Seasonal variation of gas exchange and pigmentation in branches of three grafted clones of mature ponderosa pine exposed to ozone and acid rain

acid deposition acid rain air pollution carotenoide carotenoides carotenoids chlorophylle chlorophylls clone clones clorofilas estoma gas exchange intercambio de gases ozone ozono photosynthese photosynthesis pigment pigmentos pigments pinus ponderosa seasonal variation stomata stomatal resistance stomate