African Olive (Olea europaea subsp. cuspidata) as an environmental weed in eastern Australia: a review

African Olive, Olea europaea subsp. cuspidata (Wall. ex G.Don) Cif. (family Oleaceae) is a dense-crowned tree introduced into Australia for horticulture in the mid 19th century. In recent decades, African Olive has become an aggressive woody weed, capable of forming a dense and permanent canopy in a wide range of vegetation types in south-west Sydney and beyond. Characteristics of African Olive invasion in south-west Sydney, and its seed dispersal by frugivorous birds are consistent with experience from Norfolk Island and Hawaii. We use records and aerial photographs from Mount Annan Botanic Garden and other bushland areas in south-west Sydney to describe the invasion stages and impacts of African Olive. The capacity for African Olive to establish in both temperate and subtropical zones, underlie the potential for spread well beyond current distribution in New South Wales. Research is now required to further develop control techniques and ecological restoration strategies for areas of heavy African Olive infestation. Mapping of current locations and a coordinated control strategy for African Olive is required to prevent future permanent loss of native plant diversity

A simple method for simulating drought effects on plants

Drought is expected to increase in frequency and severity in many regions in the future, so it is important to improve our understanding of how drought affects plant functional traits and ecological interactions. Imposing experimental water deficits is key to gaining this understanding, but has been hindered by logistic difficulties in maintaining consistently low water availability for plants. Here, we describe a simple method for applying soil water deficits to potted plants in glasshouse experiments. We modified an existing method (the “Snow and Tingey system”) in order to apply a gradual, moderate water deficit to 50 plant species of different life forms (grasses, vines, shrubs, trees). The method requires less maintenance and manual handling compared to other water deficit methods, so it can be used for extended periods of time and is relatively inexpensive to implement. With only a few modifications, it is possible to easily establish and maintain soil water deficits of differing intensity and duration, as well as to incorporate interacting stress factors. We tested this method by measuring physiological responses to an applied water deficit in a subset of 11 tree/shrub species with a wide range of drought tolerances and water-use strategies. For this subgroup of species, stomatal conductance was 2–17 times lower in droughted plants than controls, although only half of the species (5 out of 11) experienced midday leaf water potentials that exceeded their turgor loss (i.e., wilting) point. Leaf temperatures were up to 8°C higher in droughted plants than controls, indicating that droughted plants are at greater risk of thermal damage, relative to unstressed plants. The largest leaf temperature differences (between droughted and well-watered plants) were in species with high rates of water loss. Rapid osmotic adjustment was observed in leaves of five species when drought stress was combined with an experimental heatwave. These results highlight the potential value of further ecological and physiological experiments utilizing this simple water deficit method to study plant responses to drought stress

Extreme heat increases stomatal conductance and drought-induced mortality risk in vulnerable plant species

Tree mortality during global-change-type drought is usually attributed to xylem dysfunction, but as climate change increases the frequency of extreme heat events, it is necessary to better understand the interactive role of heat stress. We hypothesized that some drought-stressed plants paradoxically open stomata in heatwaves to prevent leaves from critically overheating. We experimentally imposed heat (>40°C) and drought stress onto 20 broadleaf evergreen tree/shrub species in a glasshouse study. Most well-watered plants avoided lethal overheating, but drought exacerbated thermal damage during heatwaves. Thermal safety margins (TSM) quantifying the difference between leaf surface temperature and leaf critical temperature, where photosynthesis is disrupted, identified species vulnerability to heatwaves. Several mechanisms contributed to high heat tolerance and avoidance of damaging leaf temperatures—small leaf size, low leaf osmotic potential, high leaf mass per area (i.e., thick, dense leaves), high transpirational capacity, and access to water. Water-stressed plants had smaller TSM, greater crown dieback, and a fundamentally different stomatal heatwave response relative to well-watered plants. On average, well-watered plants closed stomata and decreased stomatal conductance (gs) during the heatwave, but droughted plants did not. Plant species with low gs, either due to isohydric stomatal behavior under water deficit or inherently low transpirational capacity, opened stomata and increased gs under high temperatures. The current paradigm maintains that stomata close before hydraulic thresholds are surpassed, but our results suggest that isohydric species may dramatically increase gs (over sixfold increases) even past their leaf turgor loss point. By actively increasing water loss at high temperatures, plants can be driven toward mortality thresholds more rapidly than has been previously recognized. The inclusion of TSM and responses to heat stress could improve our ability to predict the vulnerability of different tree species to future droughts

School Microclimates

Outdoor school environments need to be safe, stimulate physical and cognitive development of children and encourage learning. These key requirements are jeopardised by increasing summer heat. Summer heat limits outdoor activities and has adverse effects on physical wellbeing of school children and teachers. Children are particularly vulnerable to heat as they regulate their core temperature through convection, which becomes less effective when it is hot. Based on empirical data collections, this report provides more than 20 practical recommendations on how to reduce the impacts of outdoor heat. Although these recommendations were devised based on work around a public school in Western Sydney, their universal character allows applying them to any school or other urban build infrastructure. Avoiding the use of artificial grass in unshaded spaces, shading black asphalt, allowing natural air flows and using shade materials with highly reflective upper surfaces should be fundamental principles in design and building guidelines for heat-smart schools

Functional distinctiveness of major plant lineages

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106060/1/jec12208.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/106060/2/jec12208-sup-0001-Supp_Info.pd

Rental Insights A COVID-19 Collection

This Collection offers insights from twenty of Australia’s leader academics and thinkers into the survey results of 15,000 Australian rental households. The Collection draws on data from The Australian Rental Housing Conditions Dataset funded by the Australian Research Council in partnership with six Australian universities as well an additional AHURI funded COVID-19 module

Tradeoffs between foliar silicon and carbon-based defences: evidence from vegetation communities of contrasting soil types

Silica is ubiquitous in plants and can constitute up to 10% of plant dry mass, varying with phylogeny and soil silicon availability. Plant silicon is an important alleviator of abiotic (salinity, heavy metal, drought) and biotic (herbivore and fungal pathogen) stress. As well as playing an important role in reducing the impact of abiotic stresses, silicon may be an alternative to carbon-based and other chemical defences. Knowledge of silicon function is predominantly derived from agricultural species and model systems. We investigated the abundance and role of plant silicon at a community level by comparing leaf silicon concentration with defence chemicals, carbon compound concentrations and invertebrate assemblages in vegetation communities from two different soil types with contrasting levels of plant available silicon. We found that the concentrations of silicon in the leaves did not reflect the silicon availability in the soil at a community level. The leaf silica concentration range in the vegetation communities was comparable to other diverse communities reported in the literature, suggesting that the species rather than the environment determine leaf silica concentration. Across sites, leaf silica concentration was significantly negatively correlated with concentrations of carbon, total phenols and weakly with tannins but not with other measured defence compounds. Leaf silica concentration was also negatively correlated with Coleoptera abundance, but not the abundance of any other invertebrate groups measured. Our results suggest that tradeoffs exist between phenolic- and tannin-based defences and provide evidence that leaf silicification may be a more effective defence against some chewing herbivore groups than others

Is plant ecology more siliceous than we realise?

Although silicon occurs in all plants, it is an element that is largely overlooked by many plant ecologists and most plant-related research on silicon comes from agronomy, archaeology, palaeontology and biogeochemistry. Plant silicon has many functions, acting biochemically as silicic acid and physically as amorphous silica. It contributes to cell and plant strength and enables plants to respond adaptively to environmental stresses. Consequently, plant silicon can increase plant fitness in many fundamental aspects of ecology, including plant–herbivore interactions, light interception, pathogen resistance and alleviation of abiotic stresses. Here, we provide an ecological perspective to research outcomes from diverse disciplines, showing that silicon is an important element in plant ecology that is worthy of greater attention

Alleviation of abiotic stress by silicon: what can a meta-analysis of agricultural studies tell us about ecology?

We have little idea if silicon has a large or small role in alleviating plant stress in ecology. Using predominantly agricultural taxa, hundreds of single-species studies have demonstrated the facility of silicon (Si) to alleviate diverse abiotic stresses in plants. Knowledge of the mechanisms of Si-mediated stress alleviation is progressing, but a quantitative assessment of the alleviative capacity of Si, which could elucidate plant Si function more broadly, was lacking. We combined the results of 145 experiments to statistically assess the responses of stressed plants to Si supply across multiple plant families and abiotic stresses. We interrogated our database to determine whether stressed plants increased in dry mass and net assimilation rate, oxidative stress markers were reduced, antioxidant responses were increased and whether element uptake showed consistent changes when supplied with Si. Similarities in responses across families provide strong support for a role of Si in the alleviation of abiotic stress in natural systems. We suggest this role may become more important under a changing climate and discuss where we should go from here