Date of Award


Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)


Forest Resources


Michael E. Day

Second Committee Member

Michael S. Greenwood

Third Committee Member

Benildo G. de los Reyes


The trajectory of stem wood productivity over time is a principal factor in determining the optimum ages for harvest as well as estimating rates of carbon sequestration in forests. Mechanisms controlling the age-related productivity decline in trees and the genetic foundation for this process are not well understood. We aimed to establish an analysis pipeline that integrated current whole-plant physiological and genomics paradigms for understanding the molecular basis of age-related productivity decline in red spruce (Picea rubens Sarg.). Our overarching hypothesis is that age-related patterns of productivity are not limited by physiological factors restricting carbon assimilation but by the intrinsic genetic programming associated with demand-side sinks restricting carbon allocation to apical and cambial meristems. Age-related differences in growth sink strength may be an important, perhaps the major, fundamental process in explaining the age-related changes in tree physiology. We assessed changes in sucrose, a non-structural carbohydrate (NSC) and primary transported sugar in trees, and relative expression levels of putative spruce invertases, an enzyme which irreversibly catabolizes sucrose. Samples were collected from juvenile (15y±4years), mid-age (56±8years) and old (130±36years) red spruce in the Penobscot Experimental Forest, Bradley, Maine. Percent sugar (dry mass) was quantified in sun and shade canopy locations of one year-old foliage from all age classes, and 0.5-1cm diameter twigs in mid-age and old trees in August 2008 and March, June, and August 2009. Bolewood core samples for mid-age and old age-classes were collected in all sample periods except March 2009. In June of 2009 expanding foliage from the upper 1/3 of the canopy was harvested for genetic analysis. Putative spruce invertase expressed sequence tags (EST’s) were assembled and used to fish-out potential members of the invertase family in harvested tissue. Primers developed from EST’s were preliminarily assessed for functional roles through phylogenetic tree analysis and comparison to known Arabidopsis and Populus trichocarpa sequences. Invertase expression was quantified using real-time PCR analysis. Results from our NSC analysis revealed significantly higher sugar concentrations in foliage from mid-age trees compared to juvenile and old age-classes. Both mid-age and old trees exhibited similar annual trends in twig sugar concentrations, with the highest concentrations in spring when foliar concentrations were lowest. Bolewood sugar concentrations were low, usually < 3% dry mass, with the highest sugar concentrations in spring, decreasing in August. Wood concentrations were higher in mid-age compared to old trees. Results suggest mid-age trees recover to pre-budburst sugar concentrations faster than old trees, this maybe a result of increased carbon cost of old foliage or differences in the form of carbon storage between age-classes. Invertase expression analysis was conducted for three putative spruce invertase EST primers PiCIN3, PiNIN1, and PiNIN2. Phylogenetic tree assembly revealed a close relationship between PiCIN3 and acidic cell wall invertases and PiNIN1/2 as members of the neutral invertase sub-family. qRT-PCR analysis of these three primers revealed up-regulation of all primers in the mid-age age-class and of only primer PiCIN3 in old-growth trees. These results indicate increased expression of the invertase sucrose cleaving enzyme in mid-age trees, corresponding with the life stage with the highest growth rates and increased expression of cell wall invertases in old-growth trees with potentially higher carbon foliage costs.