Responses of Acacia mellifera Seedlings to Different levels of Drought Stress

Abstract

Drought is one of the major environmental stresses that greatly limit plant growth, abundance and distribution. In this study, the effect of drought stress on some growth characteristics of Acacia mellifera seedlings (seedling height, seedling diameter, number of leaflets, shoot and root dry mass and root to shoot ratio) was investigated. Some of its drought resistance mechanisms were also identified. The drought stress treatments applied were as follows: Control (DC₀), drought cycle for 7 (DC₇),14 (DC₁₄) and21 days (DC₂₁). Results indicated that the drought stress treatments resulted in a wide variation in relative water content of leaves. Generally, results showed that all growth characteristics were negatively affected by drought stress. Moreover, It was observed that many of these characteristics were not significantly affected by (DC₇) drought stress, indicating sufficient water supply conditions and less sensitivity to limited water shortage. It was also noted that increasing the intensity of drought stress from (DC₁₄) to (DC₂₁) did not lead to a significant reduction in these traits except seedling diameter, indicating the ability of Acacia mellifera seedlings to withstand severe water shortage and the ability to develop adaptive mechanisms to resist severe drought conditions. The root to shoot ratio remained unchanged under drought stress regimes.  In addition, data obtained indicate an inverse relationship between drought stress and the measured growth characteristics. It was also noted that Acacia mellifera seedlings were able to develop several adaptive strategies to resist drought stress, including leaf shedding, low leaflet number as well as leaf rolling.

Key Words: Drought stress, Acacia mellifera, leaf relative water content, growth characteristics.