Morphological plasticity of Acacia Senegal (L) willd. seedlings within a drought gradient in north eastern Nigeria

Abstract

A reciprocal transplant experiment was set up (n=128) to investigate the morphological plasticity of A. senegal seedlings to changes in available soil  moisture in Yobe State, Nigeria. Half of the A. senegal seedlings from each of the Nguru and Gujba populations were planted in their 'home'  locations while the remaining plants swapped with seedlings from the 'away' population. Stem diameter was measured approximately every 14 days  for all plants and at the end of the experiment (430 days), 50 randomly selected seedlings from each treatment were harvested to determine  total dry mass partitioned into the shoot and roots. For root extraction, a trench 0.5 m x 1 m was dug with a spade to 1 m depth at about 80 cm  away from the base of the seedling. Soil was carefully removed using a sharp blade from the surface downward to search for the roots. A. senegal seedlings from each population showed distinct growth responses to their local environment, whether ‘home’ or ‘away’. Root: shoot ratios were  related inversely to soil moisture availability. This was mainly attributed to increasing biomass allocation to roots rather than decreasing allocation  to shoots. Seedlings that were transferred from a northern arid location to a more semi-arid site showed a greater plasticity than seedlings moved  in the opposite direction. Results suggest that, in A. senegal seedlings, (a) growth and biomass allocations allowed acclimation to local soil moisture  conditions, and (b) that there were differences in plasticity among seedlings from the northern  and southern provenances.