Abstract:
Carbon (C) allocation plays a central role in tree responses to environmental changes. Yet, fundamental questions remain about how trees allocate C to different sinks, for example, growth vs storage and defense.
In order to elucidate allocation priorities, we manipulated the whole‐tree C balance by modifying atmospheric CO2 concentrations [CO2] to create two distinct gradients of declining C availability, and compared how C was allocated among fluxes (respiration and volatile monoterpenes) and biomass C pools (total biomass, nonstructural carbohydrates (NSC) and secondary metabolites (SM)) in well‐watered Norway spruce (Picea abies) saplings. Continuous isotope labelling was used to trace the fate of newly‐assimilated C.
Reducing [CO2] to 120 ppm caused an aboveground C compensation point (i.e. net C balance was zero) and resulted in decreases in growth and respiration. By contrast, soluble sugars and SM remained relatively constant in aboveground young organs and were partially maintained with a constant allocation of newly‐assimilated C, even at expense of root death from C exhaustion.
We conclude that spruce trees have a conservative allocation strategy under source limitation: growth and respiration can be downregulated to maintain ‘operational’ concentrations of NSC while investing newly‐assimilated C into future survival by producing SM.
Description:
Supplementary material: Fig. S1 Concentrations of soluble sugars, starch and NSC (soluble sugars + starch) expressed as percentage of control (400 ppm [CO2]) at the whole‐tree level.
Fig. S2 Concentrations of soluble sugars, starch and NSC (soluble sugars + starch) at the whole‐tree level.
Fig. S3 Concentrations of phenolic compounds, monoterpenes and total secondary metabolites expressed as percentage of control (400 ppm [CO2]) at the whole‐tree level.
Fig. S4 Concentrations of phenolic compounds, monoterpenes and total secondary metabolites (phenolic compounds + monoterpenes) at the whole‐tree level.
Fig. S5 δ13C (‰) of bulk tissue, water soluble C and phenolic compounds at the whole‐tree level.
Methods S1 TD‐GC‐MS conditions for BVOC analysis.
Table S1 Internal standards, weight‐based response factors and methods used for the measurements of secondary metabolites.
Table S2 A rough estimation of allocation of newly‐assimilated carbon.
