by Claire Morin | 30 January 2019
Published in BMC Genomics 14(368). https://doi.org/10.1186/1471-2164-14-368
Background: The genomic architecture of adaptive traits remains poorly understood in non-model plants. Various approaches can be used to bridge this gap, including the mapping of quantitative trait loci (QTL) in pedigrees, and genetic association studies in non-structured populations. Here we present results on the genomic architecture of adaptive traits in black spruce, which is a widely distributed conifer of the North American boreal forest. As an alternative to the usual candidate gene approach, a candidate SNP approach was developed for association testing.
Results: A genetic map containing 231 gene loci was used to identify QTL that were related to budset timing and to tree height assessed over multiple years and sites. Twenty-two unique genomic regions were identified, including 20 that were related to budset timing and 6 that were related to tree height. From results of outlier detection and bulk segregant analysis for adaptive traits using DNA pool sequencing of 434 genes, 52 candidate SNPs were identified and subsequently tested in genetic association studies for budset timing and tree height assessed over multiple years and sites. A total of 34 (65%) SNPs were significantly associated with budset timing, or tree height, or both. Although the percentages of explained variance (PVE) by individual SNPs were small, several significant SNPs were shared between sites and among years.
Conclusions: The sharing of genomic regions and significant SNPs between budset timing and tree height indicates pleiotropic effects. Significant QTLs and SNPs differed quite greatly among years, suggesting that different sets of genes for the same characters are involved at different stages in the tree’s life history. The functional diversity of genes carrying significant SNPs and low observed PVE further indicated that a large number of polymorphisms are involved in adaptive genetic variation. Accordingly, for undomesticated species such as black spruce with natural populations of large effective size and low linkage disequilibrium, efficient marker systems that are predictive of adaptation should require the survey of large numbers of SNPs. Candidate SNP approaches like the one developed in the present study could contribute to reducing these numbers.
by Audrey Verreault | 30 January 2019
Published in Geochimica et Cosmochimica Acta 126: 18-29
Identifying the sources of S exported from catchments and the reactivity of the large soil organic S pool is crucial to understand the mid- or long-term response of forested catchments to decreasing atmospheric S deposition and global warming. Sulfur fluxes as well as S and O isotopes of SO4 were measured in precipitation, throughfall, soil solutions and streams at two boreal forest catchments respectively dominated by black spruce (BS) and balsam fir (BF) in Quebec, Canada. Overall, d34S-SO4 signature showed relatively small variations among various solution types. However, at both sites, d18O-SO4 in precipitation (averages of 10.5–11.1%o) was decreased by 3.5–3.6%o in throughfall because of the production of secondary SO4 through oxidation of SO2 deposited on the canopy. Throughfall d18O-SO4 was decreased by a further 5.4–6.6%o in the solution leaving the humus layer which was attributed to the production of secondary SO4 under the action of soil microorganisms through the oxidation of organic S during which the S atom acquired O from water and gaseous O2 present in the soil. A mixing equation based on known isotopic signature of each source suggested that ~67–81% of the S-SO4 leaving the catchments had interacted with the canopy and the humus layer. The stability of d18O-SO4 in the mineral soil solution and in the stream of both sites, suggests that SO4 does not undergo reduction–oxidation cycles after its passage through the humus layer. Despite its huge size, the organic S reservoir within the mineral soil would be largely inert. Given the chemical nature of SO4 transformation in the canopy, the humus layer would be responsible for nearly 100% of the biological production of secondary SO4 in the whole watershed at both sites. Taking into account the substantial production of dissolved organic S in the humus layer further emphasizes the crucial importance of the latter in the S cycling of boreal forests.
by Svetlana Savin | 30 January 2019
Published in American Journal of Plant Sciences 4: 749-765 https://doi.org/10-4236-ajps.2013.43A094
Lichen woodlands (LW) located in the closed-crown boreal forest are not a successional stage moving towards a closed black spruce feathermoss stand (FM), but an alternative stable state, due to their previous forest history, and the occurrence of LWs located nearby closed-crown FM stands. Therefore, afforestation in those LWs through site preparation and plantation could shift back LW into FM stands. We implemented an experimental design with different combina- tions of silvicultural treatments in both site types (LW, FM). We monitored the evolution of plant diversity and the physiology of three bio-indicators (Picea mariana, Kalmia angustifolia, Rhododendron groenlandicum) in different microsites created by the silvicultural treatments. The return to the initial composition was noticed only two years after treatments, especially in the LW stands, thus indicating a higher level of early ecosystem resilience in LWs compared to FM stands. Mean species cover, especially in the FM stands, decreased the most in the skid trails created by logging, probably due to a lack of acclimation of bryophytes to open stand conditions. Conversely, ericaceous shrubs and lichens found in the LWs were already acclimated to open stand conditions, which give to LWs a restructuring advantage com- pared to FM plant communities after silvicultural treatments. Overall, FM and LW short-term resilience was similar, indicating equally efficient ecosystem reorganization in both stands. The comparable early resilience in managed LW and FM stands, in terms of plant biodiversity, contradicts the presumed fragility of LW stands, especially in this case where LWs are assumed to be an alternative stable state created by compound disturbances. Silvicultural treatments maintained the functional group diversity in LWs, a key element for ecosystem resilience. Therefore, this study support the idea that plantation following site preparation in LWs could be a valuable management strategy to reach several objectives, such as increasing forest carbon sinks.
by equipewp | 30 January 2019
Abstract of the paper presented to the Northeastern Ecosystem Research Cooperative (NERC) – 2013 Conference. March 19-20, 2013. Saratoga Springs, New York. 1 p.
by Marie-Claude Boileau | 30 January 2019
Published in Forest Ecology and Management 330: 94-104. http://dx.doi.org/10.1016/j.foreco.2014.07.005
We used two-step shelterwood cutting to release conifer advance growth and limit development of trembling aspen (Populus tremuloïdes Michx.) suckers in a stratified mixed aspen – conifer stand, in Quebec, Canada. This study presents the 10-year response of residual trees to the establishment cutting. We examined growth and mortality of merchantable trees (diameter at breast height (DBH) ³ 9.1 cm) following the application of different cutting intensities (0%, 35%, 50%, 65%, and 100% basal area removal). Initial post-cut densities were 1100, 670, 640, 580 and 150 stems ha-1, respectively. Mortality of aspen was highest in the uncut control and 35% cut due to senescence, while mortality of paper birch (Betula papyrifera Marsh.) was highest in the 65% cut due to post-logging decadence. In the species mixture under study, the 50% cut allowed for the harvest of declining aspen without excessively opening the canopy that would be detrimental for residual paper birch. Low mortality, high recruitment and a relatively high DBH growth in this moderate cut resulted in a higher 10-year net increment in total basal area (7.0 m2 ha-1), compared to the 0%, 35%, 65%, and 100% cuts (2.6–3.7 m2 ha-1). This result was mostly attributable to balsam fir (Abies balsamea (L.) Mill.) that generated two-thirds of the net increment. Therefore, our growth results support retention of small merchantable conifer stems (DBH 9.1–15.0 cm) as a basic strategy to limit hardwood invasion.
