Abstract
Soil solarization is a well-established method to disinfect soil for efficient weed control. However, the feasibility of applying this method in the restoration of invaded natural habitats is unclear. This is because soil moisture is necessary for the success of solarization, but pre-irrigation in natural ecosystems is often not applicable, or demands high labor investment, making it unsuitable for use in restoration. The present study was based on the idea that the relatively high soil moisture in wetlands might obviate the need for pre-irrigation, rendering this method much more applicable in natural habitats. We examined the efficacy of soil solarization using natural soil moisture to control the seed bank of the invasive plant, Acacia saligna, in a wetland, using large-scale experimental plots (0.38 ha each). An old, dense A. saligna grove was cut down and the roots were removed by a bulldozer. The plot was mulched with a transparent polyethylene sheet in early July and left on the soil for 14 weeks. Soil solarization significantly reduced the viability of seeds of A. saligna that had been experimentally buried. Additionally, viability of seeds in the natural seed bank was reduced, and seedling emergence was close to zero. Exposing seeds to soil temperature and soil moisture levels equivalent to those obtained during field soil solarization under controlled conditions significantly increased the release from dormancy of the seeds, suggesting that release from dormancy during the early stage of solarization is a critical stage leading to seed weakening or mortality in the soil. Soil solarization also decreased the cover and abundance of the natural vegetation; therefore, active revegetation is required to restore the natural vegetation and to conserve endangered and endemic species.
Highlights
The world has lost 87% of its wetlands since 1700 AD (Davidson 2014)
The re-establishment of invasive plants from long-term persistent soil seed banks is one of the most important factors leading to the failure of restoration efforts (Zavaleta et al 2001; Erskine Ogden and Rejmánek 2005; Reid et al 2009; Le Maitre et al 2011)
For example, microwave soil heating has been suggested as a potential method to control the seed bank of invasive plants in natural habitats (De Wilde et al 2017; Hess et al 2018), but an applicable device has not yet been developed
Summary
The world has lost 87% of its wetlands since 1700 AD (Davidson 2014). In recent decades, the loss and degradation of the wetlands has accelerated due to anthropogenic factors, including the proliferation of invasive species. The re-establishment of invasive plants from long-term persistent soil seed banks is one of the most important factors leading to the failure of restoration efforts (Zavaleta et al 2001; Erskine Ogden and Rejmánek 2005; Reid et al 2009; Le Maitre et al 2011). Attempts to control the seed banks of invasive plants having physically dormant seeds in natural habitats have been based mainly on the use of prescribed burning (Richardson and Kluge 2008). For example, microwave soil heating has been suggested as a potential method to control the seed bank of invasive plants in natural habitats (De Wilde et al 2017; Hess et al 2018), but an applicable device has not yet been developed. Our group, using Acacia saligna as a model plant, demonstrated that soil solarization has high potential as a control method for this purpose in natural habitats undergoing restoration
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