A 'Get-Save-Return' process continuum runs on phosphorus economy among subtropical tree species

1. Plants allocate nutrients to new leaves via making a cost-benefit
trade-off between root nutrient absorption (‘get’) and leaf nutrient
resorption (‘save’). This active trade-off in nutrient acquisition
pathways may cause a passive trade-off between resorption and
decomposition (‘return’). However, whether these nutrient-associated
processes are linked and form a ‘get-save-return’ (GSR) continuum, and its
linkages with the aboveground leaf economics spectrum (LES) and the
belowground mycorrhizal association remain unclear. 2. Here, we present
the first empirical evidence of a direct link among multiple
nutrient-associated processes and tested this continuum hypothesis by
synchronously integrating root nutrient absorption, leaf nutrient
resorption, and leaf litter decomposition of 15 co-occurring tree species
hosting either arbuscular mycorrhizal or ectomycorrhizal fungi in
subtropical forests of China. 3. Across species, there was an active
trade-off between phosphorus (P) absorption and resorption, which further
caused a passive trade-off between P resorption and leaf litter
decomposition, indicating that the GSR continuum exists and runs on P
economy. However, these processes associated with nitrogen economy were
not well-linked. Interestingly, the loading scores of species on the LES
were positively correlated with root P absorption, negatively with leaf P
resorption, and positively with leaf litter decomposition. These linkages
indicate that species running in the ‘fast lane’ had greater root P
absorption, lower leaf P resorption, and faster leaf litter decomposition
than species running in the ‘slow lane’, and that the process-based GSR
continuum follows the trait-based ‘fast-slow’ LES. Furthermore, the
continuum on P economy emerged evidently in the ectomycorrhizal tree
species rather than in the arbuscular mycorrhizal tree species, indicating
critical control of mycorrhizal association over the continuum. 4.
Synthesis. Overall, these results demonstrate the existence of the GSR
continuum on tree P economy, which conforms to the economics spectrum
theory but varies with mycorrhizal association type. Our findings provide
a process-based framework for mechanistic understanding of the whole plant
nutrient economy and ecosystem nutrient cycling, and facilitate improved
predictions of biogeochemical models. --