Morphology and tissue quality of seedling root systems of Pinus taeda and Pinus ponderosa as affected by varying CO2, temperature, and nitrogen

Rising atmospheric carbon dioxide, nitrogen deposition and warmer temperatures may alter the quantity and quality of plant-derived organic matter available to soil biota, potentially altering rates of belowground herbivory and decomposition. Our objective was to simulate future growth conditions for an early successional (loblolly) and late successional (ponderosa) species of pine to determine if the physical and chemical properties of the root systems would change. Seedlings were grown for 160 days in greenhouses at the Duke University Phytotron at 35 or 70 Pa CO₂ partial pressure, ambient or ambient + 5 0C temperature, and 1 or 5 mMNH₄O₃. Roots from harvested seedlings were analyzed for changes in surface area, specific root length, mass, total nonstructural carbohydrates (TNC), and concentrations of macro-nutrients. Surface area increased in both species under elevated CO₂, due primarily to increases in root length, and this response was greatest (+138%) in loblolly pine at high temperature. Specific root length decreased in loblolly pine at elevated CO₂ but increases in mass more than compensatedfor this, resulting in net increases in total length. TNC was unaffected and nutrient concentrations decreased only slightly at elevated CO₂, possibly from anatomical changes to the root tissues.We conclude that future growth conditions will enhance soil exploration by some species of pine, but root carbohydrate levels and nutrient concentrations will not be greatly affected, leaving rates of root herbivory and decomposition unaltered. [ABSTRACT FROM AUTHOR]