Juvenile phase of seedling development in six Eurasian 5-needle Pine species: pattern and character of interspecific differences

Abstract

A species-specific trait system is formed as a result of two main factors: phylogenetic (origin, relationships) and adaptive (environment within a modern natural habitat). Traits themselves also may be ranged by theirphylogenetic stability and adaptive value. Species are usually characterized by definitive traits. Meanwhile, ontogenetic traits may alsobe useful for understanding both species' phylogenesis and adaptation to climatic conditions. The purpose of the present study is toinvestigate the juvenile shoot structure in some Eurasian Pinus species from the section strobus. In the southern part of the WesternSiberian Plain forest zone, seedling growth and development were studied on six Eurasian species: stone pines (Pinus sibirica, P. cembra,P. pumila, P. koraiensis) and white pines (P. parviflora, P. armandii). Shoot growth duration increases with an increase in vegetation season duration and the number of effective temperatures in the species' natural habitat: growth began slightly later, but it finished significantlylater. As far as shoot growth duration is concerned, the studied species were divided into 4 groups: (1) subarctic-subalpine P. pumila - 45-50 days, (2) boreal-mountain P. sibirica and P. cembra - 50-55 days, (3) nemoral from the monsoon forests P. koraiensis and P. parviflora - 60-65 days, (4) subtropical P. armandii - 75-80 days. The differences instructure and development of the juvenile shoots were not related to the climate in the natural habitat of species. On the basis of the juvenile morphogenesis duration and the presence of the mature organ type (5-needle short shoots) on the juvenile shoot, three pairs ofspecies were distinguished: P. sibirica and P. cembra (1 year, do not have short shoots); P. koraiensis and P. armandii (1 year, shortshoots are present); P. parviflora and P. pumila (2 years, short shoots are present). It is shown that there is a close relationship between the species within each pair and a new argument is added in favor of the polyphyletic origin hypothesis for modern subsection Cembrae of the genus Pinus. The more important is one or another feature for species survival: the less it is connected with its phylogenesis, and the more it is related to modern climatic conditions. For species taxonomy, neutral features in the adaptive sense are relevant where they possiblydo not absolutely influence the real plants' life. A juvenile shoot is a shoot without bud scales. It has obviously remained in the Pinus ontogeny from the time when the ancestors of the modern species grew in a climate with weakly marked seasons. For P. parviflora from the region with a temperate maritime climate, a two-year cycle of juvenile shoot development, apparently, is quite organic. For P. pumila which may be related to it and grows on an enormous area including north-eastern Siberia, it is an undesirable property that would limit the adaptive ability of species. The P. pumila seedlings demonstrate an extraordinarily high level of juvenile shoot diversity. This suggests the relatively recent origin of the species and its current active evolution.