Thirst beats hunger – declining hydration during drought prevents carbon starvation in Norway spruce saplings

Abstract

SummaryDrought-induced tree mortality results from an interaction of several mechanisms. Plant water and carbon relations are interdependent and assessments of their individual contributions are difficult. Because drought always affects both plant hydration and carbon assimilation, it is challenging to disentangle their concomitant effects on carbon balance and carbon translocation. Here, we report results of a manipulation experiment specifically designed to separate drought effects on carbon and water relations from those on carbon translocation.In a glasshouse experiment, we manipulated the carbon balance of Norway spruce saplings exposed to either drought or carbon starvation (CO 2 withdrawal), or both treatments, and compared the dynamics of carbon exchange, allocation and storage in different tissues.Drought killed trees much faster than did carbon starvation. Storage C pools were not depleted at death for droughted trees as they were for starved, well-watered trees. Hence drought has a significant detrimental effect on a plant's ability to utilize stored carbon.Unless they can be transported to where they are needed, sufficient carbon reserves alone will not assure survival of a drought except under specific conditions, such as moderate drought, or in species that maintain plant water relations required for carbon re-mobilization.

Evidence for Hydraulic Vulnerability Segmentation and Lack of Xylem Refilling under Tension

“…Moreover, investing carbon into structures (i.e. conduit walls) that would lose their function so readily seems unlikely, especially considering the functional importance of carbon in plant physiology (Mencuccini, 2003;McDowell, 2011;Sala et al, 2012;Hartmann et al, 2013;Charrier et al, 2015;Hartmann, 2015). Finally, the minimal water potential experienced by a plant on a seasonal basis is generally less negative than its C 50 value (Choat et al, 2012).…”

Cross-Talk between Physiological and Metabolic Adjustments Adopted by Quercus cerris to Mitigate the Effects of Severe Drought and Realistic Future Ozone Concentrations

“…Discrepancies in the literature are probably due to the different conditions adopted in the experiments. Most of our knowledge comes from studies of adult trees subjected to severe drought stress where water withholding is applied until plant wilting and mortality [19][20][21]. However, it should be noted that responses of young trees growing in natural and anthropic conditions can differ significantly [22].…”

Securing African forests for future drier climates: applying ecophysiology in tree improvement

“…A proposed flaw of the CSH is that die-back of isohydric plants during prolonged drought events can still be plausible without having exhausted carbon reserves (Sala et al 2010). The ability of plants to move or reallocate carbon reserves during prolonged drought may therefore still provide the necessary energy to survive (Hartmann et al 2013). Drought may therefore not directly lead to reduced carbohydrate reserves and thus tree death (Anderegg et al 2012).…”

“…Sevanto and Dickman (2015) provided an effective solution to moderate the current discrepancies in the CSH as a key mechanism in killing trees. They suggested that it is to gain a better understanding of the actual reallocation and transport of stored carbon to those plant tissues 1986;McDowell et al 2010;McDowell et al 2011;Hartmann et al 2013;Sevanto et al 2014;Anderegg et al 2015a). Since the time during which a tree is subjected to dangerous hydraulic thresholds could be more important than plant thresholds per se, it is possible to be even more precise in applying such tree die-back models (McDowell et al 2013; see also Choat et al 2012).…”