The clonal root system of balsam poplar in upland sites of Quebec and Alberta

Abstract

Balsam poplar seeds are short‐lived and require moist seedbeds soon after they are released to germinate. In addition to sexual reproduction, balsam poplar stands can regenerate clonally by root suckering. The origin of stands will in turn affect their genetic structure and root system architecture, which are poorly understood for upland forest stands. Three stands were hydraulically excavated in Quebec (moist) and Alberta (dry) to determine the origin of trees and to characterize root systems with respect to presence of parental roots and root grafts connections. Clones were identified using single‐nucleotide polymorphism (SNPs), and all stems, roots and root grafts were aged using dendrochronology techniques. All 82 excavated trees were of sucker origin, and four of the six stands contained a single clone. Parental root connections were found between 22% and 25% of excavated trees, and 53% and 48% of trees were linked with a root graft between the same or different clones, in Alberta and Quebec, respectively. Mean distance between trees connected by parental root was significantly lower than the distance between unconnected trees (0.47 ± 0.25 m vs. 3.14 ± 0.15 m and 1.55 ± 0.27 m vs. 4.25 ± 0.13 m) in Alberta and in Quebec, respectively. The excavations also revealed many dead stumps with live roots, maintained through root connections with live trees. This research highlights that balsam poplar growing in upland stands is a clonal species that can maintain relatively high genotypic diversity, with frequent root connections between trees at maturity. Maintaining an extensive root system through root connections increases the chances of a clone surviving when the above ground tree is dead and may also enhance the resilience of balsam poplar stands after disturbance.

Biomass Allocation and Root Characteristics of Early-Stage Poplars (Populus spp.) for Assessing Their Water-Deficit Response During SRC Establishment

“…Second, we hypothesised that there were between clone differences in the root diameter composition and that different root diameter classes vary in their responses to deficit watering treatments. This was expected because it was known that Tacamahaca species and P. × euramericana or P. nigra clones can differ in (fine) root morphology and turnover and in the expansion of their root systems [14,[32][33][34]. Third, we hypothesised in line with the previous hypotheses that the present clones differ in their allocation response of cumulated fine root length per total leaf area.…”

Ecological drivers of root grafting in balsam fir natural stands

“…ex Aiton or to 50% in Pinus strobus L.) (Bormann, 1966). Root grafting occurrence in balsam fir was however similar to other natural stands of boreal forest species such as Norway spruce (33%) (Külla and Lõhmnus, 1999) and balsam poplar (48%) (Adonsou et al, 2016a).…”

“…Age of trees at graft initiation was determined by calculating the difference between the age of tree and the age of the associated graft. Due to the eccentric root growth, root diameter was calculated by averaging perpendicular measurements of the longest and the shortest diameters of the root (Adonsou et al, 2016a). Root diameter at graft initiation was calculated by using the same method but measurements were realized on graft sections, before the first common growth ring between two roots (Supplementary material, Figure S2).…”

“…Mycorrhizal and suckering networks interconnecting indirectly root systems through fungal hyphae or directly through parental roots have been highlighted to alter forest stand dynamics by allowing exchanges of resources between trees (Adonsou et al, 2016a;Baret and DesRochers, 2011;Leake et al, 2004;Simard and Durall, 2004). However, root grafting, i.e.…”

Novel insights into the genetic diversity and clonal structure of natural trembling aspen (Populus tremuloidesMichx.) populations: A transcontinental study

“…Trembling aspen naturally regenerates vegetatively with suckers (Lafleur, Cazal, Leduc, & Bergeron, 2015;Long & Mock, 2012), which can often outcompete seedlings. Suckering has an important role in maintaining unique genotypes (also referred to as a 'clone' or 'genet') during disturbances and can contribute to the long-term persistence of trembling aspen in the landscape (Adonsou, DesRochers, Tremblay, Thomas, & Isabel, 2016;Bergeron & Charron, 1994;Kneeshaw & Bergeron, 1996). However, successful reproduction by seeds is considered rare, especially in dry climatic regions (Lafleur et al, 2015).…”