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The diversity‐functioning relationship is a pillar of ecology. Two significant concepts have emerged from this relationship: redundancy, the asymptotic relationship between diversity and functioning, and multifunctionality, a monotonic relationship between diversity and multiple functions occurring simultaneously. However, multifunctional redundancy, an asymptotic relationship between diversity and multiple functions occurring simultaneously, is rarely detected in research. Here we assess whether this lack of detection is due to its true rarity, or due to systematic research error. We discuss how inconsistencies in the use of terms such as 'function' lead to mismatched research. We consider the different techniques used to calculate multifunctionality and point out a rarely considered issue: how determining a function's maximum rate affects multifunctionality metrics. Lastly, we critique how a lack of consideration of multitrophic, spatiotemporal, interactions and community assembly processes in designed experiments significantly reduces the likelihood of detecting multifunctional redundancy. Multifunctionality research up to this stage has made significant contributions to our understanding of the diversity‐functioning relationship, and we believe that multifunctional redundancy is detectable with the use of appropriate methodologies. Redundancy, the asymptotic relationship between diversity and ecosystem functioning, and multifunctionality, a monotonic relationship between diversity and multiple functions occurring simultaneously, are significant ecological concepts. However multifunctional redundancy, an asymptotic relationship between diversity and multiple functions occurring simultaneously, is rarely detected. Here we critically review multifunctionality literature to assess if it is truly rare or simply a result of a lack of terminological and methodological consensus. [ABSTRACT FROM AUTHOR]

Aims: Climate change will impact plant communities and populations but also individual plant performance. Most predictive models of community responses to climate change ignore individual‐level biotic interactions despite their known importance for community diversity and functioning. Here, we consider plant fitness and diversity responses to climate change associated factors at three organisational levels: communities, populations and individual plants, to increase our understanding of how plant communities respond to climate change. Location: Montane grassland, Tasmania, Australia. Methods: In two plant communities, we manipulated temperature using open‐top chambers and removed random and dominant species biomass. Two years after experimental manipulations, we assessed the impact of treatments on species diversity, community‐ and population‐level functional traits and individual plant fitness. Results: Species diversity was affected by warming in one of the two communities, while community‐level functional trait diversity metrics were unaffected by treatments. Mean community trait values were strongly impacted by dominant species biomass removal in both communities, notably increasing specific leaf area (SLA) and specific root length. SLA showed the strongest population‐level trait response, with higher values found in warmed plots and lower values found in dominant species biomass removal plots. Neighbours had a stronger competitive effect on individual plant fitness in warmed compared to unwarmed conditions at the higher‐elevation site and facilitation was common in both communities. Conclusions: We demonstrated that over short time scales, plant communities respond to experimental warming and biomass removal across multiple organisational levels. Competitive and facilitative interactions played a significant role in determining fitness outcomes, but competitive interactions dominated under warmed conditions. We highlight the importance of local‐scale biotic interactions in mediating individual responses to warming and recommend their inclusion in future studies of how climate change will impact the long‐term structure and function of plant communities through short‐term impacts on individual plant fitness. [ABSTRACT FROM AUTHOR]

Increases in atmospheric carbon dioxide (CO2) and global air temperature affect all terrestrial ecosystems and often lead to enhanced ecosystem productivity, which in turn dampens the rise in atmospheric CO2 by removing CO2 from the atmosphere. As most terrestrial ecosystems are limited in their productivity by the availability of nitrogen (N), there is concern about the persistence of this terrestrial carbon sink, as these ecosystems might develop a progressive N limitation (PNL). An increase in the gross soil N turnover may alleviate PNL, as more mineral N is made available for plant uptake. So far, climate change experiments have mainly manipulated one climatic factor only, but there is evidence that single-factor experiments usually overestimate the effects of climate change on terrestrial ecosystems. In this study, we investigated how simultaneous, decadal-long increases in CO2 and temperature affect the soil gross N dynamics in a native Tasmanian grassland under C3 and C4 vegetation. Our laboratory 15N labeling experiment showed that average gross N mineralization ranged from 4.9 to 11.3 µg N g−1 day−1 across the treatment combinations, while gross nitrification was about ten-times lower. Considering all treatment combinations, no significant effect of climatic treatments or vegetation type (C3 versus C4 grasses) on soil N cycling was observed. [ABSTRACT FROM AUTHOR]

Background and aims Global warming is expected to increase the mortality rate of established plants in water-limited systems because of its effect on evapotranspiration. The rising CO2 concentration ([CO2]), however, should have the opposite effect because it reduces plant transpiration, delaying the onset of drought. This potential for elevated [CO2] (eCO2) to modify the warming effect on mortality should be related to prevailing moisture conditions. This study aimed to determine the impacts of warming by 2°C and eCO2 (550 lmol mol_1) on plant mortality in an Australian temperate grassland over a 6-year period and to test how interannual variation in rainfall influenced treatment effects. Methods Analyses were based on results from a field experiment, TasFACE, in which grassland plots were exposed to a combination of eCO2 by free air CO2 enrichment (FACE) and warming by infrared heaters. Using an annual census of established plants and detailed estimates of recruitment, annual mortality of all established plants was calculated. The influence of rainfall amount and timing on the relative impact of treatments on mortality in each year was analysed using multiple regression techniques. Key Results Warming and eCO2 effects had an interactive influence on mortality which varied strongly from year to year and this variation was determined by temporal rainfall patterns. Warming tended to increase densityadjusted mortality and eCO2 moderated that effect, but to a greater extent in years with fewer dry periods. Conclusions These results show that eCO2 reduced the negative effect of warming but this influence varied strongly with rainfall timing. Importantly, indices involving the amount of rainfall were not required to explain interannual variation in mortality or treatment effects on mortality. Therefore, predictions of global warming effects on plant mortality will be reliant not only on other climate change factors, but also on the temporal distribution of rainfall. [ABSTRACT FROM AUTHOR]

The relationship between species richness and productivity is important from both a basic, theoretical perspective and also because it has important ramifications for applied ecology including ecosystem restoration and the design of carbon offset plantings. While a more species-rich community is often believed to be more productive than a species-poor community, findings from observational and experimental studies differ and our understanding of the relationship comes largely from grasslands. Consequently, we aimed to determine for the first time the nature of the species richness-productivity relationship in a southern-hemisphere dry sclerophyll ecosystem. We investigated the impact of species richness on productivity, plant density and mean plant biomass at three sowing densities in three species assemblages. E ucalyptus globulus, A cacia mearnsii and A llocasuarina verticillata were each grown as monocultures and included in every subsequent level of species richness, forming three distinct species assemblages. Communities were grown in a glasshouse pot experiment for four months, then harvested and above-ground biomass measured. We found no general species richness-productivity relationship in the communities studied. There were no overall increases in productivity as species richness increased and in fact in most cases the productivity of communities with 4 and 8 species was lower than monocultures of the dominants. Importantly, density influenced the way richness affected productivity and this effect was dependent upon assemblage, indicating that species identity is a key determinant of productivity. These results demonstrate important ecological principles in a previously untested system. A key outcome of this experiment is that density alters the relationship between species richness and initial productivity in assemblages of Australian dry sclerophyll species. [ABSTRACT FROM AUTHOR]

Interactions among neighbouring plants are key determinants of plant growth. To characterise the cumulative effect of all neighbours on the growth of a focal plant, neighbourhoods are often described by 'competition' indices. Common competition indices calculate the summed size of neighbour plants (focal‐independent index [FII]) whilst others include the summed ratio of the neighbour size relative to focal plant size (focal dependent). A frequently overlooked statistical artefact is that focal‐dependent indices (FDIs) may lead to biased estimates of neighbourhood effects on plant growth when growth is size dependent.Here, we conduct a literature search to determine the most common index types used to explain neighbour effects on tree growth. We then assess the ability of two common index types—focal dependent and focal independent—to correctly infer neighbourhood effects in (1) observations of tree growth in an experimental forest in south‐east Tasmania, Australia, and (2) an artificially created dataset where tree growth is unrelated to the neighbourhood.Both indices detected the competitive neighbourhood effect on tree growth observed in our own dataset but differed in their conclusion regarding neighbour effects in the simulated data. Despite the simulated dataset being generated so there was no relationship between tree growth and their neighbourhood, the FDI detected strong, competitive neighbourhood effects when intrinsic growth was incorrectly related to tree size. In contrast, when we considered the FII as the neighbourhood metric, we correctly did not detect any neighbourhood effects in the simulated data regardless of how size‐dependent growth was described.Synthesis. 'Competition' indices are a useful method to characterise the cumulative neighbourhood effect on plant growth; however, we demonstrate that indices which include the size of the focal plant in their calculation can be biased by an inherent relationship between tree growth and initial size. Whilst this bias typically overstates the strength of competition in determining focal tree growth, we show that it can be mitigated by correctly describing intrinsic growth. We discuss the limitations of both index types, provide recommendations for performing statistical modelling and outline how to check for accurate neighbour inference. [ABSTRACT FROM AUTHOR]

Highlights: [•] The impact of limited water availability on juvenile Eucalyptus was explored. [•] Young leaves had higher secondary metabolite (PSM) concentrations than old leaves. [•] Water limitation decreased phenolics, the C:N, growth and leaf water content. [•] Terpenes, tannins and formylated phloroglucinol compounds remained stable. [•] We conclude significant species and leaf PSM variation, minimal treatment effect. [Copyright &y& Elsevier]

The rising atmospheric concentration of carbon dioxide (CO2) should stimulate ecosystem productivity, but to what extent is highly uncertain, particularly when combined with changing temperature and precipitation. Ecosystem response to CO2 is complicated by biogeochemical feedbacks but must be understood if carbon storage and associated dampening of climate warming are to be predicted. Feedbacks through the hydrological cycle are particularly important and the physiology is well known; elevated CO2 reduces stomatal conductance and increases plant water use efficiency (the amount of water required to produce a unit of plant dry matter). The CO2 response should consequently be strongest when water is limiting; although this has been shown in some experiments, it is absent from many. Here we show that large annual variation in the stimulation of above-ground biomass by elevated CO2 in a mixed C3/C4 temperate grassland can be predicted accurately using seasonal rainfall totals; summer rainfall had a positive effect but autumn and spring rainfall had negative effects on the CO2 response. Thus, the elevated CO2 effect mainly depended upon the balance between summer and autumn/spring rainfall. This is partly because high rainfall during cool, moist seasons leads to nitrogen limitation, reducing or even preventing biomass stimulation by elevated CO2. Importantly, the prediction held whether plots were warmed by 2 °C or left unwarmed, and was similar for C3 plants and total biomass, allowing us to make a powerful generalization about ecosystem responses to elevated CO2. This new insight is particularly valuable because climate projections predict large changes in the timing of rainfall, even where annual totals remain static. Our findings will help resolve apparent differences in the outcomes of CO2 experiments and improve the formulation and interpretation of models that are insensitive to differences in the seasonal effects of rainfall on the CO2 response. [ABSTRACT FROM AUTHOR]

The increasing atmospheric concentration of carbon dioxide ([CO2]) contributes to global warming and the accompanying shifts in climate. However, [CO2] itself has the potential to impact on Australia's terrestrial biodiversity, due to its importance in the photosynthetic process, which underlies all terrestrial food webs. Here, we review our knowledge regarding the impacts of elevated [CO2] on native terrestrial species and ecosystems, and suggest key areas in which we have little information on this topic. Experimental information exists for 70 (or less than 0.05%) of Australia's native terrestrial plant and animal species. Of these, 68 are vascular plants. The growth of Australian woody species is more reliably increased by elevated [CO2] than it is in grasses. At the species level, the most overwhelming responses to increased [CO2] are a reduction in plant nitrogen concentration and an increase in the production of secondary metabolites. This is of particular concern for Australia's unique herbivorous and granivorous marsupials, for which no information is available. While many plant species also displayed increased growth rates at higher [CO2], this was far from universal, indicating that changes in community structure and function are likely, leading to alterations of habitat quality. Future research should be directed to key knowledge gaps including the relationship between [CO2], fire frequency and fire tolerance and the impacts of increasing [CO2] for Australia's iconic browsing mammals. We also know virtually nothing of the impacts of the increasing [CO2] on Australia's unique shrublands and semi-arid/arid rangelands. In conclusion, there is sufficient information available to be certain that the increasing [CO2] will affect Australia's native biodiversity. However, the information required to formulate predictions concerning the long-term future of almost all organisms is far in excess of that currently available. [ABSTRACT FROM AUTHOR]

• In a water-limited system, the following hypotheses are proposed: warming will increase seedling mortality; elevated atmospheric CO2 will reduce seedling mortality by reducing transpiration, thereby increasing soil water availability; and longevity (i.e. whether a species is annual or perennial) will affect the response of a species to global changes. • Here, these three hypotheses are tested by assessing the impact of elevated CO2 (550 µmol mol−1) and warming (+2°C) on seedling emergence, survivorship and establishment in an Australian temperate grassland from autumn 2004 to autumn 2007. • Warming impacts on seedling survivorship were dependent upon species longevity. Warming reduced seedling survivorship of perennials through its effects on soil water potential but the seedling survivorship of annuals was reduced to a greater extent than could be accounted for by treatment effects on soil water potential. Elevated CO2 did not significantly affect seedling survivorship in annuals or perennials. • These results show that warming will alter recruitment of perennial species by changing soil water potential but will reduce recruitment of annual species independent of any effects on soil moisture. The results also show that exposure to elevated CO2 does not make seedlings more resistant to dry soils. [ABSTRACT FROM AUTHOR]

While the influence of elevated CO2 on the production, mass and quality of plant seeds has been well studied, the effect of warming on these characters is largely unknown; and there is practically no information on possible interactions between warming and elevated CO2, despite the importance of these characters in population maintenance and recovery. Here, we present the impacts of elevated CO2 and warming, both in isolation and combination, on seed production, mass, quality, germination success and subsequent seedling growth of Austrodanthonia caespitosa, a dominant temperate C3 grass from Australia, using seeds collected from the TasFACE experiment. Mean seed production and mass were not significantly affected by either elevated CO2 or warming, but elevated CO2 more than doubled the proportion of very light, inviable seeds ( P < 0.05) and halved mean seed N concentration ( P < 0.04) and N content ( P < 0.03). The dependence of seed germination success on seed mass was affected by an elevated CO2× warming interaction ( P < 0.004), such that maternal exposure to elevated CO2 or warming reduced germination if applied in isolation, but not when applied in combination. Maternal effects were retained when seedlings were grown in a common environment for 6 weeks, with seedlings descended from warmed plants 20% smaller ( P < 0.008) with a higher root : shoot ratio ( P < 0.001) than those from unwarmed plants. Given that both elevated CO2 and warming reduced seed mass, quality, germinability or seedling growth, it is likely that global change will reduce population growth or distribution of this dominant species. [ABSTRACT FROM AUTHOR]

• Flowering is a critical stage in plant life cycles, and changes might alter processes at the species, community and ecosystem levels. Therefore, likely flowering-time responses to global change drivers are needed for predictions of global change impacts on natural and managed ecosystems. • Here, the impact of elevated atmospheric CO2 concentration ([CO2]) (550 µmol mol−1) and warming (+2ºC) is reported on flowering times in a native, species-rich, temperate grassland in Tasmania, Australia in both 2004 and 2005. • Elevated [CO2] did not affect average time of first flowering in either year, only affecting three out of 23 species. Warming reduced time to first flowering by an average of 19.1 d in 2004, acting on most species, but did not significantly alter flowering time in 2005, which might be related to the timing of rainfall. Elevated [CO2] and warming treatments did not interact on flowering time. • These results show elevated [CO2] did not alter average flowering time or duration in this grassland; neither did it alter the response to warming. Therefore, flowering phenology appears insensitive to increasing [CO2] in this ecosystem, although the response to warming varies between years but can be strong. [ABSTRACT FROM AUTHOR]

Rising atmospheric carbon dioxide concentration ([CO2]) has the potential to stimulate ecosystem productivity and sink strength, reducing the effects of carbon (C) emissions on climate. In terrestrial ecosystems, increasing [CO2] can reduce soil nitrogen (N) availability to plants, preventing the stimulation of ecosystem C assimilation; a process known as progressive N limitation. Using ion exchange membranes to assess the availability of dissolved organic N, ammonium and nitrate, we found that CO2 enrichment in an Australian, temperate, perennial grassland did not increase plant productivity, but did reduce soil N availability, mostly by reducing nitrate availability. Importantly, the addition of 2 °C warming prevented this effect while warming without CO2 enrichment did not significantly affect N availability. These findings indicate that warming could play an important role in the impact of [CO2] on ecosystem N cycling, potentially overturning CO2-induced effects in some ecosystems. [ABSTRACT FROM AUTHOR]

• Leaf morphology varies reliably with increasing altitude in many species, and this is generally considered to be related to temperature. Changes in irradiance with elevation may confound any relationships between a morphological character and altitude, particularly if altitude of origin affects the response to irradiance. • Here we describe the interaction between irradiance and altitude of origin on leaf morphology of Southern beech, Nothofagus cunninghamii. Cuttings from each of four altitudes were grown in a glasshouse under full sunlight or 50% shade, and leaf morphology was related to irradiance, altitude of origin and accession. • There was a significant interaction between irradiance and altitude of origin for leaf length, width, thickness, area, weight, specific leaf area and stomatal density. There was no effect of altitude on leaf length to width ratio or stomatal index, nor was there an interaction between irradiance and altitude of origin for these variables. • These results show that the altitude of origin of a plant has an overriding impact on the leaf morphological response to irradiance. This must be considered in climatic reconstructions. [ABSTRACT FROM AUTHOR]

The impact of introduced ship rats (Rattus rattus) on recruitment of the megaherbPleurophyllum hookeriBuchan. (Asteraceae) was examined on subantarctic Macquarie Island, an island with no extant native terrestrial vertebrates.Pleurophyllum hookeri(Asteraceae) forms a dominant component of the Macquarie Island vegetation and is restricted to the subantarctic. The Macquarie Island population ofP. hookeriis the most extensive and intact. Introduced ship rats (Rattus rattus) are well established in tall tussock grassland of Macquarie Island. We detected rat activity for the first time withinP. hookeriherbfields, in autumn 2000. We found rats were destroying up to 90% of racemes. By excluding rats from caches of inflorescences that they had formed, we found they were having a significant negative effect on initial recruitment and seedling survival within the caches. However, because of high seedling mortality after 1 year, there was no sustained impact of the exclosures onP. hookeriseedling density. [ABSTRACT FROM AUTHOR]

Leaf morphology varies predictably with altitude, and leaf morphological features have been used to estimate average temperatures from fossil leaves. The altitude-leaf morphology relationship is confounded by the two processes of acclimation and adaptation, which reflect environmental and genetic influences, respectively. Here we describe the relationship between altitude and leaf morphology for Southern beech, Nothofagus cunninghamii (Hook.) Oerst.. Cuttings from several trees from each of four altitudes were grown in a common glasshouse experiment, and leaf morphology related to both genotype and altitude of origin. Genotype had a significant impact on leaf morphology, but in the field there was also a significant, overriding effect of altitude. This altitude effect disappeared in glasshouse-grown plants for all morphological variables other than leaf thickness and specific leaf area. These results show that, while leaf length, width and area are partially controlled by genetic factors, these variables are plastic and respond to environmental influences associated with a particular altitude. Thus altitudinal trends in leaf size in N. cunninghamii are unlikely to be the result of adaptation. [ABSTRACT FROM AUTHOR]

Plant growth is influenced by interactions with neighbouring plants. The strength and direction of the cumulative neighbourhood effect on growth can depend on neighbour properties, such as their abundance, size and proximity, as well as the degree of similarity between interacting plants and their traits, which can be captured by the species identity of neighbours. Such interactions are also influenced by the local environmental conditions that are largely determined by climate. Because neighbour and climatic effects are typically explored in isolation, particularly in long‐lived species such as trees, it is unclear how the impacts of neighbours on plant growth shift in response to temporal variation in climatic conditions.Here, we explored how neighbouring plants impact the annual growth of two eucalypts, Eucalyptus delegatensis and Eucalyptus regnans, over three growing seasons in an experimental forest in south‐east Tasmania, Australia. We assessed whether eucalypt growth rates could be described by the number, size, proximity, and species identity of neighbours, and how the strength of this effect was influenced by the growing season climatic conditions.We found that climate and neighbouring plants had an interactive impact on eucalypt growth. Neighbours had a consistent, competitive effect on the growth of both eucalypts in all three growing seasons which was strongly related to the cumulative neighbourhood biomass. The identity of neighbours was important in determining E. regnans growth only, whereby distinguishing neighbours according to functional group best described growth. Over all three growing seasons, we predicted that, on average, neighbours reduced E. delegatensis and E. regnans mean annual growth by 60.5% and 48.4%, respectively. However, the strength of the competitive effect of neighbours on eucalypt growth was related to growing season climate, being strongest when conditions were hot and dry and weakest in cool, wet conditions.Synthesis: Given the consistent results observed in two co‐occurring eucalypts, our findings suggest that drier and hotter climatic conditions increase the strength of competitive effects on tree growth. This has implications for future forest productivity given projected increased temperatures and variation in rainfall patterns globally. [ABSTRACT FROM AUTHOR]

Plant morphology and architecture are essential characteristics for all plants, but perhaps most importantly for agricultural species because economic traits are linked to simple features such as blade length and plant height. Key morphological traits likely respond to CO2 concentration ([CO2]), and the degree of this response could be influenced by water availability; however, this has received comparatively little research attention. This study aimed to determine the impacts of [CO2] on gross morphology of perennial ryegrass (Lolium perenne L.), the most widespread temperate pasture species, and whether these impacts are influenced by water availability. Perennial ryegrass cv. Base AR37 was grown in a well-fertilised FACE (free-air carbon dioxide enrichment) experiment in southern Tasmania. Plants were exposed to three CO2 concentrations (~400 (ambient), 475 and 550 µmol mol–1) at three watering-treatment levels (adequate, limited and excess). Shoot dry weight, height, total leaf area, leaf-blade separation, leaf size, relative water content and specific leaf area were determined, as well as shoot density per unit area as a measure of tillering. Plant morphology responded dramatically to elevated [CO2], plants being smaller with shorter leaf-blade separation lengths and smaller leaves than in ambient (control) plots. Elevated [CO2] increased tillering but did not substantially affect relative water content or specific leaf area. Water supply did not affect any measured trait or the response to elevated [CO2]. Observed impacts of elevated [CO2] on the morphology of a globally important forage crop could have profound implications for pasture productivity. The reductions in plant and leaf size were consistent across a range of soil-water availability, indicating that they are likely to be uniform. Elucidating the mechanisms driving these responses will be essential to improving predictability of these changes and may assist in breeding varieties suited to future conditions. Plant morphology is particularly important for agricultural species because economically important traits are linked to simple features such as blade length and plant height. We tested the combined effects of elevated CO2 and water supply on morphological traits of Lolium perenne and found that sizes of leaves and individual tillers were dramatically smaller in plants grown at elevated CO2, independent of water supply. This will have important implications for selective breeding and pasture productivity under future conditions. [ABSTRACT FROM AUTHOR]

When a plant is introduced to a new ecosystem it may escape from some of its coevolved herbivores. Reduced herbivore damage, and the ability of introduced plants to allocate resources from defence to growth and reproduction can increase the success of introduced species. This mechanism is known as enemy release and is known to occur in some species and situations, but not in others. Understanding the conditions under which enemy release is most likely to occur is important, as this will help us to identify which species and habitats may be most at risk of invasion. We compared in situ measurements of herbivory on 16 plant species at 12 locations within their native European and introduced Australian ranges to quantify their level of enemy release and understand the relationship between enemy release and time, space and climate. Overall, plants experienced approximately seven times more herbivore damage in their native range than in their introduced range. We found no evidence that enemy release was related to time since introduction, introduced range size, temperature, precipitation, humidity or elevation. From here, we can explore whether traits, such as leaf defences or phylogenetic relatedness to neighbouring plants, are stronger indicators of enemy release across species. [ABSTRACT FROM AUTHOR]

* Background and aims Drought leading to soil water deficit can have severe impacts on plants. Water deficit may lead to plant water stress and affect growth and chemical traits. Plant secondary metabolite (PSM) responses to water deficit vary between compounds and studies, with inconsistent reports of changes to PSM concentrations even within a single species. This disparity may result from experimental water deficit variation among studies, and so multiple water deficit treatments are used to fully assess PSM responses in a single species. * Methods Juvenile Eucalyptus globulus were grown for 8 weeks at one of ten water deficit levels based on evapotranspiration from control plants (100 %). Treatments ranged from 90 % of control evapotranspiration (mild water deficit) to 0 % of control evapotranspiration (severe water deficit) in 10 % steps. Plant biomass, foliar abscisic acid (ABA) levels, Ψleaf, leaf C/N, selected terpenes and phenolics were quantified to assess responses to each level of water deficit relative to a control. * Key Results Withholding ≥30 % water resulted in higher foliar ABA levels and withholding ≥40 % water reduced leaf water content. Ψleaf became more negative when ≥60 % water was withheld. Plant biomass was lower when ≥80 % water was withheld, and no water for 8 weeks (0 % water) resulted in plant death. The total oil concentration was lower and C/N was higher in dead and desiccated juvenile E. globulus leaves (0 % water). Concentrations of individual phenolic and terpene compounds, along with condensed tannin and total phenolic concentrations, remained stable regardless of water deficit or plant stress level. * Conclusions These juvenile E. globulus became stressed with a moderate reduction in available water, and yet the persistent concentrations of most PSMs in highly stressed or dead plants suggests no PSM re-metabolization and continued ecological roles of foliar PSMs during drought. [ABSTRACT FROM AUTHOR]

Summary: Vulnerability to xylem cavitation is a strong predictor of drought‐induced damage in forest communities. However, biotic features of the community itself can influence water availability at the individual tree‐level, thereby modifying patterns of drought damage.Using an experimental forest in Tasmania, Australia, we determined the vulnerability to cavitation (leaf P50) of four tree species and assessed the drought‐induced canopy damage of 2944 6‐yr‐old trees after an extreme natural drought episode. We examined how individual damage was related to their size and the density and species identity of neighbouring trees.The two co‐occurring dominant tree species, Eucalyptus delegatensis and Eucalyptus regnans, were the most vulnerable to drought‐induced xylem cavitation and both species suffered significantly greater damage than neighbouring, subdominant species Pomaderris apetala and Acacia dealbata. While the two eucalypts had similar leaf P50 values, E. delegatensis suffered significantly greater damage, which was strongly related to the density of neighbouring P. apetala. Damage in E. regnans was less impacted by neighbouring plants and smaller trees of both eucalypts sustained significantly more damage than larger trees.Our findings demonstrate that natural drought damage is influenced by individual plant physiology as well as the composition, physiology and density of the surrounding stand. [ABSTRACT FROM AUTHOR]

Summary: Large intraspecific functional trait variation strongly impacts many aspects of communities and ecosystems, and is the medium upon which evolution works. Yet intraspecific trait variation is inconsistent and hard to predict across traits, species and locations.We measured within‐species variation in leaf mass per area (LMA), leaf dry matter content (LDMC), branch wood density (WD), and allocation to stem area vs leaf area in branches (branch Huber value (HV)) across the aridity range of seven Australian eucalypts and a co‐occurring Acacia species to explore how traits and their variances change with aridity.Within species, we found consistent increases in LMA, LDMC and WD and HV with increasing aridity, resulting in consistent trait coordination across leaves and branches. However, this coordination only emerged across sites with large climate differences. Unlike trait means, patterns of trait variance with aridity were mixed across populations and species. Only LDMC showed constrained trait variation in more xeric species and drier populations that could indicate limits to plasticity or heritable trait variation.Our results highlight that climate can drive consistent within‐species trait patterns, but that patterns might often be obscured by the complex nature of morphological traits, sampling incomplete species ranges or sampling confounded stress gradients. See also the Commentary on this article by Ahrens et al., 229: 1183–1185. [ABSTRACT FROM AUTHOR]

Elevated CO2 is widely accepted to enhance terrestrial carbon sink, especially in arid and semi‐arid regions. However, great uncertainties exist for the CO2 fertilisation effects, particularly when its interactions with other global change factors are considered. A four‐factor (CO2, temperature, precipitation and nitrogen) experiment revealed that elevated CO2 did not affect either gross ecosystem productivity or ecosystem respiration, and consequently resulted in no changes of net ecosystem productivity in a semi‐arid grassland despite whether temperature, precipitation and nitrogen were elevated or not. The observations could be primarily attributable to the offset of ecosystem carbon uptake by enhanced soil carbon release under CO2 enrichment. Our findings indicate that arid and semi‐arid ecosystems may not be sensitive to CO2 enrichment as previously expected and highlight the urgent need to incorporate this mechanism into most IPCC carbon‐cycle models for convincing projection of terrestrial carbon sink and its feedback to climate change. [ABSTRACT FROM AUTHOR]

The responses of species to environmental changes will determine future community composition and ecosystem function. Many syntheses of global change experiments examine the magnitude of treatment effect sizes, but we lack an understanding of how plant responses to treatments compare to ongoing changes in the unmanipulated (ambient or background) system. We used a database of long‐term global change studies manipulating CO2, nutrients, water, and temperature to answer three questions: (a) How do changes in plant species abundance in ambient plots relate to those in treated plots? (b) How does the magnitude of ambient change in species‐level abundance over time relate to responsiveness to global change treatments? (c) Does the direction of species‐level responses to global change treatments differ from the direction of ambient change? We estimated temporal trends in plant abundance for 791 plant species in ambient and treated plots across 16 long‐term global change experiments yielding 2,116 experiment–species–treatment combinations. Surprisingly, for most species (57%) the magnitude of ambient change was greater than the magnitude of treatment effects. However, the direction of ambient change, whether a species was increasing or decreasing in abundance under ambient conditions, had no bearing on the direction of treatment effects. Although ambient communities are inherently dynamic, there is now widespread evidence that anthropogenic drivers are directionally altering plant communities in many ecosystems. Thus, global change treatment effects must be interpreted in the context of plant species trajectories that are likely driven by ongoing environmental changes. Across 16 long‐term global change experiments, we found strong patterns of change in plant species abundance in ambient plots. Experimental treatment effects were smaller than ambient change in magnitude for most species and only rarely reversed the direction of ambient change. [ABSTRACT FROM AUTHOR]

Increasing concentrations of atmospheric carbon dioxide are expected to affect carbon assimilation and evapotranspiration (ET), ultimately driving changes in plant growth, hydrology, and the global carbon balance. Direct leaf biochemical effects have been widely investigated, whereas indirect effects, although documented, elude explicit quantification in experiments. Here, we used a mechanistic model to investigate the relative contributions of direct (through carbon assimilation) and indirect (via soil moisture savings due to stomatal closure, and changes in leaf area index) effects of elevated CO2 across a variety of ecosystems. We specifically determined which ecosystems and climatic conditions maximize the indirect effects of elevated CO2. The simulations suggest that the indirect effects of elevated CO2 on net primary productivity are large and variable, ranging from less than 10% to more than 100% of the size of direct effects. For ET, indirect effects were, on average, 65% of the size of direct effects. Indirect effects tended to be considerably larger in water-limited ecosystems. As a consequence, the total CO2 effect had a significant, inverse relationship with the wetness index and was directly related to vapor pressure deficit. These results have major implications for our understanding of the CO2 response of ecosystems and for global projections of CO2 fertilization, because, although direct effects are typically understood and easily reproducible in models, simulations of indirect effects are far more challenging and difficult to constrain. Our findings also provide an explanation for the discrepancies between experiments in the total CO2 effect on net primary productivity. [ABSTRACT FROM AUTHOR]

Water deficit associated with drought can severely affect plants and influence ecological interactions involving plant secondary metabolites. We tested the effect of mild water deficit and rewatering on physiological, morphological and chemical traits of juvenile Eucalyptus globulus Labill. and Eucalyptus viminalis Labill. We also tested if responses of juvenile eucalypts to water deficit and rewatering varied within species using provenances across a rainfall gradient. Both species and all provenances were similarly affected by mild water deficit and rewatering, as only foliar abscisic acid levels differed among provenances during water deficit. Across species and provenances, water deficit decreased leaf water potential, above-ground biomass and formylated phloroglucinol compound concentrations, and increased condensed tannin concentrations. Rewatering reduced leaf carbon : nitrogen, and total phenolic and chlorogenic acid concentrations. Water deficit and rewatering had no effect on total oil or individual terpene concentrations. Levels of trait plasticity due to water deficit and rewatering were less than levels of constitutive trait variation among provenances. The overall uniformity of responses to the treatments regardless of native provenance indicates limited diversification of plastic responses when compared with the larger quantitative variation of constitutive traits within these species. These responses to mild water deficit may differ from responses to more extreme water deficit or to responses of juvenile/mature eucalypts growing at each locality. [ABSTRACT FROM AUTHOR]

The net annual exchange of carbon between the atmosphere and terrestrial ecosystems is of prime importance in determining the concentration of CO2 ([CO2]) in the atmosphere and consequently future climate. Carbon loss occurs primarily through soil respiration; it is known that respiration is sensitive to the global changes in [CO2] and temperature, suggesting that the net carbon balance may change in the future. However, field manipulations of temperature and [CO2] alter many important environmental factors so it is unclear how much of the observed alterations in soil respiration is due to changes of microbial function itself instead of changes to the physical and chemical environment. Here we focus on resolving the importance of changes in the microbial community in response to warming and elevated [CO2] on carbon mineralisation, something not possible in field measurements. We took plant material and soil inocula from a long running experiment where native grassland had been exposed to both warming and elevated CO2 and constructed a reciprocal transplant experiment. We found that the rate of decomposition (heterotrophic respiration) was strongly determined by the origin of the microbial community. The combined warming + elevated CO2 treatment produced a soil community that gave respiration rates 30% higher when provided with shoot litter and 70% for root litter than elevated CO2 treatment alone, with the treatment source of the litter being unimportant. Warming, especially in the presence of elevated CO2, increased the size of the apparent labile carbon pool when either C3 or C4 litter was added. Thus, the metabolic activity of the soil community was affected by the combination of warming and elevated CO2 such that it had an increased ability to mineralise added organic matter, regardless of its source. Therefore, soil C efflux may be substantially increased in a warmer, high CO2 world. Current ecosystem models mostly drive heterotrophic respiration from plant litter quality, soil moisture and temperature but our findings suggest equal attention will need to be paid to capturing microbial processes if we are to accurately project the future C balance of terrestrial ecosystems and quantify the feedback effect on atmospheric concentrations of CO2. [ABSTRACT FROM AUTHOR]

Our limited understanding of terrestrial ecosystem responses to elevated CO2 is a major constraint on predicting the impacts of climate change. A change in botanical composition has been identified as a key factor in the CO2 response with profound implications for ecosystem services such as plant production and soil carbon storage. In temperate grasslands, there is a strong consensus that elevated CO2 will result in a greater physiological stimulus to growth in legumes and to a lesser extent forbs, compared with C3 grasses, and the presumption this will lead in turn to a greater proportion of these functional groups in the plant community. However, this view is based on data mainly collected in experiments of three or less years in duration and not in experiments where defoliation has been by grazing animals. Grazing is, however, the most common management of grasslands and known in itself to influence botanical composition. In a long-term Free Air Carbon Dioxide Enrichment ( FACE) experiment in a temperate grassland managed with grazing animals (sheep), we found the response to elevated CO2 in plant community composition in the first 5 years was consistent with the expectation of increased proportions of legumes and forbs. However, in the longer term, these differences diminished so that the proportions of grasses, legumes and forbs were the same under both ambient and elevated CO2. Analysis of vegetation before and after each grazing event showed there was a sustained disproportionately greater removal ('apparent selection') of legumes and forbs by the grazing animals. This bias in removal was greater under elevated CO2 than ambient CO2. This is consistent with sustained faster growth rates of legumes and forbs under elevated CO2 being countered by selective defoliation, and so leading to little difference in community composition. [ABSTRACT FROM AUTHOR]

The microbial community structure of bacteria, archaea and fungi is described in an Australian native grassland soil after more than 5 years exposure to different atmospheric CO2 concentrations ([ CO2]) (ambient, + 550 ppm) and temperatures (ambient, + 2°C) under different plant functional types ( C3 and C4 grasses) and at two soil depths (0-5 cm and 5-10 cm). Archaeal community diversity was influenced by elevated [ CO2], while under warming archaeal 16S rRNA gene copy numbers increased for C4 plant Themeda triandra and decreased for the C3 plant community ( P < 0.05). Fungal community diversity resulted in three groups based upon elevated [ CO2], elevated [ CO2] plus warming and ambient [ CO2]. Overall bacterial community diversity was influenced primarily by depth. Specific bacterial taxa changed in richness and relative abundance in response to climate change factors when assessed by a high-resolution 16 S rRNA microarray ( PhyloChip). Operational taxonomic unit signal intensities increased under elevated [ CO2] for both Firmicutes and Bacteroidetes, and increased under warming for Actinobacteria and Alphaproteobacteria. For the interaction of elevated [ CO2] and warming there were 103 significant operational taxonomic units ( P < 0.01) representing 15 phyla and 30 classes. The majority of these operational taxonomic units increased in abundance for elevated [ CO2] plus warming plots, while abundance declined in warmed or elevated [ CO2] plots. Bacterial abundance (16 S rRNA gene copy number) was significantly different for the interaction of elevated [ CO2] and depth ( P < 0.05) with decreased abundance under elevated [ CO2] at 5-10 cm, and for Firmicutes under elevated [ CO2] ( P < 0.05). Bacteria, archaea and fungi in soil responded differently to elevated [ CO2], warming and their interaction. Taxa identified as significantly climate-responsive could show differing trends in the direction of response ('+' or '−') under elevated CO2 or warming, which could then not be used to predict their interactive effects supporting the need to investigate interactive effects for climate change. The approach of focusing on specific taxonomic groups provides greater potential for understanding complex microbial community changes in ecosystems under climate change. [ABSTRACT FROM AUTHOR]

In recent years, increased awareness of the potential interactions between rising atmospheric CO2 concentrations ([ CO2 ]) and temperature has illustrated the importance of multifactorial ecosystem manipulation experiments for validating Earth System models. To address the urgent need for increased understanding of responses in multifactorial experiments, this article synthesizes how ecosystem productivity and soil processes respond to combined warming and [ CO2 ] manipulation, and compares it with those obtained in single factor [ CO2 ] and temperature manipulation experiments. Across all combined elevated [ CO2 ] and warming experiments, biomass production and soil respiration were typically enhanced. Responses to the combined treatment were more similar to those in the [ CO2 ]-only treatment than to those in the warming-only treatment. In contrast to warming-only experiments, both the combined and the [ CO2 ]-only treatments elicited larger stimulation of fine root biomass than of aboveground biomass, consistently stimulated soil respiration, and decreased foliar nitrogen (N) concentration. Nonetheless, mineral N availability declined less in the combined treatment than in the [ CO2 ]-only treatment, possibly due to the warming-induced acceleration of decomposition, implying that progressive nitrogen limitation ( PNL) may not occur as commonly as anticipated from single factor [ CO2 ] treatment studies. Responses of total plant biomass, especially of aboveground biomass, revealed antagonistic interactions between elevated [ CO2 ] and warming, i.e. the response to the combined treatment was usually less-than-additive. This implies that productivity projections might be overestimated when models are parameterized based on single factor responses. Our results highlight the need for more (and especially more long-term) multifactor manipulation experiments. Because single factor CO2 responses often dominated over warming responses in the combined treatments, our results also suggest that projected responses to future global warming in Earth System models should not be parameterized using single factor warming experiments. [ABSTRACT FROM AUTHOR]

The stability of soil organic matter (SOM) pools exposed to elevated CO and warming has not been evaluated adequately in long-term experiments and represents a substantial source of uncertainty in predicting ecosystem feedbacks to climate change. We conducted a 6-year experiment combining free-air CO enrichment (FACE, 550 ppm) and warming (+2 °C) to evaluate changes in SOM accumulation in native Australian grassland. In this system, competitive interactions appear to favor C over C species under FACE and warming. We therefore investigated the role of plant functional type (FT) on biomass and SOM responses to the long-term treatments by carefully sampling soil under patches of C- and C-dominated vegetation. We used physical fractionation to quantify particulate organic matter (POM) and long-term incubation to assess potential decomposition rates. Aboveground production of C grasses increased in response to FACE, but total root biomass declined. Across treatments, C : N ratios were higher in leaves, roots and POM of C vegetation. CO and temperature treatments interacted with FT to influence SOM, and especially POM, such that soil carbon was increased by warming under C vegetation, but not in combination with elevated CO. Potential decomposition rates increased in response to FACE and decreased with warming, possibly owing to treatment effects on soil moisture and microbial community composition. Decomposition was also inversely correlated with root N concentration, suggesting increased microbial demand for older, N-rich SOM in treatments with low root N inputs. This research suggests that C-C vegetation responses to future climate conditions will strongly influence SOM storage in temperate grasslands. [ABSTRACT FROM AUTHOR]

• Species differ in their responses to global changes such as rising CO2 and temperature, meaning that global changes are likely to change the structure of plant communities. Such alterations in community composition must be underlain by changes in the population dynamics of component species. • Here, the impact of elevated CO2 (550 µmol mol−1) and warming (+2°C) on the population growth of four plant species important in Australian temperate grasslands is reported. Data collected from the Tasmanian free-air CO2 enrichment (TasFACE) experiment between 2003 and 2006 were analysed using population matrix models. • Population growth of Themeda triandra, a perennial C4 grass, was largely unaffected by either factor but population growth of Austrodanthonia caespitosa, a perennial C3 grass, was reduced substantially in elevated CO2 plots. Warming and elevated CO2 had antagonistic effects on population growth of two invasive weeds, Hypochaeris radicata and Leontodon taraxacoides, with warming causing population decline. Analysis of life cycle stages showed that seed production, seedling emergence and establishment were important factors in the responses of the species to global changes. • These results show that the demographic approach is very useful in understanding the variable responses of plants to global changes and in elucidating the life cycle stages that are most responsive. [ABSTRACT FROM AUTHOR]