Seed dormancy, nitrogen nutrition and shade acclimation of impatiens glandulifera: Implications for successful invasion of deciduous woodland

Abstract

Background: Non-native invasive plants capable of fast growth may establish and develop rapidly under the high soil nitrogen (N) and increased irradiance levels that occur in gaps at disturbed sites within deciduous woodland. However, if disturbance is transitory, then the long-term success of an invasive species within deciduous woodland will be dependent on its ability to compete with native species and acclimate to the typical conditions of low N availability and irradiance. Aims: To gain greater understanding of the ecophysiological reasons for the success of Impatiens glandulifera as a weed species in deciduous woodland. Methods: We examined N form, N concentration and irradiance effects on seed dormancy, N nutrition and shade acclimation of Impatiens. Results: Under controlled conditions, Impatiens seed required a period of wet chilling to overcome dormancy. High nitrate (NO-3) concentration and light gave substantial increases in germination over 8-12 weeks chilling and decreased time to 50% emergence over a full winter's chilling. Under high irradiance in a glasshouse, Impatiens showed N nutrition characteristics similar to those of fast growing crop and weed species. Within woodland and on high and relatively low NO-3 supply in a glasshouse, Impatiens showed a range of mechanisms of acclimation to low irradiance, in particular, increases in height, dry matter partitioning to the shoot, use of NO-3 as osmoticum in stems, specific leaf area (SLA) and leaf chloro-phyll concentration. Conclusions: High soil NO-3 concentrations and light may be factors in the synchronisation of emergence of Impatiens in disturbed sites producing a high-density and competitively strong cohort of seedlings within a short period of time. Rapid growth under high irradiance and N supply will allow Impatiens seedlings to establish quickly in disturbed woodland sites. Acclimation to low irradiance, in particular, maintenance of height and development of an exceptionally high SLA at relatively low NO-3 supply, as demonstrated could allow Impatiens to shade out competing field layer species at the low lev-els of N and irradiance typical of woodland. © 2009 Botanical Society of Scotland and Taylor & Francis.