Allelopathic effects of invasive Eucalyptus camaldulensis on germination and early growth of four native species in the Western Cape, South Africa

作者：Ruwanza Sheunesu^*; Gaertner Mirijam; Esler Karen J; Richardson David M

来源：Southern Forests, 2015, 77(2): 91-105.

DOI：10.2989/20702620.2014.965985

• allelopathy
• biological invasions
• germination
• invasive plant species
• phenolic compounds
• tree invasions

Eucalyptus camaldulensis Dehnh. (red river gum; Myrtaceae) is an invasive tree in riparian habitats of the Western Cape, South Africa, where it replaces indigenous vegetation and affects ecosystem functioning. These invasions lead to changes in river geomorphology and reduction in stream flow. The mechanisms that drive these effects are poorly understood. The potential for allelopathic effects of aqueous extracts of Eucalyptus camaldulensis tissues and of soil and litter collected beneath Eucalyptus camaldulensis trees on the germination and seedling growth of four selected native plant species was investigated in a greenhouse experiment. Soils collected beneath Eucalyptus camaldulensis trees were used in three treatments: untreated soils, sterilised soils and sterilised soils overlaid with a eucalypt litter layer. In addition, soils collected from underneath native species were used in two treatments: untreated soils and soils overlaid with a eucalypt litter layer. All soil treatments were watered with three Eucalyptus camaldulensis leaf, bark and root aqueous treatments. Compounds present in the aqueous extracts and fresh samples were identified using gas chromatography. Soil and aqueous treatments showed varying effects on germination and seedling growth of the four native species. Germination and seedling growth of Olea europaea subsp. africana and Dimorphotheca pluvialis were significantly reduced by Eucalyptus camaldulensis root and bark aqueous extracts as well as by the soils treatments. The addition of eucalypt litter to native and sterilised soils reduced shoot and root growth of all four native species. Compounds such as alpha-phellandrene, eucalyptol, p-menth-1-en-8-ol and alpha-pinene, which have the potential to inhibit germination and plant growth, were identified in Eucalyptus camaldulensis aqueous extracts and fresh samples. Although the methods applied in this study had limitations (e.g. lack of control treatment to litter addition), the results provide an additional motivation to prioritise removal of invasive Eucalyptus camaldulensis stands from riparian ecosystems. Restoration initiatives should target native species that are not negatively affected by allelopathy.

• 出版日期2015