Ecological and physiological studies of Clematis vitaba L

Content Partner: Lincoln University. Clematis vitalba L. is a deciduous perennial climber native to central Europe and southern England which has become a major invasive weed species in New Zealand native forest remnants. In forest remnants, C. vitalba tends to establish in forest gaps, forest margins and recently disturbed areas. A field distribution survey and, field and laboratory based studies of germination, growth, nitrogen (N) nutrition and light-level acclimation were conducted with the overall objective of determining reasons for the success C. vitalba in New Zealand forest remnants. The field site was at Dennistoun Bush, a native forest remnant located at Peel Forest, central Canterbury, New Zealand. Based on a distribution survey, a field based growth experiment and the investigation of naturally established C. vitalba (Chapter 2), it is shown that low light level is the primary factor associated with the limited establishment of C. vitalba in undisturbed forest and, that increased N availability following disturbance may be important in the successful establishment at high light levels. Chapter 3 sets out to determine if the pattern of C. vitalba distribution in the field can be related to the influence of environmental factors on germination. It is shown that moist chilling, applied N (as NO₃⁻ or NH₄⁺) and light can reduce seed dormancy when applied at levels that are likely to occur in the field. It is concluded that the potential for germination is unlikely to be an important factor limiting the establishment of C. vitalba in undisturbed forest. It is proposed that the interaction of chilling, N and light, combined with sporadic seed release are important in the rapid establishment of C. vitalba in disturbed sites and therefore the success of C. vitalba in forest gaps and margins. A model for the mechanism of dormancy reduction in C. vitalba seed is proposed. Chapter 4 investigates the influence of N on growth and N assimilation. The response of C. vitalba to increased applied N is compared to the response of barley (Hordeum vulgare). It is shown that the growth, N assimilation and N storage characteristics displayed by C. vitalba are consistent with plant species adapted to environments with high NO₃⁻ availability and, consistent with the establishment of C. vitalba in recently disturbed sites. This is further substantiated by the unusual characteristic where the potential for NO₃⁻ assimilation (nitrate reductase activity) is increased unde