The Effect of Matric and Osmotic Potential Stresses on Seed Germination of Siris (Albizia lebbeck) Tree

Two separate laboratory experiments were conducted tostudy germination of Siris tree seeds exposed to matric (ψm) and osmotic(ψo) potential stresses. The first experiment comprised .5, .10,.15, .20, and .25 kPa ψm at 20.C soil temperature and zeroψo andthe second experiment comprised 0.0, .76.12, .152.3, .304.5, and.609.0 kPa ψ o at 20.C soil temperature and .12.2 kPa ψm. Distilledwater was added to sandy soil achieving the desired ψm levels in thefirst experiment. Sodium chloride solution was added to the sandy soilto achieve the desired ψo levels in the second experiment. Ten seeds ofSiris were sown in each plastic container (0.15 m I.D. and 0.20 mheight). The seeds were fresh (six months old) and had no pretreatment.The plastic containers were covered using clear polyethylene bag formaintaining the level of matric potential during germination. Parametersrecorded were, namely, number of germinated seeds, germinationpercentages, germination rate, and lengths of both radicle andshoot of the emerged seedlings. The results revealed that significantlygreat germination percentage and germination rate were associated withthe level of .10 kPa ψm than the other levels used, and tended to decreasedrastically as the level of ψm decreased/increased around this level. For optimum germination, the calculated ψm was found to be.12.2 kPa. The length of both radicle and shoot decreased linearly as ψm level decreased. Likewise, both the germination percentage andgermination rate decreased linearly as osmotic potential, ψo, decreased.The threshold osmotic potential for germination was calculated to be.1154.8 kPa ψo, below which germination was inhibited. Lowering theosmotic potential level resulted in delay of seed germination.