Signatures of natural selection in a foundation tree along Mediterranean climatic gradients.

Temperature and precipitation regimes are rapidly changing, resulting in forest dieback and extinction events, particularly in Mediterranean-type climates (MTC). Forest management that enhance forests' resilience is urgently required, however adaptation to climates in heterogeneous landscapes with multiple selection pressures is complex. For widespread trees in MTC we hypothesized that: patterns of local adaptation are associated with climate; precipitation is a stronger factor of adaptation than temperature; functionally related genes show similar signatures of adaptation; and adaptive variants are independently sorting across the landscape. We sampled 28 populations across the geographic distribution of Eucalyptus marginata (jarrah), in South-west Western Australia, and obtained 13,534 independent single nucleotide polymorphic (SNP) markers across the genome. Three genotype-association analyses that employ different ways of correcting population structure were used to identify putatively adapted SNPs associated with independent climate variables. While overall levels of population differentiation were low (FST  = 0.04), environmental association analyses found a total of 2336 unique SNPs associated with temperature and precipitation variables, with 1440 SNPs annotated to genic regions. Considerable allelic turnover was identified for SNPs associated with temperature seasonality and mean precipitation of the warmest quarter, suggesting that both temperature and precipitation are important factors in adaptation. SNPs with similar gene functions had analogous allelic turnover along climate gradients, while SNPs among temperature and precipitation variables had uncorrelated patterns of adaptation. These contrasting patterns provide evidence that there may be standing genomic variation adapted to current climate gradients, providing the basis for adaptive management strategies to bolster forest resilience in the future.

qPCR Assays for Sensitive and Rapid Detection of Quambalaria Species from Plant Tissues.

Several species from the genus Quambalaria (order Microstromatales) cause diseases on eucalypts (Eucalyptus and related genera) both in plantations and natural ecosystems. We developed real-time quantitative PCR (qPCR) assays to rapidly detect and distinguish five Quambalaria species. The design of the species-specific qPCR assay for each species, Q. pitereka (PIT), Q. coyrecup (COR), Q. cyanescens (CYN), Q. pusilla (PUS), and Q. eucalypti (EUC), was based on the ITS region and was evaluated for specificity and sensitivity. The PIT, COR, and CYN qPCR assays could amplify as little as 10 fg µl-1 from pure cultures, whereas PUS and EUC qPCR assays could amplify 100 fg µl-1 of their target species. The PIT, COR, and CYN qPCR assays were further validated using naturally and artificially infected samples of their plant host Corymbia calophylla. These assays will be used for rapid diagnostics and future experiments on the infection process.

Underappreciated plant vulnerabilities to heat waves.

With climate change, heat waves are becoming increasingly frequent, intense and broader in spatial extent. However, while the lethal effects of heat waves on humans are well documented, the impacts on flora are less well understood, perhaps except for crops. We summarize recent findings related to heat wave impacts including: sublethal and lethal effects at leaf and plant scales, secondary ecosystem effects, and more complex impacts such as increased heat wave frequency across all seasons, and interactions with other disturbances. We propose generalizable practical trials to quantify the critical bounding conditions of vulnerability to heat waves. Collectively, plant vulnerabilities to heat waves appear to be underappreciated and understudied, particularly with respect to understanding heat wave driven plant die-off and ecosystem tipping points.

Carbon consequences of drought differ in forests that resprout.

Prolonged drought and intense heat-related events trigger sudden forest die-off events and have now been reported from all forested continents. Such die-offs are concerning given that drought and heatwave events are forecast to increase in severity and duration as climate change progresses. Quantifying consequences to carbon dynamics and storage from die-off events are critical for determining the current and future mitigation potential of forests. We took stand measurements five times over 2+ years from affected and unaffected plots across the Northern Jarrah Forest, southwestern Australia, following an acute drought/heatwave in 2011. We found a significant loss of live standing carbon (49.3 t ha-1 ), and subsequently a significant increase in the dead standing carbon pool by 6 months post-die-off. Of the persisting live trees, 38% experienced partial mortality contributing to the rapid regrowth and replenishment (82%-88%) of labile carbon pools (foliage, twigs, and branches) within 26 months. Such regrowth was not substantial in terms of net carbon changes within the timeframe of the study but does reflect the resprouting resilience of this forest type. Dead carbon generated by the die-off may persist for centuries given low fragmentation and decay rates resulting in low biogenic emission rates relative to other forest types. However, future fire may threaten persistence of both dead and live pools via combustion and mortality of live tissue and impaired regrowth capacity. Resprouting forests are commonly regarded as resilient systems, however, a changing climate could see vulnerable portions of forests become carbon sources rather than carbon sinks.

A qPCR Assay for the Detection of Phytophthora cinnamomi Including an mRNA Protocol Designed to Establish Propagule Viability in Environmental Samples.

Phytophthora cinnamomi causes root and collar rot in many plant species in natural ecosystems and horticulture. A species-specific primer and probe PCIN5 were designed based on a mitochondrial locus encoding subunit 2 of cytochrome c oxidase (cox2). Eight PCR primers, including three forward and five reverse, were designed and tested in all possible combinations. Annealing temperatures were optimized for each primer pair set to maximize both specificity and sensitivity. Each set was tested against P. cinnamomi and two closely related clade 7 species, P. parvispora and P. niederhauseri. From these tests, five primer pairs were selected based on specificity and, with a species-specific P. cinnamomi probe, used to develop quantitative real-time PCR (qPCR) assays. The specificity of the two most sensitive qPCR assays was confirmed using the genomic DNA of 29 Phytophthora isolates, including 17 isolates of 11 species from clade 7, and representative species from nine other clades (all except clade 3). The assay was able to detect as little as 150 ag of P. cinnamomi DNA and showed no cross-reaction with other Phytophthora species, except for P. parvispora, a very closely related species to P. cinnamomi, which showed late amplification at high DNA concentrations. The efficiency of the qPCR protocol was evaluated with environmental samples including roots and associated soil from plants artificially infected with P. cinnamomi. Different RNA isolation kits were tested and evaluated for their performance in the isolation of RNA from environmental samples, followed by cDNA synthesis, and qPCR assay. Finally, a protocol was recommended for determining the presence of P. cinnamomi in recalcitrant environmental samples.

Phytophthora Contamination in a Nursery and Its Potential Dispersal into the Natural Environment.

A detailed site investigation of a eucalypt nursery suffering disease losses revealed the causal agent to be Phytophthora boodjera. The pathogen was detected in vegetation surrounding the nursery production area, including the lawn, under the production benches during the growing season, and, most importantly, from plant debris in used trays. However, it was not found in the container substrate, water supplies, or production equipment or on the workers themselves. The sterilization methods used by the nursery were shown to be ineffective, indicating that a more rigorous method was required. Boiling trays for 15 min or steaming at 65°C for 60 min eradicated P. boodjera. This pathogen was more pathogenic to the eucalypts tested in their early seedling stage than P. cinnamomi. Tracing of out-planting to revegetation sites showed that P. boodjera was able to spread into the environment. Dispersal via out-planting to native vegetation may affect seedling recruitment and drive long-term shifts in native plant species. Inadequate nursery hygiene increases the risk of an outbreak and can limit the success of biosecurity efforts as well as damage conservation efforts.

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. cinnamomi based on the pathogen's 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. cinnamomi 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. cinnamomi was determined by high-throughput sequencing (HTS). While not detected using traditional isolation methods, HTS detected P. cinnamomi 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. cinnamomi 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.

Analysis of volatiles from stored wheat and Rhyzopertha dominica (F.) with solid phase microextraction-gas chromatography mass spectrometry.

BACKGROUND: Volatile organic compounds (VOCs) contribute significantly to food flavour and can be used as indicators of quality, age of storage, and hygiene condition of stored products. The VOCs in the headspace of three different samples - healthy wheat, Rhyzopertha dominica, and wheat with R. dominica - were analysed at 25°C by solid phase micro-extraction (SPME) coupled with gas chromatography-flame ionisation detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). All the experimental conditions were kept consistent except a polar column and a non-polar column were used to assess the differences in volatile fingerprints. RESULTS: A total of 114 volatiles were identified by both the polar and non-polar columns, of which 48 were specific to one of the three samples tested. The volatiles were mainly carbonyl chemical compounds such as aldehydes, ketones and alcohols. GC-MS results showed slightly more VOCs were identified from the polar column. The total number for the three samples was 43 from the polar column compared to 39 from the non-polar column. Conversely, 30 VOCs unique to a given sample were identified from the non-polar column compared to 18 from the polar column. CONCLUSION: The use of both polar and non-polar columns is essential to capture the full range of VOCs produced by the three specific sample types investigated. The data can form the basis of enquiry into the relationship between storage and grain quality, and insect infestation and grain quality by observing the impact that these circumstances have on the production of volatile organic compounds.

Do state-and-transition models derived from vegetation succession also represent avian succession in restored mine pits?

State-and-transition models are increasingly used as a tool to inform management of post-disturbance succession and effective conservation of biodiversity in production landscapes. However, if they are to do this effectively, they need to represent faunal, as well as vegetation, succession. We assessed the congruence between vegetation and avian succession by sampling avian communities in each state of a state-and-transition model used to inform management of post-mining restoration in a production landscape in southwestern Australia. While avian communities differed significantly among states classified as on a desirable successional pathway, they did not differ between desirable and deviated states of the same post-mining age. Overall, we concluded there was poor congruence between vegetation and avian succession in this state-and-transition model. We identified four factors that likely contributed to this lack of congruence, which were that long-term monitoring of succession in restored mine pits was not used to update and improve models, states were not defined based on ecological processes and thresholds, states were not defined by criteria that were important in structuring the avian community, and states were not based on criteria that related to values in the reference community. We believe that consideration of these four factors in the development of state-and-transition models should improve their ability to accurately represent faunal, as well as vegetation, succession. Developing state-and-transition models that better incorporate patterns of faunal succession should improve the ability to manage post-disturbance succession across a range of ecosystems for biodiversity conservation.

Suppression of the auxin response pathway enhances susceptibility to Phytophthora cinnamomi while phosphite-mediated resistance stimulates the auxin signalling pathway.

BACKGROUND: Phytophthora cinnamomi is a devastating pathogen worldwide and phosphite (Phi), an analogue of phosphate (Pi) is highly effective in the control of this pathogen. Phi also interferes with Pi starvation responses (PSR), of which auxin signalling is an integral component. In the current study, the involvement of Pi and the auxin signalling pathways in host and Phi-mediated resistance to P. cinnamomi was investigated by screening the Arabidopsis thaliana ecotype Col-0 and several mutants defective in PSR and the auxin response pathway for their susceptibility to this pathogen. The response to Phi treatment was also studied by monitoring its effect on Pi- and the auxin response pathways. RESULTS: Here we demonstrate that phr1-1 (phosphate starvation response 1), a mutant defective in response to Pi starvation was highly susceptible to P. cinnamomi compared to the parental background Col-0. Furthermore, the analysis of the Arabidopsis tir1-1 (transport inhibitor response 1) mutant, deficient in the auxin-stimulated SCF (Skp1 - Cullin - F-Box) ubiquitination pathway was also highly susceptible to P. cinnamomi and the susceptibility of the mutants rpn10 and pbe1 further supported a role for the 26S proteasome in resistance to P. cinnamomi. The role of auxin was also supported by a significant (P < 0.001) increase in susceptibility of blue lupin (Lupinus angustifolius) to P. cinnamomi following treatment with the inhibitor of auxin transport, TIBA (2,3,5-triiodobenzoic acid). Given the apparent involvement of auxin and PSR signalling in the resistance to P. cinnamomi, the possible involvement of these pathways in Phi mediated resistance was also investigated. Phi (especially at high concentrations) attenuates the response of some Pi starvation inducible genes such as AT4, AtACP5 and AtPT2 in Pi starved plants. However, Phi enhanced the transcript levels of PHR1 and the auxin responsive genes (AUX1, AXR1and AXR2), suppressed the primary root elongation, and increased root hair formation in plants with sufficient Pi. CONCLUSIONS: The auxin response pathway, particularly auxin sensitivity and transport, plays an important role in resistance to P. cinnamomi in Arabidopsis, and phosphite-mediated resistance may in some part be through its effect on the stimulation of the PSR and auxin response pathways.

Spatio-temporal water dynamics in mature Banksia menziesii trees during drought.

Southwest Australian Banksia woodlands are highly diverse plant communities that are threatened by drought- or temperature-induced mortality due to the region's changing climate. We examined water relations in dominant Banksia menziesii R. Br. trees using magnetic leaf patch clamp pressure (ZIM-) probes that allow continuous, real-time monitoring of leaf water status. Multiple ZIM-probes across the crown were complemented by traditional ecophysiological measurements. During summer, early stomatal downregulation of transpiration prevented midday balancing pressures from exceeding 2.5 MPa. Diurnal patterns of ZIM-probe and pressure chamber readings agreed reasonably well, however, ZIM-probes recorded short-term dynamics, which are impossible to capture using a pressure chamber. Simultaneous recordings of three ZIM-probes evenly spaced along leaf laminas revealed intrafoliar turgor gradients, which, however, did not develop in a strictly basi- or acropetal fashion and varied with cardinal direction. Drought stress manifested as increasing daily signal amplitude (low leaf water status) and occasionally as rising baseline at night (delayed rehydration). These symptoms occurred more often locally than across the entire crown. Microclimate effects on leaf water status were strongest in crown regions experiencing peak morning radiation (East and North). Extreme spring temperatures preceded the sudden death of B. menziesii trees, suggesting a temperature- or humidity-related tipping point causing rapid hydraulic failure as evidenced by collapsing ZIM-probe readings from an affected tree. In a warmer and drier future, increased frequency of B. menziesii mortality will result in significantly altered community structure and ecosystem function.

Headspace Solid-Phase Microextraction and Gas Chromatography-Mass Spectrometry for Analysis of VOCs Produced by Phytophthora cinnamomi.

Volatile organic compounds (VOCs) from Phytophthora cinnamomi-infected lupin seedlings were collected by headspace solid-phase microextraction (HS-SPME). The sampling was done 28 to 44, 52 to 68, and 76 to 92 h after inoculation (HAI). The HS-SPME samples were analyzed by gas chromatography-flame ionization detector (GC-FID) to assess the differences in volatile compounds between the P. cinnamomi-infected lupin seedlings and the control. Three specific peaks were identified after 52 to 68 h with the infected lupin seedlings, at which time there were no visible aboveground symptoms of infection. Subsequently, the VOCs of five different substrates (V8A, PDA, lupin seedlings, soil, and soil + lupin seedlings) infected with P. cinnamomi and the corresponding controls were analyzed by gas chromatography-mass spectrometry (GC/MS). A total of 87 VOCs were identified. Of these, the five most abundant that were unique to all five inoculated substrates included: 4-ethyl-2-methoxyphenol, 4-ethylphenol, butyrolactone, phenylethyl alcohol, and 3-hydroxy-2-butanone. Therefore, these metabolites can be used as markers for the identification of P. cinnamomi in different growing environments. Some VOCs were specific to a particular substrate; for example, 2,4,6-rrimethyl-heptanes, dl-6-methyl-5-hepten-2-ol, dimethyl trisulfide, 6,10-dimethyl- 5,9-undecadien-2-ol, and 2-methoxy-4-vinylphenol were specific to P. cinnamomi + V8A; heptanes and 5-methyl-3-heptaneone were specific to P. cinnamomi + PDA; 3-methyl-1-butanol, ethyl acetate, 2-methyl-propanoic acid, ethyl ester, and ethyl ester 2-methyl-butanoic acid were specific to P. cinnamomi-inoculated lupin seedlings; and benzyl alcohol and 4-ethyl-1, 2-dimethoxybenzene were only detected in the headspace of inoculated soil + lupin seedlings. Results from this investigation have multiple impacts as the volatile organic profiles produced by the pathogen can be utilized as an early warning system to detect the pathogen from contaminated field soil samples. Data from this investigation have also illuminated potential metabolic pathways utilized by the oomycete during infection which may serve as potential targets for the development of specific control strategies.

Optimization of Headspace Solid-Phase Microextraction Conditions for the Identification of Phytophthora cinnamomi Rands.

A robust technique was developed to identify Phytophthora cinnamomi using headspace solid-phase microextraction (HS-SPME) combined with gas chromatography (GC) coupled to a flame ionization detector (FID) for analyzing volatile organic compounds (VOCs). Six fiber types were evaluated and results indicated that the three-phase fiber 50/30 µm divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) had the highest extraction efficiency for both polar and nonpolar GC columns. The maximum extraction efficiency (equilibrium absorption) was achieved 16 h after fiber exposure in the HS. Absorbed compounds on the fiber were completely desorbed in the GC injector after 5 min at 250°C. Compared with the nonpolar column, the polar column showed optimum separation of VOCs released from P. cinnamomi. Under the optimized HS-SPME and GC/FID conditions, lower detection limits for the four external standards was found to be between 1.57 to 27.36 ng/liter. Relative standard deviations <9.010% showed that the method is precise and reliable. The method also showed good linearity for the concentration range that was analyzed using four standards, with regression coefficients between 0.989 and 0.995, and the sensitivity of the method was 104 times greater than that of the conventional HS method. In this study, the VOC profiles of six Phytophthora spp. and one Pythium sp. were characterized by the optimized HS-SPME-GC method. The combination of the VOCs creates a unique pattern for each pathogen; the chromatograms of different isolates of P. cinnamomi were the same and the specific VOC pattern of P. cinnamomi remained consistently independent of the growth medium used. The chromatograms and morphological studies showed that P. cinnamomi released specific VOCs at different stages of colony development. Using the optimized HS-SPME GC method, identification of P. cinnamomi from 15 in vivo diseased soil samples was as high as 100%. Results from this study demonstrate the feasibility of this method for identifying P. cinnamomi and the potential use of this method for physiological studies on P. cinnamomi.

Acclimation responses of Arabidopsis thaliana to sustained phosphite treatments.

Phosphite (H2PO⁻3) induces a range of physiological and developmental responses in plants by disturbing the homeostasis of the macronutrient phosphate. Because of its close structural resemblance to phosphate, phosphite impairs the sensing, membrane transport, and subcellular compartmentation of phosphate. In addition, phosphite induces plant defence responses by an as yet unknown mode of action. In this study, the acclimation of Arabidopsis thaliana plants to a sustained phosphite supply in the growth medium was investigated and compared with plants growing under varying phosphate supplies. Unlike phosphate, phosphite did not suppress the formation of lateral roots in several Arabidopsis accessions. In addition, the expression of well-documented phosphate-starvation-induced genes, such as miRNA399d and At4, was not repressed by phosphite accumulation, whilst the induction of PHT1;1 and PAP1 was accentuated. Thus, a mimicking of phosphate by phosphite was not observed for these classical phosphate-starvation responses. Metabolomic analysis of phosphite-treated plants showed changes in several metabolite pools, most prominently those of aspartate, asparagine, glutamate, and serine. These alterations in amino acid pools provide novel insights for the understanding of phosphite-induced pathogen resistance.

Seedling mycorrhizal type and soil chemistry are related to canopy condition of Eucalyptus gomphocephala.

The health of Eucalyptus gomphocephala is declining within its natural range in south-western Australia. In a pilot study to assess whether changes in mycorrhizal fungi and soil chemistry might be associated with E. gomphocephala decline, we set up a containerized bioassay experiment with E. gomphocephala as the trap plant using intact soil cores collected from 12 sites with E. gomphocephala canopy condition ranging from healthy to declining. Adjacent soil samples were collected for chemical analysis. The type of mycorrhiza (arbuscular or ectomycorrhizal) formed in containerized seedlings predicted the canopy condition of E. gomphocephala at the sites where the cores were taken. Ectomycorrhizal fungi colonization was higher in seedling roots in soil taken from sites with healthy canopies, whereas colonization by arbuscular mycorrhizal fungi dominated in roots in soil taken from sites with declining canopies. Furthermore, several soil chemical properties predicted canopy condition and the type of mycorrhizal fungi colonizing roots. These preliminary findings suggest that large-scale studies should be undertaken in the field to quantify those ectomycorrhiza (ECM) fungi sensitive to E. gomphocephala canopy decline and whether particular ECM fungi are bioindicators of ecosystem health.

Corn defense responses to nitrogen availability and subsequent performance and feeding preferences of beet armyworm (Lepidoptera: Noctuidae).

Many studies have reported the effect of nitrogen (N) fertilization on plant constitutive defense responses; however, little is known about their effects on plant induced defense patterns and its consequence for insect herbivores. In our experiments, the effects of N availability on growth, nutritional quality (N content, protein/carbohydrate [P:C] ratio, modified gross energy [MGE]), and constitutive phenolics of corn, Zea mays L. were quantified. Moreover, the indirect effects of N fertilization on the beet armyworm, Spodoptera exigua Hübner through larval performance and feeding preference were examined. N fertilization increased plant growth, and depressed defense traits by increasing N content and the P:C ratio, as well as decreasing the constitutive concentration of phenolics. Subsequently, beet armyworm showed higher performance and preferentially fed on high-N corn because of its low defense traits. After beet armyworm feeding, high-N corn significantly deterred larval feeding, and had negative effects on the performance of beet armyworm through decreasing P:C ratio and increasing induced phenolics. On the contrary, there were no significant changes in P:C ratio and phenolics in low-N corn after feeding damage. Larval performance and preference were also not affected by induced compounds in low-N corn, which suggested that the expression of induced defense was dependent on N availability. The result indicates that N availability can exert a variety of bottom-up effect on plant defense patterns to influence insect population dynamics, and thereby may represent a source of variation in plant-insect interactions.

Potassium Phosphonate Induces Resistance in Sweet Chestnut against Ink Disease Caused by Phytophthora Species.

Ink disease, caused by Phytophthora spp., represents a serious threat to sweet chestnuts throughout their distribution area. Among the control strategies, new perspectives have been offered by using potassium phosphonate, which indirectly controls Phytophthora diseases by acting on both host physiology and host-pathogen interactions. In this study, we tested in planta the effectiveness of trunk injection with K-phosphonate against seven different Phytophthora species associated with ink disease. For the two most aggressive species, P. cinnamomi and P. ×cambivora, the treatments were repeated at two different environmental conditions (a mean temperature of 14.5 °C vs. 25 °C) and tree phenology stages. The results obtained in this study demonstrated that K-phosphonate could contain the development of Phytophthora infection in phloem tissues. However, its effectiveness varied based on the concentration applied and the Phytophthora species tested. A concentration of 280 g/L of K-phosphonate was the most effective, and in some cases, callus formation around the necrotic lesion was detected. Overall, this study broadens the knowledge of endotherapic treatments with K-phosphonate as an effective measure for managing chestnut ink disease. Interestingly, the increase in mean temperature had a positive impact on the development of P. cinnamomi lesions on chestnut phloem tissues.

Germination temperature sensitivity differs between co-occurring tree species and climate origins resulting in contrasting vulnerability to global warming.

Climate change is shifting temperatures from historical patterns, globally impacting forest composition and resilience. Seed germination is temperature-sensitive, making the persistence of populations and colonization of available habitats vulnerable to warming. This study assessed germination response to temperature in foundation trees in south-western Australia's Mediterranean-type climate forests (Eucalyptus marginata (jarrah) and Corymbia calophylla (marri)) to estimate the thermal niche and vulnerability among populations. Seeds from the species' entire distribution were collected from 12 co-occurring populations. Germination thermal niche was investigated using a thermal gradient plate (5-40°C). Five constant temperatures between 9 and 33°C were used to test how the germination niche (1) differs between species, (2) varies among populations, and (3) relates to the climate of origin. Germination response differed among species; jarrah had a lower optimal temperature and thermal limit than marri (T o 15.3°C, 21.2°C; ED50 23.4°C, 31°C, respectively). The thermal limit for germination differed among populations within both species, yet only marri showed evidence for adaptation to thermal origins. While marri has the capacity for germination at higher thermal temperatures, jarrah is more vulnerable to global warming exceeding safety margins. This discrepancy is predicted to alter species distributions and forest composition in the future.

Physiological and cannabinoid responses of hemp (Cannabis sativa) to rock phosphate dust under tropical conditions.

Growing a high-value crop such as industrial hemp (Cannabis sativa L.) in post-mining environments is economically and environmentally attractive but faces a range of biotic and abiotic challenges. An opportunity to investigate the cultivation of C. sativa presented itself as part of post-mining activities on Christmas Island (Australia) to profitably utilise disused phosphate (PS) quarries. Challenges to plant growth and cadmium (Cd) uptake were addressed in this study using potted plants under fully controlled conditions in a growth chamber. A complete nutritional spectrum, slow-release fertiliser was applied to all plants as a control treatment, and two levels of rock PS dust, a waste product of PS mining that contains 35% phosphorus (P) and 40ppm of naturally occurring Cd, were applied at 54 and 162gL-1 . After 12weeks, control plants (no PS dust) significantly differed in phenological development, with no flower production, lower aboveground biomass and reduced photosynthesis efficiency than those with P applied as rock dust. Compared with the controls, the 54gL-1 level of P dust increased shoot biomass by 38%, while 162gL-1 increased shoot biomass by 85%. The concentration of Δ9 -tetrahydrocannabinol also increased with the higher P levels. Cd uptake from PS dust by C. sativa was substantial and warrants further investigation. However, there was no increase in Cd content between the 54 and 162gL-1 application rates in seed and leaf. Results indicate that hemp could become a high-value crop on Christmas Island, with the readily available rock PS dust providing a source of P.

Changes to the Bacterial Microbiome in the Rhizosphere and Root Endosphere of Persea americana (Avocado) Treated With Organic Mulch and a Silicate-Based Mulch or Phosphite, and Infested With Phytophthora cinnamomi.

Plant growth and responses of the microbial profile of the rhizosphere soil and root endosphere were investigated for avocado plants infested or not infested with Phytophthora cinnamomi and the changes were compared in plants grown with various soil additives or by spraying plants with phosphite. Soil treatments were organic mulches or silica-based mineral mulch. Reduction of root growth and visible root damage was least in the infested plants treated with phosphite or mineral mulch applied to the soil. Rhizosphere soils and root endospheres were analyzed for bacterial communities using metabarcoding. Bacterial abundance and diversity were reduced in infested rhizospheres and root endospheres. The presence or absence of mineral mulch resulted in greater diversity and larger differences in rhizosphere community composition between infested and non-infested pots than any other treatment. Some rhizosphere bacterial groups, especially Actinobacteria and Proteobacteria, had significantly higher relative abundance in the presence of Phytophthora. The bacterial communities of root endospheres were lower in abundance than rhizosphere communities and not affected by soil treatments or phosphite but increased in abundance after infection with P. cinnamomi. These findings suggested that the addition of silicate-based mineral mulch protects against Phytophthora root rot, which may be partly mediated through changes in rhizosphere bacterial community composition. However, the changes to the microbiome induced by spraying plants with phosphite are different from those resulting from the application of mineral mulch to the soil.