Carbon allocation during defoliation: testing a defense-growth trade-off in balsam fir

Abstract

During repetitive defoliation events, carbon can become limiting for trees. To maintain growth and survival, the resources have to be shared more efficiently, which could result in a trade-off between the different physiological processes of a plant. The objective of this study was to assess the effect of defoliation in carbon allocation of balsam fir [Abies balsamea (L.) Mill.] to test the presence of a trade-off between allocation to growth, carbon storage, and defense. Three defoliation intensities [control (C-trees, 0% defoliation), moderately (M-trees, 41–60%), and heavily (H-trees, 61–80%) defoliated] were selected in order to monitor several variables related to stem growth (wood formation in xylem), carbon storage in stem and needle (non-structural soluble sugars and starch), and defense components in needles (terpenoids compound) from May to October 2011. The concentration of starch was drastically reduced in both wood and leaves of H-trees with a quasi-absence of carbon partitioning to storage in early summer. Fewer kinds of monoterpenes and sesquiterpenes were formed with an increasing level of defoliation indicating a lower carbon allocation for the production of defense. The carbon allocation to wood formation gradually reduced at increasing defoliation intensities, with a lower growth rate and fewer tracheids resulting in a reduced carbon sequestration in cell walls. The hypothesis of a trade-off between the allocations to defense components and to non-structural (NCS) and structural (growth) carbon was rejected as most of the measured variables decreased with increasing defoliation. The starch amount was highly indicative of the tree carbon status at different defoliation intensity and future research should focus on the mechanism of starch utilization for survival and growth following an outbreak.

Genetic control and evolutionary potential of a constitutive resistance mechanism against the spruce budworm (Choristoneura fumiferana) in white spruce (Picea glauca)

“…Recent studies in conifers have also reported a lack of evidence for trade-offs between constitutive defense levels and growth. In balsam fir (Abies balsamea), a member of the Pinaceae along with spruce, Deslauriers et al (2015) assessed the effect of defoliation on carbon allocation and found no evidence of trade-off with growth. In the same way, no evidence for trade-offs was found between growth and defense in Pinus pinaster (Sampedro et al 2011) and Pinus radiata (Moreira et al 2013).…”

Contributions of insects and droughts to growth decline of trembling aspen mixed boreal forest of western Canada

“…In Canada, aspen forests are primarily damaged by defoliator insects, especially forest tent caterpillar and large aspen tortrix (Cooke & Lorenzetti, 2006;Hogg, Brandt, et al, 2002;Huang et al, 2008). Following repeated and heavy defoliation, trees may lose vigor and cannot acquire adequate amounts of carbohydrates to support radial growth (Deslauriers, Caron, & Rossi, 2015;Hudgeons et al, 2007;Kosola, Dickmann, Paul, & Parry, 2001). Where some trees die as a result of insect outbreaks or drought, reductions in competition levels could lead to increases in growth of surviving trees (Axelson, Alfaro, & Hawkes, 2009;Berg, Henry, Fastie, De Volder, & Matsuoka, 2006;Bretfeld, Doerner, & Franklin, 2015).…”

Interactive effects of defoliation and water deficit on growth, water status, and mortality of black spruce (Picea mariana (Mill.) B.S.P.)

“…Outbreaks of the eastern spruce budworm (Choristoneura fumiferana Clemens) are currently one of the major natural disturbances in the boreal forest (Bergeron et al 1995;Rossi and Morin 2011;Simard et al 2012). These events cause marked reductions in tree growth and increased stand mortality (Bouchard et al 2005;Zhang et al 2014). Drought is another important stress with rates of tree mortality in Canada's boreal forest increasing by 1.9% year −1 in the eastern part to 4.9% year −1 in the western portion between 1963 and 2008 (Peng et al 2011).…”