Carbon dioxide assimilation and growth of red spruce (Picea rubens Sarg.) seedlings in response to ozone, precipitation chemistry, and soil type.

The influence of ozone, mist chemistry, rain chemistry, and soil type on CO2 assimilation and growth of red spruce (Picea rubens Sarg.) seedlings was investigated over a 4-month period under controlled laboratory and glasshouse conditions. Growth was evaluated through interval estimates of aboveground relative growth rates (RGR) and the partitioning of biomass components at harvest to root, stem, and needle fractions. Precipitation chemistry treatments and O3 exposure dynamics were based on reported characteristics of air chemistry and/or deposition in high-elevation forests of eastern North America. The two soils were collected from Camels Hump in the Green Mountains of Vermont and Acadia National Park on the Maine coast. Soil from Acadia had higher organic content, higher levels of extractable base cations, and lower levels of extractable aluminum and heavy metals. The only treatment variables that consistently influenced the growth of P. rubens were soil type and rain chemistry. In comparison with seedlings grown in soil from Acadia National Park, those grown in Camels Hump soil had significantly less needle (27%), stem (33%), and root (26%) biomass at harvest and statistically lower aboveground RGR within 2 months after initiation of the treatments. Seedlings grown in Camels Hump soil had significantly higher levels of aluminum (6.5X), copper (1.4X), and nickel (2.7X) in new needle tissue. The only influence of precipitation chemistry on the growth of P. rubens was a pattern of greater root and shoot biomass in seedlings experiencing the more acidic rain treatments. Interactive effects among the main treatment variables (e.g., acidic mist and O3, acidic rain and soil type) on seedling growth were not notable. Rates of CO2 assimilation and transpiration on a per gram needle dry weight basis [mol·g-1·s-1] were not influenced by any of the main treatment variables or their interaction. Because neither soil type nor precipitation chemistry influenced the efficiency of CO2 assimilation per gram dry weight of needle tissue, the physiological mechanism underlying the growth response of P. rubens is attributed to a change in either whole-plant allocation of carbon resources or a direct toxic effect in the rhizosphere on root growth.