutrient conservation and belowground nutrient acquisition in alpine coniferous forests

Aboveground nutrient conservation via resorption processes and belowground
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 aboveground nutrient
conservation and belowground 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 show 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., tradeoff
or synergy) between belowground nutrient acquisition and aboveground
nutrient conservation strategies in alpine ECM conifers and highlight that
the preference for belowground nutrient acquisition strategies could
influence the aboveground nutrient utilization strategy. This is
insightful for a holistic understanding of the adaptation and responses of
alpine forests to climatic change.