Five willow varieties cultivated across diverse field environments reveal stem density variation associated with high tension wood abundance

Abstract

Sustainable and inexpensive production of biomass is necessary to make biofuel production feasible, but represents a challenge. Five short rotation coppice willow cultivars, selected for high biomass yield, were cultivated on sites at four diverse regions of Quebec in contrasting environments. Wood composition and anatomical traits were characterized. Tree height and stem diameter were measured to evaluate growth performance of the cultivars according to the diverse pedoclimatic conditions. Each cultivar showed very specific responses to its environment. While no significant variation in lignin content was observed between sites, there was variation between cultivars. Surprisingly, the pattern of substantial genotype variability in stem density was maintained across all sites. However, wood anatomy did differ between sites in a cultivar (producing high and low density wood), suggesting a probable response to an abiotic stress. Furthermore, twice as many cellulose-rich G-fibers, comprising over 50% of secondary xylem, were also found in the high density wood, a finding with potential to bring higher value to the lignocellulosic bioethanol industry.

Keywords: biofuels; density; tension wood; willow (Salix sp.); wood anatomy.

FIGURE 1

Site localization in Québec province, Canada: Saint-Roch-de-l′Achigan (SR), Beloeil (B), Saint-Siméon (S-S), and La Pocatière (LP).

FIGURE 2

Tree height (A – by site; C – by genotype) and stem diameter (B – by site; D – by genotypes) from five willow cultivars in their second year of a harvest cycle (Salix viminalis 5027, S. dasyclados SV1, S. miyabeana SX61, S. miyabeana SX64, S. miyabeana SX67) sampled at four field trials in Québec: Saint-Roch-de-l′Achigan, Beloeil, S-S, and LP. Error bars represent standard error, n = 4 blocks (6 trees per block). Tukey′s Honestly Significant Difference (HSD) pairwise post hoc test (α = 0.05) are represented by letters a–c.

FIGURE 3

Five willow cultivars in their second year of a harvest cycle (Salix viminalis 5027, S. dasyclados SV1, S. miyabeana SX61, S. miyabeana SX64, S. miyabeana SX67) sampled at four field trials in Québec: Saint-Roch-de-l′Achigan, Beloeil, S-S and LP. (A) Variation in extractives (toluene-ethanol/water extraction); (B) lignin content expressed as a percentage of dry matter and (C) total polyphenolics content (methanol-extractable). Error bars represent standard error, n = 4 blocks (four trees per block). Tukey’s HSD pairwise post hoc test (α = 0.05) are represented by letters a–b.

FIGURE 4

Stem density was assessed using oven dried specific gravity (grams per cubic centimeters) from five willow cultivars in their second year of a harvest cycle (Salix viminalis 5027, S. dasyclados SV1, S. miyabeana SX61, S. miyabeana SX64, S. miyabeana SX67) sampled at four field trials in Québec: Saint-Roch-de-l′Achigan, Beloeil, S-S and LP. Error bars represent standard error, n = 4 blocks (four trees per block). Tukey’s HSD pairwise post hoc test (α = 0.05) are represented by letters a–d.

FIGURE 5

SX64 cultivar (S. miyabeana) in its third year of a harvest cycle sampled at two field trials in Québec: Saint-Roch-de-l′Achigan and LP. (A) Measured Anatomical traits: (i) pith proportion, (ii) fiber cell diameter, and (iii) vessels number per 1 mm2; (B) Variation of G fibers determined by different image analytical methods: Method A (Manual) involved manual drawing around stained g-fiber, Method B (Pixel distribution) quantified pixels in a bin from 0 to 100, Method C (Blind distribution) quantified pixels in a bin from 0 to 127 and Method D (Black and White) count black pixels of monochrome. Error bars represent standard error (n = 3 trees, one per randomized block). All comparisons between Saint Roch and La Pocatiere presented in this figure are significantly different (t-test, p < 0.05).

FIGURE 6

(A) 40 μm transverse section of a stem from SX64 cultivated at Saint-Roch de l′Achigan (left – most dense) and at LP (right – least dense). Stained in 1% Chlorazol Black E in methoxyethanol and 1% aqueous Safranin O. (B) Polarization of G fibers determined by Method C (Blind distribution) from SX64 cultivar (S. miyabeana) in its third year of a harvest cycle sampled at two field trials: Saint-Roch-de-l′Achigan and LP. Error bars represent standard error (n = 3 trees, one per randomized block). t-test pairwise post hoc test (α = 0.05) are represented by letters a–b.