High Morphological Differentiation in Crown Architecture Contrasts with Low Population Genetic Structure of German Norway Spruce Stands

Abstract

High elevation sites in the low mountain ranges in Germany are naturally covered by Norway spruce (Picea abies (Karst.) L.) stands. Historically, large scale anthropogenic range expansion starting in the mid to late 18th century had a huge impact on the forest composition throughout Germany. Utilisation and exploitation often led to artificial regeneration, mostly carried out using seeds from allochthonous provenances. Usually, autochthonous (natural) high elevation Norway spruce trees have narrow crown phenotypes, whereas lowland trees have broader crowns. Narrow crown phenotypes are likely the result of adaptation to heavy snow loads combined with high wind speeds. In the present study, neighbouring stand pairs of putative autochthonous and allochthonous origin with contrasting phenotypes in high elevation sites were investigated with 200 samples each. These stands are located in the Ore Mountains, the Thuringian Forest, and the Harz Mountains. Additionally, a relict population with the typical narrow high elevation phenotypes was sampled in Thuringia, known as “Schlossbergfichte”. The objective of the study was to quantify supposedly adaptive phenotypic differences in crown architecture and the genetic differentiation of 11 putatively neutral nuclear microsatellite markers (i.e., simple sequence repeats (nSSRs)). The high differentiation of morphological traits (PST = 0.952–0.989) between the neighbouring autochthonous and allochthonous stands of similar age contrasts with the very low neutral genetic differentiation (FST = 0.002–0.007; G″ST = 0.002–0.030), suggesting that directional selection at adaptive gene loci was involved in phenotypic differentiation. Comparing the regions, a small isolation by distance effect for the Harz Mountains was detected, suggesting landscape resistance restricting gene flow. Finally, the differentiation of the very old autochthonous (up to 250 years) stand “Schlossbergfichte” with typical high elevation phenotypes could cohere with the sampling of a relict genepool.

Genetic Structure of Norway Spruce Ecotypes Studied by SSR Markers

“…In our study, the estimated parameters of mean heterozygosity (Ho = 0.601, He = 0.705) are comparable to previously published studies [34,[66][67][68][69][70]; similarly, in our case, these are accompanied by a low level of genetic differentiation among populations. Similar values were observed despite the variety of experimental and sampling design, targeting various features and traits of interest.…”

“…Similar values were observed despite the variety of experimental and sampling design, targeting various features and traits of interest. Our mean value of expected heterozygosity (H e = 0.705) is similar to that in German (H e = 0.74) [34] and Lithuanian populations (H e = 0.71) [66]. Higher mean values were determined in Serbia (H e = 0.89) [69], Tyrol (H e = 0.87) [67], Slovenia (H e = 0.92) [44], and the Czech Republic (0.86) [68].…”

“…Hence, primers developed by Pfeiffer et al [48] and Scotti et al [51] are very frequently used [43,71,74]. Also, the primer sequences published by Fluch et al [54], Rungis [47] and Besnard et al [52] have been utilized frequently [20,34,66,69,70,[75][76][77]. The maximal total number of SSR markers used in studies so far (11 primer pairs) was found in Cvjetkovic et al [70], who exploited three sources [47,51,54]; in contrast, Caré et al [34] yielded five primer sources [48,49,51,52,75].…”

“…We finally exploited six sources of primer sequences [47][48][49]51,52,54]. When considering the number of primer pairs pooled into one PCR reaction in previous publications, this varied from 1 (single) [66,71] to 3 [34,43,69,74,78] and 6 primer pairs assembled into one multiplex reaction [44,70]. Here, we present a more efficient genotyping protocol, combining 16 markers into just two multiplexes: multiplex 1 contains seven markers, whereas multiplex 2 was established from nine markers.…”

“…To our knowledge, no studies have focused on the genetic differentiation among distinctive tree forms (ecotypes). Caré et al [34] focused on a high-elevation ecotype; however, they compared this morphotype to neighboring allochthonous stands without any effort to reveal the genetic basis of other ecotypic groups. Conifers are typically outbreeding, which is characterized by high gene flow and facilitated by long-distance pollen and seed dispersal.…”