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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. [ABSTRACT FROM AUTHOR]

Abstract: Restoration of degraded arid and semi‐arid land faces the challenge of reinstating vegetation communities exposed to limited and variable rainfall events that in combination with a deficit of original topsoil may exceed thresholds for seedling development. In a series of glasshouse experiments, we evaluated variation in drought responses of (i) 21 arid zone plant species from the mining intensive Pilbara region of Western Australia in an original topsoil substrate and (ii) four selected species (Acacia inaequilatera, Acacia spondylophylla, Eucalyptus leucophloia and Triodia epactia) in three different soil substrates (topsoil, overburden material and a blend of both soil materials) that may be considered as an alternative substrate for restoration. Seedling drought responses were tested using ecophysiological indicators (e.g. stomatal conductance and leaf water potential (Ψleaf) at the time of stomatal closure, among others) during soil drying. Our results showed that plant life form and morphological traits interact with ecophysiological indicators to show that trees are significantly less tolerant to drought‐related stress than shrubs and herbs (p ≤ 0·05). When grown in overburden material seedlings experienced a decline in overall plant growth (87% in T. epactia and 62% in E. leucophloia) and ecophysiological drought tolerance. These responses are evidence of the low quality of the overburden substrate, which has a depleted nutrient content and low water retention capacity. Overall, this study highlights the sensitivity of early seedling development and the importance of facilitating seedling recruitment and survival to secure successful arid zone restoration. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Demographic recruitment processes, such as seed germination and seedling emergence, are critical transitional phases to the re-establishment of degraded plant populations, but often fail due to rainfall not supporting plant requirements. Using species from the widespread arid Australian perennial grass genus Triodia, we investigated the interactions of seeds in different dormancy states and their functional germination envelope in response to water stress after simulated pulse rainfall events., Seed dormancy was alleviated in Triodia species to varying degrees by wet/dry cycling or by removing floret structures from seeds. The seeds were then exposed to different rainfall frequency and quantity events mimicking the 25th, median, 75th and 95th percentile rainfall events found in natural habitats for the study species in the north-west Australian arid zone., Under 95th percentile rainfall conditions recruitment was highest, but still limited to 35% germination and 10% emergence of cleaned seeds (i.e. the least dormant state evaluated). This was related to the functional germination envelope as indicated by more negative base water potential thresholds (Ψb50) for cleaned seeds (≥ −0·33 MPa) compared to intact florets (≥ −0·26 MPa). As a result, the maximum cumulative time where soil water potentials were optimal for germination (Ψsoil ≥ Ψb50) was 1·6-2·6 times longer for cleaned seeds in large frequent rainfall events when compared to intact florets. Furthermore, seed dormancy, that usually prolongs seed survival, was linked to a short-term reduction in seed viability, which may further reduce recruitment rates., Synthesis and applications. Our findings indicate that large frequent rainfall events raised soil water potentials above critical thresholds for germination and are important for successful plant establishment. If recruitment bottlenecks are a result of seed dormancy and variable rainfall for arid grass species, then this study shows benefits for alleviating seed dormancy prior to seeding in restoration sites, as this increases the environmental envelope for germination. [ABSTRACT FROM AUTHOR]

Topsoil replacement is a standard procedure in restoration of mined landscapes as it provides a source of propagules via the soil seed bank, as well as provides favourable physical, chemical and microbiological properties for plant establishment. With the availability of topsoil frequently limited in mining, soil cover designs that maximise the use of this resource across the newly-created surfaces after mining should be considered. In this paper, we examine the use of different soil covers and their influence on seedling recruitment for restoration of a Threatened Ecological Community (TEC) with limited topsoil. The properties of a standard topsoil and topsoil diluted with waste-rock to optimise spread were compared between two topsoil sources with different textures and a fine-textured waste material that is a mining by-product. We studied the physicochemical and hydrological traits of five soil covers (unblended TEC topsoil; TEC topsoil mixed with waste rock; fines; fines mixed with waste rock, and waste rock) with two TEC topsoil sources (plateau and hillslope). Soil characterisation included texture, gravel content, soil surface crust strength, soil moisture and temperature, and surface infiltration. Finally, we quantified seedling emergence for four key taxa sown ( Acacia acuminata, Allocasuarina acutivalvis , Melaleuca nematophylla, Waitzia nitida ) and the seedling community arising from the topsoil seedbank and naturally dispersed seeds, and related this emergence with the soil properties. The standard topsoil cover promoted the greatest seedling emergence showing marked differences between the two topsoil provenances. Importantly, the addition of waste rock to topsoil did not compromise the ability of topsoil to support seedling emergence and is therefore a useful strategy to maximise this resource. Overall, our results show the importance of hydrological properties of soil covers for seedling recruitment and highlight the importance of topsoil selection in restoration success. [ABSTRACT FROM AUTHOR]