Does bristlecone pine senesce?
Abstract
We evaluated hypotheses of senscence in old trees by comparing putative biomarkers of aging in great basin bristlecone pine ( Pinus longaeva) ranging in age from 23 to 4713 years. To teast a hypothesis that water and nutrient conduction is impaired in old trees we examined cambial products in the xylem and phloem. We found no statiscally significant age-related changes in tracheid diameter, or in several other parameters of xylem and phloem related cambial function. The hypothesis of continuously declining annual shoot growth increments was tested by comparing trees of varying ages in regard to stem unit production and elongation. No stastically significant agre-related differences were found. The hypothesis that aging results from an accumulation of deleterious mutations was addressed by comparing pollen viabilitym seed weight, seed germinability, seedling biomass accumulation, and frequency of putative mutations, in trees of varying ages. None of these parameters had a statistically significant relationship to tree age. Thus, we found no evidence of mutational aging. It appears that the great longevity attained by some Great Basin bristlecone pines is unaccompanied by deterioration meristem function in embryos, seedlings. or mature trees, In intuitively necessary manifestation of senescence. We conclude that the concept of senescence does not apply to these trees.