Patterns of stem respiration within tree, with age, and among species in Pacific Northwest trees

An increment core-based, laboratory method was used to measure tissue-level respiration under controlled temperature (termed respiratory potential) of eleven tree species from three age classes. Respiratory potential was calculated on a basis of core dry-mass, volume, carbon, or nitrogen content and live bole volume. Methods tests suggested that core carbon dioxide production was indicative of parenchyma cell respiration, and that wounding and extracting artifacts were minimal. Core respiratory potential (mass-based) decreased from inner bark to sapwood/heartwood boundary with inner bark 2–11 times higher than outer sapwood, which was in turn 1.3–2 times higher than inner sapwood. Heartwood respiratory potential was 2–10% that of outer sapwood, and was likely a product of microbe respiration or diffusion of stored carbon dioxide. For stems measured at multiple heights, sapwood rings of the same calendar year had 50% higher respiratory potentials at treetops than at bases. Increased respiratory potential near apical (treetops) and cambial (inner bark) meristems suggested that parenchyma respiration was driven by proximity to substrate supply and/or involvement in cell formation and expansion.; Comparisons were also made among species. At breast height, species with narrow sapwood thickness (e.g. Pseudotsuga menziesii) had 50% higher core respiratory potentials (volume-based) than species with wide sapwood thickness (e.g. Pinus ponderosa). This pattern was not shown for inner bark, or sapwood in the crown. Whole-tree respiratory potential was higher in species of lower relative live bole volume (inner bark plus sapwood), except young Pinus ponderosa, where high relative live bole volume corresponded to high respiratory potential.; Additionally, possible physiological sources for the observed variations in respiratory potential were examined. Inner bark of Pinus ponderosa had higher total nitrogen and nonstructural carbohydrate contents, corresponding to higher respiratory potentials as compared to Pseudotsuga menziesii. In contrast, sapwood nitrogen was similar between the two species, and lower total nonstructural carbohydrates in Pinus ponderosa sapwood corresponded to higher respiratory potentials as compared to Pseudotsuga menziesii. Percent ray parenchyma volume of Pseudotsuga menziesii averaged 16% higher than Pinus ponderosa. Generally, nonstructural carbohydrate content was a better indicator of sapwood respiratory potential than either tissue nitrogen content or parenchyma anatomy.