Practical applications of soil microbiota to improve ecosystem restoration: current knowledge and future directions.

Soil microbiota are important components of healthy ecosystems. Greater consideration of soil microbiota in the restoration of biodiverse, functional, and resilient ecosystems is required to address the twin global crises of biodiversity decline and climate change. In this review, we discuss available and emerging practical applications of soil microbiota into (i) restoration planning, (ii) direct interventions for shaping soil biodiversity, and (iii) strategies for monitoring and predicting restoration trajectories. We show how better planning of restoration activities to account for soil microbiota can help improve progress towards restoration targets. We show how planning to embed soil microbiota experiments into restoration projects will permit a more rigorous assessment of the effectiveness of different restoration methods, especially when complemented by statistical modelling approaches that capitalise on existing data sets to improve causal understandings and prioritise research strategies where appropriate. In addition to recovering belowground microbiota, restoration strategies that include soil microbiota can improve the resilience of whole ecosystems. Fundamentally, restoration planning should identify appropriate reference target ecosystem attributes and - from the perspective of soil microbiota - comprehensibly consider potential physical, chemical and biological influences on recovery. We identify that inoculating ecologically appropriate soil microbiota into degraded environments can support a range of restoration interventions (e.g. targeted, broad-spectrum and cultured inoculations) with promising results. Such inoculations however are currently underutilised and knowledge gaps persist surrounding successful establishment in light of community dynamics, including priority effects and community coalescence. We show how the ecological trajectories of restoration sites can be assessed by characterising microbial diversity, composition, and functions in the soil. Ultimately, we highlight practical ways to apply the soil microbiota toolbox across the planning, intervention, and monitoring stages of ecosystem restoration and address persistent open questions at each stage. With continued collaborations between researchers and practitioners to address knowledge gaps, these approaches can improve current restoration practices and ecological outcomes.

Improving Seed Morphology and Germination Potential in Australian Native Grasses Using Seed Enhancement Technologies.

Difficult to handle seed material and poor germination commonly limit the uptake of native grasses in restoration and commercial-scale seeding efforts. Seed enhancement technologies (SETs) offer valuable solutions for improving the handling of seed material and optimising germination. This study considered eight widespread Australian native grasses; two representative of Mediterranean to temperate climates ('cool-climate' species) and six representative of arid to subtropical climates ('warm-climate' species). Through a series of experiments, this study logically selected and applied SET treatments to improve seed handling and germination for each study species. Seed handling was prioritised and addressed using flash flaming and/or acid digestion, while hydropriming was used following seed-handling treatments to enhance germination. Flash flaming and acid digestion were both applied to successfully reduce or remove bulky floret structures while maintaining or improving germination. Flaming at 110 ± 10 °C with continuous exposure for 10 min and acid digestion concentrations of 75-80% with exposure times of 1-2.5 min were generally successful. Sub-optimal concentrations of sulphuric acid often compromised germination. Hydropriming did not improve germination outcomes when applied following flaming or acid digestion. Optimising SETs for germination, emergence and establishment in different environments, and the viability and costs of application on larger seed batches are key considerations for the implementation and upscaling of SETs in the future.

Variable seed bed microsite conditions and light influence germination in Australian winter annuals.

Environmentally cued germination may play an important role in promoting coexistence in Mediterranean annual plant systems if it causes niche differentiation across heterogeneous microsite conditions. In this study, we tested how microsite conditions experienced by seeds in the field and light conditions in the laboratory influenced germination in 12 common annual plant species occurring in the understorey of the York gum-jam woodlands in southwest Western Australia. Specifically, we hypothesized that if germination promotes spatial niche differentiation, then we should observe species-specific germination responses to light. In addition, we hypothesized that species' laboratory germination response may depend on the microsite conditions experienced by seeds while buried. We tested the laboratory germination response of seeds under diurnally fluctuating light and complete darkness, which were collected from microsites spanning local-scale environmental gradients known to influence community structure in this system. We found that seeds of 6 out of the 12 focal species exhibited significant positive germination responses to light, but that the magnitude of these responses varied greatly with the relative light requirement for germination ranging from 0.51 to 0.86 for these species. In addition, germination increased significantly across a gradient of canopy cover for two species, but we found little evidence to suggest that species' relative light requirement for germination varied depending on seed bank microsite conditions. Our results suggest that variability in light availability may promote coexistence in this system and that the microsite conditions seeds experience in the intra-growing season period can further nuance species germination behaviour.

A global review of seed enhancement technology use to inform improved applications in restoration.

Seed-based restoration often experiences poor success due to a range of edaphic and biotic issues. Seed enhancement technologies (SETs) are a novel approach that can alleviate these pressures and improve restoration success. Broadly, SETs have been reviewed for agricultural and horticultural purposes, for specific types of SETs such as coating or priming, or for focal ecosystems. However, information is lacking for SETs within a restoration focused context, and how they are being used to alleviate certain barriers. This review aimed to synthesise the current literature on SETs to understand what SETs are being tested, in which sectors and locations they are being tested, what issues are faced within restoration using SETs, and how SETs are being used to approach these issues. Priming was highlighted as the main SET investigated. Inoculation, pesticide application and magnetic fields were also commonly tested (SETs we termed 'prospective techniques'). SET research mainly occurred in the agricultural sector. More recently, other sectors, such as restoration and rangeland management, have increased efforts into SET research. The restoration sector has focused on extruded pelleting and coating (with activated carbon), in combination with herbicide application, to overcome invasive species, and coating with certain additives to alleviate edaphic issues. Other sectors outside restoration were largely focused on evaluating priming for overcoming these barriers. The majority of priming research has been completed on crop species and differences between these species and ecosystems must be considered in future restoration efforts that focus on native seed use. Generally, SETs require further refinement, including identifying ideal additives and their optimum concentrations to target certain issues, refining formulations for coating and extruded pelleting and developing flash flaming. A bet-hedging approach using multiple SETs and/or combinations of SETs may be advantageous in overcoming a wide range of barriers in seed-based restoration.

Drivers of seedling establishment success in dryland restoration efforts.

Restoration of degraded drylands is urgently needed to mitigate climate change, reverse desertification and secure livelihoods for the two billion people who live in these areas. Bold global targets have been set for dryland restoration to restore millions of hectares of degraded land. These targets have been questioned as overly ambitious, but without a global evaluation of successes and failures it is impossible to gauge feasibility. Here we examine restoration seeding outcomes across 174 sites on six continents, encompassing 594,065 observations of 671 plant species. Our findings suggest reasons for optimism. Seeding had a positive impact on species presence: in almost a third of all treatments, 100% of species seeded were growing at first monitoring. However, dryland restoration is risky: 17% of projects failed, with no establishment of any seeded species, and consistent declines were found in seeded species as projects matured. Across projects, higher seeding rates and larger seed sizes resulted in a greater probability of recruitment, with further influences on species success including site aridity, taxonomic identity and species life form. Our findings suggest that investigations examining these predictive factors will yield more effective and informed restoration decision-making.

Global change impacts on arid zone ecosystems: Seedling establishment processes are threatened by temperature and water stress.

Recruitment for many arid-zone plant species is expected to be impacted by the projected increase in soil temperature and prolonged droughts associated with global climate change. As seed dormancy is considered a strategy to avoid unfavorable conditions, understanding the mechanisms underpinning vulnerability to these factors is critical for plant recruitment in intact communities, as well as for restoration efforts in arid ecosystems. This study determined the effects of temperature and water stress on recruitment processes in six grass species in the genus Triodia R.Br. from the Australian arid zone. Experiments in controlled environments were conducted on dormant and less-dormant seeds at constant temperatures of 25°C, 30°C, 35°C, and 40°C, under well-watered (Ψsoil = -0.15 MPa) and water-limited (Ψsoil = -0.35 MPa) conditions. Success at three key recruitment stages-seed germination, emergence, and survival-and final seed viability of ungerminated seeds was assessed. For all species, less-dormant seeds germinated to higher proportions under all conditions; however, subsequent seedling emergence and survival were higher in the more dormant seed treatment. An increase in temperature (35-40°C) under water-limited conditions caused 95%-100% recruitment failure, regardless of the dormancy state. Ungerminated seeds maintained viability in dry soil; however, when exposed to warm (30-40°C) and well-watered conditions, loss of viability was greater from the less-dormant seeds across all species. This work demonstrates that the transition from seed to established seedling is highly vulnerable to microclimatic constraints and represents a critical filter for plant recruitment in the arid zone. As we demonstrate temperature and water stress-driven mortality between seeds and established seedlings, understanding how these factors influence recruitment in other arid-zone species should be a high priority consideration for management actions to mitigate the impacts of global change on ecosystem resilience. The knowledge gained from these outcomes must be actively incorporated into restoration initiatives.

Flash Flaming Improves Flow Properties of Mediterranean Grasses Used for Direct Seeding.

The demand for native grasses is increasing in restoration and agriculture, though their use is often limited due to seed handling challenges. The external structures surrounding the grass seed (i.e., the floret) possess hairs, awns, and appendages which create blockages in conventional seeding equipment. Flash flaming is a patented technology which allows precision exposure of floret material to flames to singe off hairs and appendages. We used two grasses native to Mediterranean ecosystems of Western Australia (Amphipogon turbinatus R.Br. and Neurachne alopecuoidea R.Br.) to evaluate the effects of different flaming techniques on flow properties and germination. Flaming significantly improved flowability in both species and had both neutral (A. turbinatus) and negative (N. alopecuroidea) effects on germination. Flaming torch size influenced germination, though flaming temperature (low or high) and whether this was kept constant or alternating had no effect. The best evaluation of germination following flaming was achieved by cleaning flamed florets to seed and/or germinating in the presence of karrikinolide (KAR1) or gibberellic acid (GA3). We suggest that flaming settings (particularly torch size) require species-specific evaluation and optimisation. Removing seeds from flamed florets and germination testing this material in the presence of stimulants may be a useful protocol for future flaming evaluations.

Inorganic soil amendments alter seedling performance of native plant species in post-mining arid zone rehabilitation.

Rehabilitation of degraded drylands is challenged by environmental and anthropogenic constraints, such as limited availability of locally-sourced topsoil and poor quality alternative soil substrates. Current rehabilitation practices, at times, utilise inorganic soil amendments to improve the physicochemical and biological characteristics of reconstructed soil profiles. These approaches may be appropriate for dryland rehabilitation, but there is limited research available regarding the benefits of using these amendments. Here, we present a study in the Pilbara region of Western Australia, an arid landscape subject to intensive mining that currently uses inorganic soil amendments (gypsum and urea) in post-mining rehabilitation. The aim of this study was to assess the effectiveness of these amendments to (1) promote seed germination, seedling emergence and seedling growth across five plant species and, (2) re-instate soil quality in mine waste substrates. A series of glasshouse experiments assessed eight application combinations of these amendments in two alternative substrates and compared these to unamended substrates and topsoil. Soil amendments had a limited influence on seed germination, were detrimental to seedling emergence and resulted in increased seedling mortality. Mortality in the waste ranged from 2 to 61% but increased to 7-92% in amended waste. Seedling growth improved with high doses of amendments in waste, with a 1.3-5.6-fold increase across all plant species. Soil quality was relatively unaffected by amendments with soil nitrogen ranging from 0.01 to 0.08%, organic carbon from 0.01 to 0.12% and soil microbial activity from 2.3 to 2.4 ppm-CO2 in the amended and unamended waste. The use of soil amendments in mine rehabilitation requires consideration of the trade-off between initial reductions in seedling recruitment and enhanced seedling development at later stages. Future rehabilitation should consider the timing of amendment application to avoid detrimental impacts on seedling recruitment and maximise the benefits to seedling growth.

A research agenda for seed-trait functional ecology.

Trait-based approaches have improved our understanding of plant evolution, community assembly and ecosystem functioning. A major challenge for the upcoming decades is to understand the functions and evolution of early life-history traits, across levels of organization and ecological strategies. Although a variety of seed traits are critical for dispersal, persistence, germination timing and seedling establishment, only seed mass has been considered systematically. Here we suggest broadening the range of morphological, physiological and biochemical seed traits to add new understanding on plant niches, population dynamics and community assembly. The diversity of seed traits and functions provides an important challenge that will require international collaboration in three areas of research. First, we present a conceptual framework for a seed ecological spectrum that builds upon current understanding of plant niches. We then lay the foundation for a seed-trait functional network, the establishment of which will underpin and facilitate trait-based inferences. Finally, we anticipate novel insights and challenges associated with incorporating diverse seed traits into predictive evolutionary ecology, community ecology and applied ecology. If the community invests in standardized seed-trait collection and the implementation of rigorous databases, major strides can be made at this exciting frontier of functional ecology.

Seed dormancy regulates germination response to smoke and temperature in a rhizomatous evergreen perennial.

Seed dormancy status regulates the response of seeds to environmental cues that can trigger germination. Anigozanthos flavidus (Haemodoraceae) produces seeds with morphophysiological dormancy (MPD) that are known to germinate in response to smoke, but embryo growth dynamics and germination traits in response to temperatures and after-ripening have not been well characterized. Seeds of A. flavidus, after-ripened for 28 months at 15 °C/15 % relative humidity, were incubated on water agar, water agar containing 1 µM karrikinolide (KAR1) or 50 µM glyceronitrile at 5, 10, 15, 20, 25, 20/10 and 25/15 °C for 28 days. After incubation at 5, 10 and 25 °C for 28 days, seeds were transferred to 15 °C for another 28 days. Embryo growth dynamics were tested at 5, 10, 15 and 25 °C. Results demonstrated that fresh seeds of A. flavidus had MPD and the physiological dormancy (PD) component could be broken by either glyceronitrile or dry after-ripening. After-ripened seeds germinated to ≥80 % at 15-20 °C while no additional benefit of germination was observed in the presence of the KAR1 or glyceronitrile. Embryo length significantly increased at 10 °C, and only slightly increased at 5 °C, while growth did not occur at 25 °C. When un-germinated seeds were moved from 5-10 °C to 15 °C for a further 28 days, germination increased from 0 to >80 % in significantly less time indicating that cold stratification may play a key role in the germination process during winter and early spring in A. flavidus. The lower germination (<50 %) of seeds moved from 25 to 15 °C was produced by the induction of secondary dormancy. Induction of secondary dormancy in seeds exposed to warm stratification, a first report for Anigozanthos species, suggests that cycling of PD may be an important mechanism of controlling germination timing in the field.

Ecological niche and bet-hedging strategies for Triodia (R.Br.) seed germination.

Background and Aims: Regeneration dynamics in many arid zone grass species are regulated by innate seed dormancy mechanisms and environmental cues (temperature, moisture and fire) that result in infrequent germination following rainfall. This study investigated bet-hedging strategies associated with dormancy and germination in arid zone Triodia species from north-west Australia, by assessing (1) the effects of the mechanical restriction imposed by the indehiscent floral bracts (i.e. floret) covering the seed and (2) the impact of dormancy alleviation on florets and cleaned seeds (i.e. florets removed) when germinated under water stress. Methods: The initial dormancy status and germination for six species were tested on intact florets and cleaned seeds, across temperatures (10-40 °C) with and without the fire-related stimulant karrikinolide (KAR1), and under alternating light or constant dark conditions. Physiological dormancy alleviation was assessed by wet/dry cycling florets over a period of 10 weeks, and germination was compared against untreated florets, and cleaned seeds across a water potential gradient between 0 and -1.5 MPa. Key Results: Florets restricted germination (<45 %) at all temperatures and, despite partial alleviation of physiological dormancy (wet/dry cycling for 8 weeks), intact florets germinated only at high water potentials. Cleaned seeds showed the highest germination (40-90 %) across temperatures when treated with KAR1, and germinated at much lower water potentials (-0.4 and -0.9 MPa). Triodia pungens was the most responsive to KAR1, with both seeds and florets responding, while for the remaining five species, KAR1 had a positive effect for seeds only. Conclusions: Only after seed dormancy was alleviated by removing florets and when KAR1 was applied did germination under water stress increase. This suggests that seeds of these Triodia species are cued to recruit following fire and during periods of high precipitation. Climate change, driven by large shifts in rainfall patterns, is likely to impact Triodia recruitment further in arid zone grasslands.

A review of germination and early growth as a proxy for plant fitness under petrogenic contamination - knowledge gaps and recommendations.

Germination-an important stage in the life cycle of plants-is susceptible to the presence of soil contaminants. Since the early 1990s, the use of germination tests to screen multiple plant species to select candidates for phytoremediation has received much attention. This is due to its inexpensive methodology and fast assessment relative to greenhouse or field growth studies. Surprisingly, no comprehensive synthesis is available of these studies in the scientific literature. As more plant species are added to phytoremediation databases, it is important to encapsulate the knowledge thus far and revise protocols. In this review, we have summarised previously-documented effects of petroleum hydrocarbons on germination and seedling growth. The methods and materials of previous studies are presented in tabulated form. Common practice includes the use of cellulose acetate filter paper, plastic Petri dishes, and low numbers of seeds and replicates. A general bias was observed for the screening of cultivated crops as opposed to native species, even though the latter may be better suited to site conditions. The relevance of germination studies as important ecotoxicological tools is highlighted with the proposed use of root imaging software. Screening of novel plant species, particularly natives, is recommended with selection focussed on (i) species phylogeny, (ii) plant morphological and functional traits, and (iii) tolerance towards harsh environmental stresses. Recommendations for standardised protocols for germination and early growth monitoring are made in order to improve the robustness of statistical modelling and species selection in future phytoremediation evaluations and field programs.

Discovery of fairy circles in Australia supports self-organization theory.

Vegetation gap patterns in arid grasslands, such as the "fairy circles" of Namibia, are one of nature's greatest mysteries and subject to a lively debate on their origin. They are characterized by small-scale hexagonal ordering of circular bare-soil gaps that persists uniformly in the landscape scale to form a homogeneous distribution. Pattern-formation theory predicts that such highly ordered gap patterns should be found also in other water-limited systems across the globe, even if the mechanisms of their formation are different. Here we report that so far unknown fairy circles with the same spatial structure exist 10,000 km away from Namibia in the remote outback of Australia. Combining fieldwork, remote sensing, spatial pattern analysis, and process-based mathematical modeling, we demonstrate that these patterns emerge by self-organization, with no correlation with termite activity; the driving mechanism is a positive biomass-water feedback associated with water runoff and biomass-dependent infiltration rates. The remarkable match between the patterns of Australian and Namibian fairy circles and model results indicate that both patterns emerge from a nonuniform stationary instability, supporting a central universality principle of pattern-formation theory. Applied to the context of dryland vegetation, this principle predicts that different systems that go through the same instability type will show similar vegetation patterns even if the feedback mechanisms and resulting soil-water distributions are different, as we indeed found by comparing the Australian and the Namibian fairy-circle ecosystems. These results suggest that biomass-water feedbacks and resultant vegetation gap patterns are likely more common in remote drylands than is currently known.

Soil respiration dynamics in fire affected semi-arid ecosystems: Effects of vegetation type and environmental factors.

Soil respiration (Rs) is the second largest carbon flux in terrestrial ecosystems and therefore plays a crucial role in global carbon (C) cycling. This biogeochemical process is closely related to ecosystem productivity and soil fertility and is considered as a key indicator of soil health and quality reflecting the level of microbial activity. Wildfires can have a significant effect on Rs rates and the magnitude of the impacts will depend on environmental factors such as climate and vegetation, fire severity and meteorological conditions post-fire. In this research, we aimed to assess the impacts of a wildfire on the soil CO2 fluxes and soil respiration in a semi-arid ecosystem of Western Australia, and to understand the main edaphic and environmental drivers controlling these fluxes for different vegetation types. Our results demonstrated increased rates of Rs in the burnt areas compared to the unburnt control sites, although these differences were highly dependent on the type of vegetation cover and time since fire. The sensitivity of Rs to temperature (Q10) was also larger in the burnt site compared to the control. Both Rs and soil organic C were consistently higher under Eucalyptus trees, followed by Acacia shrubs. Triodia grasses had the lowest Rs rates and C contents, which were similar to those found under bare soil patches. Regardless of the site condition (unburnt or burnt), Rs was triggered during periods of higher temperatures and water availability and environmental factors (temperature and moisture) could explain a large fraction of Rs variability, improving the relationship of moisture or temperature as single factors with Rs. This study demonstrates the importance of assessing CO2 fluxes considering both abiotic factors and vegetation types after disturbances such as fire which is particularly important in heterogeneous semi-arid areas with patchy vegetation distribution where CO2 fluxes can be largely underestimated.