Seed inoculation with effective root‐nodule bacteria enhances revegetation success

Abstract

Summary1. Extensive clearing of native vegetation in Australia has contributed to major environmental problems, including land degradation, dryland salinity, soil erosion and loss of biodiversity. Re-establishing cover with deep-rooted perennial species is a major focus for conservation and sustainable land management, particularly with regard to hydrological control of recharge and saline discharge areas. However, considerable expense is involved in large-scale revegetation programmes and cost effectiveness is a real concern. 2. Low-cost revegetation approaches are needed that require little maintenance yet can substantially enhance reliable establishment and growth of native trees and shrubs. We evaluated results from direct-seeding field trials that examined the benefits of using native Australian Acacia species inoculated with effective strains of nitrogen-fixing rootnodule bacteria to revegetate degraded landscapes. 3. On average, inoculation led to a 118% increase in establishment of acacia seedlings, indicating that the use of elite strains of native bacteria can substantially reduce seed requirements. This is a major benefit given the expense of collecting sufficient native seed and the impacts of this activity on remnant population viability. 4. Particularly at sites experiencing harsher climatic conditions, subsequent survival of inoculated seedlings was significantly greater than for uninoculated controls. Moreover, inoculated acacias grew 10-58% faster than uninoculated controls during the critical early phase of establishment, although this varied among species and sites. 5. Synthesis and applications . Inoculation of Acacia species or other native leguminous shrubs and trees with elite strains of native rhizobia as part of direct-seeding techniques has the potential to increase the scope, rate and success of land restoration world-wide. Re-establishment of important plant-soil interactions in degraded soils can contribute significantly to the development of biodiverse self-regenerating native ecosystems in agricultural landscapes.

Reduced availability of rhizobia limits the performance but not invasiveness of introduced Acacia

“…Although seedling growth was reduced away from conspecifics, which we might expect if soil rhizobia populations decline in the absence of a host plant (Parker 2001;Thrall et al 2005), the reduction in growth was not strong or statistically significant. Other studies that have examined the influence of soil biota on species performance have found that interactions with natural enemies in the soil are generally more pronounced in species' native ranges (e.g.…”

“…Highly promiscuous plant hosts are able to nodulate with a wide range of rhizobia strains and at low bacterial densities, while less promiscuous hosts show greater strain specificity and require higher bacterial densities before they nodulate (Roughley 1987;Bhuvaneswari, Lesniak & Bauer 1988;Thrall, Burdon & Woods 2000;Thrall et al 2005Thrall et al , 2007. In addition, plant hosts themselves influence the availability of rhizobia in the soil (Thrall, Burdon & Woods 2000), with rhizobia population numbers increasing rapidly in response to compatible plant hosts (Purchase & Nutman 1957;Parker 2001) and declining when they are absent (Thrall et al 2001).…”

Rehabilitation of degraded dryland ecosystems – review

“…Some of the relevant issues presented in the literature which could be used in a cost-benefit analysis include: the economic case for government intervention and the overall cost of dryland degradation (Kirby and Blyth 1987;Beresford 2001;Roberts and Pannell 2009;Graham et al 2010), spatial modelling and identification of dryland areas affected by salinization (Graham 1992;Ive et al 1992;Horwood 1994;Kirkby 1996;Furby et al 2010), farmers and community perceptions about the salinization problem and the proposed alternatives (Greiner 1997;Hartley et al 1998;Kington et al 2003;Khan et al 2008;Kingwell et al 2008); landscape or river basin management options (Greiner 1998;Callow 2011Callow , 2012, modelling of on-farm management alternatives and economic trade-offs (John et al 2005;Cheng et al 2009;Finlayson et al 2010;Graham et al 2010), reintroduction of native trees and shrubs (Schofield 1992;Dorrough and Moxham 2005;Thrall et al 2005), and the effects of dryland degradation on human health (Jardine et al 2007(Jardine et al , 2008a(Jardine et al , 2008b(Jardine et al , 2011Speldewinde et al 2009Speldewinde et al , 2011.…”

The effect of soil inoculants on seed germination of native and invasive species

“…The role of the microbial soil community in restoration ecology has been most studied in terms of its influence on plant establishment and health. For example, mycorrhizal fungi inoculants are often a supplement to native seed in restoration projects because of the fungi's ability to form mutualistic associations with many plant species, improving nutrient uptake by plant roots (Allen et al 2003;Aprahamian et al 2016;Thrall et al 2005). Likewise, soil bacterial communities can promote plant growth by fixing atmospheric nitrogen, therefore restoration practitioners may D r a f t 4 include leguminous natives in their projects to improve soil fertility (Perez-Fernandez et al 2016;Requena et al 2001).…”