Rovenance variation of salt tolerance and seedling nutrition in acacia Tortilis (Forsk.) Hayne

Abstract

Variation of growth and salt tolerance was studied at increasing external salinity in sevenseed provenances of Acacia tortilis from saline (Sigor, Katilu, Mwatate and Isiolo) and nonsaline (Kibwezi, Wamba and Kitui) regions of Kenya and under stable saline conditions in Kitui, Isiolo and Mwatate provenances. The traits that may help provenances adapt to saline environments were more conspicuous in saline provenances. These were: (i) higher biomass production with and without salt treatment, except Isiolo provenance, (ii) maintaining low shoot Na concentration, (iii) greater leaf Na tolerance and (iv) more responsiveness to salt stress, suggested by the salt-induced growth reduction and leaf-fall. While these adaptations were not universally distributed among saline provenances, all provenances possessed one or more of these adaptations. Seedling survival was not related to putative salinity of sites. However, the high survival rates and low shoot Na concentration of Sigor, suggests that Na exclusion could have promoted longer-term survival of this Acacia tortilis provenance. Other elements (K, Ca, Mg and N) were not consistently correlated with salinity of seed origins, suggesting that mineral nutrient levels responded to diverse plant and salt stress variables, including seedling age and organ, and salt application methods (increasing or stable). However, canonical analysis revealed that interactions among nutrients could have been site dependent. This technique separated provenances, both within and between site categories, using concentrations of shoot Na, root Ca and root Mg. Ecotypes may have differentiated based on varied mechanisms of ion balances, which evolved differently depending on edaphic conditions. The study suggests that use of saline provenances may also increase biomass production in non-saline regions of Kenya.