Journal of Arid Environments (1995) 29:15-23 Seed dormancy and persistence of Acacia berlandieri and Leucaena pulverulenta in a semi-arid environment

Seed longevity of the leguminous hrubs Acacia berlandieri and Leucaena pulverulenta was evaluated under field conditions at the soil surface and at 3-5 cm depth. Abiotic influences on seed longevity and dormancy were investigated by comparing seeds maintained at 5°C with seeds experiencing fluctuating day/night temperatures (40°C/20°C vs. 50°C/30°C) under dry and moist conditions. Acacia seed demonstrated no dormancy and initial germinability was> 82 % in the laboratory. Viability of Leucaena seed was>97%, but seed coat dormancy limited germination to < 7%. Persistence of Acacia seeds in the soil seed bank varied with depth. After 42 days the viable seed population of Acacia was reduced by 10 and 80 % for surface and buried seeds, respectively, and no viable seeds were present after 3"5 months of burial. In contrast, Leucaena seeds on the soil surface xhibited no significant decline in viability over 60 days and attrition of buried seed was <11%. After 3"5, 6 and 12 months of burial, 86, 81 and 71 % of the Leucaena seeds dispensed remained viable, but the hard seed coat limited germination to5