Responses of Pinus clausa, Pinus serotina and Pinus taeda seedlings to anaerobic solution culture. I. Changes in growth and root morphology

Abstract

Seedlings of pond pine (Pinus serotina Michx.), sand pine [P. clausa (Engelm.) Sarg.] and two edaphic seed sources of loblolly pine (P. taeda L., dry‐ and wet‐site seed sources) were grown in non‐circulating, continuously flowing solution culture under aerobic (250 μM O2) and anaerobic (≤ 23 μM O2) conditions. Survival was 100% for all seedlings at 11 weeks. Although shoot height, biomass and leaf emergence of loblolly and pond pine seedlings were not significantly affected by 15 or 30 days of anaerobic growth conditions, root biomass was significantly reduced. Sand pine suffered the largest reduction in biomass, showing extensive root dieback and shoot chlorosis with retarded leaf development. These anaerobically induced symptoms of flooding injury were less severe in dry‐site loblolly pine, and absent in wet‐site loblolly and pond pine seedlings. Adventitious or new, secondary roots, and stem or taproot lenticels were particularly abundant under the 30‐day anaerobic treatment in wet‐site loblolly and pond pine seedlings, present to a lesser degree in dry‐site loblolly pine, and nearly absent in sand pine seedlings. These results indicate that much of the immediate damage from flooding is due to the anoxic condition of the root rather than to the build‐up of phytotoxins or soil nutrient imbalances. On the basis of overall seedling vigor, root plasticity and growth, we suggest the following flooding‐tolerance/intolerance species (seed source) gradient: pond pine ≥ wet‐site loblolly pine > dry‐site loblolly pine > sand pine.