Foliar injury responses of ponderosa pine seedlings to ozone, wet and dry acidic deposition, and drought

Abstract A 3-year field study of the potential interactions of ozone (O 3 ), wet and dry acidic deposition, and soil water availability on foliar injury responses of 18 ponderosa pine ( Pinus ponderosa Laws.) families was conducted in the Sierra Nevadas of California. Thirty-six 2-year-old seedlings in each of 30 open-top chambers (plus six ambient air plots) were exposed to combinations of three levels of O 3 [charcoal-filtered (CF), non-charcoal filtered (NF), and NF plus 1.5 times ambient O 3 (NF150)]; three simulated rain pH treatments (pH 3.5, 4.4, 5.3); two levels of dry deposition (60% filtration of ambient dry deposition and 90% filtration), and two irrigation regimes (approximately weekly watering vs irrigation every other week) for three growing seasons. One-third of the trees were harvested at the end of each year. O 3 , irrigation level, amount of dry deposition, and family (genotype) significantly affected degree of foliar injury responses to O 3 . The interactions of O 3 with irrigation amount and O 3 with dry deposition were also statistically significant. Drought-stressed seedlings had significantly less O 3 injury than well-watered trees, but seedlings exposed to 60% filtration of dry deposition had significantly greater O 3 injury than those in the 90% filtered treatments. Ponderosa pine families differed greatly in susceptibility to O 3 , ranging from two with an average of > 20% O 3 injury to several with nearly no O 3 injury. These results reflect the complex patterns ofponderosa pine responses to natural and pollutant stresses and emphasize the importance of long-term, multifactorial experiments to elucidate those patterns.