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Title: Allelopathic Effects of the Invasive Prosopis juliflora (Sw.) DC. on Selected Native Plant Species at Middle Awash, Southern Afar Rift of Ethiopia.
Authors: Samuel, Getachew
Advisors: Sebsebe Demissew(Prof.)
Tadessse Wolde(Dr.)
Keywords: Allelopathy
aqueous extract
canopy closure
germination percentage
germination rate
habitat
plant diversity
P. juliflora
Copyright: Jan-2010
Date Added: 25-Jul-2012
Publisher: Addis Ababa University
Abstract: The allelopathic effect of aqueous extracts of leaf, bark and root of Prosopis juliflora was studied on germination percentage, germination rate and seedling growth of Acacia nilotica, Acacia tortilis (both members of the legume Family, Fabaceae), Cenchrus cillaris and Enteropogon rupestris (both members of the grass Family, Poaceae). Effects of soil amended with decaying plant parts of P. juliflora and it’s under canopy soil were analyzed on germination percentage of the above selected plants to observe the field situation. Vegetation sampling in different habitat types in the area was made to identify the target plant species. Comparison of canopy characteristics among P. juliflora, A. nilotica and A. tortilis was also made to observe differences if any in canopy closure. P. juliflora was recorded in all habitat types in the study area: open Acacia woodland, riverine and swamp vegetation types. P. juliflora was observed invading the different habitats and affecting the plant diversity there in. Low plant diversity was recorded in P. juliflora dominated fields. Even if the canopy closure of P. juliflora was not significantly different from other trees, its growth characteristics and dense thickets formation restrict light to the ground flora and block winds. This results in the death of under canopy vegetation and hence low plant diversity. Leaf, bark and root aqueous extract of P. juliflora at 0, 0.5, 0.8, 1, 2 and 6% were prepared and their effect studied on germination percent, germination rate and seedling growth of the selected plant species in the study. Germination of A. nilotica and A. tortilis was not affected by all treatment types. Leaf and root extracts at higher concentrations inhibited germination of C. cillaris and E. rupestris. Bark extract facilitated germination of C. cillaris at lower concentrations. In general all treatment types speeded up the germination rate for A. nilotica and A. tortilis at the beginning, while these slow down the germination rate of C. cillaris and E. rupesteris. Shoot and root growth of the study species was inhibited by leaf extracts. Bark x xi extracts were stimulatory to shoot and root growth of the species under study at lower concentrations except for C. cillaris. C. cillaris root growth was not affected by bark extracts at lower concentrations. Root extracts were stimulatory at lower concentrations while it was inhibitory at higher concentrations to shoot and root growth of the study species except for C. cillaris. C. cillaris shoot growth was not affected by root extracts at lower concentrations. Seed germination of all study species except A. nilotica was inhibited by the amended and under canopy soil. The effect was high on the grasses than on the tree species studied and root growth was more inhibited than shoot growth. Suppression of seed germination, facilitation or retardation of the germination speed and seedling growth of the study species suggests that these responses are attributed to an allelopathic effect of P. juliflora on the test species. These results indicate that the effect is species specific and leaf seems to contain greater number / amount of inhibitors than does bark and root. Bark seems to contain the least. Heavy accumulations of leaf litter under P. juliflora result in accumulation of toxic substances in soil layers, inhibiting growth of other species. This may be one of the main reasons for its invasiveness and low plant diversity seen under its canopy.
Description: A Thesis submitted to the School of Graduate Studies of Addis Ababa University in partial fulfillment of the requirement for the degree of Master of Science in Biology (Botanical Science)
URI: http://hdl.handle.net/123456789/3488
Appears in:Thesis - Biology

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