Earlywood structure of evergreen conifers near forest line is habitat driven but latewood depends on species and seasons

摘要

Quantitative wood anatomy can provide detailed insight into adaptation of trees to changing environment, especially on the borders of species distribution ranges. This study investigated wood anatomy of Pinus sylvestris L., Pinus sibirica Du Tour, and Picea obovata Ledeb. near the forest line in the Western Sayan Mountains, where local climate changes rapidly. Anatomical traits reflecting three developmental stages of conifer tracheids (division = cell number, cell enlargement = radial diameter, and secondary wall deposition = cell wall thickness) were calculated for earlywood, latewood and total tree ring over 50 years. Similar earlywood anatomical structure and low between-trait correlations (r = 0.21 horizontal ellipsis 67) were observed in all species, which supports prevalence of external impact on its formation, i.e. that shared habitat, climate, and similar habitus provide common trade-off between hydraulic efficiency and safety. Also, stronger nonlinearity of relationship between cell number and radial diameter in earlywood decreased correlations between them. In latewood, anatomical traits are strongly interconnected (r = 0.63 horizontal ellipsis 93) for all species. However, Siberian pine has significantly less pronounced latewood; later switch from earlywood and different strategy of carbon allocation are proposed as possible reasons. Length of vegetative season and sum of temperatures above thresholds 5 degrees C and 8 degrees C have no significant correlations with anatomical traits, but extremes of these temperature variables led to forming more pronounced latewood (higher proportion of latewood cells with thicker walls) during warm/long vegetative seasons than during short/cool ones.