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

Martina Tomasella,Karl-Heinz Häberle,Anna Machlet,Benjamin Hesse,Rainer Matyssek,Andrea Nardini

doi:10.1038/s41598-017-14645-w

Martina Tomasella, Karl-Heinz Häberle + Show 4 more

Open Access

https://doi.org/10.1038/s41598-017-14645-w

Copy DOI

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.

Highlights

Increase in duration, intensity and frequency of dry spells, coupled with rising temperatures, enhance drought stress experienced by plants[1]
In the current model proposed for embolism repair, developed during the past few decades[17], soluble sugars are transferred from parenchyma cells into embolized xylem ducts, in order to establish an osmotic gradient that reclaims water from VACs and/or phloem[18] to the conduits and allows for repair
In this study we present an experiment performed on Norway spruce (Picea abies), a conifer currently threatened by climate change in Central Europe[35]

Summary

Introduction

Intensity and frequency of dry spells, coupled with rising temperatures, enhance drought stress experienced by plants[1]. In the current model proposed for embolism repair, developed during the past few decades[17], soluble sugars are transferred from parenchyma cells (i.e. vessel associated cells, VACs) into embolized xylem ducts, in order to establish an osmotic gradient that reclaims water from VACs and/or phloem[18] to the conduits and allows for repair. This mechanism requires the presence of living cells in the proximity of the embolized conduits, so that both spatial arrangement and amount of woody parenchyma would be important traits affecting the process[19]. In previous studies conducted on this species, drought has been reported to affect carbon allocation and translocation, with differences between aboveground and belowground organs[5,6]

Methods

Results

Discussion

Conclusion