Seasonal carbohydrate dynamics and growth in Douglas-fir trees experiencing chronic, fungal-mediated reduction in functional leaf area

Abstract

Stored non-structural carbohydrates (NSCs) could play an important role in tree survival in the face of a changing climate and associated stress-related mortality. We explored the effects of the stomata-blocking and defoliating fungal disease called Swiss needle cast on Douglas-fir carbohydrate reserves and growth to evaluate the extent to which NSCs can be mobilized under natural conditions of low water stress and restricted carbon supply in relation to potential demands for growth. We analyzed the concentrations of starch, sucrose, glucose and fructose in foliage, twig wood and trunk sapwood of 15 co-occurring Douglas-fir trees expressing a gradient of Swiss needle cast symptom severity quantified as previous-year functional foliage mass. Growth (mean basal area increment, BAI) decreased by ∼80% and trunk NSC concentration decreased by 60% with decreasing functional foliage mass. The ratio of relative changes in NSC concentration and BAI, an index of the relative priority of storage versus growth, more than doubled with increasing disease severity. In contrast, twig and foliage NSC concentrations remained nearly constant with decreasing functional foliage mass. These results suggest that under disease-induced reductions in carbon supply, Douglas-fir trees retain NSCs (either actively or due to sequestration) at the expense of trunk radial growth. The crown retains the highest concentrations of NSC, presumably to maintain foliage growth and shoot extension in the spring, partially compensating for rapid foliage loss in the summer and fall.

Responses of sapwood ray parenchyma and non‐structural carbohydrates of Pinus sylvestris to drought and long‐term irrigation

“…If this pattern would only show in control trees, one could argue that water deficit will limit cell division and enlargement (Hsiao & Acevedo 1974), NSC mobilization and transport in the phloem (Sevanto 2014), but the same relationship between %NSC, TNC and ring width showed in the irrigated trees for which we can reasonably exclude any significant water limitation. Our results thus suggest an active control of carbon storage as opposed to a passive overflow storage of carbon not used for growth (Sala, Woodruff & Meinzer 2012;Saffell et al 2014).…”

“…Our results thus suggest an active control of carbon storage as opposed to a passive overflow storage of carbon not used for growth (Sala, Woodruff & Meinzer ; Saffell et al . ).…”

To die or not to die: early warnings of tree dieback in response to a severe drought

“…; Hartmann, Ziegler & Trumbore ), while above‐ground tissues use sugars for osmoregulation or to rebuild the crown (Saffell et al . ). Overall, our findings confirm that the sapwood concentrations of SS reflect crown defoliation in the two pine species whereas needle chemical variables (NSC, N, δ 13 C) do not.…”

Temperate and boreal forest tree phenology: from organ-scale processes to terrestrial ecosystem models

“…There is evidence that even under severe stress conditions, C reserves are never fully depleted (Gruber et al 2012;Hartmann et al 2013;Klein et al 2014) and that reserve storage may, in certain cases, be favored at the expense of growth (Wiley et al 2013;Saffell et al 2014). Recent studies have demonstrated that, within a given growing season, the formation of C reserves occurs earlier in mature trees compared to young trees in experiments conducted under the same pedoclimatic conditions and leaf phenology (Gilson et al 2014).…”