John Scott

The ecophysiology of seed persistence: a mechanistic view of the journey to germination or demise

Seed persistence is the survival of seeds in the environment once they have reached maturity. Seed persistence allows a species, population or genotype to survive long after the death of parent plants, thus distributing genetic diversity through time. The ability to predict seed persistence accurately is critical to inform long‐term weed management and flora rehabilitation programs, as well as to allow a greater understanding of plant community dynamics. Indeed, each of the 420000 seed‐bearing plant species has a unique set of seed characteristics that determine its propensity to develop a persistent soil seed bank. The duration of seed persistence varies among species and populations, and depends on the physical and physiological characteristics of seeds and how they are affected by the biotic and abiotic environment. An integrated understanding of the ecophysiological mechanisms of seed persistence is essential if we are to improve our ability to predict how long seeds can survive in soils, both now and under future climatic conditions. In this review we present an holistic overview of the seed, species, climate, soil, and other site factors that contribute mechanistically to seed persistence, incorporating physiological, biochemical and ecological perspectives. We focus on current knowledge of the seed and species traits that influence seed longevity under ex situ controlled storage conditions, and explore how this inherent longevity is moderated by changeable biotic and abiotic conditions in situ, both before and after seeds are dispersed. We argue that the persistence of a given seed population in any environment depends on its resistance to exiting the seed bank via germination or death, and on its exposure to environmental conditions that are conducive to those fates. By synthesising knowledge of how the environment affects seeds to determine when and how they leave the soil seed bank into a resistance–exposure model, we provide a new framework for developing experimental and modelling approaches to predict how long seeds will persist in a range of environments.

Current and projected global distribution of Phytophthora cinnamomi, one of the world's worst plant pathogens

Globally, Phytophthora cinnamomi is listed as one of the 100 worst invasive alien species and active management is required to reduce impact and prevent spread in both horticulture and natural ecosystems. Conversely, there are regions thought to be suitable for the pathogen where no disease is observed. We developed a climex model for the global distribution of P.xa0cinnamomi based on the pathogens response to temperature and moisture and by incorporating extensive empirical evidence on the presence and absence of the pathogen. The climex model captured areas of climatic suitability where P.xa0cinnamomi occurs that is congruent with all available records. The model was validated by the collection of soil samples from asymptomatic vegetation in areas projected to be suitable by the model for which there were few records. DNA was extracted, and the presence or absence of P.xa0cinnamomi was determined by high-throughput sequencing (HTS). While not detected using traditional isolation methods, HTS detected P.xa0cinnamomi at higher elevations in eastern Australia and central Tasmania as projected by the climex model. Further support for the climex model was obtained using the large data set from south-west Australia where the proportion of positive records in an area is related to the Ecoclimatic Index value for the same area. We provide for the first time a comprehensive global map of the current P.xa0cinnamomi distribution, an improved climex model of the distribution, and a projection to 2080 of the distribution with predicted climate change. This information provides the basis for more detailed regional-scale modelling and supports risk assessment for governments to plan management of this important soil-borne plant pathogen.

Translocation or bust! A new acclimatization agenda for the 21st century?

There is little doubt that the species most at risk of extinction from rapid climate change are short-range endemics facing insurmountable dispersal barriers to potentially suitable alternative regions. Thomas [1] proposes that the only hope of avoiding extinction for these species is to undertake planned translocations. He argues that the benefits of translocation will outweigh the associated risks where translocations take place within the same broad geographic area and where the recipient areas lack local endemics [1].

Impact of insects and fungi on doublegee (Emex australis) in the Western Australian wheatbelt.

Biotic influences on doublegee(Emex australis Steinheil) seed production wereinvestigated as a precursor to the introduction of new insect biologicalcontrol agents for this weed, and to investigate the cause of doublegeedecline in the northern and central wheatbelt of Western Australia since 1990.The symptoms of the decline are doublegee plants of reduced size withdistorted leaves, collapsed stems, and smaller achenes(the spiny seed-bearing fruit) that crumble when mature.Three sites were investigated in 1992 by surveys for insects and fungi, andinsect and fungus exclusion experiments. Emex stem blight (Phomopsis emicis R. G. Shivas) waspresent at the 3 study sites. The Watheroo site had comparatively high levelsof dock aphids (Brachycaudus rumexicolens Patch) ondoublegee plants, the Badgingarra site had a comparatively high density ofdock sawfly (Lophyrotoma analis Costa) on doublegee, andvery few insects were present on doublegee at the Wongan Hills site. Viruseswere not detected in samples of plants showing the effects of decline. The exclusion experiment showed a significant effect of removing insects andfungi on achene dry weight at the Watheroo site. There was no treatment effectat the Badgingarra and Wongan Hills sites. The biology of the fungus and theaphid lead to the conclusion that the primary cause of doublegee decline isthe dock aphid. This indicates that biological control againstE. australis might be achieved by using insects thatindirectly affect seed quality.

A conceptual model to describe the decline of European blackberry (Rubus anglocandicans), a weed of national significance in Australia

Human activities have had an adverse impact on ecosystems on a global scale and have caused an unprecedented redispersal of organisms, with both plants and pathogens moving from their regions of origin to other parts of the world. Invasive plants are a potential threat to ecosystems globally, and their management costs tens of billions of dollars per annum. Rubus anglocandicans (European blackberry) is a serious invasive species in Australia. Herbicide and cultural control methods are generally inefficient or require multiple applications. Therefore, a biological control program using stem and leaf rust strains is the main option in Australia. However, biological control using rusts has been patchy, as host factors, climate, and weather can alter the impact of the rust at different locations. In 2007, Yeoh and Fontanini noticed that blackberry plants on the banks of the Donnelly and Warren rivers in the southwest of Western Australia were dying in areas that were being regularly monitored for the impact of rust as a biological control agent. The symptoms on blackberry became known as the disease blackberry decline. Continuous and intensive investigations are required to discover the different biotic and abiotic components associated with specific declines in plant populations. The only agent so far introduced to Australia for the biological control of blackberry is the rust Phragmidium violaceum.

Human-mediated introduction of Livistona palms into central Australia: Conservation and management implications

Molecular phylogenies and their application to biogeographic questions, as illustrated by Kondo et al. [[1][1]] in their study of Livistona palms in Australia, are providing unprecedented insight into speciation and the historical movement of taxa around the world [[2][2]]. While such studies often

Zero-tolerance biosecurity protects high-conservation-value island nature reserve

Barrow Island, north-west coast of Australia, is one of the world’s significant conservation areas, harboring marsupials that have become extinct or threatened on mainland Australia as well as a rich diversity of plants and animals, some endemic. Access to construct a Liquefied Natural Gas (LNG) plant, Australia’s largest infrastructure development, on the island was conditional on no non-indigenous species (NIS) becoming established. We developed a comprehensive biosecurity system to protect the island’s biodiversity. From 2009 to 2015 more than 0.5 million passengers and 12.2 million tonnes of freight were transported to the island under the biosecurity system, requiring 1.5 million hrs of inspections. No establishments of NIS were detected. We made four observations that will assist development of biosecurity systems. Firstly, the frequency of detections of organisms corresponded best to a mixture log-normal distribution including the high number of zero inspections and extreme values involving rare incursions. Secondly, comprehensive knowledge of the island’s biota allowed estimation of false positive detections (62% native species). Thirdly, detections at the border did not predict incursions on the island. Fourthly, the workforce detected more than half post-border incursions (59%). Similar approaches can and should be implemented for all areas of significant conservation value.

Combining asset- and species-led alien plant management priorities in the world’s most intact Mediterranean-climate landscape

AbstractnMinimising the spread and impact of alien plants is a crucial component of land management for biodiversity conservation. Alien plant management typically focuses on either controlling selected alien species (‘species-led’), or on minimizing invasions within selected biodiversity or cultural assets (‘asset-led’). Here, we compare and combine species- and asset-led approaches to prioritise alien plant management activities in the world’s largest Mediterranean-climate woodland, located in south-western Australia. Our species-led approach focused on identifying aliens likely to be increasingly problematic in future with a changing climate. Our asset-led approach used comprehensive flora survey data to identify key predictors of contemporary alien presence, with the purpose of minimising alien occurrence across the asset of a relatively little-disturbed landscape. Most aliens were associated with climates more mesic than are predicted to occur in the region in future. A limited range of alien taxa (12xa0%) are predicted to be both highly invasive in the future and feasibly eradicated or contained, and it is these that should be subject to species-led management. A consistent set of management-related predictors of contemporary alien presence were identified, including closer proximity to towns, buildings and water points, and occurrence on a geology and soil type associated with prospective mineral deposits. Addressing the highest management priorities of each approach would appear to be a complementary and parsimonious way forward for regional-scale alien management for biodiversity conservation, as this tackles the processes associated with contemporary alien spread (asset-led approach) while taking a precautionary approach to pre-empt future problematic invasions (species-led approach).

Weeds in Australian Arid Regions

Spread across the vast landscapes that geographically dominate Australia’s arid interior are over 400 alien plant species making up between 0 and 9.7% of the flora, depending on the region being considered. Few of these introductions are genuinely invasive species, and an even smaller proportion is documented as having a negative impact on their local ecosystem. However, those negative impacts that do occur are far ranging and difficult to manage, because of the distances and remoteness of the area, a lack of economic incentives for control, and contention regarding the economic, environmental and social benefits and costs of some species. Management of the weeds of arid regions must involve all aspects of the biosecurity continuum, including quarantine and containment. Depending on the size of invaded areas and the particular species, options can include mechanical control, herbicide applications, fire and grazing in various combinations and biological control. Management will need to respond to changes in climate with research required into adaptive responses.

Host range and potential distribution of the rust fungus, Miyagia pseudosphaeria, a biological control agent for Sonchus species

Sonchus species (Sowthistles) have a world-wide distribution and are serious weeds of crops and the environment. We assessed the suitability of the rust, Miyagia pseudosphaeria, for use in biological control of Sonchus species in Australia and elsewhere. Testing of a limited range of plant species showed the host-range of the rust to be restricted to Sonchus species. We measured spore germination and development of the rust on the host plant in relation to temperature. These measurements, the biology and distribution of the rust, and that of the host S. oleraceus, were used to model the potential world distribution of the rust in CLIMEX. The model indicated that there was limited potential for further spread in Australia; the rust already being widespread. The rust is not present in Canada, but the CLIMEX model indicated that cold temperature will be the main limiting factor for the rust should it be introduced, compromising its suitability as a biological control agent. In South America the rust could potentially be introduced as a biological control agents in areas with Mediterranean and subtropical climate. Molecular studies in combination with more comprehensive inoculation and temperature studies are needed to establish if there are pathotypes of the rust that might be more suitable for use in biological control.