ABSTRACT
Leaf level gas-exchange measurements can be made on detached foliage to address the challenge of access to the crown of tall trees. However, detachment may impact leaf gas exchange. This necessitates the study of gas-exchange characteristics of foliage on detached branches to assess the feasibility of using detached branches for gas-exchange analysis. We compared photosynthetic parameters and stomatal conductance in foliage of attached and detached branches of balsam fir [Abies balsamea (L.) Mill.] during the growing season. Data were analyzed using a linear mixed-effect model, with fixed and random effects (branch status and measurement month, and tree number, respectively). Branch detachment had no significant effects on: (i) photosynthesis at the current ambient CO2 concentration (400 µmol mol-1, A 400); (ii) maximum rates of Ribulose-1,5-bisphosphate (RuBP) carboxylation (V cmax) and regeneration (J max); (iii) the ratio of J max to V cmax (i.e., J max:V cmax), and (iv) stomatal conductance (g s) during the study period (p = 0.120-0.335). There was a strong seasonal effect on all gas-exchange variables (p ≤ 0.001-0.015). Gas-exchange measurements made on detached foliage during the warm summer months should be performed with care. Reliable gas-exchange measurements can be obtained using balsam fir foliage on detached branches 50-80 cm in length, in cooler growing-season months, up to 30 min after detachment.
ABSTRACT
The extent of the effect of projected changes in climate on trees remains unclear. This study investigated the effect of climatic variation on morphological traits of balsam fir [Abies balsamea (L.) Mill.] provenances sourced from locations spanning latitudes from 44° to 51°N and longitudes from 53° to 102°W across North America, growing in a common garden in eastern Canada. Lower latitude provenances performed significantly better than higher latitude provenances (p < .05) with regard to diameter at breast height (DBH), height (H), and crown width (CW), a distinction indicative of genotypic control of these traits. There was, however, no significant difference among provenances in terms of survival (p > .05), an indication of a resource allocation strategy directed at survival relative to productivity in higher latitude provenances as seen in their lower DBH, H, and CW compared to the lower latitude provenances. Temperature had a stronger relationship with DBH, H, and CW than precipitation, a reflection of adaptation to local conditions in populations of the species along latitudinal gradients. Both climatic variables had some effect on tree survival. These results suggest that the response of balsam fir to climatic variation will likely not be uniform in the species, but differ based on genetic characteristics between populations located in the northern and southern parts of the species' range. Population differences in response to climatic variation may be evident earlier in growth traits, compared to survival in balsam fir. The findings of this study will facilitate modeling in the species that is reflective of genetic variation in response to climatic conditions, and guide provenance selection for utilization in terms of productivity or resilience as well as breeding programs directed at obtaining species that possibly combine both traits.