Post-drought hydraulic recovery is accompanied by non-structural carbohydrate depletion in the stem wood of Norway spruce saplings

Abstract

Hydraulic failure and carbon starvation are recognized as main causes of drought-induced forest decline. As water transport and carbon dynamics are strictly interdependent, it is necessary to clarify how dehydration-rehydration cycles are affecting the relations between stem embolism and non-structural carbohydrates (NSC). This is particularly needed for conifers whose embolism repair capability is still controversial. Potted Norway spruce saplings underwent two drought-re-irrigation cycles of same intensity, but performed in two consecutive summers. During the second cycle, stem percent loss of hydraulic conductivity (PLC) and NSC content showed no carry-over effects from the previous drought, indicating complete long-term recovery. The second drought treatment induced moderate PLC (20%) and did not affect total NSCs content, while starch was converted to soluble sugars in the bark. After one week of re-irrigation, PLC recovered to pre-stress values (0%) and NSCs were depleted, only in the wood, by about 30%. Our data suggest that spruce can repair xylem embolism and that, when water is newly available, NSCs stored in xylem parenchyma can be mobilized over short term to sustain respiration and/or for processes involved in xylem transport restoration. This, however, might imply dependency on sapwood NSC reserves for survival, especially if frequent drought spells occur.

Nutrient Uptake and Utilization by Fragrant Rosewood (Dalbergia odorifera) Seedlings Cultured with Oligosaccharide Addition under Different Lighting Spectra

“…This suggests that CO may promote sugar utilization without having an impact on starch depletion. With regard to the involvement of CO presence in the promotion of RCD by the LED treatment relative to the control, the depleted sugars in the stem may be used for new cell formation in woody tissues [41]. However, to our knowledge, there is rare evidence to explain the mechanism for the CO-addition effect on carbohydrate metabolism, which needs be studied in future works.…”

The Possible Role of Non-Structural Carbohydrates in the Regulation of Tree Hydraulics

“…Evidence for vessel refilling under moderately negative xylem pressure has been provided in several plant species [8,19,40,67,85]. According to the existing model for refilling, VACs would be involved in the restoration of conduit functionality by generating an osmotic driving force and supplying water for refilling [20,42].…”

“…In woody tissues, the most abundant NSC specimens, mainly stored in parenchyma cells, are starch (the main insoluble storage compound) and low molecular weight sugars (glucose, fructose and sucrose). In some tree families, oligosaccharides such as stachyose and raffinose (sugars involved in phloem transport together with sucrose), and polyols such as pinitol, are also relevant and abundant [7,8]. Lipid stores are also particularly abundant in some genera such as Tilia, Pinus, Picea and Larix [9].…”

Priming xylem for stress recovery depends on coordinated activity of sugar metabolic pathways and changes in xylem sap pH

“…These models are consistent with observations of NSC accumulation dynamics in parenchyma cells of drought‐stressed plants. For instance, embolism presence has been shown to alter carbohydrate metabolism and the partitioning between starch and soluble sugars in xylem parenchyma (Salleo, Trifilò, Esposito, Nardini, & Lo Gullo, ; Secchi & Zwieniecki, ; Tomasella et al, ), resulting in the accumulation of high levels of NSC content in trees subjected to short‐term drought events (Trifilò et al, ). Additionally, the ability to recover from embolism has been found to be species specific and correlated with the concentration of soluble carbohydrates accumulated at the stem level (Savi et al, ).…”