The effects of defoliation on carbon allocation: can carbon limitation reduce growth in favour of storage?

Abstract

There is no consensus about how stresses such as low water availability and temperature limit tree growth. Sink limitation to growth and survival is often inferred if a given stress does not cause non-structural carbohydrate (NSC) concentrations or levels to decline along with growth. However, trees may actively maintain or increase NSC levels under moderate carbon stress, making the pattern of reduced growth and increased NSCs compatible with carbon limitation. To test this possibility, we used full and half defoliation to impose severe and moderate carbon limitation on 2-year-old Quercus velutina Lam. saplings grown in a common garden. Saplings were harvested at either 3 weeks or 4 months after treatments were applied, representing short- and longer-term effects on woody growth and NSC levels. Both defoliation treatments maintained a lower total leaf area than controls throughout the experiment with no evidence of photosynthetic up-regulation, and resulted in a similar total biomass reduction. While fully defoliated saplings had lower starch levels than controls in the short term, half defoliated saplings maintained control starch levels in both the short and longer term. In the longer term, fully defoliated saplings had the greatest starch concentration increment, allowing them to recover to near-control starch levels. Furthermore, between the two harvest dates, fully and half defoliated saplings allocated a greater proportion of new biomass to starch than did controls. The maintenance of control starch levels in half defoliated saplings indicates that these trees actively store a substantial amount of carbon before growth is carbon saturated. In addition, the allocation shift favouring storage in defoliated saplings is consistent with the hypothesis that, as an adaptation to increasing carbon stress, trees can prioritize carbon reserve formation at the expense of growth. Our results suggest that as carbon limitation increases, reduced growth is not necessarily accompanied by a decline in NSC concentrations. Therefore, a lack of NSC decline may not be evidence that reduced tree growth under cold or water stress is caused by sink limitation.

Ecophysiological aspects of the interaction between Cameraria ohridella and Guignardia aesculi on Aesculus hippocastanum

“…3), the increment from the first period was determined by amount of synthesised secondary metabolites rather than leaf damage, which was low at the time. It is likely that amount of assimilative organs loss affects growth of saplings like in Wiley et al (2013). Furthermore, the leaf damage caused a slight decrease in stem volume increment when its dynamics took place later.…”

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).…”

Species-specific competition and N fertilization regulate non-structural carbohydrate contents in two Larix species

“…carbon supply (photosynthesis) and carbon demand (respiration, growth or export) (Smith and Stitt, 2007;Sala et al, 2012;Dietze et al, 2014;Wiley et al, 2013). Any factor affecting carbon supply and demand would inevitably influence the carbon dynamics of plants.…”

“…Attributes of non-structural carbohydrate storages are assumed to be an important life history trait (Canham et al, 1999;Gleason and Ares, 2004;Dietze et al, 2014). Recent studies have discovered that plants with higher NSC storages in leaves, stems or roots have a stronger ability to survive under drought stress (Adams et al, 2009(Adams et al, , 2013O'Brien et al, 2014O'Brien et al, , 2015, reduced light (Myers and Kitajima, 2007) and defoliation (Wiley et al, 2013). Additionally, NSC is actively maintained for signaling among cells and tissues (Lalonde et al, 1999;Smeekens, 2000;Smith and Stitt, 2007;Secchi and Zwieniecki, 2011).…”