Effects of chilling, light and nitrogen-containing compounds on germination, rate of germination and seed imbibition of Clematis vitalba L.

Abstract

Effects of chilling (5°C) period, light and applied nitrogen (N) on germination (%), rate of germination (d to 50 % of total germination; T50%) and seed imbibition were examined in Clematis vitalba L. In the absence of chilling, light and N, germination was minimal (3 %). When applied alone, both chilling and N increased germination. Chilling for 12 weeks increased germination to 64%, and 2.5 mM NO8/- or NH4/+ increased germination to 10-12%. Light did not increase germination when applied alone, but did when applied in combination with chilling and/or N. Half the seed germinated when light was combined with 2.5 mM NO3/- or NH4/+. The influence of chilling, light and/or N ongermination was greater when combined, than when either factor was applied alone. Both oxidized (NO8/-) and reduced (NH4/+) forms of N increased germination, but non-N-containing compounds did not, suggesting the response was due to N and not ionic or osmotic effects. Without additional N, T50% decreased from 16-20 d at zero chilling, to around 5 d at 8 and 12 weeks chilling. Although T50% was not influenced by an increase in NO3/- or NH4/+ from 0.5 to 5.0 mM, it did increase with additional applied N thereafter. However, the magnitude of the N effect was small compared to that of chilling. Like germination, seed imbibition increased with a longer chilling period, but in contrast imbibition decreased slightly with increased applied NO3/- or NH4/+. It is argued that increased imbibition is not directly related to an increase in total germination, but that it may be related to the rate of germination. Possible mechanisms involved in the reduction indormancy of C. vitalba seed are discussed.