Seasonal changes in above- and belowground carbohydrate concentrations of ponderosa pine along a pollution gradient

Seasonal patterns of carbohydrate concentration in coarse and fine roots, s tem or bole, and foliage of ponderosa pine (Pinus ponderosa Laws) were desc ribed across five tree-age classes from seedlings to mature trees at an atm ospherically clean site. Relative to all other tree-age classes, seedlings exhibited greater tissue carbohydrate concentration in stems and foliage, a nd greater shifts in the time at which maximum and minimum carbohydrate con centration occurred, To determine the effect of environmental stressors on tissue carbohydrate concentration, two tree-age classes (40-year-old and ma ture) were compared at three sites along a well-established, long-term O-3 and N deposition gradient in the San Bernardino Mountains, California, Maxi mum carbohydrate concentration of 1-year-old needles declined with increasi ng pollution exposure in both tree-age classes. Maximum fine root monosacch aride concentration was depressed for both 40-year-old and mature trees at the most polluted site. Maximum coarse and fine root starch concentrations were significantly depressed at the most polluted site in mature trees. Max imum bole carbohydrate concentration of 40-year-old trees was greater for t he two most polluted sites relative to the cleanest site: the hole appeared to be a storage organ at sites where high O-3 and high N deposition decrea sed root biomass.