THE EFFECTS OF ROOTZONE SALINITY AND HYPOXIA ON SHOOT AND ROOT-GROWTH IN TRIFOLIUM SPECIES

The effect of concurrent salinity (0-60 mM NaCl) and rootzone hypoxia (flooding for up to 15 d) on shoot and root growth and shoot ion concentrations of six species of Trifolium {T. subterraneum L., T.fragiferum L., T. michelianum Savi., T. isthmocarpum Bot., T. purpureum Lois., and T. repens L.), was studied in two greenhouse experiments. There was a significant salinity x flooding effect for shoot yield but no significant salinity x flooding x species interaction although individual species differed significantly (P < 0 001) in their growth response to the saline or flooded conditions separately. Concentrations of Na and Cl in the shoots of all species increased with increasing periods of saline flooding and there was a significant salinity x flooding interaction. Sodium and Cl concentrations were significantly higher {P < 0Ό01) in T. purpureum, the species in which shoot growth was most depressed by saline flooding, than in other species. In T. michelianum, T.fragiferum and T. repens, fresh and dry weight of roots increased with flooding under both saline and non-saline conditions while in T. subterraneum root growth decreased. A significant proportion of the increased root growth in the first three species occurred as new adventitious roots. These roots had higher percentages of internal gas spaces within the root tissue even in the presence of salinity compared with roots from non-flooded conditions. There were also significantly more gas spaces in the total root tissue in T.fragiferum and T. repens under saline-flooding than in roots of T. subterraneum. Electron micrographs of the root cross sections illustrated the presence of these gas spaces or aerenchyma. Trifolium fragiferum, T. repens and T. michelianum are more likely to be suited to growth in soils prone to high salinity and to flooding than are T. subterraneum, T. purpureum and 7*. isthmocarpum. © 1993 1999 Academic Press. © 1993 Annals of Botany Company.