Measuring recent effective gene flow among large populations in Pinus sylvestris: Local pollen shedding does not preclude substantial long-distance pollen immigration

Molecular characterisation of Pinus sylvestris (L.) in Ireland at the western limit of the species distribution

BACKGROUND

Scots pine (Pinus sylvestris L.) underwent significant population declines across much of northwest Europe during the mid-to-late Holocene and was thought to have become extirpated in Ireland from about 400 AD. However, most extant populations are plantations reintroduced from Scotland. Others are naturalised therefrom and one in Western Ireland is a putative relict. In this paper, Scots pine in Ireland are genetically described for the first time.

RESULTS

Using two mitochondrial (mtDNA) loci, eight chloroplast (cpSSR) and 18 nuclear (nSSR) loci, the genetic composition and diversity of 19 Irish Scots pine populations is described and compared to other European populations. All trees sampled in Ireland were fixed for mitotype a, which is the most common across northwest Europe. By contrast, cpSSR (HCP = 0.967) and nSSR (He = 0.540) variation was high, and comparable with estimates for other regions across the species range. Differentiation at both sets of loci were similarly low (cpSSR FST = 0.019; nSSR FST = 0.018), but populations from continental Europe were significantly differentiated from all Irish populations based on nSSR variation.

CONCLUSIONS

All Irish Scots pine are likely part of a common Irish-Scottish gene pool which diverged from continental Scots pine following post-glacial recolonisation. A high genetic diversity and an absence of evidence of inbreeding suggests the regional decline of Scots pine did not critically reduce allelic variation. The post-glacial relationship between Irish and Scottish pine is discussed, and a suggestion from recent palaeoecological work that reintroduced Scots pine be managed as a native species is now further supported by genetic data.

Microgeographic variation in early fitness traits of Pinus sylvestris from contrasting soils

PREMISE

The possibility of fine-scale intraspecific adaptive divergence under gene flow is established by theoretical models and has been confirmed empirically in tree populations distributed along steep altitudinal clines or across extreme edaphic discontinuities. However, the possibility of microgeographic adaptive divergence due to less severe but more frequent kinds of soil variation is unclear.

METHODS

In this study, we looked for evidence of local adaptation to calcareous versus siliceous soil types in two nearby Mediterranean Pinus sylvestris populations connected via pollen flow. Using a greenhouse experiment, we tested for variation in early (up to three years of age) seedling performance among open-pollinated maternal families originating from each edaphic provenance when experimentally grown on both types of natural local substrate.

RESULTS

Although seedlings were clearly affected by the edaphic environment, exhibiting lower and slower emergence as well as higher mortality on the calcareous than in the siliceous substrate, neither the performance on each substrate nor the plasticity among substrates varied significantly with seedling edaphic provenance.

CONCLUSIONS

We found no evidence of local adaptation to a non-extreme edaphic discontinuity over a small spatial scale, at least during early stages of seedling establishment. Future studies on microgeographic soil-driven adaptation should consider long-term experiments to minimize maternal effects and allow a potentially delayed expression of edaphic adaptive divergence.

Study of the Pollen Grain Metabolome under Deposition of Nitrogen and Phosphorus in Taxus baccata L. and Juniperus communis L

Nitrogen plays an important role in both quantitative and qualitative aspects of plant reproduction, including pollen grain compounds and seed production. Recent studies have pointed out that pollen grains produced by male plants of T. baccata and J. communis subjected to a long period of fertilizer supplementation have lower in vitro germination ability and higher nitrogen content. To gain molecular insights into these observations, we conducted GC-MS analysis of both species to characterize the metabolomes of dry, mature pollen grains, which allowed for the identification and quantification of more than 200 metabolites. The results demonstrated that fertilizer supplementation impacts the relative content of 14 metabolites in J. communis (9 downregulated and 5 upregulated) and 21 in T. baccata (6 downregulated and 15 upregulated). Although plants showed little similarity in patterns, in metabolite profiles, both up and down fold-changes were observed. This is the first report on the gymnosperm pollen grain metabolomic profile and changes induced by long-term nitrogen and phosphorus supplementation. Pollen grains produced by fertilizer-supplemented male individuals had significantly lower relative content of linolenic acid, 5,6-dihydrouracil, maltotriose, galactonic acid, D-xylulose, and glycerol-α-phosphate but higher content of sorbitol, glucosamine, and 1,5-anhydro-D-glucitol as well as n-acetyl-d-hexosamine, dimethyl phthalate, glycine, galactose-6-phosphate, D-fructose-6-phosphate, pyroglutamic acid, and 3-(3-hydroxyphenyl)-3-hydroxypropionic acid. Thus, in pollen grain samples earlier shown to have different germination abilities, the presence of different metabolites indicates a significant environmental impact on the quality of gymnosperm pollen grains.