Sexual reproduction efficiency and genetic diversity of endangered Betula humilis Schrk. populations from edge and sub-central parts of its range

Abstract

Outcrossed mating systems play a very important role in the persistence of endangered, selfincompatible plants such as shrub birch, Betula humilis Schrk. The goal of this study was to estimate, for the first time, the effectiveness of sexual reproduction in threatened edge and sub-central populations of shrub birch. The amplified fragment length polymorphism (AFLP) method revealed that all of the individuals at each locality had different genotypes. The matrix incompatibility count (MIC) suggested that the effectiveness of recombination was similar among all the populations of shrub birch under study. However, taking into account the greater germination ability of seeds in subcentral populations, we conclude that sexual reproduction in those populations can be more efficient. The germination capacity of seeds depends on their mass, which was significantly lower in dry or more shaded sites compared to wet or more exposed sites. Nonsignificant results of multiple regression models suggest that chemical parameters of the habitat (pH, EC, NH 4 + , PO 4 3− ) had no influence on the reproductive output of B. humilis. The discrepancy between the still quite substantial genetic diversity and the poor sexual reproduction in shrub birch populations can be explained by the production of a few phosphorus-rich seeds, insufficient time for a decrease in genetic variation in the disappearing part of the range or hybridization with close congeners.

Habitat requirements and germination performance of some relict populations of Ligularia sibirica (Asteraceae) from Romania

“…As germination capacity may vary depending on the annual variations in environmental conditions (especially temperature and humidity), further studies are needed to define their role in flowering and fructification periods and in germination. Other glacial relicts (such as Betula humilis) indicated similar effects (Chrzanowska et al 2016).…”

“…Among various types of germination requirements, temperature, water balance, and light, alongside the population and individual characteristics (population density and size, the number of flowering individuals, length of inflorescence, seed size and mass) are regarded as very important (Zheng et al 2004, Luzuriaga et al 2006, He et al 2007, Vandewoestijne et al 2009, Heinken-Šmídová 2012, Hornemann et al 2012, Grzyl et al 2014, Chrzanowska et al 2016 seed size affects their dispersal and germination, as well as the characteristics of the seedling (He et al 2007, Rewicz et al 2016. Seed mass may affect plant fitness through the probability of dispersal, emergence, survival, and growth of the offspring (Harper et al 1970, Westoby et al 1992, Giménez-Benavides et al 2005, Pérez-Harguindeguy et al 2013.…”

Genetic diversity and sexual reproduction in relict populations of Betula nana

“…The germination capacity of B. humilis seeds was significantly reduced at dry or more shaded sites compared to wet or sun-exposed sites (Chrzanowska et al 2016). In the LIN population, shading by Ledum palustre and Vaccinium uliginosum and high water level were responsible for the low number of flowering ramets (Ejankowski 2008;2010).…”

“…Greater seed germination ability has also been indicated as a determinant of better sexual reproduction of endangered Betula humilis Schrk. in the subcentral localities than in the marginal ones (Chrzanowska et al 2016). However, it is difficult to say why some seeds were not able to germinate without mechanical destruction of their coats.…”

“…Because frost treatment enhances germination ability in Arctic species (Alsos et al 2013), one possible explanation is the too short time of frost treatment. B. nana seeds were maintained for one and a half months at -20 °C, which was much longer than in the more successful germination trial of B. humilis (Chrzanowska et al 2016). On the other hand, seeds of B. nana var.…”