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

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 (A) to stomatal conductance (g(s)), was assessed in foliage under two levels of photosynthetically active radiation (PAR; i.e., 300 and 1200 mu mol m(-2) s(-1)) in 63-year-old balsam fir [Abies balsamea (L.) Mill.] provenances derived from seed sources from across the species' natural range (namely, within 44-51 degrees N latitudes and 53-102 degrees 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 (p < 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 mu mol 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 (p > 0.05). Diameter at breast height in 2014 was significantly greater than DBH1998 (p < 0.05). The relationships between DBH2014 and climatic variables at the provenance source were statistically significant (p < 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.

Automated summary

The study focused on the physio-morphological responses of northern tree species to climate change, with provenance and light intensity significantly influencing intrinsic water-use efficiency and diameter at breast height. The results highlighted the importance of selecting balsam fir based on stomatal conductance, shade tolerance, and consistent growth under variable climatic conditions for sustained growth under projected forest dynamics accompanying changes in regional climate. Temperature variables were strong indicators of diameter at breast height increment, while the relationship between intrinsic water-use efficiency and radial growth was evident.