Flooding, root temperature, physiology and growth of two Annona species

The effects of root zone temperature (RZT) and flooding on physiology and growth of Annona glabra L. (pond apple) and A. muricata L. (soursop) were investigated. Trees planted in containers were exposed to RZTs of 5, 10, 20, 25 or 35 degreesC in controlled root temperature chambers. Trees at each RZT were either non-flooded (control) or continuously flooded. There were four replications over time for each treatment combination. Pond apple was more flood-tolerant than soursop. A combination of flooding and RZTs of 5 and 10 degreesC resulted in tree mortality of both species by Week 4. Only trees that appeared to develop morphological adaptations survived continuous flooding. In both species, net CO2 assimilation (A) decreased to nearly zero within 1 week following exposure to RZTs of 5 or 10 degreesC and became consistently negative over the remaining experimental period. Flooding reduced leaf chlorohyll index (measured with a SPAD meter), A and plant growth, and increased root electrolyte leakage from soursop. Optimum growth occurred at RZTs of 25 to 35 degreesC for non-flooded pond apple trees and at 20 to 25 degreesC for flooded trees. Soursop exhibited maximum growth at RZTs of 35 degreesC under non-flooded conditions and at 25 degreesC under flooded conditions.