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

Abstract

A series of experiments was conducted to assess net CO2 assimilation and growth responses to waterlogging of grafted and seedling trees in the genus Annona. Seedlings of A. glabra, A. muricata and A. squamosa L., and scions of 'Gefner' atemoya (A. squamosa x A. cherimola Mill.), '49-11' ('Gefner' atemoyax A. reticulata L.), '4-5' ('Priestley' atemoya x A. reticulata), A. reticulata grafted onto either A. glabra, A. reticulata or A. squamosa rootstocks were flooded for up to 60 d. Soil anaerobiosis occurred on the third day of flooding. Seedlings of A. glabra and A. muricata, and the scions '49-11', 'Gefner' atemoya, and A. reticulata grafted onto A. glabra rootstock were 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 growth and net CO2 assimilation rates, and resulted in 20-80% tree mortality. Stem anatomical responses to longterm flooding (12 continuous months) were assessed in seedlings of A. glabra and A. muricata, and trees of '49-11' grafted 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 pre-existing xylem near the pith or in xylem tissue that was formed during flooding. Thus, flood tolerance did not involve aerenchyma formation in the stem.