|dc.description.abstract||The remnants of the Caledonian Pine Forest represent the north western boundary of
the Eurasian Pinus sylvestris (L.) distribution. Remnant populations occupy a diverse
range of environments within Scotland, subject to a steep rainfall gradient, and previous
investigations have found evidence of local adaptation. Additionally, studies of biochemical
and molecular markers have indicated that Scotland’s native pinewoods originated
from more than one glacial refugium.
Whole-genome-shotgun (WGS) sequencing was employed for the discovery of mitochondrial
(mt) variants that may provide further insight into the origins of P. sylvestris
populations both in Scotland and mainland Europe. DNA extractions were performed
on megagametophyte tissue from Scottish, Finnish, and Spanish populations. Three
members of the closely related P. mugo species complex were also sequenced. Using
similarity-based approach, 160kbp of putative mitochondrial sequence was recovered by
comparison of de novo assembled contigs with the mtgenome of the gymnosperm Cycas
taitungensis. In total, 16 novel variants were identified among samples, which may be
used in future phylogeographic studies.
A study of needle characters was performed for eight native populations of P. sylvestris
in an outdoor provenance/progeny trial of 192 saplings. A negative correlation was
detected between longitude and the number of stomatal rows present on needle surfaces.
It was posited that this may be an adaptive response to lower water availability in
eastern pinewoods, possibly in conjunction with increasing altitude.
The west coast of Scotland is one of the wettest regions in Europe: western pinewoods
may receive in excess of 3,000mm of rainfall in a year, compared with an average of
800mm eastern sites. To determine whether native pinewoods are differentially adapted
to waterlogging, a glasshouse based provenance/progeny trial of 432 saplings from nine
native populations was undertaken, in which 50% were subject to a long-term waterlogging
treatment, and the remainder used as a control. Two studies were then conducted.
In the first, responses to the treatment were assessed in terms of phenological and growth
traits. Bud flush was delayed in response to waterlogging, and growth was impeded relative
to the control. Although population differences were observed, treatment × population
interactions were not detected. In the second study physiological traits known
to be sensitive to plant stress and water balance were measured at intervals throughout
the experiment. Prior to the commencement of the treatment needle δ13C was found
to exhibit interpopulation differentiation, and was positively correlated with longitude.
This seems likely to represent differential selection for water use efficiency between eastern
and western pinewoods. Photochemical efficiency and stomatal conductance were
found to be reduced by waterlogging, and needle δ13C was increased. After generalising
populations into ‘high’ and ‘low’ rainfall groups (monthly averages of 214.9mm and
72.8mm, respectively), high rainfall populations were observed to maintain consistently
higher photochemical efficiency under waterlogging the low rainfall populations. In addition,
the low rainfall group exhibited greater variability in response to flooding (in
terms of phenotypic and additive genetic variance) which may be indicative of a lack of
past selection pressure.||en