Soil temperature, physiology, and growth of containerized Annona species

The effects of soil temperature on physiology and growth of Annona glabra L. (pond apple) seedling trees, A. muricata L. (soursop) seedling trees, and A. squamosa L. x A. cherimola Mill. cv. Gefner ('Gefner' atemoya) nursery trees grafted on A. squamosa L. (sugar apple) rootstock in containers were investigated. Trees were exposed to soil temperatures of 5, 10, 20, 25 or 35degreesC in controlled soil temperature chambers in a glasshouse. The leaf chlorophyll index was the lowest at 5 or 10degreesC, and the highest at 35degreesC for all species tested. Net CO2 assimilation decreased to nearly zero within one week for each species exposed to 5 or 10degreesC and became consistently negative over the remaining experimental period. The fresh and dry weights of roots, stems, and leaves decreased almost linearly as soil temperature decreased for 'Gefner' atemoya on sugar apple rootstock and soursop. There was a quadratic relationship between soil temperature and organ fresh and dry weights for pond apple, with the greatest fresh and dry weights occurring at soil temperatures of 25degreesC. In general, reduced growth at lower temperatures was observed within 1 to 2 weeks after soil temperature treatments were initiated. Soursop and 'Gefner' atemoya on sugar apple rootstock are less tolerant of low soil temperatures than pond apple. Soursop and sugar apple were best adapted to soil temperatures of 25-35degreesC and pond apple to 20-25degreesC. (C) 2004 Elsevier B.V. All rights reserved.