Rooting responses of three oak species to low oxygen stress

Rooting characteristics were compared in blue (Q. douglasii), valley (Q. lobata), and cork oak (Q. suber) seedlings under hypoxic (low oxygen) conditions. A 50 percent reduction in root growth occurred in all species at an oxygen level of 4 percent, or an oxygen diffusion rate of 0.3 mu g cm(-2)min(-1). Blue oak formed few lateral roots regardless of oxygen level, but valley and cork oak root production decreased under hypoxic conditions. Four percent soil oxygen might be viewed as a minimum requirement for sustaining root growth of oaks in the field, and differences in root branching morphology may be correlated with tolerance of root hypoxia.