A reciprocal transplant experiment to study morphological plasticity of A. senegal (L) Willd. seedlings within a drought gradient in northern Nigeria. Jibo, AU 1,2 and Barker, MG 1 1 Institute of Environmental and Biological Sciences, University of Aberdeen 2 School of General Studies Mai Idris Alooma Polytechnic, Geidam Yobe State, Nigeria 3 Okorie FC Studies on Drought in the Sub-Saharan Region of Nigeria using satellite remote sensing and precipitation data. JNCASR. 4 Hess,T. Stephens, W. and Maryah, U. 1995, Rain trends in the northeast arid zone of Nigeria Agricultural and Meteorology. Vol 74 no 1 pp Fig 1 3 Methods  A reciprocal transplant experiment was used to investigate growth plasticity of Acacia senegal seedlings in soil moisture gradient in Yobe, Nigeria (Fig 1).  Seedlings from different provenances were left at ‘home’ or transferred ‘away’ to a different part of the soil moisture gradient  Northern site, Nguru (12.53°N, 10.28°E) is arid. Southern site, Gujba (11.30°N, 11.56°E) is semi-arid.  A reciprocal transplant experiment was used to investigate growth plasticity of Acacia senegal seedlings in soil moisture gradient in Yobe, Nigeria (Fig 1).  Seedlings from different provenances were left at ‘home’ or transferred ‘away’ to a different part of the soil moisture gradient  Northern site, Nguru (12.53°N, 10.28°E) is arid. Southern site, Gujba (11.30°N, 11.56°E) is semi-arid. 2 Hypotheses The investigation focussed on root growth responses H 1 root/shoot ratios will be related inversely to soil moisture availability H 2 there will be a difference in plasticity among seedlings from the northern and southern provenances The investigation focussed on root growth responses H 1 root/shoot ratios will be related inversely to soil moisture availability H 2 there will be a difference in plasticity among seedlings from the northern and southern provenances  Seedlings of Acacia senegal show growth responses to soil moisture gradients, both between and within sites.  More biomass was allocated to roots (higher root:shoot ratio) at the more arid site. This may confer drought avoidance while reducing overall growth rate.  Seedlings from difference provenances adjusted their biomass allocation when shifted within the moisture gradient.  There was evidence of differences in plasticity among seedlings from different provenances.  There may be implications performance of A. senegal if there are further shifts in rainfall.  Seedlings of Acacia senegal show growth responses to soil moisture gradients, both between and within sites.  More biomass was allocated to roots (higher root:shoot ratio) at the more arid site. This may confer drought avoidance while reducing overall growth rate.  Seedlings from difference provenances adjusted their biomass allocation when shifted within the moisture gradient.  There was evidence of differences in plasticity among seedlings from different provenances.  There may be implications performance of A. senegal if there are further shifts in rainfall. Drought is recurrent in the semi-arid part of West Africa 3. The Sahelian zone of Nigeria (11° N) has seen a shift in the rainfall climate zone. During the last 40 years the rainfall belt has moved southward by about 60 km. Annual rainfall has declined by about 100  150 mm 4 Do economically important Acacia senegal (gum Arabic) trees have the capacity to respond to these changes? Drought is recurrent in the semi-arid part of West Africa 3. The Sahelian zone of Nigeria (11° N) has seen a shift in the rainfall climate zone. During the last 40 years the rainfall belt has moved southward by about 60 km. Annual rainfall has declined by about 100  150 mm 4 Do economically important Acacia senegal (gum Arabic) trees have the capacity to respond to these changes? 1 Introduction Fig. 4. Mean tap root length (+SE). Means with different letters are significantly different (P<0.001) When transferred ‘away’, seedlings from both provenances did not fully acquire the root length characteristics of the ‘home’ provenance Fig. 4. Mean tap root length (+SE). Means with different letters are significantly different (P<0.001) When transferred ‘away’, seedlings from both provenances did not fully acquire the root length characteristics of the ‘home’ provenance A Fig 2. Mean root/shoot ratio (+SE). Means with different letters are significantly different (P<0.001). Values were higher in lower soil moisture conditions. When transferred ‘away’, seedlings from both provenances only partially acquired root:shoot characteristics of the ‘home’ provenance Fig 2. Mean root/shoot ratio (+SE). Means with different letters are significantly different (P<0.001). Values were higher in lower soil moisture conditions. When transferred ‘away’, seedlings from both provenances only partially acquired root:shoot characteristics of the ‘home’ provenance A B ●Nguru (arid) Nigeria ●Gujba (semi-arid) 25m HA A H HA AH Each treatment n=64 A= Away H= Home =Seedlings from Nguru provenances =Seedlings from Gujba provenances Fig 1 4 Results H 1 root:shoot ratio H 2 plasticity in tap root growth 5 Discussion Fig. 3. Soil moisture content at different soil depths in Nguru (arid) and Gujba (semi-arid) Soil moisture was higher at the semi-arid site, especially at greater depths Fig. 3. Soil moisture content at different soil depths in Nguru (arid) and Gujba (semi-arid) Soil moisture was higher at the semi-arid site, especially at greater depths PR2 moisture probe (Delta-T Devices) AB Fig.5 A & B. Tap root length of A.senegal in Nguru (arid) & Gujba (semi- arid)