Water availability is a critical driver of population dynamics in arid zones, and plant recruitment is typically episodic in response to rainfall. Understanding species’ germination thresholds is key for conservation and restoration initiatives. Thus, we investigated the role of water availability in the germination traits of keystone species in an arid ecosystem with stochastic rainfall. We measured seed germination responses of five arid species, along gradients of temperature and water potential under controlled laboratory conditions. We then identified the cardinal temperatures and base water potentials for seed germination, and applied the hydrotime model to assess germination responses to water stress. Optimum temperatures for germination ranged from 15 to 31 °C under saturated conditions (0 MPa), and three species had low minimum temperatures for germination (<3 °C). A small proportion of seeds of all species germinated under dry conditions (Ψ ≤ −1 MPa), although base water potential for germination (Ψ b50) ranged from −0.61 to −0.79 MPa. Species adhered to one of two germination traits: (i) the risk-takers which require less moisture availability for germination, and which can germinate over a wider range of temperatures irrespective of water availability (Casuarina pauper and Maireana pyramidata), and (ii) the risk-avoiders which have greater moisture requirements, a preference for cold climate germination, and narrower temperature ranges for germination when water availability is low (Atriplex rhagodioides, Maireana sedifolia and Hakea leucoptera). High seed longevity under physiological stress in H. leucoptera, combined with a risk-avoiding strategy, allows bet-hedging. The hydrotime model predicted lower base water potentials for germination than observed by the data, further supporting our assertion that these species have particular adaptations to avoid germination during drought. This study provides insights into the complex physiological responses of seeds to environmental stress, and relates seed germination traits to community dynamics and restoration in arid zones.
15Lower dormancy with rapid germination for arid seeds 2 16 Abstract 17 Seed germination traits are key drivers of population dynamics, yet they are under-18 represented in community ecology studies, which have predominately focussed on adult plant 19 and seed morphological traits. We studied the seed traits and germination strategy of eight 20 woody plant species to investigate regeneration strategies in the arid zone of eastern 21 Australia. To cope with stochastic and minimal rainfall, we predict that arid seeds will either 22 have rapid germination across a wide range of temperatures, improved germination under 23 cooler temperatures, or dormancy and/or longevity traits to delay or stagger germination 24 across time. To understand how temperature affects germination responses, seeds of eight 25 keystone arid species were germinated under laboratory conditions, and under three diurnal 26 temperatures (30/20°C, 25/15°C and 17/7°C) for 30 days. Seeds of species in this study are 27 currently stored for minesite restoration projects, hence we tested for decline in seed viability 28 across 24 months in dry storage at similar storage conditions (≈20°C). Six of the eight arid 29 species studied had non-dormant, rapidly germinating seeds, and only two species had 30 physiological dormancy traits. Seed longevity differed widely between species, from one 31 recalcitrant species surviving only months in storage (P50 = <3 months) and one serotinous 32 species surviving for many years (P50 = 84 months). Our results highlight the importance of 33 understanding the reproductive strategies of plant species in arid environments. Rapid 34 germination, the dominant seed trait of species included in this study, allows arid species to 35 capitalise on sporadic rainfall. However, some species also exhibit dormancy and delayed 36 germination; this an alternative strategy which spreads the risk of germination failure over 37 time. We highlight important seed traits and germination strategies of plants from an arid 38 zone with stochastic rainfall and discuss the implications for their restoration. 39 40 Lower dormancy with rapid germination for arid seeds 3 41 Introduction 42 Seed traits and germination strategies drive plant community dynamics and provide insight 43 into species' adaptations to environmental filters [1] and community composition [2]. Despite 44 this, seed traits are under-represented in community ecology studies [3-5]. Knowledge of 45 seed traits and germination strategies is necessary to describe plant niches, to anticipate 46 population dynamics under changes in land use [6], and to assess plant responses to the 47 environment [7]. By studying seed traits and germination responses we can obtain 48 ecologically meaningful data about the functional properties of plant communities that 49 improve predictions of plant assemblages under natural, and anthropogenic, environmental 50 change [8]. 51Seed traits and germination strategies, which are often unrelated to other plant traits [9], 52 can inform us about the repro...
Seed germination traits are key drivers of population dynamics, yet they are under-represented in community ecology studies, which have predominately focussed on adult plant and seed morphological traits. We studied the seed traits and germination strategy of eight woody plant species to investigate regeneration strategies in the arid zone of eastern Australia. To cope with stochastic and minimal rainfall, we predict that arid seeds will either have rapid germination across a wide range of temperatures, improved germination under cooler temperatures, or dormancy and/or longevity traits to delay or stagger germination across time. To understand how temperature affects germination responses, seeds of eight keystone arid species were germinated under laboratory conditions, and under three diurnal temperatures (30/20°C, 25/15°C and 17/7°C) for 30 days. We also tested for decline in seed viability across 24 months in a dry-aging treatment (~20°C). Six of the eight arid species studied had non-dormant, rapidly germinating seeds, and only two species had physiological dormancy traits. Seed longevity differed widely between species, from one recalcitrant species surviving only months in aging (P50 = <3 months) and one serotinous species surviving for many years (P50 = 84 months). Our results highlight the importance of understanding the reproductive strategies of plant species in arid environments. Rapid germination, the dominant seed trait of species included in this study, allows arid species to capitalise on sporadic rainfall. However, some species also exhibit dormancy and delayed germination; this an alternative strategy which spreads the risk of germination failure over time.
The biogeochemical properties of soils drive ecosystem function and vegetation dynamics, and hence soil restoration after mining should aim to reinstate the soil properties and hydrological dynamics of remnant ecosystems. The aim of this study is to assess soil structure in two vegetation types in an arid ecosystem, and to understand how these soil properties compare to a reconstructed soil profile after mining. In an arid ecosystem in southeast Australia, soil samples were collected at five depths (to 105 cm) from remnant woodland and shrubland sites, and sites either disturbed or totally reconstructed after mining. We assessed soil physico-chemical properties and microbial activity. Soils in the remnant arid ecosystem had coarse-textured topsoils that overlay clay horizons, which allows water to infiltrate and avoid evaporation, but also slows drainage to deeper horizons. Conversely, reconstructed soils had high sand content at subsoil horizons and high bulk density and compaction at surface layers (0-20 cm). Reconstructed soils had topsoils with higher pH and electrical conductivity. The reconstructed soils did not show increased microbial activity with time since restoration. Overall, the reconstructed soil horizons were not organized in a way that allowed rainfall infiltration and water storage, as is imperative to arid-zone ecosystem function. Future restoration efforts in arid ecosystems should focus on increasing sand content of soils near the surface, to reduce evaporative water loss and improve soil quality and plant health.
We study the seed traits and germination strategies of arid plant species to investigate their regeneration strategies and classify seed dormancy. Seeds of eight keystone species were germinated under three dirunal temperatures (30/20C, 25/15C and 17/7C) for 30 days. We also tested for decline in seed viability across 24 months in dry aging, and relieved physiological dormancy in Atriplex through an after-ripening treatment.
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