Impact of air pollution on ring width and tracheid dimensions in Abies religiosa in the Mexico City basin

Abstract

Annual ring width and characteristics of latewood tracheids were characterized for the past 100 years for old trees of Abies religiosa growing in the Desierto de Los Leones within the air-polluted Mexico City basin. Sampled trees had lost nearly 50% of their branches and leaves. Radial variation in most measured characteristics followed typical trends for maturation until the 1970s, when trees were about 70 years old. From that decade onward, there was a continued reduction in annual ring width as well as a reduction in cell wall thickening and tracheid length, but an increase in lumen diameter. These xylem modifications started before the first visual symptoms of leaf damage were detected. We suggest that changes in annual ring width and tracheid size are caused by air pollution rather than by tree age.