Spatiotemporal variation in ecophysiological traits align with high resolution niche modelling in the short-range banded ironstone endemic Aluta quadrata.

Defining plant ecophysiological responses across natural distributions enables a greater understanding of the niche that plants occupy. Much of the foundational knowledge of species' ecology and responses to environmental change across their distribution is often lacking, particularly for rare and threatened species, exacerbating management and conservation challenges. Combining high-resolution species distribution models (SDMs) with ecophysiological monitoring characterized the spatiotemporal variation in both plant traits and their interactions with their surrounding environment for the range-restricted Aluta quadrata Rye & Trudgen, and a common, co-occurring generalist, Eremophila latrobei subsp. glabra (L.S.Sm.) Chinnock., from the semi-arid Pilbara and Gascoyne region in northwest Western Australia. The plants reflected differences in gas exchange, plant health and plant water relations at sites with contrasting suitability from the SDM, with higher performance measured in the SDM-predicted high-suitability site. Seasonal differences demonstrated the highest variation across ecophysiological traits in both species, with higher performance in the austral wet season across all levels of habitat suitability. The results of this study allow us to effectively describe how plant performance in A. quadrata is distributed across the landscape in contrast to a common, widespread co-occurring species and demonstrate a level of confidence in the habitat suitability modelling derived from the SDM in predicting plant function determined through intensive ecophysiology monitoring programmes. In addition, the findings also provide a baseline approach for future conservation actions, as well as to explore the mechanisms underpinning the short-range endemism arid zone systems.

Local adaptation to climate inferred from intraspecific variation in plant functional traits along a latitudinal gradient.

Ascertaining the traits important for acclimation and adaptation is a critical first step to predicting the fate of populations and species facing rapid environmental change. One of the primary challenges in trait-based ecology is understanding the patterns and processes underpinning functional trait variation in plants. Studying intraspecific variation of functional traits across latitudinal gradients offers an excellent in situ approach to assess associations with environmental factors, which naturally covary along these spatial scales such as the local climate and soil profiles. Therefore, we examined how climatic and edaphic conditions varied across a ~160-km latitudinal gradient to understand how these conditions were associated with the physiological performance and morphological expression within five spatially distinct populations spanning the latitudinal distribution of a model species (Stylidium hispidum Lindl.). Northern populations had patterns of trait means reflecting water conservation strategies that included reduced gas exchange, rosette size and floral investment compared to the southern populations. Redundancy analysis, together with variance partitioning, showed that climate factors accounted for a significantly greater portion of the weighted variance in plant trait data (22.1%; adjusted R2 = 0.192) than edaphic factors (9.3%; adjusted R2 = 0.08). Disentangling such independent and interactive abiotic drivers of functional trait variation will deliver key insights into the mechanisms underpinning local adaptation and population-level responses to current and future climates.

Same, same, but different: dissimilarities in the hydrothermal germination performance of range-restricted endemics emerge despite microclimatic similarities.

Seed germination responses for most narrow-range endemic species are poorly understood, imperilling their conservation management in the face of warming and drying terrestrial ecosystems. We quantified the realized microclimatic niches and the hydrothermal germination thresholds in four threatened taxa (Tetratheca erubescens, Tetratheca harperi, Tetratheca paynterae subsp. paynterae and Tetratheca aphylla subsp. aphylla) that are restricted to individual Banded Ironstone Formations in Western Australia. While T. aphylla subsp. aphylla largely failed to germinate in our trials, all other species demonstrated extended hydrothermal time accumulation (186-500°C MPa days), cool minimum temperatures (7.8-8.5°C), but broad base water potential thresholds (-2.46 to -5.41 MPa) under which germination occurred. These slow germination dynamics are suggestive of cool and wet winter months, where soil moisture is retained to a greater capacity in local microsites where these species occur, rather than the warmer and drier conditions in the surrounding arid environment. Hydrothermal time-to-event modelling showed that each species occupied unique hydrothermal germination niches, which correspond with the microclimatic differences the species are exposed to. Our results provide a baseline understanding for environmental and germination thresholds that govern the recruitment, and ultimately the population structure and persistence, of these short-range endemic plants. In addition, our results can aid future conservation, as well as restoration actions such as translocation to bolster population numbers and to mitigate against losses due to anthropogenic disturbance and global environmental change.

Soil moisture and temperature drive emergence delays associated with fire seasonality in eucalypt forests.

Many ecosystems are well adapted to fire, although the impacts of fire seasonality and its effect on post-fire recruitment are less well understood. Late summer or autumn fires within eucalypt forests with a Mediterranean-type climate allow for seedling emergence during the cooler and wetter seasons. The emergence and survival after spring fires may be impacted by higher soil temperatures and water stress, delaying recruitment until the subsequent winter period. During this delay, seeds may be exposed to predation and decay, which reduce the viable seed bank. This study examines post-fire recruitment dynamics in a eucalypt forest ecosystem (Northern Jarrah Forest (NJF) of southwestern Western Australia) and whether it may be vulnerable to human-induced changes to fire season. Here, we compare in situ post-fire seedling emergence patterns between autumn and spring burns and account for a potential ecological mechanism driving seasonal differences in emergence by determining the thermal germination requirements of seeds for 15 common species from the NJF. Our results demonstrate that 93% of species had thermal optima between 10°C and 20°C, analogous with soil temperatures measured during the germination window (late April to October). Concurrent in situ post-fire emergence was highest 144 days after an autumn (seasonal) fire, followed by a 10-72% decline. In contrast, there was no emergence within the first 200 days following a spring (aseasonal) fire. We conclude that aseasonal fire in the NJF can lead to a complete delay in recruitment in the first season post-fire, resulting in a lower inter-fire growth period and increasing the potential for further reductions in recruitment through seed predation and decay. The study suggests that aseasonal fire has an immediate and significant impact on initial recruitment in the NJF, but further research is required to determine any longer-term effects of this delay and its implications for fire management in southwestern Western Australia.

Germination physiology of Cochlospermum fraseri (Bixaceae), a deciduous tree from Northern Australia with physical seed dormancy.

Cochlospermum fraseri ('Kapok', Bixaceae) is a deciduous tree widely distributed throughout semi-arid and monsoon tropical northern Australia, and an important species for ecological restoration in the region. We aimed to better understand the seed biology and ecology of C. fraseri to determine the mechanisms by which seed dormancy might be alleviated, and the conditions that support germination to inform the use of this species in restoration. Dormancy breaking treatments (wet heat, dry heat, scarification) commonly applied to species with physical seed dormancy (PY) were tested along with stratification at 5-35°C (nine treatments). Following dormancy alleviation, seeds were germinated at nine temperatures (5 to 40°C) and five water potentials (0 to -0.8 MPa) to understand environmental thresholds that regulate germination physiology in non-dormant seeds. A proportion of seeds (<0.3) lose dormancy naturally in response to warm (25 to 35°C) moist conditions, which dislodges the hypostase plug that prevents water uptake, whilst neither dry (≥100°C) nor wet (~100°C) heat were effective. Dormancy loss was also achieved by exposing seeds to concentrated (95-98% v/v) sulphuric acid for 3-7 hours, after which high proportions (>0.75) of germination were observed. Cochlospermum fraseri seeds possess PY, which is alleviated by seasonal temperatures that occur when soil moisture is high, allowing seeds to employ a risk-adverse strategy and maximize establishment success in episodic environments with stochastic rainfall events. The understanding of dormancy alleviation requirements gained here adds to our knowledge of PY worldwide and recruitment dynamics in the Australian monsoonal tropics and will aid land managers and restoration practitioners by informing both seeding sites and optimal time for in situ sowing as well as the potential capacity of this species to form a persistent soil seed bank.

Integrating animal physiology into the adaptive management of restored landscapes.

Global-scale ecological changes and intensifying habitat destruction and have caused alarming declines in wildlife populations, resulting in a great need for concerted efforts towards their conservation. Despite this, animals are frequently overlooked in restoration and management initiatives and therefore populations often do not reassemble following disturbance without re-establishing habitat that meets their abiotic and biotic requirements. However, restoration ecologists broadly lack insight into the physiological mechanisms that can govern the responses of fauna to environmental change and management. Therefore, we conducted a literature search for studies reporting a mechanistic understanding of faunal habitat suitability and selection in restored landscapes to deliver an updated perspective on the integration of animal ecophysiology and restoration ecology. Of the 75,442 studies that we identified discussing ecological restoration in the last 50 years, only 8,627 (11.4%) did so in the context of fauna from which 912 studies (1.2%) examined habitat selection, 35 studies (0.05%) integrated physiology and only 15 studies (0.02%) explored thermal biology, despite temperature being one of the most pervasive drivers of physiological functioning. To combat this, we developed a conceptual framework that can guide restoration ecophysiology and promote innovative, multidisciplinary research through an established adaptive management structure. While physiological tools and approaches are currently underutilised in restoration practice, integrating them into ecological restoration, and environmental management more broadly, will offer exciting new opportunities to describe, explain and predict the responses of fauna to environmental change occurring, and that yet to come.

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.

High-resolution distribution modeling of a threatened short-range endemic plant informed by edaphic factors.

Short-range endemic plants often have edaphic specializations that, with their restricted distributions, expose them to increased risk of anthropogenic extinction.Here, we present a modeling approach to understand habitat suitability for Ricinocarpos brevis R.J.F.Hend. & Mollemans (Euphorbiaceae), a threatened shrub confined to three isolated populations in the semi-arid south-west of Western Australia. The model is a maximum entropy species distribution projection constructed on the basis of physical soil characteristics and geomorphology data at approximately 25 m2 (1 arc-second) resolution.The model predicts the species to occur on shallow, low bulk density soils that are located high in the landscape. The model shows high affinity (72.1% average likelihood of occurrence) for the known populations of R. brevis, as well as identifying likely locations that are not currently known to support the species. There was a strong relationship between the likelihood of R. brevis occurrence and soil moisture content that the model estimated at a depth of 20 cm.We advocate that our approach should be standardized using publicly available data to generate testable hypotheses for the distribution and conservation management of short-range endemic plant species for all of continental Australia.

The risk-takers and -avoiders: germination sensitivity to water stress in an arid zone with unpredictable rainfall.

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.

Lower dormancy with rapid germination is an important strategy for seeds in an arid zone with unpredictable rainfall.

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.

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.

Measuring metabolic rates of small terrestrial organisms by fluorescence-based closed-system respirometry.

We explore a recent, innovative variation of closed-system respirometry for terrestrial organisms, whereby oxygen partial pressure (PO2 ) is repeatedly measured fluorometrically in a constant-volume chamber over multiple time points. We outline a protocol that aligns this technology with the broader literature on aerial respirometry, including the calculations required to accurately convert O2 depletion to metabolic rate (MR). We identify a series of assumptions, and sources of error associated with this technique, including thresholds where O2 depletion becomes limiting, that impart errors to the calculation and interpretation of MR. Using these adjusted calculations, we found that the resting MR of five species of angiosperm seeds ranged from 0.011 to 0.640 ml g-1 h-1, consistent with published seed MR values. This innovative methodology greatly expands the lower size limit of terrestrial organisms that can be measured, and offers the potential for measuring MR changes over time as a result of physiological processes of the organism.

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.

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.