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Karri (Eucalyptus diversicolor F. Muell.) forest is an endemic forest type of southwest Western Australia (SWWA), noted for having the tallest trees in the region, and providing commercial, ecological and conservation value. To inform management aimed at optimising these values, a thinning trial was commenced in 1992. The aim of this study was to evaluate the effects of thinning on individual tree growth, stand level growth and allometry of karri trees in even-aged stands. Mixed effect models were used to compare the effect of different levels of thinning on individual tree growth and stand level growth of karri. We developed allometric equations modelling the relationship between diameter at breast height (DBH) and height, and tested whether thinning affected this allometric relationship. Thinning enhanced DBH, height and crown width (CW) growth of individual trees by up to 149%, 56% and 108% respectively in heavily thinned stands, with stand basal area growth optimised at retained basal areas of 13 m2 ha−1. Thinning had a significant effect on allometry of DBH with height, height-DBH ratio (HDR) and CW. Reduction in stand density through thinning from below increased diameter growth of individual trees. Stand level basal area growth is optimised at an intermediate level of thinning. Thinning can be a good management tool for even-aged karri forest because it may promote the diameter and thereby basal area growth, good health of individual trees, and potential ecological benefits including accelerated development of larger tree crowns typical of mature forest.

Purpose Biotic and abiotic properties of soils can hinder or facilitate ecological restoration, and management practices that impact edaphic factors can strongly influence plant growth and restoration outcomes. Salvaged topsoil is an invaluable resource for mine-site restoration, and a common practice is topsoil transfer from mined areas to restoration sites. However, direct transfer is often not feasible, necessitating storage in stockpiles. We evaluated the effects of topsoil stockpiling on plant performance across diverse ecosystems impacted by mining throughout Western Australia. Methods We conducted a bioassay experiment using a widespread native Acacia species to assess how topsoil storage might impact plant growth, physiology, and nodulation by N-fixing bacteria using soils from native reference vegetation and stockpiled soils from six mine sites across Western Australia. Results Plant responses varied across mine sites, but overall plants performed better in soils collected from native vegetation, exhibiting greater biomass, more root nodules, and higher water-use efficiency compared to those grown in stockpiled soils. Soil physiochemistry showed few and minor differences between native soils and stockpiles. Conclusion Results strongly suggest observed differences in plant performance were biotic in nature. This study highlights the negative effects of topsoil storage on the biological integrity of soil across diverse ecosystems, with important implications for mine-site restoration; our results show that topsoil management can strongly influence plant performance, and stockpiled soils are likely inferior to recently disturbed topsoil for restoration purposes. We also use this study to illustrate the utility of bioassays for assessing soil quality for ecological restoration.

The origin of allometric scaling patterns that are multiples of one-fourth has long fascinated biologists. While not universal, quarter-power scaling relationships are common and have been described in all major clades. Several models have been advanced to explain the origin of such patterns, but questions regarding the discordance between model predictions and empirical data have limited their widespread acceptance. Notable among these is a fractal branching model that predicts power-law scaling of both metabolism and physical dimensions. While a power law is a useful first approximation to some data sets, nonlinear data compilations suggest the possibility of alternative mechanisms. Here, we show that quarter-power scaling can be derived using only the preservation of volume flow rate and velocity as model constraints. Applying our model to land plants, we show that incorporating biomechanical principles and allowing different parts of plant branching networks to be optimized to serve different functions predicts nonlinearity in allometric relationships and helps explain why interspecific scaling exponents covary along a fractal continuum. We also demonstrate that while branching may be a stochastic process, due to the conservation of volume, data may still be consistent with the expectations for a fractal network when one examines sub-trees within a tree. Data from numerous sources at the level of plant shoots, stems, and petioles show strong agreement with our model predictions. This theoretical framework provides an easily testable alternative to current general models of plant metabolic allometry.

Non-mycorrhizal species such as Banksia (Proteaceae) that depend on root exudates to acquire phosphorus (P) are prominent in south-western Australia, a biodiversity hotspot on severely P-impoverished soils. We investigated the consequences of an exudate-releasing P-mobilising strategy related to control of iron (Fe) acquisition in two Banksia species, B. attenuata R.Br. and B. laricina C. Gardner, that differ greatly in their geographical distribution and rarity. We undertook solution culture experiments to measure root-mediated Fe reduction (FeR) in non-cluster and cluster roots at four stages of cluster-root development, and whole root systems for plants grown at 2 to 300 μM Fe (as Fe-EDTA). As a positive control, we used Pisum sativum (cv. Dunn) to validate the FeR assay. Unlike typical Strategy I species, both Banksia species showed no significant variation in FeR, for either cluster or non-cluster roots, when grown at a wide range of Fe supply. For roots of different developmental stages, we measured a range for B. attenuata cluster roots of 0.13 ± 0.03 to 1.29 ± 0.14 μmol Fe3+ reduced g−1 FW h−1 and 0.56 ± 0.11 to 1.10 ± 0.24 μmol Fe3+ reduced g−1 FW h−1 in non-cluster roots. Similarly, for B. laricina cluster-roots, FeR ranged from 0.22 ± 0.07 to 1.21 ± 0.37 μmol Fe3+ reduced g−1 FW h−1, and in non-cluster roots from 0.56 ± 0.11 to 0.71 ± 0.08 μmol Fe3+ reduced g−1 FW h−1. We also observed only minor differences for whole-root system FeR, and even though B. attenuata showed signs of leaf Fe deficiency in the 2 μM Fe treatment, its FeR was the lowest of both species across all treatments at 0.079 ± 0.009 μmol Fe3+ reduced g−1 FW h−1, compared with the fastest rate of 0.20 ± 0.014 μmol Fe3+ reduced g−1 FW h−1 for B. laricina in the 28 μM Fe treatment. Taking plants through a pulse from low to high Fe, then back to low Fe supply did not elucidate any significant response in FeR. Although Fe acquisition is tightly controlled in the investigated Banksia species, such control is not based on regulation of FeR, which challenges the model that is commonly accepted for Strategy I species.

Nutrient-poor ecosystems globally exhibit high plant diversity. One mechanism enabling the co-existence of species in such ecosystems is facilitation among plants with contrasting nutrient-acquisition strategies. The ecophysiological processes underlying these interactions remain poorly understood. We hypothesized that root positioning plays a role between sympatric species in nutrient-poor vegetation. We investigated how the growth traits of the focal mycorrhizal non-cluster-rooted Hibbertia racemosa change when grown in proximity of non-mycorrhizal Banksia attenuata, which produces cluster roots that increase nutrient availability, compared with growth with conspecifics. Focal plants were placed in the centre of rhizoboxes, and biomass allocation, root system architecture, specific root length (SRL), and leaf nutrient concentration were assessed. When grown with B. attenuata, focal plants decreased root investment, increased root growth towards B. attenuata, and positioned their roots near B. attenuata cluster roots. SRL was greater, and the degree of localized root investment correlated positively with B. attenuata cluster-root biomass. Total nutrient contents in the focal individuals were greater when grown with B. attenuata. Focal plants directed their root growth towards the putatively facilitating neighbour's cluster roots, modifying root traits and investment. Preferential root positioning and root morphological traits play important roles in positive plant-plant interactions.

Our understanding of how water dynamics determines the probability of tree mortality during drought is incomplete. Here we help address this shortcoming by coupling approaches from the disciplines of ecophysiology, geophysics and remote sensing in a woodland ecosystem undergoing protracted drying. Water uptake and use strategies varied between the dominant canopy species of the ecosystem. At one extreme were species that tightly regulate their water status, which is broadly consistent with the definition of isohydry. The higher leaf temperatures revealed by thermal imagery of these isohydric species are likely a reflection of reduced latent cooling owing to a stringent control of transpiration rate. Where silty sediments occur in the root zone, this strategy may have the effect of limiting the water sources available to these species during prolonged drought because of an insufficient hydraulic gradient for water uptake. In contrast were species that allowed their water status to fluctuate, operating in a fashion more consistent with anisohydry. For these species, latent cooling owing to relatively high transpiration rates maintained leaf temperatures near, or below, the ambient air temperature. The resulting drawdown in leaf water potential between soil and leaves in these anisohydric species may generate a sufficient hydraulic gradient to enable water uptake from silty soil during seasonal or prolonged droughts. In this way the spatial distribution of fine textured soil could indicate areas where the isohydric hydraulic control strategy is disadvantageous during prolonged droughts or where annual soil water recharge has fallen below a critical threshold.

Root-released carboxylates enhance the availability of manganese (Mn), which enters roots through transporters with low substrate specificity. Leaf Mn concentration ([Mn]) has been proposed as a signature for phosphorus (P)-mobilising carboxylates in the rhizosphere. Here we test whether leaf [Mn] provides a signature for root functional types related to P acquisition. Across 727 species at 66 sites in Australia and New Zealand, we measured leaf [Mn] as related to root functional type, while also considering soil and climate variables. To further assess the specific situations under which leaf [Mn] is a suitable proxy for rhizosphere carboxylate concentration, we studied leaf [Mn] along a strong gradient in water availability on one representative site. In addition, we focused on two systems where a species produced unexpected results. Controlling for background site-specific variation in leaf [Mn] with soil pH and mean annual precipitation, we established that mycorrhizal species have significantly lower leaf [Mn] than non-mycorrhizal species with carboxylate-releasing root structures, e.g., cluster roots. In exception to the general tendency, leaf [Mn] did not provide information about root functional types under seasonally waterlogged conditions, which increase iron availability and thereby interfere with Mn-uptake capacity. Two further exceptions were scrutinised, leading to the conclusion that they were ‘anomalous’ in not functioning like typical species in their families, as expected according to the literature. Leaf [Mn] variation provides considerable insights on differences in belowground functioning among co-occurring species. Using this approach, we concluded that, within typical mycorrhizal families, some species actually depend on a carboxylate-releasing P-mobilising strategy. Likewise, within families that are known to produce carboxylate-releasing cluster roots, some do not produce functional cluster roots when mature. An analysis of leaf [Mn] can alert us to such ‘anomalous’ species.

This study aimed to determine the structure of the bacterial community inhabiting the roots and rhizosheath of sweet potato cultivars, and how these bacterial communities respond to P addition and subsequent changes in carboxylate exudation by sweet potato roots. Five sweet potato cultivars were grown with and without P addition in a low P soil in a glasshouse: Beauregard and Northern Star (both international cultivars) and Whagi Besta, Maraso and Marasunda which originate from Papua New Guinea. Rhizosheath carboxylates were measured and the root/rhizosheath bacterial community analysed using 16S rRNA gene sequencing. Carboxylate amount per g root weight was reduced (citrate) or increased (malate and oxalate) with addition of P. Carboxylate amount also positively correlated (citrate, oxalate and shikimate) or negatively correlated (malate) to bacterial alpha diversity when no P was added. P addition decreased bacterial diversity, altered the structure of the bacterial community (taxa and predicted function) and led to an enrichment of bacteria related to known P-solubilising bacteria (Burkholderia and Massilia) as well as to functions related to biosynthesis. This study provides a first indication of types and putative roles of root/rhizosheath bacteria in sweet potato cultivars originating from a wide range of environments including marginal and P-impoverished soils and high-P agricultural systems.

Plants that produce specialised cluster roots, which mobilise large quantities of poorly available nutrients such as phosphorus (P), can provide a benefit to neighbouring plants that produce roots in the cluster rhizosphere, as demonstrated previously in pot studies. To be effective, such roots must be present within the short time of peak cluster activity. We tested if this requirement is met, and quantified potential P benefits, in a hyperdiverse Mediterranean woodland of southwest Australia where cluster-rooted species are prominent. Using minirhizotrons, we monitored root dynamics during the wet season in the natural habitat. We found non-cluster roots intermingling with all 57 of the observed cluster roots of the studied tree species, Banksia attenuata. Almost all (95%) of these cases were observed in a high-moisture treatment simulating the 45-year average, but not present when we intercepted some of the rainfall. We estimate that cluster-root activity can increase P availability to intermingling roots to a theoretical maximum of 80% of total P in the studied soil. Due to their high P-remobilisation efficiency (89%), which results from P rapidly being relocated from cluster roots within the plant, senesced Banksia cluster roots are a negligible P source for other roots. We conclude that, rather than serving as a P source, it is the cluster-root activity, particularly the exudation of carboxylates, that may improve the coexistence of interacting species that are capable of root intermingling, thus potentially promoting species diversity in nutrient-poor habitats, and that this mechanism will be less effective in a drying climate.

Leptospermum polygalifolium Salisb. can accumulate high concentrations of dihydroxyacetone (DHA), precursor of the antimicrobial compound methylglyoxal found in honey obtained from floral nectar of Leptospermum spp. Floral nectar dynamics over flower lifespan depends on internal and external factors that invariably impact nectar quality. Current models to estimate nectar quality in Leptospermum spp. overlook time of day, daily (24 h), and long-term dynamics of nectar exudation and accumulation over flower lifespan. To explain the dynamics of nectar quality over flower lifespan, accumulated nectar from flowers of different ages was collected from two L. polygalifolium clones, and then re-collected 24 h later from the same flowers. High-Performance Liquid Chromatography was used to quantify DHA amount and total equivalents of glucose + fructose (Tsugar) per flower in the nectar. DHA and Tsugar amount per flower differed with flower age and between clones. In accumulated nectar, the amount of DHA and Tsugar per flower rose to a broad peak post-anthesis before decreasing. Immediately after peaking DHA declined more quickly than Tsugar in accumulated nectar due to a greater decrease in the exudation of DHA than for Tsugar. The DHA : Tsugar ratios in accumulated nectar and in nectar exuded over the next 24 h were similar and decreased with flower age, indicating that exudation and reabsorption occurred concomitantly across flower development. Hence there is a balance between exudation and reabsorption. A quantitative model suggested that flowers have the potential to exude more DHA and Tsugar than actually accumulated.

We introduce the AusTraits database - a compilation of values of plant traits for taxa in the Australian flora (hereafter AusTraits). AusTraits synthesises data on 448 traits across 28,640 taxa from field campaigns, published literature, taxonomic monographs, and individual taxon descriptions. Traits vary in scope from physiological measures of performance (e.g. photosynthetic gas exchange, water-use efficiency) to morphological attributes (e.g. leaf area, seed mass, plant height) which link to aspects of ecological variation. AusTraits contains curated and harmonised individual- and species-level measurements coupled to, where available, contextual information on site properties and experimental conditions. This article provides information on version 3.0.2 of AusTraits which contains data for 997,808 trait-by-taxon combinations. We envision AusTraits as an ongoing collaborative initiative for easily archiving and sharing trait data, which also provides a template for other national or regional initiatives globally to fill persistent gaps in trait knowledge., Measurement(s)plant traitTechnology Type(s)digital curationSample Characteristic - OrganismViridiplantaeSample Characteristic - LocationAustralia Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.14545755

Long‐term studies of vegetation recovery following post‐mining restoration in low‐productivity, high‐stress areas are limited, but essential for understanding underlying ecological processes and evaluating management practices. This study's goal was to describe temporal patterns of recovery (up to 37 years) in vegetation structure, floristic diversity, and composition following post‐mining restoration at two sites, and identify potential drivers of restoration outcomes, in the nutrient‐poor, seasonally dry, species‐rich, fire‐prone kwongan vegetation of southwest Western Australia. Vegetation development is progressing and restoration measures are within range of native reference values, but there is large variation in both patterns observed and restoration outcomes. Several patterns described share similarities with post‐fire recovery of kwongan, and post‐disturbance recovery of other low‐productivity, high‐stress, fire‐prone systems. However, differences in some patterns between sites indicate differences in the underlying mechanisms of recovery. Many management and environmental variables emerge as significant drivers of restoration outcomes but age, fire, and the planting of seedlings account for the largest amount of variation. Adaptive management at both sites appears to be facilitating improved restoration outcomes over time. Using a combination of space‐for‐time, plot level, and linear mixed effects modeling perspectives to examine patterns provides greater insights into restoration recovery than a chronosequence perspective alone. This study will inform restoration practices and outcomes not only in kwongan but in other comparable systems also.

Summary • The influence of soil P level and plant development on carboxylate concentrations in the rhizosphere of lateral roots of chickpea (Cicer arietinum) cultivars Heera and Tyson were studied to investigate the relationship between carboxylate exudation and P acquisition by chickpea. • Two chickpea cultivars were grown in soil supplied with 0–100 µg P g−1. Plants were harvested four times during plant development. In two other experiments, carboxylate concentrations were measured along root sections, using plants grown in soil or in hydroponics. • Carboxylate concentrations in the rhizosphere of lateral roots steadily increased with plant development for cv. Heera, but not for Tyson. Carboxylate concentrations increased with increasing distance from the root apex in soil. This increase might be due to accumulation, because an experiment with plants in hydroponics showed that older segments released at least as much carboxylates as younger segments. • Carboxylate concentrations in the rhizosphere of chickpea appear to be developmentally controlled. Unlike some other plant species, there is no simple correlation with plant or soil P status.

Background and Aims The perennial C4 grass Urochloa humidicola is widely planted on infertile acidic and waterlogging-prone soils of tropical America. Waterlogging results in soil anoxia, and O2 deficiency can reduce nutrient uptake by roots. Interestingly, both nutrient deficiencies and soil waterlogging can enhance root cortical cell senescence, and the increased gas-filled porosity facilitates internal aeration of roots. We tested the influence of nutrient supply and root-zone O2 on root traits, leaf nutrient concentrations and growth of U. humidicola. Methods Plants were grown in pots in a completely randomized design under aerated or stagnant deoxygenated hydroponic conditions and six nutrient regimes, with low to high concentrations of all essential elements, for 28 d in a controlled-temperature greenhouse. The standard acid solution (SAS) used was previously designed based on infertile acidic soils of the tropical America savannas, and step increases in the concentration of SAS were used in aerated or deoxygenated 0.1 % agar solution, which mimics changes in gas composition in waterlogged soils. Measurements included shoot and root growth, root porosity, root anatomy, radial O2 loss, and leaf tissue nutrient concentrations. Key Results Shoot dry mass was reduced for plants in stagnant compared with aerated conditions at high, but not at low, levels of mineral nutrition. In low-nutrition stagnant solution, roots were shorter, of greater porosity and had smaller radial thickness of the stele. Suberized lamellae and lignified sclerenchyma, as well as a strong barrier to radial O2 loss, were documented for roots from all treatments. Leaf nutrient concentrations of K, Mg and Ca (but not N, P and S) were higher in aerated than in stagnant conditions. Conclusions Under low-nutrient conditions, plant growth in stagnant solution was equal to that in aerated solution, whereas under higher-nutrient regimes growth increased but dry mass in stagnant solution was less than in aerated solution. Slow growth in low-nutrient conditions limited any further response to the low O2 treatment, and greater porosity and smaller stele size in roots would enhance internal O2 movement within roots in the nutrient-limited stagnant conditions. A constitutive barrier to radial O2 loss and aerenchyma facilitates O2 movement to the tips of roots, which presumably contributes to maintaining nutrient uptake and the tolerance of U. humidicola to low O2 in the root-zone.

The nature of community patterns and environmental drivers in kwongan mediterranean‐type shrubland on nutrient‐poor soils occurring in Western Australia remain poorly examined. We aimed to determine whether (i) classification of the kwongan vegetation of the northern Swan Coastal Plain would be ecologically informative and (ii) which environmental drivers underpin the plant community patterns. The study area was positioned on the northern Swan Coastal Plain, locality of Cooljarloo (30°39′ S, 115°22′ E), situated 170 km north of Perth, Western Australia. Compositional (518 species × 337 releves) and environmental data set (29 variables × 87 releves) describing time since last fire, soil chemical and physical properties, and terrain characteristics were analysed using classification and ordination techniques. OptimClass assisted in the selection of a robust data transformation, resemblance function and clustering algorithm to identify the vegetation patterns. Major ecological drivers of the vegetation patterns were detected using distance‐based redundancy analysis (db‐RDA). Classification revealed major groupings of Wet Heath and Banksia Woodland distinguishable by the high prevalence of myrtyoid and proteoid taxa, respectively. On floristic‐sociological grounds, we recognised four Wet Heath and two Banksia Woodland communities. The Wet Heath was constrained to areas of higher litter depth (db‐RDA axis 1: 9%). Soil chemical and physical properties explained the highest proportion (17%) of the compositional variance, while the terrain‐ and fire‐related variables explained 2% and

Since March 2015 the UWA in collaboration with the BGPA has conducted a time-lapse microgravity study of groundwater storage in Kings Park. Data collection has focused on seasonal to inter-annual change, with bi-monthly measurements extending across multiple days. Relative measurements are taken with a Scintrex CG-5 gravity meter and are referred to the Helena Valley reference station, which is located in the granite-dominated Perth Hills. Interim results (July 2017) suggest that measurement methods are sufficiently sensitive to characterize change, with measurement precision of ~2 microgals, or approximately 40 mm of stored water. Two-month storage-changes are defined from the gravity data, and usage is further defined as rainfall minus storage-change. Storage-changes are positively correlated with rainfall (r=+0.697) and negatively-correlated with solar exposure (r=-0.555). Thus, a fairly strong signal is seen of increase during the winter wet season, and decrease during the summer dry season. Usage is weakly positively correlated with solar exposure (r=+0.202) but also shows dry periods in late summer, where estimated usage is near-zero despite high solar exposure, and a high-usage period at the start of the wet season. Interannual change is substantial, and seems to be strongly linked to the Indian Ocean Dipole, which was strongly positive in winter 2015, strongly negative in winter 2016 and positive to neutral in winter 2017.

Water relations of saplings of two Eucalyptus species (E. leptopoda Benth. and E. loxophleba Benth.) were investigated on engineered cover systems (soil spread over mine waste rock) with soil depths of 0.3, 0.5 and 0.7 m in a semi-arid climate during summer. Objectives were (1) to assess the influence of soil depth on plant water availability; and (2) to better understand the impact of water availability and diurnal environmental fluctuations on key physiological parameters such as transpiration (E), stomatal conductance (gs), net photosynthesis (A), intercellular CO2 concentration (Ci), and mid-day leaf water potential (ΨMD) as they relate to regulation of plant water status. Physiological responses of plants to environmental factors differed between plants in shallow versus deep soils and species. Plants on deeper soils were less affected by high vapour pressure deficit (VPD), temperature, and irradiance due to increased plant available water, partly provided by their less confined roots, resulting in higher overall gs, E, A, and ΨMD. Stomatal closure reduced A but not Ci, indicating that high temperature and radiation were also significantly contributing to the diurnal decline in A through reversible photoinhibition. Greater soil depth in natural (semi-) arid ecosystems and on constructed or restored substrates may minimise plant sensitivity to higher temperature, VPD and irradiance through plant available moisture, especially in areas most vulnerable to climate warming and drying.

QUESTIONS: The community patterns in kwongan, a mediterranean‐type scrub on nutrient‐poor soils occurring in Western Australia, are poorly understood due to only few, focused studies using disparate sampling designs. We aimed to determine whether (a) classification of the kwongan vegetation of the Eneabba Sandplains leads to an ecologically informative classification scheme, and (b) we could identify environmental drivers underpinning the plant community patterns. LOCATION: Township of Eneabba (29°82′S, 115°27′E), approximately 250 km north of Perth, Western Australia, covering 1,210 km². METHODS: We used a data set consisting of 512 releves, collected following the standard field methodology of the Braun‐Blanquet approach, and accompanied by an extensive set of environmental data consisting of 94 variables representing climate, fire, soil and terrain properties across 189 releves. The data were classified and ordinated by a series of multivariate analyses. OptimClass assisted in the selection of the most robust classification procedure. Distance‐based redundancy analysis (db‐RDA) inferred the major ecological drivers of the vegetation patterns. RESULTS: Numerical classification, nonmetric multidimensional scaling, and syntaxonomic tabular analysis revealed two major community groups (MCG A and B), eight community groups, and 17 communities in the kwongan vegetation of the study area. All vegetation units are characterised in terms of floristic composition and position along major ecological gradients in the studied area. The MCGs separated along a composite gradient of soil‐texture and exchangeable cations. The first two db‐RDA axes explained 21% of the total variance which is very low, considering the high number of environmental variables used. CONCLUSIONS: Our study provides a comprehensive insight into the high variability of vegetation types in hyper‐diverse kwongan scrub at a landscape spatial scale; it is the first syntaxonomic account of the Western Australian kwongan vegetation, presenting a complete tabular comparative analysis. The studied major community groups segregate along a soil‐texture and an exchangeable‐cation content gradient. At a community scale, environmental filtering explained a small fraction of the vegetation–environment relationship. We suggest that the unexplained portion of the vegetation‐environment relationship might be a product of slow‐acting neutral processes in this hyper‐diverse system; this assertion is amenable to rigorous future testing.

Made available in DSpace on 2021-06-25T15:03:38Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-03-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) UWA Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Questions Environmental filters limit the set of potentially coexisting species in plant communities. Paradoxically, some of the world's most biodiverse communities are subjected to strong abiotic filters. We explored how environmental heterogeneity provides conditions for niche segregation in a harsh megadiverse ecosystem, focusing on fine-scale factors that drive seedling recruitment. Due to the environmental stress (mainly nutrient and water scarcity), we expected the prevalence of positive plant interactions over negative ones to contribute to species coexistence. Location Ironstone outcrop (canga) at Serra da Calcada, southeast Brazil. Methods We characterised microhabitats with one or neither of two dominant shrubs Mimosa calodendron (Fabaceae) and Lychnophora pinaster (Asteraceae), and assessed which micro-environmental attributes affect seedling survival, growth, and abundance, as well as adult richness in the ecosystem. Results Spatial heterogeneity in the community was mostly driven by differences in substrate properties, and plots with Mimosa calodendron and Lychnophora pinaster exhibited different biotic and abiotic conditions from those lacking these species. Microhabitats under both shrubs had greater adult richness, and those occupied by Mimosa calodendron had greater seedling abundance, suggesting positive effects of environmental conditions associated with these plants. Nevertheless, we identified two potential negative plant-plant interactions: larger crown area of the two dominant shrubs was associated with lower species richness, and greater understorey plant cover with lower seedling abundance. Over one year, 63% of the recorded seedlings survived, but measured attributes failed to predict survival. Seedling relative growth rates were species-specific and lower in microsites where the rocky substrate is fragmented. The most abundant seedling taxa occurred in association with specific microhabitats. Conclusions Our study suggested that fine-scale spatial heterogeneity determines the outcome of plant-plant interactions in a stressful ecosystem. Micro-environmental heterogeneity allows for the spatial segregation of species recruitment, thereby broadening the range of viable strategies within a harsh megadiverse ecosystem. Univ Fed Minas Gerais, Dept Bot, Av Antonio Carlos 6627, BR-31270110 Belo Horizonte, MG, Brazil Univ Western Australia, Sch Biol Sci, Perth, WA, Australia Univ Estadual Paulista, Dept Zool, Rio Claro, Brazil Univ Fed Minas Gerais, Dept Genet Ecol & Evolucao, Belo Horizonte, MG, Brazil Univ Estadual Paulista, Dept Zool, Rio Claro, Brazil CAPES: 88881.068071/2014-01 FAPESP: 2017/07954-0

Cassava is often grown in low-fertility soils and has a reputation for having modest nutrient requirements. The storage roots that are harvested, however, contain relatively large amounts of potassium (K). We carried out a field experiment in Laos to determine the growth response to K fertiliser and to examine the field&rsquo, s K balance over the cropping season. Four different rates of K (0-40-80-120 kg K2O equivalents ha&minus, 1) were applied to cassava variety Rayong11. Harvests were done at 8 and 10 months after planting, when the crop was at early and full maturity respectively, to assess if any benefits for productivity or K balance could be achieved by early harvest. We found a positive effect of K fertiliser (up to 39% yield increase compared to no K fertiliser at early harvest, 21% at late harvest) and a positive effect of late harvest (on average a 35% increase compared to early harvest) on cassava root yield. Low-K crops benefited more from a late harvest. At 10 months, the harvested cassava contained 99&ndash, 142 kg K ha&minus, 1, indicating that there was a net removal of K from the fields, even at high K fertilisation levels. This experiment was carried out in comparatively fertile soil with relatively high background K levels, yet, yield benefits of K fertilisation were observed and soil K reserves were depleted by the harvest. It can be concluded that K fertilisation of cassava is advisable for better yields and to avoid progressive depletion of the soil K capital.

Lack of O2 and high concentrations of iron (Fe) and manganese (Mn) commonly occur in waterlogged soils. The development of a barrier to impede radial O2 loss (ROL) is a key trait improving internal O2 transport and waterlogging tolerance in plants. We evaluated the ability of the barrier to ROL to impede the entry of excess Fe into the roots of the waterlogging-tolerant grass Urochloa humidicola. Plants were grown in aerated or stagnant deoxygenated nutrient solution with 5 µM or 900 µM Fe. Quantitative X-ray microanalysis was used to determine cell-specific Fe concentrations at two positions behind the root apex in relation to ROL and the formation of apoplastic barriers. At a mature zone of the root, Fe was ‘excluded’ at the exodermis where a suberized lamella was evident, a feature also associated with a strong barrier to ROL. In contrast, the potassium (K) concentration was similar in all root cells, indicating that K uptake was not affected by apoplastic barriers. The hypothesis that the formation of a tight barrier to ROL impedes the apoplastic entry of toxic concentrations of Fe into the mature zones of roots was supported by the significantly higher accumulation of Fe on the outer side of the exodermis.

Competition from neighbouring trees generally has a negative effect on the growth of an individual tree; however, the magnitude of competition is expected to vary with size and proximity of the tree and its competitors. Eucalypt forests (natural/plantation) are widespread throughout the world, and have high economic, ecological and conservation importance. Recent work carried out in eucalypt forest of Western Australia showed that growth of individual trees could be explained by a flexible novel competition index that accounts for proximity and size of competitors. This study aimed to further test and extend those methods, by applying them to long-term time-series data on thinned and unthinned plots of two important new species (karri and marri) in a more productive environment. More specifically, we aimed to compare the usefulness of different competition indices (CIs) including a novel index using crown-width; develop models to understand and predict the growth of karri and marri individuals, using tree size and age; test whether including measures of neighbourhood competition would improve growth predictions for these species; validate the predictive ability of the models and analyse the sensitivity of their parameters; and investigate how many neighbouring trees or what neighbourhood distance needed to be considered when accounting for competition. Our new crown-width CI was useful, but not as useful as previous diameter-based CI. Diameter and age were significant predictors, and prediction was further improved by inter-tree competition. Leave-one-out cross-validation showed that our models are well validated, and sensitivity of karri model parameters was

Successful mine site restoration in semi-arid regions is limited by availability of topsoil and water, and saline soils are a common feature of these regions and pose an additional stressor to vegetation establishment. We tested the growth and development of a salt-tolerant species on saline topsoil incorporating 25%, 50%, 75% and 88% waste rock, examining soil water content and plant water use to determine how waste rock content affected plant-water relations, growth and development. Under well-watered conditions higher percentages of waste rock lowered the volumetric water content of the total soil mix, causing a reduction in stomatal conductance. Under drought conditions, higher waste rock content reduced rates of water loss and allowed stomatal conductance to be maintained over a longer period. There was no significant or optimal relationship between waste rock content and plant growth, indicating that the addition of waste rock to topsoil has complex effects on plant-water relations and growth. We demonstrate that augmentation of limited topsoil resources with waste rock is a promising option for improving plant resistance to drought in mine site restoration.

Growth of an individual tree in a forest depends on multiple factors amongst which size, age and stand density can be of particular importance. The ability to understand how these factors influence individual growth can help understand forest growth and dynamics more generally. The overall objective of this study was to analyse the growth of individual trees of jarrah (Eucalyptus marginata), a wide-spread species having ecological and economic importance in south west Western Australia (SWWA). More specifically, we investigated (1) how well individual tree growth could be explained by considering tree size at the start of the growth period; (2) whether this explanation could be improved by also accounting for competition from neighbouring trees in different ways, (3) how many neighbouring trees or what neighbourhood distance needed to be considered when accounting for competition; and (4) whether neighbouring tree growth could be a useful indication of competition. Tree size was significant in explaining growth. Explanation was improved when competition was included in the models, based on R2 (which ranged from 0.31 to 0.68). A new spatial competition index (CI) developed in this study performed better than previously developed CIs. Explanation of diameter growth was optimized by accounting for competition from the 10 to 12 closest competitors or competitors within ~10 m from the base of the subject tree. As competition from neighbours had a significant negative effect on growth, we recommend including neighbourhood competition when explaining/predicting growth and considering thinning treatments to minimize the effect of competition on growth. The modelling approaches developed in this study are likely to be useful tools for understanding and managing individual tree growth of any species in the world where competition among trees restricts individual growth. Novelties include the first model explaining individual jarrah growth; an effective new competition index; an approach to testing how many neighbouring trees or what neighbourhood distance needs to be considered when accounting for competition; and the idea of neighbouring tree growth being a useful indication of competition.

Rehabilitation of mine sites in semi-arid landscapes is hindered by poor quality mine waste substrates, a byproduct of mining used as alternative growth media. Inorganic soil amendments, such as gypsum and urea, are sometimes used to improve the chemical and physical quality of mine waste substrates and increase native plant establishment. However, limited research is available regarding the medium and long-term effectiveness of these amendments in semi-arid post-mining landscapes. In this study, inorganic amendments were incorporated into two alternative mine substrates (mine waste and a topsoil:waste blend) in large 0.8 m3 above-ground mesocosms in the semi-arid Pilbara region of Western Australia. These mesocosms were bare soil or seeded with one of two different mixes of plant species to determine how amendments and species diversity altered plant growth and survival, and substrate quality compared to stockpiled topsoil over a 21-month period. The unamended waste had a lower electrical conductivity (EC), soil carbon (C), soil nitrogen (N) and C/N ratio compared to the topsoil. The amendments had a strong initial effect on soil quality, increasing N, soil EC and N-mineralisation in the amended waste compared to all other soil treatments. However, N levels returned to non-amended levels after the first year and the amendments had limited influence on plant growth. Plant survival was higher in the amended substrates with the more diverse plant community, which increased substrate microbial activity to levels significantly greater than the unamended waste. The use of inorganic amendments may be ineffective at increasing long-term substrate quality and growth of native plants but may support seedling survival that in turn will improve soil chemical and biological properties of waste substrates.

Hydraulic redistribution (HR), the movement of water from wet to dry patches in the soil via roots, occurs in different ecosystems and plant species. By extension of the principle that HR is driven by gradients in soil water potential, HR has been proposed to occur for plants in saline soils. Despite the inherent spatial patchiness and salinity gradients in these soils, the lack of direct evidence of HR in response to osmotic gradients prompted us to ask the question: are there physical or physiological constraints to HR for plants in saline environments? We propose that build-up of ions in the root xylem sap and in the leaf apoplast, with the latter resulting in a large predawn disequilibrium of water potential in shoots compared with roots and soil, would both impede HR. We present a conceptual model that illustrates how processes in root systems in heterogeneous salinity with water potential gradients, even if equal to those in non-saline soils, will experience a dampened magnitude of water potential gradients in the soil–plant continuum, minimizing or preventing HR. Finally, we provide an outlook for understanding the relevance of HR for plants in saline environments by addressing key research questions on plant salinity tolerance

Leaf veins supply the mesophyll with water that evaporates when stomata are open to allow CO2 uptake for photosynthesis. Theoretical analyses suggest that water is optimally distributed in the mesophyll when the lateral distance between veins (dx) is equal to the distance from these veins to the epidermis (dy), expressed as dx:dy ≈ 1. Although this theory is supported by observations of many derived angiosperms, we hypothesize that plants in arid environments may reduce dx:dy below unity owing to climate-specific functional adaptations of increased leaf thickness and increased vein density. To test our hypothesis, we assembled leaf hydraulic, morphological, and photosynthetic traits of 68 species from the Eucalyptus and Corymbia genera (termed eucalypts) along an aridity gradient in southwestern Australia. We inferred the potential gas-exchange advantage of reducing dx beyond dy using a model that links leaf morphology and hydraulics to photosynthesis. Our observations reveal that eucalypts in arid environments have thick amphistomatous leaves with high vein densities, resulting in dx:dy ratios that range from 1.6 to 0.15 along the aridity gradient. Our model suggests that, as leaves become thicker, the effect of reducing dx beyond dy is to offset the reduction in leaf gas exchange that would result from maintaining dx:dy at unity. This apparent overinvestment in leaf venation may be explained from the selective pressure of aridity, under which traits associated with long leaf life span, high hydraulic and thermal capacitances, and high potential rates of leaf water transport confer a competitive advantage.

Establishing vegetation on disturbed sites in arid environments is difficult due to decreased water availability caused by altered soil properties: depth, compaction, and hydraulic characteristics. Plants cope with moisture stress through a combination of traits, including physiological strategies such as anisohydry and isohydry. We used a typical mine restoration substrate in a glasshouse pot experiment to investigate drought tolerance of nine Pilbara region Acacia species classified according to habitat preferences defined by preferred soil type: alluvial (fine textured), sandy, rocky, and generalists without a clear soil preference. Seedlings were examined to (1) determine physiological shoot, and morphological shoot and root traits associated with drought tolerance, and (2) identify if these traits were correlated with species’ soil preferences. Species from alluvial, rocky, and one sandy soil species were more anisohydric. These species had higher stomatal conductance at more negative leaf water potentials. Alluvial soil species had greater total biomass allocation to lateral roots, whereas two coarser textured soil species had high allocation to tap roots. Soil preference was a poor predictor of plant water relations, presumably due to complex soil profiles in nature associated with widely differing hydraulic characteristics, and interactions among plant functional traits influencing water uptake, transport and loss.

Jarrah (Eucalyptus marginata) forest is one of the most widespread native forest types of south west Western Australia (SWWA) and provides timber, firewood, wildlife habitat, water production, catchment protection and recreation. To inform management aimed at optimizing these values, a thinning trial in even aged regrowth forest was commenced in 1965. A second thinning and N and P fertilizer treatment was applied in 1986. The effect of thinning and fertilizer on tree and stand level growth and allometry was evaluated. Thinning resulted in higher values of under bark diameter at breast height (DBHUB) and tree height, and lower values of height diameter ratio (HDR), stand basal area under bark (BAUB) and stem number per unit area. Growth of DBHUB increased with a decrease in stand density. Growth of stand BAUB peaked at intermediate stand densities. Fertilizer increased growth in DBHUB and stand BAUB. Height growth was significantly greater in thinned plots. Thinning had a significant effect on the allometric relation between diameter at breast height over bark (DBHOB) and each of height, HDR and crown width (CW) while fertilizer had a significant effect on the allometric relation between DBHOB and each of height and HDR. Height and CW increased with an increase in DBHOB but HDR decreased. Larger sized trees resulting from thinning and addition of fertilizer are likely to provide a higher volume of timber, firewood, fruits (important food for threatened cockatoos), and improved visual amenity. As thinning had a positive effect on diameter and height growth and self-thinning in jarrah is relatively low (0.20% yr−1), thinning may be a valuable management tool to accelerate development of larger trees which can be beneficial for both timber production and conservation.

The rapid expansion of urban areas worldwide is leading to native habitat loss and ecosystem fragmentation and degradation. Although the study of urbanisation's impact on biodiversity is gaining increasing interest globally, there is still a disconnect between research recommendations and urbanisation strategies. Expansion of the Perth metropolitan area on the Swan Coastal Plain in south-western Australia, one of the world's thirty-six biodiversity hotspots, continues to affect the Banksia Woodlands (BWs) ecosystem, a federally listed Threatened Ecological Community (TEC). Here, we utilise the framework of a 1989 review of the state of knowledge of BWs ecology and conservation to examine scientific advances made in understanding the composition, processes and functions of BWs and BWs' species over the last 30 years. We highlight key advances in our understanding of the ecological function and role of mechanisms in BWs that are critical to the management of this ecosystem. The most encouraging change since 1989 is the integration of research between historically disparate ecological disciplines. We outline remaining ecological knowledge gaps and identify key research priorities to improve conservation efforts for this TEC. We promote a holistic consideration of BWs with our review providing a comprehensive document that researchers, planners and managers may reference. To effectively conserve ecosystems threatened by urban expansion, a range of stakeholders must be involved in the development and implementation of best practices to conserve and maintain both biodiversity and human wellbeing.

C4 perennial Urochloa spp. grasses are widely planted in extensive areas in the tropics. These areas are continuously facing waterlogging events, which limits plant growth and production. However, no commercial cultivar combining excellent waterlogging tolerance with superior biomass production and nutritional quality is available. The objective of this study was to identify root traits that can be used for selecting waterlogging tolerant species of Urochloa. Root respiration, root morphological, architectural and anatomical traits were evaluated in eight contrasting Urochloa spp. genotypes grown under aerated or deoxygenated stagnant solutions. Moreover, modelling of internal aeration was used to relate differences in root traits and root growth in waterlogged soils. Increased aerenchyma formation in roots, reduced stele area and development of a fully suberised exodermis are characteristics improving internal aeration of roots and therefore determining waterlogging tolerance in these C4 forage grasses. Waterlogging-tolerant genotypes had steeper root angles and greater root lengths than the waterlogging-sensitive genotypes. In stagnant conditions, waterlogging-tolerant genotypes had a greater proportion of aerenchyma and reduced stele area in root cross-sections, had deeper roots, steeper root angle and larger root biomass, which in turn, allowed for greater shoot biomass. Total root length had the strongest positive influence on shoot dry mass and can therefore be used as proxy for selecting waterlogging tolerant Urochloa genotypes.

The rapid expansion of urban areas worldwide is leading to native habitat loss and ecosystem fragmentation and degradation. Although the study of urbanisation’s impact on biodiversity is gaining increasing interest globally, there is still a disconnect between research recommendations and urbanisation strategies. Expansion of the Perth metropolitan area on the Swan Coastal Plain in south-western Australia, one of the world’s thirty-six biodiversity hotspots, continues to affect the Banksia Woodlands (BWs) ecosystem, a federally listed Threatened Ecological Community (TEC). Here, we utilise the framework of a 1989 review of the state of knowledge of BWs ecology and conservation to examine scientific advances made in understanding the composition, processes and functions of BWs and BWs’ species over the last 30 years. We highlight key advances in our understanding of the ecological function and role of mechanisms in BWs that are critical to the management of this ecosystem. The most encouraging change since 1989 is the integration of research between historically disparate ecological disciplines. We outline remaining ecological knowledge gaps and identify key research priorities to improve conservation efforts for this TEC. We promote a holistic consideration of BWs with our review providing a comprehensive document that researchers, planners and managers may reference. To effectively conserve ecosystems threatened by urban expansion, a range of stakeholders must be involved in the development and implementation of best practices to conserve and maintain both biodiversity and human wellbeing.

This study investigated the relationship between osmotic potential at full hydration (π100) and turgor loss point (ΨTLP) in wheat (Triticum aestivum) to determine the potential of using π100 to predict ΨTLP under well-watered (WW) and drought (WS) conditions. Two methods for determining π100 were tested: pressure–volume (PV) analysis and freezing point osmometry. The study also measured π100 in a range of 38 field-grown wheat cultivars to determine whether there is genetic variation in π100 under field conditions. π100 correlated with ΨTLP using both methods under both water treatments, particularly WS. Genetic variation of π100 in the field, under rainfed conditions, was greater than controlled conditions and ranged from −0.94 to −1.95 MPa. Overall, the evidence supports development of π100 as a novel tool for plant breeders to screen large populations of wheat and identify genotypes with lower ΨTLP, an integrative trait that is related to drought tolerance.

The concepts of traits, plant functional types (PFT), and functional communities are effective tools for the study of complex phenomena such as plant community assembly. Here, we (1) suggest a procedure formalising the classification of response traits to construct a PFT system; (2) integrate the PFT, and species compositional data to formally define functional communities; and, (3) identify environmental drivers that underpin the functional-community patterns. A species–trait data set featuring species pooled from two study sites (Eneabba and Cooljarloo, Western Australia), both supporting kwongan vegetation (sclerophyllous scrub and woodland communities), was subjected to classification to define PFTs. Species of both study sites were replaced with the newly derived PFTs and projected cover abundance-weighted means calculated for every plot. Functional communities were defined by classifications of the abundance-weighted PFT data in the respective sites. Distance-based redundancy analysis (using the abundance-weighted community and environmental data) was used to infer drivers of the functional community patterns for each site. A classification based on trait data assisted in reducing trait-space complexity in the studied vegetation and revealed 26 PFTs shared across the study sites. In total, seven functional communities were identified. We demonstrate a putative functional-community pattern-driving effect of soil-texture (clay—sand) gradients at Eneabba (42% of the total inertia explained) and that of water repellence at Cooljarloo (36%). Synthesis. This paper presents a procedure formalising the classification of multiple response traits leading to the delineation of PFTs and functional communities. This step captures plant responses to stresses and disturbance characteristic of kwongan vegetation, including low nutrient status, water stress, and fire (a landscape-level disturbance factor). Our study is the first to introduce a formal procedure assisting their formal recognition. Our results support the role of short-term abiotic drivers structuring the formation of fine-scale functional community patterns in a complex, species-rich vegetation of Western Australia.

In a time when global climate variability threatens the sustainability and productivity of arid ecosystems, the development of effective strategies to recover and protect soil resources and biota is crucial for the survival of these landscapes. With 20% of arid systems degraded and estimates of up to 10 Mha of land degrading each year, this issue is of global importance. In the semi-arid Pilbara region of north-west Western Australia, climatic projections suggest reductions in annual rainfall and high unpredictability of rain events. However, as these ancient landscapes are already degraded due to meteorological processes and anthropogenic activities, such as mining, the rehabilitation of this land is severely challenging. Here, we present a case study that examines, under different rainfall scenarios, the effect of two inorganic amendments (gypsum and urea) on substrate quality and growth of two plant species (Acacia inaequilatera and Triodia wiseana) native to the Pilbara region. Through an extensive glasshouse experiment, two doses of inorganic amendments were tested and compared to unamended mining waste (overburden) substrates extracted from an iron-ore mine of moderately alkaline pH and low nitrogen status. Our results showed that the addition of urea (nitrogen-based fertiliser) produced a three-fold increase of plant growth in A. inaequilatera and up to a 25-fold increase in T. wiseana compared to unamended substrates when grown under the higher watering regime but this effect was not evident in the lower water regimes. The inorganic amendments decreased pH and increased EC, total nitrogen and N-mineralisation but did not have a significant effect on soil microbial activity. Overall, water was the dominant driver for determining the effectiveness of the substrate amendments to improve the quality of mine waste substrates and increase plant growth. This study contributes to unravelling the role of inorganic amendments in post-mining rehabilitation in arid regions faced with climate change.

Plants invest their carbon resource in various strategies to enhance phosphorus (P) uptake and use when growing in low P soils. Sweet potato has evolved and persisted in P-impoverished soils, but exhibits highly variable growth and yield. Variation among sweet potato cultivars in ability to access and use P may affect growth and yield: the influence of root system traits in this regard has been little researched. In this study we explored the root traits and rhizosphere chemistry of three sweet potato cultivars under P deficient and sufficient conditions. Three sweet potato cultivars, two native to Papua New Guinea (Tambul Mai and Whagi Besta) and one internationally grown commercial cultivar (Beauregard), were grown with seven levels of P (0–360 mg P kg−1 soil added as KH2 PO4) for 84 days in a glasshouse in low P soil. Dry mass yield, tissue P concentration, root exudation of organic acids, colonisation by arbuscular mycorrhizal fungi (AMF) and root morphological and physiological traits were measured. All cultivars maintained a constant tissue P concentration below 1.0 mg P g −1 DM when P supply was low. There were few distinct differences among the cultivars in the response to P addition for growth, total root length, specific root length, root tissue density, average root diameter, root mass fraction and colonisation by AMF. Four organic acids were exuded by roots. Malate and fumarate were abundant only in cultivars from Papua New Guinea, while citrate and oxalate were common across all cultivars. Under P deficiency, all sweet potato cultivars used internal P efficiently, preferentially allocating carbon to shoots and to supporting AMF and organic acid release, rather than to increasing the root mass or forming specialised root structures. Among the root factors studied, the type of organic acid exuded was noteworthy, with citrate and malate being reported for the first time.

There is increasing concern about tree mortality around the world due to climatic extremes and associated shifts in pest and pathogen dynamics. Yet, empirical studies addressing the interactive effect of biotic and abiotic stress on plants are very rare. Therefore, in this study, we examined the interaction between drought stress and a canker pathogen, Quambalaria coyrecup, on the eucalypt – Corymbia calophylla (marri), which is experiencing increasing drought stress. We hypothesized that drought stress would increase marri’s susceptibility to canker disease, and cankers would have the largest negative effect on plants that are already drought stressed before pathogen inoculation. To test the hypotheses, in a glasshouse, marri saplings were exposed to drought either before or after pathogen inoculation, or were well-watered or droughted throughout the experiment either with or without inoculation. Canker development was greater in well-watered saplings than in droughted saplings, with the fastest development occurring in well-watered saplings that had experienced drought stress before inoculation. Irrespective of water treatments, marri saplings employed phenol-based localized biochemical defence against the pathogen. Drought reduced photosynthesis and growth, however, a negative effect of canker disease on saplings’ physiological performance was only observed in well-watered saplings. In well-watered saplings, canker-induced loss of sapwood function contributed to reduced whole-plant hydraulic conductance, photosynthesis and growth. The results provide evidence that timing of drought stress influences host physiology, and host condition influences canker disease susceptibility through differences in induced biochemical defence mechanisms. The observations highlight the importance of explicitly incorporating abiotic and biotic stress, as well as their interactions, in future studies of tree mortality in drought-prone regions worldwide.

Background and aims: In Australia’s Mediterranean hyperdiverse vegetation, species that produce cluster roots to mobilise poorly-available nutrients (e.g. Banksia spp.) are an important functional and structural component. Cluster roots are only active during the wet season, indicating a strong dependence on suitable surface soil moisture conditions. Winter rainfall in this region is declining due to global climate change, with a delayed commencement of rains and a decline in precipitation. It is unknown how lower soil moisture levels will affect the root dynamics of these globally-significant plant communities. Methods: We determined the root dynamics and root lifespan with minirhizotrons with or without irrigation to simulate reduced rainfall scenarios. Results: We found a major effect of irrigation on the early production (0.24 m m−2 d−1 increase), occurrence (97% increase) of cluster roots and only slight effects on lifespan (~10 days less) of all root types. With irrigation, the resultant greater soil moisture levels increased the deployment of cluster roots. Apart from cluster roots, the dynamics of other roots did not decline at lower soil moisture levels, suggesting that this system shows some resilience to decreased rainfall. Conclusions: Future research should focus on assessing if climate-altered cluster-root activity may be promoting compositional shifts in plant communities with additional restraining effects on root trait diversity. Fil: Teste, Francois. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; Argentina. University of Western Australia; Australia Fil: Marchesini, Victoria Angela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; Argentina. University of Western Australia; Australia Fil: Veneklaas, Erik J.. University of Western Australia; Australia Fil: Dixon, Kingsley W.. University of Western Australia; Australia. Curtin University; Australia Fil: Lambers, Hans. University of Western Australia; Australia

PREMISE OF THE STUDY Cluster-root (CR) formation is a desirable trait to improve phosphorus (P) acquisition as global P resources are dwindling. CRs in some lupine species are suppressed at higher P status. Whether increased growth rate enhances CR formation due to a "dilution" of leaf P concentration is unknown. We investigated interactive effects of leaf P status and relative growth rate (RGR) on CR formation in two Lupinus species, which differ in their CR biomass investment. Variation in RGR was imposed by varying day length. METHODS Lupinus albus and L. pilosus were grown hydroponically with KH2PO4 at a day length of 6, 10, or 14 h. We used a slightly higher P supply at longer day lengths to avoid a decline in leaf P concentration, which would induce CRs. Cluster-root percentage, leaf P concentrations, and RGR were determined at 22, 38, and 52 d after sowing. KEY RESULTS Lupinus species grown at similar root P availability, but with a faster growth rate, as dependent on day length, showed a greater CR percentage. Because our aim to achieve exactly the same leaf P concentrations at different day lengths was only partially achieved, we carried out a multiple regression analysis. This analysis showed the CR percentage was strongly and negatively correlated with plant P status and only marginally and positively correlated with RGR. CONCLUSIONS The two Lupinus species invariably formed fewer cluster roots at higher leaf P status, irrespective of RGR. Differences in RGR or leaf P concentration cannot explain the species-specific variation in cluster-root investment.