Impact of carbohydrate supply on stem growth, wood and respired CO2  13C: assessment by experimental girdling

Abstract

The present study examines the impact of the C source (reserves vs current assimilates) on tree C isotope signals and stem growth, using experimental girdling to stop the supply of C from leaves to stem. Two-year-old sessile oaks (Quercus petraea) were girdled at three different phenological periods during the leafy period: during early wood growth (Girdling Period 1), during late wood growth (Girdling Period 2) and just after growth cessation (Girdling Period 3). The measured variables included stem respiration rates, stem radial increment, delta(13)C of respired CO(2) and contents of starch and water-soluble fraction in stems (below the girdle) and leaves. Girdling stopped growth, even early in the growing season, leading to a decrease in stem CO(2) efflux (CO(2R)). Shift in substrate use from recently fixed carbohydrate to reserves (i.e., starch) induced (13)C enrichment of CO(2) respired by stem. However, change in substrate type was insufficient to explain alone all the observed CO(2R) delta(13)C variations, especially at the period corresponding to large growth rate of control trees. The below-girdle mass balance suggested that, during girdling periods, stem C was invested in metabolic pathways other than respiration and stem growth. After Girdling Period 1, the girdle healed and the effects of girdling on stem respiration were reversed. Stem growth restarted and total radial increment was similar to the control one, indicating that growth can be delayed when a stress event occurs early in the growth period. Concerning tree ring, seasonal shift in substrate use from reserves (i.e., starch) to recently fixed carbohydrate is sufficient to explain the observed (13)C depletion of tree ring during the early wood growth. However, the inter-tree intra-ring delta(13)C variability needs to be resolved in order to improve the interpretation of intra-seasonal ring signals in terms of climatic or ecophysiological information. This study highlighted, via carbohydrate availability effects, the importance of the characterization of stem metabolic pathways for a complete understanding of the delta(13)C signals.

Temporal dynamics of nonstructural carbohydrates and xylem growth inPinus sylvestrisexposed to drought

“…Carry-over effects of stored products in tree ring formation from one year to the next were also detected by Helle and Schleser (2004) and Keel et al (2007). However, as demonstrated by several authors (Maunoury-Danger et al 2010;Maier et al 2010) a seasonal shift in substrate use from reserves to recently fixed carbohydrate during active radial growth might occur.…”

The Contribution of Carbon and Water in Modulating Wood Formation in Black Spruce Saplings

“…While some girdling studies indicated that NSC reserves in the stem were not sufficient to sustain growth below the girdle in the short term or the long term (de Schepper et al, 2010;Maier et al, 2010), others demonstrated that stem reserves could be used to restart growth (Daudet et al, 2005; Maunoury-Danger et al, 2010). This assumption imposes source-sink relationships between xylem ray parenchyma cells and living cells (Olano et al, 2013).…”

“…Reserves often are used at growth resumption in early spring (Oribe et al, 2003;Begum et al, 2013), but most xylem is formed with newly synthesized NSCs Beck, 1990, 1994;Kagawa et al, 2006). The ray parenchyma cells in xylem also could act as a source of NSCs to sustain growth when assimilates coming from the leaf become scarce (Maunoury-Danger et al, 2010;Olano et al, 2013), such as during a water deficit. As the molecular networks driving cell division and expansion largely rely on the availability of carbohydrates to provide energy and biomass (Lastdrager et al, 2014), xylem formation is an ideal system in which to study sourcesink relationships and the C dependence of growth metabolism.…”

The effect of stem girdling on xylem and phloem formation in Scots pine

“…Stem girdling, as one of the most practical methods to provoke artificial stress (Stone 1974;Wilson 1998), was broadly used over the decades in horticulture to manage the growth and reproduction of several deciduous and evergreen tree species (Weinburger and Cullinan 1932;Lilleland and Brown 1936;Crane and Campbell 1957;Lewis and McCarty 1973;Winkler et al 1974;Powell and Cash Howell 1985;Fernandez-Escobar et al 1987;Augusti et al 1998;Day and DeJong 1999;Rivas et al 2008). Girdling has been practiced in the forestry and logging industry as a pre-harvest treatment to change wood properties (MacDougal 1943;Noel 1970;Lopez et al 2015) by manipulating annual ring width, wood density, duration of cambial activity, and latewood production (Wilson and Gartner 2002;Domec and Pruyn 2008;Maunoury-Danger et al 2010;Sellin et al 2013). More recently, several researchers have applied girdling for physiological experiments primarily to manipulate carbohydrate distribution within plants (De Schepper and Steppe 2011) and to study phloem-xylem interactions (Fishman et al 2001;Wilson and Gartner 2002;Zwieniecki et al 2004;Salleo et al 2006;Morandi et al 2007;Domec and Pruyn 2008;Tombesi et al 2014).…”