The characteristic dominance of Acacia tortilis species in the Sahel plays a major ecological and economic role for its populations. However, in recent years, the high pastoral pressure has compromised the natural regeneration of the species and it becomes therefore important to investigate the effect of substrate and water stress on the growth of A. tortilis plants in nurseries. An experimental design made of 72 seedlings divided into 4 treatments with different proportions of substrate and watering was put in place. During the six months study, 3 seedlings were destroyed every month, and growth parameters were measured. These include the height, diameter at the collar, pivot length and diameter, number and length of lateral roots, number of nodes, number of branches, number of leaves and number of spines. Results show that the height, the collar diameter, the pivot diameter, total number of roots, number of lateral roots, number of branches, number of leaves are significantly different among treatments. The substrate containing 1/4 manure and 3/4 sand + watering twice a day recorded the best growth height (112.1±4.4 cm); number of branches (39.3±24.2); leaf biomass (301.67±97.99 g) and total number of roots (34±1.7) after 6 months of follow-up. The average root pivot length of Tr4 treatment seedlings (115.5±18.2 cm) is 4 times greater than their average height during the 6-month follow-up. The average root pivot length of Tr4 treatment seedlings is 4 times greater than their average height during the 6-month follow-up. After 3 months in nursery, the substrate containing sand only + watering once a week ensures a good development of the rooting root system to young seedlings, allowing them to better explore soil horizons. Hence, for a reforestation program, the substrate containing sand only + watering once a week is the best suited.

The aim of this study was to investigate inter-specific variation in drought tolerance and survival among three provenances of Acacia tortilis subspecies Raddiana and subspecies Spirocarpa under water stress. The seeds were collected from White Nile (Elgetiana), Kassala (Halfa Elgadida) and River Nile (Shandi) states, where the association of the two subspecies occurs in their natural habitats. The seeds of each subspecies per each provenance were sown under three irrigation frequencies. Relative growth rate, relative water contents, biomass production and mortality rates were measured. At the end of growth measurements water was totally with held from all the seedlings and mortality was counted at one week interval. The results revealed significant irrigation treatment and subspecies effects in relative growth rate, leaf relative water content and seedlings mortality, where no significant differences exist between the provenances. Water stress increased relative water content and d...

Water stress is the most important factor limiting early survival and growth of seedlings in arid and semi-arid zones. Many woody species develop adaptive mechanisms in response to water stress. This study assesses survival rate, growth and dry matter distribution in response to water stress in four dryland species (Senegalia dudgeonii, Senegalia gourmaensis, Vachellia nilotica and Vachellia tortilis). A total of 240 seedlings (60 per species) were grown using a completely randomized block design with three replicates in each of three water treatments (control = 100 percent of field capacity; moderate water stress = 50 percent of field capacity; severe water stress = 25 percent of field capacity) with a 7 day watering frequency. Data were collected on seedling survival, height, collar diameter, leaf production and dry matter distribution. Survival rate of the four species was not affected by water stress. However, the morphological responses to water stress were significantly differ...

Drought-induced tree mortality has been recently increasing and is expected to increase further under warming climate. Conversely, tree species that survive under arid conditions might provide vital information on successful drought resistance strategies. Although Acacia (Vachellia) species dominate many of the globe's deserts, little is known about their growth dynamics and water-use in situ. Stem diameter dynamics, leaf phenology, and sap flow were monitored during 3 consecutive years in five Acacia raddiana trees and five Acacia tortilis trees in the Arid Arava Valley, southern Israel (annual precipitation 20-70 mm, restricted to October-May). We hypothesized that stem growth and other tree activities are synchronized with, and limited to single rainfall or flashflood events. Unexpectedly, cambial growth of both Acacia species was arrested during the wet season, and occurred during most of the dry season, coinciding with maximum daily temperatures as high as 45 °C and vapor p...

Seed of Acacia senegal (L.Willd) were collected from four different geographical sites, viz: El-Fashir and Hawata from Sudan, Windou-tiengloy from Senegal and Dha-bi-ji from Pakistan. Based on moisture gradients provenances were divided into xeric (El-Fahir and Dha-bi-ji) and mesic (Hawata and Windou-tiengloy). Effects of soil drying on genotypic variations in physiological responses of the seedlings grown in large polythene bags were evaluated under natural nursery conditions. After acclimation a half of seedlings from each provenance were withheld from water and a half were kept well-watered throughout the course of experiment. Stomatal conductance, net photosynthesis, transpiration rate, internal CO2 concentration, and instantaneous water use efficiency were assessed on day 1, 3, 6, and 11 from the start of soil drying. Xeric provenances maintained higher stomatal conductance and transpiration relative to mesic under drying soil. Drought did not induce significant change in photo...