School of Agriculture, Food and Ecosystem Sciences - Research Publications

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    Riparian fungal communities respond to land-use mediated changes in soil properties and vegetation structure
    Waymouth, V ; Miller, RE ; Kasel, S ; Ede, F ; Bissett, A ; Aponte, C (SPRINGER, 2022-06)
    Abstract Purpose Owing to their topographic location and nutrient rich soils, riparian forests are often converted to pastures for grazing. In recent decades, remnant riparian forests cleared for grazing pastures have been restored with native species. The impacts of such land-use changes on soil fungal communities are unclear, despite the central roles that soil fungi play in key ecosystem processes. We investigated how soil fungal taxonomic and functional composition are affected by land-use change at different depths, and if variation in soil fungal communities is related to edaphic properties and extant vegetation. Methods The study was conducted in six waterways in south-eastern Australia, each comprising three land-use types: remnant riparian forest, cleared forest converted to pasture, and pastures restored with native plants. We surveyed three strata of vegetation and sampled top-soil and sub-soil to characterise physicochemical properties and soil fungal communities. ITS1 region sequences were used to assign soil fungal taxonomic and functional composition. Results Fungal taxonomic and functional composition infrequently varied with land-use change or soil depth. Overall, environmental properties (soil and vegetation) explained 35–36% of variation in both fungal taxonomic and functional composition. Soil fungal taxonomic composition was related to soil fertility (N, P, K, pH and Ca) and ground cover characteristics, whereas functional composition was related to clay content, sub-canopy cover and tree basal area. Conclusion Across the six studied waterways, fungal taxonomic and functional composition were more strongly associated with land-use mediated changes in site-scale soil physicochemical properties and vegetation structure than broad-scale classes of land-use type.
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    Counting the cost of revegetation: is direct seeding cheaper than planting tube-stock?
    Ede, F ; Greet, J ; Dabal, R ; Robertson, D ; Smith, R (University of New England, Armidale, 2018)
    Direct seeding is often assumed to be cheaper than planting tube–stock, but limited data exist to compare the relative costs of the two techniques. At four riparian sites in Victoria, we assessed the number of plants established over time in the months after direct seeding or planting. The costs of surviving plants and of weed management were calculated. Plants were 11 times cheaper when established by seeding ($1.88/plant) than when planted ($21.03/plant). Incorporating weed management costs, direct seeding was 1.3–2.4 times more cost–effective than planting tube–stock, although costs were high for both techniques.
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    Pre-emergence processes limit seedling recruitment in two direct seeded Acacia spp.
    McKendrick, SA ; Ede, FJ ; Miller, RE ; Greet, J (ELSEVIER, 2022-02-01)
    The use of direct seeding for revegetation often results in poor recruitment outcomes. For many species, it is unclear where recruitment bottlenecks occur in the transitions between early life-history stages and how soil moisture conditions affect these bottlenecks. Thus, we asked: (1) which life-history stage transitions are most limiting to seedling recruitment? and (2) how do soil moisture levels affect recruitment? Using a field-based trial, we quantified the recruitment process from a seed to seedling for two woody Acacia species. Using a novel technique, in which seeds were confined to germination caches (small baskets), along with the use of germination bags, we assessed pre-emergence processes at regular intervals. Seeds sown directly into the soil in adjacent rows were intensively monitored to assess post-emergence processes. To investigate the effects of soil moisture on seedling recruitment, a glasshouse experiment assessed transitions between life-history stages under three different soil moisture treatments. In the field, the transition between a seed and germinated seed limited recruitment more than all other life-history stage transitions combined, with 32%–50% of seeds not germinating for the two species. Approximately one third of seeds of both species died prior to germinating, with few seeds remaining dormant. In the glasshouse trial, seed germination increased with increasing soil moisture, however, so did the extent of seed death. Our results suggest that the transition from a seed to germinated seed was the most limiting bottleneck to recruitment, mostly due to seed mortality rather than dormancy processes, with pathogen attack the most likely cause. As increased soil moisture both promoted germination but also seed mortality, understanding the optimal soil moisture thresholds that maximise germination and the transition to an established plant is essential in maximising direct seeding outcomes. Identifying the life-history stage transitions most limiting to plant recruitment may allow management to target specific bottlenecks in order to improve direct seeding outcomes.
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    Should I plant or should I sow? Restoration outcomes compared across seven riparian revegetation projects
    Greet, J ; Ede, F ; Robertson, D ; McKendrick, S (WILEY, 2020-01)
    Summary To revegetate native plant communities, it is often cheaper to direct seed than to plant nursery‐grown stock. However, the outcomes of direct seeding can be quite variable, and it is unclear whether direct seeding or planting is more likely to facilitate the restoration of diverse plant communities. To address this question, we compared the outcomes of each method across several recent riparian revegetation projects where both direct seeding and tube‐stock planting were used. We surveyed riparian revegetation projects at seven sites within the greater Melbourne area that had been revegetated between 1 and 4 years previously. Sites were all on land previously used for agriculture or degraded public land and ranged in environmental and climatic conditions. Woody plant density, establishment of target species, species richness, species diversity (evenness) and plant heights were assessed. Direct seeding tended to result in higher plant densities and similar species richness, but lower rates of species establishment and diversity compared with planting. A median of 67% of target species established via direct seeding compared with 100% for planting, with direct seeded areas often dominated by one or two species. In general, overall revegetation outcomes were often driven by climatic and site factors, rather than revegetation method. We suggest that to achieve good restoration outcomes from revegetation in riparian areas, a bet‐hedging or combined approach using both sowing and planting may be the best strategy.
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    Soil Bacterial Community Responds to Land-Use Change in Riparian Ecosystems
    Waymouth, V ; Miller, RE ; Kasel, S ; Ede, F ; Bissett, A ; Aponte, C (MDPI, 2021-02)
    Riparian forests were frequently cleared and converted to agricultural pastures, but in recent times these pastures are often revegetated in an effort to return riparian forest structure and function. We tested if there is a change in the soil bacterial taxonomy and function in areas of riparian forest cleared for agricultural pasture then revegetated, and if soil bacterial taxonomy and function is related to vegetation and soil physicochemical properties. The study was conducted in six riparian areas in south-eastern Australia, each comprising of three land-use types: remnant riparian forest, cleared forest converted to pasture, and revegetated pastures. We surveyed three strata of vegetation and sampled surface soil and subsoil to characterize physicochemical properties. Taxonomic and functional composition of soil bacterial communities were assessed using 16S rRNA gene sequences and community level physiological profiles, respectively. Few soil physiochemical properties differed with land use despite distinct vegetation in pasture relative to remnant and revegetated areas. Overall bacterial taxonomic and functional composition of remnant forest and revegetated soils were distinct from pasture soil. Land-use differences were not consistent for all bacterial phyla, as Acidobacteria were more abundant in remnant soils; conversely, Actinobacteria were more abundant in pasture soils. Overall, bacterial metabolic activity and soil carbon and nitrogen content decreased with soil depth, while bacterial metabolic diversity and evenness increased with soil depth. Soil bacterial taxonomic composition was related to soil texture and soil fertility, but functional composition was only related to soil texture. Our results suggest that the conversion of riparian forests to pasture is associated with significant changes in the soil bacterial community, and that revegetation contributes to reversing such changes. Nevertheless, the observed changes in bacterial community composition (taxonomic and functional) were not directly related to changes in vegetation but were more closely related to soil attributes.
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    Unravelling the Paradox of Loss of Genetic Variation during Invasion: Superclones May Explain the Success of a Clonal Invader
    Caron, V ; Ede, FJ ; Sunnucks, P ; Zhang, Y (PUBLIC LIBRARY SCIENCE, 2014-06-10)
    Clonality is a common characteristic of successful invasive species, but general principles underpinning the success of clonal invaders are not established. A number of mechanisms could contribute to invasion success including clones with broad tolerances and preferences, specialist clones and adaptation in situ. The majority of studies to date have been of plants and some invertebrate parthenogens, particularly aphids, and have not necessarily caught invasion at very early stages. Here we describe the early stages of an invasion by a Northern Hemisphere Hymenopteran model in three different land masses in the Southern Hemisphere. Nematus oligospilus Förster (Hymenoptera: Tenthredinidae), a sawfly feeding on willows (Salix spp.), was recently introduced to the Southern Hemisphere where it has become invasive and is strictly parthenogenetic. In this study, the number of N. oligospilus clones, their distribution in the landscape and on different willow hosts in South Africa, New Zealand and Australia were assessed using 25 microsatellite markers. Evidence is presented for the presence of two very common and widespread multilocus genotypes (MLGs) or 'superclones' dominating in the three countries. Rarer MLGs were closely related to the most widespread superclone; it is plausible that all N. oligospilus individuals were derived from a single clone. A few initial introductions to Australia and New Zealand seemed to have occurred. Our results point towards a separate introduction in Western Australia, potentially from South Africa. Rarer clones that were dominant locally putatively arose in situ, and might be locally favoured, or simply have not yet had time to spread. Data presented represent rare baseline data early in the invasion process for insights into the mechanisms that underlie the success of a global invader, and develop Nematus oligospilus as a valuable model to understand invasion genetics of clonal pests.
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    Post-sowing weed control technique can affect woody seedling numbers, with early hand-weeding potentially more beneficial than early spraying
    Ede, F ; Greet, J (WILEY, 2021-09)
    Summary Direct seeding is increasingly being used as a cost‐effective revegetation technique. Successful outcomes from direct seeding rely on effective weed control, particularly during the vulnerable seedling establishment phase. Post‐sowing weed control options are constrained by the need to protect seedlings from damage and few studies have compared the effectiveness of different weed control techniques. We evaluated the effect of preliminary hand weeding (with subsequent spraying), spraying monthly or spraying quarterly with glyphosate, on woody seedling emergence, survival and growth in trials sown either in spring or autumn at a riparian site in Victoria, southeastern Australia. Seedling numbers were recorded monthly for 6 months and at 12 months after sowing, with seedling survival and heights assessed at 12 months. Total seedling numbers were higher in subplots initially hand weeded than in subplots sprayed on either a monthly or quarterly basis, regardless of when direct seeding occurred, but weed control treatment had no effect on seedling survival. These results indicate that post‐sowing spraying limited rates of seedling emergence, either directly or indirectly. For direct seeding, hand weeding in the first few months after sowing may maximise rates of woody seedling emergence, while spraying with glyphosate may inhibit seedling emergence.