Does bristlecone pine senesce?

We evaluated hypotheses of senescence in old trees by comparing putative bi omarkers of aging in Great Basin bristlecone pine (Pinus longaeva) ranging in age from 23 to 4713 years. To lest a hypothesis that water and nutrient conduction is impaired in old trees we examined cambial products in the xyl em and phloem. We found no statistically significant age-related changes in tracheid diameter, or in several other parameters of xylem and phloem rela ted to cambial function. The hypothesis of continuously declining annual sh oot growth increments was tested by comparing trees of varying ages in rega rd to stem unit production and elongation. No statistically significant age -related differences were found. The hypothesis that aging results from an accumulation of deleterious mutations was addressed by comparing pollen via bility, seed weight, seed germinability, seedling biomass accumulation, and frequency of putative mutations, in trees of varying ages. None of these p arameters had a statistically significant relationship to tree age. Thus, w e found no evidence of mutational aging. It appears that the great longevit y attained by some Great Basin bristlecone pines is unaccompanied by deteri oration of meristem function in embryos, seedlings, or mature trees, an int uitively necessary manifestation of senescence. We conclude that the concep t of senescence does not apply to these trees. (C) 2001 Elsevier Science In c. All rights reserved.