Influence of flooding on net CO2 assimilation, growth and stem anatomy of Annona species

A series of experiments was conducted to assess net CO2 assimilation and gr owth responses to waterlogging of grafted and seedling trees in the genus A nnona. Seedlings of A. glabra, A. muricata and A. squamosa L., and scions o f 'Gefner' atemoya (A. squamosa x A. cherimola Mill.),'49-11' ('Gefner' ate moya x A. reticilata L.),'4-5' ('Priestley' atemoya x A. retialata), A. ret iculata grafted onto either A. glabra, A. reticulata or A. squamosa rootsto cks were flooded for up to 60 d. Soil anaerobiosis occurred on the third da y of flooding. Seedling-a of A. glabra and A. muricata, and the scions '49- 11','Gefner' atemoya, and A. reticulata grafted onto A. glabra rootstock we re considered flood tolerant based on their ability to survive and grow in flooded conditions. Scions of the normally flood-sensitive A. reticulata, ' Gefner' atemoya, and '49-11' tolerated root waterlogging when grafted onto the flood-tolerant species, A. glabra. In contrast, flooding of A. squamosa seedlings and rootstocks, and A. reticulata rootstocks greatly reduced gro wth and net CO2 assimilation rates, and resulted in 20-80 % tree mortality. Stem anatomical responses to long-term flooding (12 continuous months) wer e assessed in seedlings of A. glabra and A. muricata, and trees of;49-11' g rafted onto A. glabra. Flooded trees developed hypertrophied stem lenticels , particularly in A. glabra, and enlarged xylem cells resulting in thicker stems with reduced xylem density. Flooding did not increase air spaces in p re-existing xylem near the pith or in xylem tissue that was formed during f looding. Thus, flood tolerance did not involve aerenchyma formation in the stem. (C) 1999 Annals of Botany Company.