Changes in Respiration Rate and Energy of Activation after Chilling and Forcing Dormant Apple Trees

Dormant apple trees (Malus domestics Borkh., cv . MM. 111) were chilled at SC for O, 500, 1000, or 1500 hours and then forced at 10, 20, or 30C for 21 days. Budbreak and root growth were recorded after forcing, and shoot and root respiration was measured at 5, 10, 20, and 30C to determine Q 10 and energy of activation values. Budbreak, root growth, and respiration generally increased with chilling and forcing temperature. The Q 10 of shoot respiration increased significantly with increasing chilling when measured before forcing; however, after forcing, Q 10 decreased with chilling. Root respiration Q 10 was not as influenced as shoot respiration by chilling either before or after forcing. Energy of activation for shoot and root respiration decreased significantly with chilling after forcing at each temperature.