The bud break process and its variation among local populations of boreal black spruce.

Sergio Rossi,Jean Bousquet

doi:10.3389/fpls.2014.00574

Abstract

Phenology of local populations can exhibit adaptations to the current environmental conditions resulting from a close interaction between climate and genotype. The bud break process and its variations among populations were analyzed in greenhouse by monitoring the growth resumption in black spruce [Picea mariana (Mill.) BSP] seedlings originating from seeds of five stands across the closed boreal forest in Quebec, Canada. Bud break lasted 15 days and occurred earlier and quicker in northern provenances. Provenance explained between 10.2 and 32.3% of the variance in bud break, while the families accounted for a smaller but still significant part of the variance. The late occurrence of one phenological phase corresponded to a delayed occurrence of the others according to linear relationships. A causal model was proposed in the form of a chain of events with each phase of bud break being related to the previous and successive one, while no link was observed between non-adjacent phases. The adaptation of black spruce populations along the latitudinal gradient points toward a strategy based on rapid physiological processes triggered by temperature increase inducing high metabolic activity. The variation observed in bud break reflects an evolutionary trade-off between maximization of security and taking advantage of the short growing season. This work provides evidence of the phenological adaptations of black spruce to its local environmental conditions while retaining sizeable genetic diversity within populations. Because of the multigenic nature of phenology, this diversity should provide some raw material for adaptation to changing local environmental conditions.

Highlights

In cold climates, most physiological processes of plants occur during a short lapse of time when the environmental factors, mainly temperature, are favorable to growth and reproduction
Bud break is an example of phenological event of growth resumption that constitutes an intriguing and widely studied model trait composed by sequential events during which the embryonic shoots and leaves rapidly proliferate and emerge from the bud scales
Leafing of black spruce is composed by a distinctive chain of events producing effects on the contiguous phases, where the timings of occurrence of each phase influence those of the successive one

Summary

Introduction

Most physiological processes of plants occur during a short lapse of time when the environmental factors, mainly temperature, are favorable to growth and reproduction. The activity of meristems involves a number of biochemical processes resulting in a sequence of stages of development or maturation. These stages are identified according to morphological or anatomical changes and can last from a few days, in primary meristems, to several weeks, in the secondary meristem (Rossi et al, 2013; Rossi, 2014). A full understanding of the mechanisms of growth resumption in spring, a key adaptive trait in plants, is problematic because of the interaction of the abiotic (climate) and biotic (genotype) factors underlying this physiological process. Boreal tree species, those with wide geographic distributions, show genetic variations at a regional scale in response to variation of climatic factors (Beaulieu et al, 2001; Andalo et al, 2005)

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