The fate of recently fixed carbon after drought release: towards unravelling C storage regulation in Tilia platyphyllos and Pinus sylvestris

Abstract

Carbon reserves are important for maintaining tree function during and after stress. Increasing tree mortality driven by drought globally has renewed the interest in how plants regulate allocation of recently fixed C to reserve formation. Three-year-old seedlings of two species (Tilia platyphyllos and Pinus sylvestris) were exposed to two intensities of experimental drought during ~10 weeks, and C pulse labelling was subsequently applied with rewetting. Tracking the C label across different organs and C compounds (soluble sugars, starch, myo-inositol, lipids and cellulose), together with the monitoring of gas exchange and C mass balances over time, allowed for the identification of variations in C allocation priorities and tree C balances that are associated with drought effects and subsequent drought release. The results demonstrate that soluble sugars accumulated in P. sylvestris under drought conditions independently of growth trends; thus, non-structural carbohydrates (NSC) formation cannot be simply considered a passive overflow process in this species. Once drought ceased, C allocation to storage was still prioritized at the expense of growth, which suggested the presence of 'drought memory effects', possibly to ensure future growth and survival. On the contrary, NSC and growth dynamics in T. platyphyllos were consistent with a passive (overflow) view of NSC formation.

The 18O‐signal transfer from water vapour to leaf water and assimilates varies among plant species and growth forms

“…MRT WSC values derived from decay constant values after a 13 CO 2 pulse-labelling ranged between 5 to 25 hr for beech and pine saplings across the season (Desalme et al, 2017) and 57.6 hr for nondrought stressed beech saplings (Ruehr et al, 2009) and were thus lower or similar to those of the present study. MRT Sugars values of broadleaf and conifer saplings ranged between 14 and 22 hr Galiano Pérez et al, 2017) and were lower compared with MRT Sugars values of 28 and 40 hr for broadleaf and conifer plants in the present study, respectively. However, MRT values of assimilates likely depend on the experimental conditions, and the incorporation rate and allocation processes might differ between 13 C and 18 O labels, as observed in a multi-isotope labelling experiment (Studer et al, 2015).…”

Homeostatic levels of nonstructural carbohydrates after 13 yr of drought and irrigation inPinus sylvestris

“…As a result of the increased biomass production, the total NSC pools of irrigated trees were consequently larger than those of control trees. By contrast, seedlings of the same species prioritized the allocation of new assimilates to storage pools at the expense of growth shortly after drought had stopped, even though the drought did not cause any NSC depletion (Galiano Pérez et al ., ). This process might have taken place in our adult trees as well, in the first months or maybe years after the onset of irrigation, but acclimation to long‐term irrigation eliminated the short‐term need for higher storage input.…”

Living on next to nothing: tree seedlings can survive weeks with very low carbohydrate concentrations

“…(), who found similar NSC concentrations in sun or shade but less growth in shaded branches. In drought‐stressed scots pines, sugar accumulation was also shown to occur independently of growth trends (Galiano et al ., ).…”