Provenance Variation in the Response of Cordia africana Seedlings to Soil Drying

Page(s): 11 (2), 247-270, 21 Ref.The morphological and physiological responses of seedlings of three Cordia africana (L.) provenances to soil drying were studied to evaluate the possible adaptational mechanisms responsible for the survival of this species in drought-prone environments. The seeds were collected from three sites along the natural habitat of C. africana in Sudan (viz: Edamazin, Jebel Marra and Kordofan). The experiment was conducted under natural conditions, using long soil columns with high water holding capacity. Drought had significant impacts on the physiological and morphological characteristics of C. africana seedlings, regardless of seed origin. However, the results revealed considerable intraspecific variation in the response of seedlings to drought among the studied provenances. The Kordofan provenance sustained the highest stomatal conductance, leaf water potential and transpiration rate under limited soil water availability, an attestation of drought-avoidance mechanisms. Seedlings from Edamazin and Jebel Marra origins showed simultaneous reduction in stomatal conductance, leaf water potential and transpiration rate as soil drying intensified, a characteristic response associated with drought-tolerance genotypes. Drought resulted in a significant reduction in total biomass of all provenances, which was a function of reduced shoot weight, but the root weight was not affected. The root/shoot ratio of water-stressed seedlings increased by more than 1.6 times in all provenances. The Kordofan provenance showed the highest root/shoot ratio in the dry treatment, which might explain its superiority in the maintenance of shoot water status as drought intensified. With the exception of the Kordofan provenance, the root distribution profile was adversely affected by soil drying. The results indicated that the Kordofan provenance may be a more suitable seed source for afforestation in drought-prone environments.Khartoum University Pres