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Abstract:
Drought-induced tree mortality has received much attention in the recent past.
hydraulic framework links tree hydraulics with carbon dynamics and proposes two non-exclusive mortality
mechanisms: carbon starvation (CS) and hydraulic failure (HF). CS is often referred to as the (partial)
depletion of non-structural carbohydrates (NSC) in response to stomatal closure, reduced C assimilation and
sustained C storage dependency during longer droughts. HF describes a lethal level of xylem dysfunction from
runaway embolism during severe droughts. While HF can be readily inferred from the percentage loss of
conductivity in vascular tissues at the time of death, CS is much more difficult to assess.
Starvation is usually defined as a lack of food leading to suffering or death. In plants photosynthetic sugars
play many functional roles, not only as a source of catabolic energy. For example, sugars are important for
osmotic regulation of cell pressure and recent studies suggest a potential link between xylem parenchyma
sugars and embolism repair following drought. Hence, carbon limitation could have a direct impact on tree
hydraulics and HF; however, empirical evidence for such a mechanism is still inconclusive.
Although HF appears to be predominant during drought mortality, our limited understanding of the roles of
NSC in hydraulic function precludes any premature refutation of CS as a mechanism in drought-induced tree mortality.
