Physiological and Morphological Variation in Balsam Fir Provenances Growing in New Brunswick, Canada

• Main Authors: Matthew E. Akalusi, Charles P.-A. Bourque
• Format: Article
• Language: English
• Published: MDPI AG 2021-02-01
• Series: Forests
• Subjects: diameter growth; intrinsic water-use efficiency; photosynthesis; stomatal conductance; species shade tolerance
• Online Access: https://www.mdpi.com/1999-4907/12/2/186

There is a need to understand the physio-morphological responses of northern tree species to climate change. The hypothesis of the current study was that provenance and light intensity were both influential in the control of intrinsic water-use efficiency (iWUE). Diameter at breast height (DBH)-increment was hypothesized as being more affected by provenance. Intrinsic water-use efficiency (iWUE), the ratio of photosynthesis (<i>A</i>) to stomatal conductance (<i>g</i>_s), was assessed in foliage under two levels of photosynthetically active radiation (PAR; i.e., 300 and 1200 μmol m^-2 s^-1) in 63-year-old balsam fir [<i>Abies balsamea</i> (L.) Mill.] provenances derived from seed sources from across the species’ natural range (namely, within 44°–51° N latitudes and 53°–102° W longitudes) and cultivated in a common garden in eastern Canada. Diameter at breast height (DBH) of provenances from the common garden were measured when they were 42 and 58 years old (DBH₁₉₉₈, DBH₂₀₁₄). The results confirmed the hypotheses regarding the roles of provenance on iWUE and DBH (<i>p </i>< 0.05), but showed a diminished role of PAR on iWUE. The lowest and highest mean iWUE and DBH among the provenances ranged between 0.028 and 0.031 and 0.079–0.083 μmol mmol⁻¹ and 11.82–12.78 and 16.38–18.44 cm, respectively. Stomatal conductance of balsam fir had a strong relationship with iWUE at both light settings, whereas A had a weaker relationship with iWUE. There were no significant relationships between iWUE at the two light settings and climatic variables at the provenance source (<i>p </i>> 0.05). Diameter at breast height in 2014 was significantly greater than DBH1998 (<i>p </i>< 0.05). The relationships between DBH2014 and climatic variables at the provenance source were statistically significant (<i>p </i>< 0.05). There was a significant positive relationship between iWUE and DBH measured in 2014. Survivorship of provenances was shown to vary with DBH-increment. The results show that for present-day and future forest management, (i) selection in balsam fir, in relation to iWUE should ideally be based on a criterion of intraspecific stomatal conductance; (ii) shade tolerance of balsam fir, population differentiation, and consistent pace of DBH-growth under variable climatic conditions are important factors in the species’ sustained growth under changes in forest dynamics projected to accompany changes in regional climate; (iii) temperature variables are strong indicators of DBH-increment in balsam fir; (iv) the effect of tree size on its survival is maintained under variable climatic conditions; and (v) there is a clear association between iWUE and the species’ radial growth.