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Trade-offs exist for xerophytic shrubs between functional traits, involving in water loss and assimilate accumulation, can contribute to its survival and growth rate regulation in arid environments. However, growth analysis based on plant functional traits has been focused on the study of herbs and woody species. It is still unclear how the functional traits of xerophytic shrubs regulate their growth rate. In this study, we selectedeight xerophytic shrubs as samples to analyze the regulation process of the functional traits of shrubs on growth rate. Plants were cultivated for three years, and three harvests (every one year) were carried out. Factors explaining between-species differences in relative growth rate (RGR) varied, depending on whether different ages were considered. The results showed that RGR was positively correlated with net assimilation rate, but there was a significant negative correlation with leaf area ration (LAR), specific leaf area (SLA), and leaf biomass ratio in the age 1. However, in the age 2, RGR showed a significant positive correlation with the morphological traits (i.e., leaf area ration and specific leaf area), but not with physiological traits (i.e., net assimilation rate) and leaf biomass allocation. Our results suggested that the fluctuation of environmental factors affects the regulation path of the plant functional traits on RGR of xerophytic shrubs. However, the analysis of causality model showed that no matter in which age, net assimilation rate and leaf area ration principally drive the variation in RGR among xerophytic shrubs.

Italian ryegrass (Lolium multiflorum) is a widely cultivated forage with high nutritional value and good palatability. Salinity, however, is a negative factor to lessen output and quality in Italian ryegrass. The aim of this study was to elucidate the salt tolerance mechanism of two Italian ryegrass cultivars, 'Abundant' and 'Angus'. Under hydroponic conditions, two cultivars of Italian ryegrass with different salt tolerance were exposed to 0 and 300 mM NaCl solution for 1 week, respectively. The results showed that salt stress decreased relative growth rate and relative water content, especially in salt-sensitive 'Angus'. The salt-tolerant 'Abundant' cultivar alleviated reactive oxygen species (ROS) induced burst and cell damage. However, 'Angus' exhibited a greater activity of superoxide dismutase (SOD) and peroxidase (POD) than 'Abundant'. Additionally, 'Abundant' exhibited higher photosynthetic efficiency than 'Angus' under salt stress condition. Salt treatment significantly increased the Na/K, Na/Mg, and Na/Ca ratios in the leaves and roots of both cultivars, with a pronounced effect in salt-sensitive 'Angus'. The metabolite analysis of leaf polar extracts revealed 41 salt responsive metabolites in both cultivars, mainly consisting of amino acids, organic acids, fatty acids, and sugars. Following exposure to salt conditions, salt-sensitive 'Angus' had a higher level of metabolites and more uniquely upregulated metabolites were detected. Based on these findings, we conclude that the 'Abundant' cultivar emerged as a favorite in saline-alkali soil, while the 'Angus' cultivar is suitable for planting in normal soil. It appears that the high salt tolerance of 'Abundant' is partly to prevent the plant from ionic homeostasis disruption.

BACKGROUND Nitrogen (N) is essential to crop yield improvement and it can change crops' ability to defend against herbivores. To maximize economic yield, a higher amount of N-fertilizer is often applied than the minimum required. Azotobacter is a good alternative to reduce N fertilizer application. In this study, we studied the yield and secondary defensive chemicals of maize, as well as the response of the key maize insect pest, Mythimna separata, as fed on maize plants inoculated with Azotobacter chroococcum and cultivated at different N fertilizer rates (i.e. the control rate of nitrogen fertilizer (CR), 80%CR and 60%CR) from 2018 to 2019. RESULTS A. chroococcum inoculation just positively increased yield production of maize at 80%CR. Moreover, reduced N-fertilizer application and A. chroococcum inoculation had opposite impacts on the foliar contents of jasmonic acid (JA), isoleucine conjugate of JA (JA-Ile) and DIMBOA in maize, and they both negatively decreased the pupation rate and fecundity, and positively increased the eclosion rate and approximate digestibility (AD) of M. separata (P

Herbivory is a major energy transfer within ecosystems; an open question is under what circumstances it can stimulate aboveground seasonal primary production. Despite multiple field demonstrations, past theory considered herbivory as a continuous process and found stimulation of seasonal production to be unlikely. Here, we report a new theoretical model that explores the consequences of discrete herbivory events, or episodes, separated in time. We discovered that negative density (biomass) dependence of plant growth, such as might be expected from resource limitation of plant growth, favors stimulation of seasonal production by infrequent herbivory events under a wide range of herbivory intensities and maximum plant relative growth rates. Results converge to those of previous models under repeated, short‐interval herbivory, which generally reduces seasonal production. Model parameters were estimated with new and previous data from the Serengeti ecosystem. Patterns of observed frequent and large magnitude stimulated production in these data agreed generally with those predicted by the episodic herbivory model. The model thus may provide a new framework for evaluating the sustainability and impact of herbivory., The issue of whether herbivores can stimulate plant production remains controversial. Here we develop a theoretical framework for understanding how discrete or episodic herbivory events can stimulate plant production under a wide variety of conditions without increasing nutrient availability. The model predictions, based on new data for relative growth rates of grassland plants, agree reasonably well with previously published data for grazing impacts on above‐ground production in the Serengeti.

The responses of Urochloa brizantha and Megathyrsus maximus young seedlings to salt stress with NaCl at 0 (control), 25, 50 and 100 mmol/L under hydroponic conditions were studied. The relative growth rate of U. brizantha leaves was reduced at 50 and 100 mmol/L NaCl, whereas that of M. maximus leaves was not affected. Moreover, high oxidative damages, low chlorophyll content and severe reduction of osmotic potential were observed in U. brizantha leaves when subjected to 100 mmol/L NaCl. This grass also showed high accumulation of proline and soluble sugars in leaves and roots. M. maximus efficiently regulated leaf K⁺ concentration and restricted Na⁺ transport by retention in roots. The leaf K⁺/Na⁺ ratio was higher in M. maximus than in U. brizantha at 50 and 100 mmol/L NaCl. Overall, both grasses displayed different mechanisms to reduce the deleterious effects of salinity, but the control of ion homeostasis exhibited by M. maximus contributed notably to improved performance of this grass when grown under saline conditions.

Helicoverpa armigera is intensively researched in laboratory settings, yet developmental rates can vary considerably even under controlled conditions. Here, dietary choice and light spectra were tested as possible factors influencing this variability, a range of fitness indicators were collected and dietary choice behaviour in early instars was observed. We show that early instars of H. armigera exhibited self-selection of nutrient intake, a novel finding. Larvae given a choice between two artificial diets varying in macronutrient ratios were heavier, exhibited a higher relative growth rate, shorter developmental time and longer eclosion time compared with larvae reared on a single diet. Wing size relative to body mass was higher for larvae on extreme no choice treatments and smallest for those on the choice diets, indicating a potential adaptation to escape poor nutrient landscapes. Light spectra had an effect on the size of pupae, with H. armigera reared under white LED light having larger pupae than those reared under fluorescent white light. Larvae reared under LED light took longer to emerge from pupation. Giving larvae a choice of diets with a range of nutrients may reduce developmental variability rather than assuming that one diets suits all.

The distribution of invasive and native species in wetlands is determined by hydrological conditions; whereas conditions such as water depth fluctuations, variations in the nutrient concentrations are expected to affect the growth and physiological traits of plants. For the assessment of such effects, we conduct greenhouse experiment with three factors; 1) water depth of 5 cm and 15 cm (static and fluctuated); 2) three levels of nutrient concentrations (i) full‐strength Hoagland solution (N1), (ii) ¼‐strength Hoagland solution (N2), and (iii) 1/8‐strength Hoagland solution (N3); and 3) species, invasive Wedelia trilobata (L.) and its congener, native Wedelia chinensis (Osbeck.) under mono and mixed culture. Water depth of 5 cm combined with any of the nutrient treatments significantly restrained the photosynthesis, intracellular CO2 concentration and leaf chlorophyll of both W. trilobata and W. chinensis. Increase in the water depth to 15 cm with low‐nutrient treatment N3 did not sustain the physiological traits of W. chinensis under mono and mixed planting. A great loss was noted in the growth of W. chinensis at 15 cm static and fluctuated water depth with low‐nutrient treatment (N3) and under mixed culture. In addition, water depth fluctuations with both low‐ and high‐nutrient treatments significantly affected the root‐shoot ratio, relative growth rate, and interspecific interaction among these two species. W. trilobata benefited more from competitive interaction index (CII) under fluctuated water depth at 15 cm with high nutrients, and the value of CII was clearly positive. Therefore, higher competitive ability may contribute to the invasiveness of W. trilobata in wetlands., In this work, the affect of water depth fluctuation with different nutrient treatments on the growth has been predicted for Wedelia trilobata. Furthermore, our work focused on an important element as competitive interaction index among invasive Wedelia trilobata and its native W. chinensis for prediction of invasiveness of Wedelia trilobata in wetland ecosystem.

The perennial weed, Cirsium arvense (creeping, Canada or Californian thistle), is notorious for its ability to tolerate defoliation by mowing, herbivores or herbicides. The tolerance of 36 genotypes of C. arvense was examined by establishing pairs of clonal replicates that were assigned to a clipped or unclipped treatment. Three clippings were applied from spring to early summer to simulate repeated mowing. The average final percentage reduction caused by the repeated clipping was 18%, 72%, 32% and 50% for shoot biomass, root biomass, number of shoots and shoot height respectively. While nearly all genotypes were negatively affected by clipping, some overcompensated, and achieved greater shoot biomass, number of shoots, or increased height than their unclipped counterparts. No genotype was able to overcompensate, or fully tolerate, the lost root biomass due to repeated clipping. Genetic variation for tolerance to defoliation was detected for the number of shoots, maximum shoot height and for relative height growth rate. For relative growth rate, significant genetic variation was not detected until after the third clipping event, indicating that genotypes were equally tolerant to a moderate degree of defoliation, but upon more severe defoliation, genetic differences were evident. Since repeated defoliation is a recommended control technique, selection for more tolerant genotypes is possible and should be considered for the management of this weed.

AIM: A better understanding of plant communities can be achieved by incorporating data of traits and dynamics into surveys. Wood density is a good predictor for growth and mortality in trees, but to date, no studies of lianas include all three. We examine how liana communities respond to environmental gradients and forest fragmentation in terms of abundance, diversity, size structure, mortality, relative growth rate and wood density, and tested how the latter three are related to each other in liana species. LOCATION: Xishuangbanna, SW China. METHODS: We repeated a survey of lianas (stems >0.5 cm diameter) in 47 plots, distributed in forest fragments of various size, on different bedrock (limestone or sandstone), over an elevational range and across different topographic elements (ridge, slope, valley). We gathered wood density data for 116 of 166 species, covering 90% of all surveyed stems. We also determined relative growth rate, mortality, stem diameter and basal area. RESULTS: At the species level, liana mortality and relative growth rate were lower at higher wood density, and mortality was higher with greater relative growth rate. At the plot level, liana communities in valleys had high relative growth and mortality rates as well as high abundance and diversity. Forest on limestone hosted few species but more large‐stemmed liana individuals, and communities had higher wood density weighted by basal area. Liana abundance, relative growth rates and mortality were greater and average wood density lower towards fragment edges, but the explanatory power of these models was low. CONCLUSION: Habitat was the major factor shaping liana communities, whereas fragmentation was not an important predictor in our study. Resource‐rich environments such as valleys harbour diverse liana communities with high mortality and relative growth rates. This pattern matches earlier studies on survival/growth trade‐offs among plant species. The relationship between growth rates, mortality and wood density in lianas follows the same trade‐offs as found in trees.

Tropical forest productivity is often thought to be limited by soil phosphorus (P) availability. Phosphorus availability might therefore constrain potential increases in growth as the atmospheric CO₂ concentration increases, yet there is little experimental evidence with which to evaluate this hypothesis. We hypothesized that while all species would respond more strongly to elevated CO₂ when supplied with extra P, the responses of individual species would also depend on their habitat associations with either high‐ or low‐P soils. We further hypothesized that this effect would be exacerbated by a reduction in transpiration rate under elevated CO₂, as transpiration may aid in P acquisition. We used a pot experiment to test the effects of P addition on the physiological and growth response to elevated CO₂ of eight tropical tree species with contrasting distributions across a soil P gradient in Panamanian lowland forests. Seedlings were grown in an ambient (400 ppm) or elevated (800 ppm) CO₂‐controlled glasshouse in either a high‐ or low‐P treatment to quantify the effects of P limitation on relative growth rate (RGR), transpiration, maximum photosynthetic rate and foliar nutrients. We found evidence of limitation by P and CO₂ on growth, photosynthesis, foliar nutrients and transpiration. However, the affinity of a species for P, defined as the species distribution relative to P availability, was not correlated with RGR or transpiration responses to elevated CO₂ in either the low‐P or high‐P treatments. Transpiration rates decreased under elevated CO₂, but foliar P was greater for some species under elevated CO₂, suggesting a greater capacity for upregulation of P acquisition in species associated with low‐P soils. Our results show that tropical forest responses to elevated CO₂ will be species‐specific and not necessarily explained by P affinities based on distribution, which poses challenges for predictions of community‐wide responses. A free Plain Language Summary can be found within the Supporting Information of this article.

Coastal salt marsh plants employ various combinations of morphological and physiological adaptations to survive under saline conditions. Little information is available on salinity tolerance mechanisms of Halopeplis perfoliata, a C3 stem succulent halophyte. We investigated the growth, photosynthesis and antioxidant defence mechanisms of H. perfoliata under saline conditions (0, 150, 300 and 600 mM NaCl) in an open greenhouse. Optimal shoot succulence, projected shoot area and relative growth rate were obtained in the low (150 mm NaCl) salinity treatment, while growth was inhibited at the highest salinity (600 mm NaCl). The CO2 compensation point and carbon isotope composition of biomass confirmed C3 photosynthesis. Increases in salinity did not affect the photosynthetic pigment content or maximum quantum efficiency of PSII of H. perfoliata. Assimilation of CO2 (A) also remained unaffected by salinity. A modest effect on some gas exchange and photochemistry parameters was observed at 600 mm NaCl. With increasing salinity, there was a continual increase in respiration, suggesting utilisation of energy to cope with saline conditions. Under 300 and 600 mm NaCl, there was an increase in H2 O2 and MDA with a concomitant rise in AsA, GR content and CAT activity. Hence, H. perfoliata appears to be an obligate halophyte that can grow up to seawater salinities by modulating photosynthetic gas exchange, photochemistry and the antioxidant defence systems.

Quantitative estimates of crop growth for regionally dominant cropping systems are imperative for various agricultural applications. Here, we studied growth patterns for maize, soybean, sorghum, and winter wheat grown under optimal growing conditions in South-Central Nebraska during two growing seasons (2016–2017). The objectives were to measure and compare crop-specific growth indicators such as canopy height (CH), leaf area index (LAI) and aboveground biomass (AGB), crop growth rate (GR), relative growth rate (RGR) and their normalized (LAI per plant[LAIpP], LAI per canopy height[LAIpCH], AGB per plant [AGBpP], and AGB per canopy height [AGBpCH]), and integrative forms (net assimilation rate [NAR] and leaf area ratio [LAR]). Crop-specific sub-seasonal magnitudes and patterns were found, which were uniform across years. Crop growth indices were empirically modeled using heat accumulation (NCTU), owing to strong correlation (mostly R² > 0.80) and transferability. Sensitivity of biomass production between sampling events to heat accumulated between these events was quantified, which was higher for C4 crops (2.9–3.3 g m–² °C–¹) than C3 crops (0.64–1.01 g m–² °C–¹). Empirical models for estimating relatively complex growth indices were presented using indices such as CH and LAI. Moreover, LAR and RGR were highly correlated (R = 0.86) across all crops, while NAR and RGR were moderately correlated (R = 0.43), although substantial crop-specific variability existed among these indices. The data, comparisons and models presented are the first investigated values for these crops in Midwest under uniform conditions, and are valuable for applications in remote estimation of crop growth, crop models, crop resource use, and other related applications.

Nocturnal stomatal conductance contributes to water loss at night without carbon gain in C3 or C4 plants because photosynthesis does not occur in the dark. The functional relevance of nocturnal conductance thus remains an unresolved conundrum. Here, we review and re-analyse previously published datasets on nocturnal conductance (gn ) globally (176 species) to synthesize our current understanding on its potential biological function and to identify remaining research gaps. We found that gn was positively correlated with relative growth rate, which is compatible with the postulate that circadian-driven nocturnal conductance enhances predawn stomatal conductance, thereby priming stomata for photosynthesis in early daylight. The variation in gn across plant species and functional types was not consistent with the hypotheses that the main function of gn is to: remove excess CO2, which might limit growth; enhance oxygen delivery to the functional sapwood; enhance nutrient supply; or that gn is due to stomatal leakiness. We suggest further study regarding the potential of gn to be an important functional and ecological trait influencing competitive outcomes and we outline a research programme to achieve that objective.

The application of functional traits to predict and explain plant species’ distributions and vital rates has been a major direction in functional ecology for decades, yet numerous physiological traits have not yet been incorporated into the approach. Using commonly measured traits such as leaf mass per area (LMA) and wood density (WD), and additional traits related to water transport, gas exchange and resource economics, including leaf vein, stomatal and wilting traits, we tested hypotheses for Hawaiian wet montane and lowland dry forests (MWF and LDF, respectively): (1) Forests would differ in a wide range of traits as expected from contrasting adaptation; (2) trait values would be more convergent among dry than wet forest species due to the stronger environmental filtering; (3) traits would be intercorrelated within “modules” supporting given functions; (4) relative growth rate (RGR) and mortality rate (m) would correlate with a number of specific traits; with (5) stronger relationships when stratifying by tree size; and (6) RGR and m can be strongly explained from trait‐based models. The MWF species’ traits were associated with adaptation to high soil moisture and nutrient supply and greater shade tolerance, whereas the LDF species’ traits were associated with drought tolerance. Thus, on average, MWF species achieved higher maximum heights than LDF species and had leaves with larger epidermal cells, higher maximum stomatal conductance and CO2 assimilation rate, lower vein lengths per area, higher saturated water content and greater shrinkage when dry, lower dry matter content, higher phosphorus concentration, lower nitrogen to phosphorus ratio, high chlorophyll to nitrogen ratio, high carbon isotope discrimination, high stomatal conductance to nitrogen ratio, less negative turgor loss point and lower WD. Functional traits were more variable in the MWF than LDF, were correlated within modules, and predicted species’ RGR and m across forests, with stronger relationships when stratifying by tree size. Models based on multiple traits predicted vital rates across forests (R2 = 0.70–0.72; p

Growth patterns of aquatic macrophytes have been shown to vary in response to hydrological properties; however, such properties are typically characterized by water level fluctuation, flow velocity, flooding season, and sedimentation, but not by water exchange rate (WER). Herein, we experimentally investigated how WER (three levels: exchange 0%, 20%, and 40% of total water per day) affects water and sediment properties, and the consequences that these variations have on the individual responses of two submerged macrophytes, Hydrilla verticillata and Myriophyllum aquaticum which were planted in two different sediment types (sand and clay). In the experiment without ramets, it was found that turbidity, pH value, and dissolved carbon dioxide concentration of the system water were statistically unaffected by WER, while water dissolved oxygen (DO) concentration and sediment oxidation–reduction potential (ORP, in both sediments) consistently increased with increasing WER, regardless of experimental time. In the experiment containing ramets, biomass accumulation and relative growth rate (RGR) of both species gradually increased with increasing WER regardless of sediment type. The mechanisms were related to (a) increased oxygen availability, as indicated by gradually increased water DO concentration and sediment ORP; and (b) enhanced phosphorus (P) and nitrogen (N) absorbing abilities associated with stimulated root growth, reflected in increased mean root length, specific root length, and the root/above‐ground biomass ratio, with increasing WER. Additionally, in the experiments containing ramets, significant linear relationships were consistently detected between sediment ORP and root parameters, root parameters and plant nutrients (N and P), and plant nutrients and plant growth conditions (biomass accumulation and RGR). These results demonstrate that WER plays an important role in determining oxygen availability and thus impacts the growth of submerged macrophytes by altering the ability of roots to absorb nutrients, indicating that ecosystem functions are more sensitive to WER than previously recognized.

Green spruce aphid Elatobium abietinum is an important defoliating pest of Sitka spruce Picea sitchensis that may become more damaging in the future as a result of climate change. Mild winters and higher spring temperatures increase E. abietinum population densities, although this positive response to warmer conditions might be over‐ridden if E. abietinum is adversely affected by exceptionally high summer temperatures. In laboratory experiments, aphids exposed to temperatures above 25 °C became more restless and were more likely to drop from the shoot, and subsequently showed a reduction in mean relative growth rate. In contrast, survival was not reduced significantly unless temperatures exceeded 35 °C. Field data from Radnor Forest in Wales indicated that E. abietinum populations in the autumn were inversely correlated with mean and maximum summer temperatures, at temperatures below those that had a negative impact in the laboratory. The greater sensitivity of populations in the field to high summer temperatures may reflect higher temperatures at the needle surface compared with the temperature of the surrounding air, or associated increases in natural enemy activity. The results from the present study indicate that high temperatures during mid‐summer have a significant impact on E. abietinum individuals and populations and, ultimately, may influence how the aphid responds to climate change.

The large variation in seed mass among species inspired a vast array of theoretical and empirical research attempting to explain this variation. So far, seed mass variation was investigated by two classes of studies. One class focuses on species varying in seed mass within communities, while the second focuses on variation between communities, most often with respect to resource gradients. Here, we develop a model capable of simultaneously explaining variation in seed mass within and between communities. The model describes resource competition (for both soil and light resources) in annual communities and incorporates two fundamental aspects: light asymmetry (higher light acquisition per unit biomass for larger individuals) and growth allometry (negative dependency of relative growth rate on plant biomass). Results show that both factors are critical in determining patterns of seed mass variation. In general, growth allometry increases the reproductive success of small-seeded species while light asymmetry increases the reproductive success of large-seeded species. Increasing availability of soil resources increases light competition, thereby increasing the reproductive success of large-seeded species and ultimately the community (weighted) mean seed mass. An unexpected prediction of the model is that maximum variation in community seed mass (a measure of functional diversity) occurs under intermediate levels of soil resources. Extensions of the model incorporating size-dependent seed survival and disturbance also show patterns consistent with empirical observations. These overall results suggest that the mechanisms captured by the model are important in determining patterns of species and functional diversity.

Characterizing patterns of variation in plant traits across species and environmental gradients is critical for understanding performance of species in ecosystems. One‐dimensional pattern of variation has been demonstrated in leaf traits, which is known as the leaf economic spectrum. However, it is unclear whether such a spectrum exists for root traits. For roots of 15 species from temperate grasslands, we determined respiration rate, relative growth rate, life span and 10 morphological, chemical and anatomical root traits. We further evaluated pairwise and multiple‐trait relationships by Pearson's correlation and principle component analysis including phylogenetic contrasts. We found that root functions were related to three clusters of variation. Root respiration rate and relative growth rate were positively correlated with average root diameter (AD), but they were negatively correlated with specific root length (SRL). In contrast, root life span was not correlated with AD, but it was positively correlated with SRL. These results are inconsistent with the presumption of the root economic spectrum. The principle components analysis revealed a multi‐dimensional pattern of variation in root traits among the 15 coexisting herbaceous species. Moreover, species within the same phylogenetic clades tended to have similar root trait syndromes. Most of the root traits exhibited a significant phylogenetic signal. Synthesis. Our results do not support a one‐dimensional root economic spectrum in the coexisting herbaceous species of temperate grasslands. In contrast, the pattern of variation in root traits was multi‐dimensional. We further demonstrated that species in different phylogenetic clades possess diverse root trait syndromes for efficient resource acquisition. Our findings provide a next step in understanding root functions and plant strategies in temperate grasslands.

1. Plants defend themselves from insect herbivore attack using a range of physical and chemical defences which are in many cases regulated by phytohormones such as jasmonates. While much more is known about how jasmonates regulate defence against above‐ground herbivores (e.g. herbivores of leaves), there is increasing interest in how they influence below‐ground defences. 2. For the Poaceae, most below‐ground studies focus on highly domesticated cereals. Here it is demonstrated how exogenous application of methyl jasmonate (MeJA) to the leaf blades of a non‐domesticated pasture grass (Microlaena stipoides) caused a more than two‐fold decrease in relative growth rate (RGR) of a root‐feeding chafer (Dermolepida albohirtum). MeJA treatment did not affect root consumption rates, but substantially reduced the efficiency of conversion of ingested food to body mass. 3. Non‐targeted metabolomics identified significant changes in the metabolome of MeJA‐induced plants, with three compounds (a galactolipid, a trihydroxy fatty acid and a lysophospholipid) found to be correlated with herbivore RGR, although their roles in herbivore defence remain uncertain. 4. This study suggests that an important Australian pasture grass can become better defended against root herbivores via enhanced jasmonate activity.

Global climate change is likely to impact all plant life. Vascular epiphytes represent a life form that may be affected more than any other by possible changes in precipitation leading to water shortage, but negative effects of drought may be mitigated through increasing levels of atmospheric CO2 . We studied the response of three epiphytic Aechmea species to different CO2 and watering levels in a full-factorial climate chamber study over 100 days. All species use crassulacean acid metabolism (CAM). Response variables were relative growth rate (RGR), nocturnal acidification and foliar nutrient levels (N, P, K, Mg). Both elevated CO2 and increased water supply stimulated RGR, but the interaction of the two factors was not significant. Nocturnal acidification was not affected by these factors, indicating that the increase in growth in these CAM species was due to higher assimilation in the light. Mass-based foliar nutrient contents were consistently lower under elevated CO2 , but most differences disappeared when expressed on an area basis. Compared to previous studies with epiphytes, in which doubling of CO2 increased RGR, on average, by only 14%, these Aechmea species showed a relatively strong growth stimulation of up to +61%. Consistent with earlier findings with other bromeliads, elevated CO2 did not mitigate the effect of water shortage.

The importance of calcium in nickel tolerance was studied in the nickel hyperaccumulator plant Alyssum inflatum by gene transformation of CAX1, a vacuolar membrane transporter that reduces cytosolic calcium. CAX1 from Arabidopsis thaliana with a CaMV35S promoter accompanying a kanamycin resistance gene was transferred into A. inflatum using Agrobacterium tumefaciens. Transformed calli were sub-cultured three times on kanamycin-rich media and transformation was confirmed by PCR using a specific primer for CAX1. At least 10 callus lines were used as a pool of transformed material. Both transformed and untransformed calli were treated with varying concentrations of either calcium (1–15 mM) or nickel (0–500 µM) to compare their responses to those ions. Increased external calcium generally led to increased callus biomass, however, the increase was greater for untransformed callus. Further, increased external calcium led to increased callus calcium concentrations. Transformed callus was less nickel tolerant than untransformed callus: under increasing nickel concentrations callus relative growth rate was significantly less for transformed callus. Transformed callus also contained significantly less nickel than untransformed callus when exposed to the highest external nickel concentration (200 µM). We suggest that transformation with CAX1 decreased cytosolic calcium and resulted in decreased nickel tolerance. This in turn suggests that, at low cytosolic calcium concentrations, other nickel tolerance mechanisms (e.g., complexation and vacuolar sequestration) are insufficient for nickel tolerance. We propose that high cytosolic calcium is an important mechanism that results in nickel tolerance by nickel hyperaccumulator plants.

The traditional paradigm is that plant growth at high latitudes is generally nitrogen (N) limited, whereas phosphorus (P) limitation occurs at low latitudes. However, this latitudinal pattern of nutrient limitation is not empirically tested and the underlying mechanisms are far from clear. Here we performed a coordinated experiment of N and/or P addition at three forest sites in China, a subtropical forest, a warm-temperate forest and a cold-temperate forest. By measuring relative growth rate (RGR) and leaf nutrient traits among different tree size groups, we assessed how they vary with nutrient addition and tree sizes and uncovered the likely mechanisms underlying these observed responses. Our results revealed that P addition enhanced the RGR of small trees (DBH 15cm) was not impacted by any nutrient addition treatment or soil nutrient variations at any site. Leaf P concentration and resorption efficiency in both small and large trees mostly showed a linear response to soil available P at subtropical and warm-temperate sites, while leaf N:P ratio in small trees elevated linearly with soil available N:P ratio at a cold-temperate site. Overall, this study presents robust experimental evidence that growth in small trees, not large trees, is primarily limited by P in subtropical and warm-temperate forests, but is co-limited by N and P in cold-temperate forests. This size-dependent nutrient limitation highlights the importance of considering tree size classes when assessing nutrient limitation in forest. A is available for this article.

Predictions of upslope range shifts for tree species with warming are based on assumptions of moisture stress at lower elevation limits and low‐temperature stress at high‐elevation limits. However, recent studies have shown that warming can reduce tree seedling establishment across the entire gradient from subalpine forest to alpine via moisture limitation. Warming effects also vary with species, potentially resulting in community shifts in high‐elevation forests. We examined the growth and physiology underlying effects of warming on seedling demographic patterns. We evaluated dry mass (DM), root length, allocation above‐ and below‐ground, and relative growth rate (RGR) of whole seedlings, and their ability to avoid or endure water stress via water‐use efficiency and resisting turgor loss, for Pinus flexilis, Picea engelmannii and Pinus contorta seeded below, at and above tree line in experimentally warmed, watered and control plots in the Rocky Mountains, USA. We expected that growth and allocation responses to warming would relate to moisture status and that variation in drought tolerance traits would explain species differences in survival rates. Across treatments and elevations, seedlings of all species had weak turgor‐loss resistance, and growth was marginal with negative RGR in the first growth phase (−0.01 to −0.04 g g⁻¹ day⁻¹). Growth was correlated with soil moisture, particularly in the relatively small‐seeded P. contorta and P. engelmannii. Pinus flexilis, known to have the highest survivorship, attained the greatest DM and longest root but was also the slowest growing and most water‐use efficient. This was likely due to its greater reliance on seed reserves. Seedlings developed 15% less total DM, 25% less root DM and 11% shorter roots in heated compared with unheated plots. Higher temperatures slightly increased DM, root length and RGR where soils were wettest, but more strongly decreased these variables under drier conditions. Synthesis. The surprising heat inhibition of tree seedling establishment at the cold edge of forests appears to have a physiological basis: newly germinated seedlings have poor moisture stress tolerance, which appears related to marginal initial growth and heavy reliance on seed reserves. Variation in these attributes among tree species at tree line helps explain their different climate responses.

Epiphytic bromeliads represent a major component of Neotropical forests, but the potential effect of climate change on these plants is unclear. We investigated whether and how bromeliads are affected by the predicted 3°C temperature rise by the end of the century. We conducted growth experiments with 17 epiphytic bromeliad species at different temperatures to determine their fundamental thermal niches. By comparing those with niches for germination, we tested whether ontogenetic niche shift or niche contraction occurs in Bromeliaceae. Applying a classical growth analysis, we assessed the relative importance of the underlying growth components on interspecific variations in growth. Members of two bromeliad subfamilies differed in their response to elevated temperatures: Tillandsioideae may be negatively affected, whereas Bromelioideae moved closer to their thermal optimum. Across different ontogenetic stages, thermal niche characteristics revealed both niche shift and niche contraction. Interspecific variation in growth was driven almost exclusively by net assimilation rate at all temperatures. We conclude that the vulnerability of tropical plants to a future increase in temperature may be more variable than suggested by previous studies. We emphasize the importance of assessing niche breadth over multiple life stages and the need for better microclimatic data to link laboratory data with field conditions.

Herbivory has long been recognized as a significant driver of plant population dynamics, yet its effects along environmental gradients are unclear. Understanding how weather modulates plant–insect interactions can be particularly important for predicting the consequences of exotic insect invasions, and an explicit consideration of weather may help explain why the impact can vary greatly across space and time. We surveyed two native prickly pear cactus species (genus Opuntia) in the Florida panhandle, USA, and their specialist insect herbivores (the invasive South American cactus moth, Cactoblastis cactorum, and three native insect species) for five years across six sites. We used generalized linear mixed models to assess the impact of herbivory and weather on plant relative growth rate (RGR) and sexual reproduction, and we used Fisher's exact test to estimate the impact of herbivory on survival. Weather variables (precipitation and temperature) were consistently significant predictors of vital rate variation for both cactus species, in contrast to the limited and varied impacts of insect herbivory. Weather only significantly influenced the impact of herbivory on Opuntia humifusa fruit production. The relationships of RGR and fruit production with precipitation suggest that precipitation serves as a cue in determining the trade‐off in the allocation of resources to growth or fruit production. The presence of the native bug explained vital rate variation for both cactus species, whereas the invasive moth explained variation only for O. stricta. Despite the inconsistent effect of herbivory across vital rates and cactus species, almost half of O. stricta plants declined in size, and the invasive insect negatively affected RGR and fruit production. Given that fruit production was strongly size‐dependent, this suggests that O. stricta populations at the locations surveyed are transitioning to a size distribution of predominantly smaller sizes and with reduced sexual reproduction potential.

The green microalga Dictyosphaerium chlorelloides was identified as promising microorganism for biotechnological production of exopolysaccharides (EPS). In stationary phase the culture suspension solidifies to thick gel, with very high viscosity and high content of EPS which may be interesting for many biotechnological applications. To develop cultivation protocol for maximum biomass/polysaccharide production, the optimum conditions for growth and polysaccharides production were determined in this study using the crossed gradient cultivation method. Temperature and irradiance requirements of Dictyosphaerium chlorelloides were evaluated by statistical analyses for growth rate/biomass, extracellular (EPS) and intracellular (IPS) polysaccharides contents in crossed gradients of temperature (4–45°C) and irradiance (2–18 W m−2, 9.1 – 82.3 μmol m−2 s−1). The maximum relative growth rate was observed at temperatures around 19.2°C and relatively low irradiances in range 2.6–11 W m−2 (11.9–50.3 μmol m−2 s−1). The maximum IPS production was observed at temperatures around 19.2°C and irradiance around 11 W m−2 (50.3 μmol m−2 s−1). The maximum production of EPS was observed at temperatures around 25.7°C and similar irradiances as IPS production. Due to temperature separation of growth and EPS production, development of cultivation protocol based controlled temperature manipulation is possible. This article is protected by copyright. All rights reserved

Summary The understorey of tropical forests is heterogeneous across time, and plants that inhabit this layer may exhibit adaptations (e.g. trait plasticity) that enable them to exploit this variability to their advantage. We tested the hypothesis that two widespread understorey herbs would perform equally well in a variable as in a constant environment, using a 2-year shade-house experiment. We measured demographic traits (growth and survival), a physiological trait (maximum photosynthetic capacity), and life-history traits (leaf life span and biomass allocation) of Heliconia tortuosa and Calathea crotalifera. We investigated how these traits were affected by light availability at the seedling stage, precipitation, and whether individuals experienced a constant or variable light environment. Whether or not a variable environment was favourable for plants depended upon precipitation and the environment in which individuals started life. At low precipitation, plants in a variable light environment grew more than those in a constant environment, but only when individuals had lived as seedlings in low light. At high precipitation, plants in a constant environment grew more than those in a variable environment, regardless of early conditions. Survival was lower in a variable environment at low precipitation, and more so at high precipitation. Photosynthetic capacity was lower for individuals in a variable environment than in a constant environment when they had lived in high light as seedlings. Calathea grew faster and survived more poorly than Heliconia, independently of the treatments. Calathea grew more at high than low precipitation while Heliconia grew more at low than high precipitation. Leaf life span and biomass allocation did not differ among treatments, although Calathea had a significantly greater proportion of its biomass above-ground vs. that of Heliconia. Synthesis. Environmental variability had a neutral or positive effect on biomass allocation, photosynthetic capacity, and leaf life span for these species. Survival was the only trait that was always lower in a variable environment. The effect of environmental variability was dependent on early life conditions as well as precipitation, suggesting that generalist species may experience high fitness as forest environments become more variable by maintaining high growth at the expense of survival.

The effects of resource stoichiometry and growth rate on the elemental composition of biomass have been examined in a wide variety of organisms, but the interaction among these effects is often overlooked. To determine how growth rate and resource imbalance affect bacterial carbon (C): nitrogen (N): phosphorus (P) stoichiometry and elemental content, we cultured two strains of aquatic heterotrophic bacteria in chemostats at a range of dilution rates and P supply levels (C:P of 100:1 to 10,000:1). When growing below 50% of their maximum growth rate, P availability and dilution rate had strong interactive effects on biomass C:N:P, elemental quotas, cell size, respiration rate, and growth efficiency. In contrast, at faster growth rates, biomass stoichiometry was strongly homeostatic in both strains (C:N:P of 70:13:1 and 73:14:1) and elemental quotas of C, N, and P were tightly coupled (but not constant). Respiration and cell size increased with both growth rate and P limitation, and P limitation induced C accumulation and excess respiration. These results show that bacterial biomass stoichiometry is relatively constrained when all resources are abundant and growth rates are high, but at low growth rates resource imbalance is relatively more important than growth rate in controlling bacterial biomass composition.

Bidens frondosa is a new invasive species in China. However, the mechanisms underlying its invasiveness are still not understood. This study compared the new invader with its invasive congener, Bidens pilosa, and two native congeners, Bidens biternata and Bidens tripartita, in terms of their morphology, growth, biomass allocation and photosynthetic parameters across variant light and water conditions, aiming to explore the traits that are associated with the invasiveness of the invasive species. All these species are annual herbs. The results showed that the four congeners had a similar tendency of plasticity in their morphological and growth traits to varying light and water, but their response was quantitatively different. Most of the morphological and growing variables, as well as the photosynthetic parameters, were affected more strongly by manipulated light levels. Although B. frondosa had a lower total biomass and relative growth rate than the invasive congener, B. pilosa, the trait values related to growth (e.g. plant height, total biomass, relative growth rate and specific leaf area) and the mean value of the plasticity index were higher for the invasive B. frondosa than for the native B. tripartita. These could contribute to the invasiveness of the invasive species. In addition, the native species, B. biternata, is a vigorous weed with a strong adaptive capacity across various light and water gradients, suggesting that it has the potential to be invasive if introduced into areas with suitable conditions for growth.

Relative growth rate (RGR) plays an important role in plant adaptation to the light environment through the growth potential/survival trade-off. RGR is a complex trait with physiological and biomass allocation components. It has been argued that herbivory may influence the evolution of plant strategies to cope with the light environment, but little is known about the relation between susceptibility to herbivores and growth-related functional traits. Here, we examined in 11 evergreen tree species from a temperate rainforest the association between growth-related functional traits and (i) species’ shade-tolerance, and (ii) herbivory rate in the field. We aimed at elucidating the differential linkage of shade and herbivory with RGR via growth-related functional traits. We found that RGR was associated negatively with shade-tolerance and positively with herbivory rate. However, herbivory rate and shade-tolerance were not significantly related. RGR was determined mainly by photosynthetic rate (Amax) and specific leaf area (SLA). Results suggest that shade tolerance and herbivore resistance do not covary with the same functional traits. Whereas shade-tolerance was strongly related to Amax and to a lesser extent to leaf mass ratio (LMR) and dark respiration (Rd), herbivory rate was closely related to allocation traits (SLA and LMR) and slightly associated with protein content. The effects of low light on RGR would be mediated by Amax, while the effects of herbivory on RGR would be mediated by SLA. Our findings suggest that shade and herbivores may differentially contribute to shape RGR of tree species through their effects on different resource-uptake functional traits. This article is protected by copyright. All rights reserved.

Changes in plant traits induced by herbivore damage can produce a negative feedback to increasing herbivore densities. Several aspects of these plant-mediated feedbacks are predicted to influence herbivore population dynamics, but the degree to which feedbacks are non-linear, whether their strength varies among plant genotypes, and whether they occur via changes in the quality of plant tissue or the amount of tissue available have rarely been examined. In this study, we damaged five genotypes of the perennial weed Carolina horsenettle, Solanum carolinense L. (Solanaceae), with eight densities of the false potato beetle, Leptinotarsa juncta (Germar) (Coleoptera: Chysomelidae, Chrysomelini). To account for plant quantity available to beetles, we measured the leaf area of each plant after imposing larval density treatments. We then measured the oviposition preference of L. juncta adults for damaged vs. undamaged plants and the relative growth rate (RGR) of L. juncta larvae on each plant, as well as plant trypsin proteinase inhibitor (tryPI) expression. We found that L. juncta females strongly preferred to oviposit on undamaged S. carolinense, and that preference for a plant decreased as the density of damaging larvae increased. In addition, we found decreased larval RGR and increased production of tryPIs with greater initial larval density. Effects of larval density on insect preference, performance, and tryPI expression were linear and did not vary among plant genotypes. Larval density effects were not solely due to reduced plant quantity, as plant leaf area had no effect on oviposition preference or larval performance. This suggests that effects were most likely due to changes in the quality of plant tissue. Thus, negative feedback on increasing larval density can be mediated by the effects of induced resistance on both oviposition preference and larval performance. Published models suggest that the linear, quality-mediated feedbacks observed in this experiment are predicted to stabilize herbivore population dynamics.

We propose an operational definition of soil "fertility" that is applicable to plant community ecology and develop a method of measuring and quantifying it, using structural equations modeling, that is generalizable to soils in different regions whose fertility has different causes. To do this, we used structural equation modeling (SEM). The measurement submodel predicts the latent "generalized fertility," FG , of a soil using four indicator variables: the relative growth rates of Festuca rubra, Trifolium pratense, Triticum aestivum, and Arabidopsis thaliana. The direct causes of FG in this study were the supply rates of NO3 - , P, and K as well as three indirect causes consisting of three physical soil properties, but these can change between studies. The model was calibrated using 76 grassland soils from southern Quebec, Canada and independently tested using aboveground net primary productivity (NPP) of the natural vegetation over two growing seasons. Both the measurement submodel and the full SEM fit the data well. The FG values predicted 51% of the variance in NPP and were a better predictor than any other single variable, including the actual nutrient flux rates. Furthermore, this model can be applied to grassland soils anywhere because of its modular nature in which the causes and effects of soil fertility are clearly separated.

Slugs feed on some plant species but not on others for reasons that are not yet fully understood. We re-examined the two largest studies on the preference of Arion lusitanicus for different plant species. Briner & Frank (1998) measured the consumption index of slugs (CIB) based on the dry leaf mass eaten per day per gram of slug mass. Kozlowski & Kozlowska (2009) also measured a consumption index of slugs (CIK) but on the basis of the area eaten per day per gram of slug mass. The two indices showed a moderate positive rank correlation. Briner & Frank (1998) found that slugs preferred annual to perennial plants and crops rather than wild species. On the other hand, Kozlowski & Kozlowska (2009) found no statistically significant difference in slug preference for annuals, biennials or perennials. Using botanical databases we selected plant traits related to slug herbivory and analysed 141 species. We first analysed the two data sets separately and found that CIB was higher for seedlings with a higher relative growth rate although this result was only marginally statistically significant. In addition, we found that annuals were consumed more than perennials and that cultivated plants were consumed more than wild plants. This is in agreement with the conclusions of Briner & Frank (1998). For CIK slugs consumed less from plants with high dry matter content (DMC). The use of classification and regression tree models solves the problem of analysing datasets with missing values. Regarding CIB, the tree models indicated that life cycle was the major branch. Within perennials, cultivated/wild origin of plants was the most important predictor of slug feeding. Within wild perennials slugs ate more from plants with low specific leaf area (SLA), i.e. relatively thick leaves. Within annuals we found the unexpected result that slugs ate more from plant species with either alkaloids or glucosinolates than from species without one of these compounds. For CIK, the results of tree models showed that slugs preferred shade-intolerant plants to shade-tolerant plant species. Within the shade-tolerant group slugs fed more on leaves with low DMC. We only partially understand which factors make plants acceptable to slugs. We discuss this issue along with the pros and cons of the two methods used to calculate CI.

Predicted increases in atmospheric concentrations of CO2 may alter the susceptibility of many plants to insect herbivores due to changes in plant nutrition and defences. Silicon plays a critical role in plant defence against herbivores, so increasing such silicon‐based defences in plants may help remediate situations where plants become more susceptible to herbivores. Sugar cane (Saccharum spp. hybrid) was subjected to fully factorial treatment combinations of ambient (aCO2) or elevated (eCO2) atmospheric CO2 concentrations; ambient silicon or silicon supplementation; insect‐free or subject to root herbivory by greyback canegrub (Dermolepida albohirtum). A glasshouse study was used to determine how these factors affected rates of photosynthesis, growth, chemistry (concentrations of silicon, carbon, nitrogen and non‐structural carbohydrates). Changes in canegrub mass were determined in the glasshouse pot study, together with more detailed assessment of how eCO2 and silicon supplementation affected performance and feeding behaviour (relative growth rate and relative consumption) in a 24‐h feeding efficiency assay. Elevated CO2 and silicon supplementation increased rates of photosynthesis (+32% and 14%, respectively) and sugar cane biomass (+45% and 69%, respectively). Silicon supplementation increased silicon concentrations in both leaves and roots by 54% and 75%, respectively. eCO2 caused root C : N to increase by 12%. Canegrub performance and consumption increased under eCO2; relative growth rate (RGR) increased by 116% and consumed 57% more root material (suggestive of compensatory feeding). Silicon application reversed these effects, with large decreases in mass change, RGR and root consumption (65% less root mass consumed). Synthesis and applications. Our results suggest future atmospheric carbon dioxide concentrations could lead to increased crop damage by a below‐ground herbivore. Increasing bioavailable silicon in soil stimulated silicon‐based defences which dramatically decreased herbivory and herbivore performance. Our findings suggest future pest management strategies could benefit from characterising deficiencies in bioavailable silicon in agricultural soils and targeted application of silicon fertilisers. Moreover, future breeding programmes should exploit variation in silicon uptake between cultivars to enhance silicon uptake in new crop varieties. Silicon‐based plant defence proved to be highly beneficial for remediating the negative effects of atmospheric change on sugar cane susceptibility to herbivory and could be applicable in other crops.

Understanding how carbon source and sink strengths limit plant growth is a critical knowledge gap that hinders efforts to maximise crop yield. We investigated how differences in growth rate arise from source-sink limitations, using a model system comparing a fast-growing domesticated annual barley (Hordeum vulgare cv. NFC Tipple) with a slow-growing wild perennial relative (Hordeum bulbosum). Source strength was manipulated by growing plants at sub-ambient and elevated CO2 concentrations ([CO2 ]). Limitations on vegetative growth imposed by source and sink were diagnosed by measuring relative growth rate, developmental plasticity, photosynthesis and major carbon and nitrogen metabolite pools. Growth was sink limited in the annual but source limited in the perennial. RGR and carbon acquisition were higher in the annual, but photosynthesis responded weakly to elevated [CO2 ] indicating that source strength was near maximal at current [CO2 ]. In contrast, photosynthetic rate and sink development responded strongly to elevated [CO2 ] in the perennial, indicating significant source limitation. Sink limitation was avoided in the perennial by high sink plasticity: a marked increase in tillering and root:shoot ratio at elevated [CO2 ], and lower non-structural carbohydrate accumulation. Alleviating sink limitation during vegetative development could be important for maximising growth of elite cereals under future elevated [CO2 ].

A fundamental goal in ecology is to link variation in species function to performance, but functional trait–performance investigations have had mixed success. This indicates that less commonly measured functional traits may more clearly elucidate trait–performance relationships. Despite the potential importance of leaf vein traits, which are expected to be related to resource delivery rates and photosynthetic capacity, there are few studies, which examine associations between these traits and demographic performance in communities. Here, we examined the associations between species traits including leaf venation traits and demographic rates (Relative Growth Rate, RGR and mortality) as well as the spatial distributions of traits along soil environment for 54 co‐occurring species in a subtropical forest. Size‐related changes in demographic rates were estimated using a hierarchical Bayesian approach. Next, Kendall's rank correlations were quantified between traits and estimated demographic rates at a given size and between traits and species‐average soil environment. Species with denser venation, smaller areoles, less succulent, or thinner leaves showed higher RGR for a wide range of size classes. Species with leaves of denser veins, larger area, cheaper construction costs or thinner, or low‐density wood were associated with high mortality rates only in small size classes. Lastly, contrary to our expectations, acquisitive traits were not related to resource‐rich edaphic conditions. This study shows that leaf vein traits are weakly, but significantly related to tree demographic performance together with other species traits. Because leaf traits associated with an acquisitive strategy such as denser venation, less succulence, and thinner leaves showed higher growth rate, but similar leaf traits were not associated with mortality, different pathways may shape species growth and survival. This study suggests that we are still not measuring some of key traits related to resource‐use strategies, which dictate the demography and distributions of species.

The authors investigated the effect of binary mixtures of zinc (Zn), copper (Cu), cadmium (Cd), and nickel (Ni) on the growth of a freshwater diatom, Navicula pelliculosa. A 7 × 7 full factorial experimental design (49 combinations in total) was used to test each binary metal mixture. A 3-d fluorescence microplate toxicity assay was used to test each combination. Mixture effects were predicted by concentration addition and independent action models based on a single-metal concentration-response relationship between the relative growth rate and the calculated free metal ion activity. Although the concentration addition model predicted the observed mixture toxicity significantly better than the independent action model for the Zn-Cu mixture, the independent action model predicted the observed mixture toxicity significantly better than the concentration addition model for the Cd-Zn, Cd-Ni, and Cd-Cu mixtures. For the Zn-Ni and Cu-Ni mixtures, it was unclear which of the 2 models was better. Statistical analysis concerning antagonistic/synergistic interactions showed that the concentration addition model is generally conservative (with the Zn-Ni mixture being the sole exception), indicating that the concentration addition model would be useful as a method for a conservative first-tier screening-level risk analysis of metal mixtures. Environ Toxicol Chem 2016;35:2765-2773. © 2016 SETAC.

Summary A plant's growth rate is seen as a central element of its ecological strategy, and as determined by its traits. Yet the literature is inconsistent about the empirical correlation between functional traits and growth, casting doubt on the capacity of some prominent traits to influence growth rate. We propose that traits should influence growth in a way that depends on the size of individual plants. We outline mechanisms and hypotheses based on new theoretical work and test these predictions in tree species using a meta-analysis of 103 studies (> 500 correlations) for five traits (specific leaf area, wood density, maximum height, seed mass and maximum assimilation rate). We also recorded data for 14 other traits commonly used in the trait literature. To capture the effects of plant size, we tested for a shift in the direction of correlation between growth rates and each trait across three ontogenetic stages: seedling, sapling and adult. Results were consistent with predictions, although there were some limitations arising from unequal numbers of observation across ontogenetic stages. Specific leaf area was correlated with relative growth rate in seedlings but not in adult plants. Correlations of growth with wood density were not affected by ontogenetic stage. Seed mass, assimilation rate and maximum height were correlated with relative growth rate only in one ontogenetic stage category: seedlings, seedlings and adults, respectively. Although we were able to confirm several of our theoretical predictions, major knowledge gaps still exist in the trait literature. For example, for one-third of the traits considered, the majority (> 75%) of reported correlations with growth came from the same ontogenetic stage. Synthesis. We show for some traits, how trait–growth correlations change in a predictable way with plant size. Our understanding of plant strategies should shift away from describing species as having a fixed growth strategy throughout their life (on a continuous axis from slow to fast growth), in favour of a size-dependent growth trajectories.

Summary Root, stem and leaf traits are thought to be functionally coordinated to maximize the efficiency of acquiring and using limited resources. However, evidence is mixed for consistent whole-plant trait coordination among woody plants, and we lack a clear understanding of the adaptive value of root traits along soil resource gradients. If fine roots are the below-ground analogue to leaves, then low specific root length (SRL) and high tissue density should be common on infertile soil. Here, we test the prediction that root, stem and leaf traits and relative growth rate respond in unison with soil fertility gradients. We measured fine root, stem and leaf traits and relative growth rate on individual seedlings of 66 tree species grown in controlled conditions. Our objectives were (i) to determine whether multiple root traits align with growth rate, leaf and stem traits and with each other and (ii) to quantify the relationships between community-weighted mean root traits and two strong soil fertility gradients that differed in spatial extent and community composition. At the species level, fast growth rates were associated with low root and stem tissue density and high specific leaf area. SRL and root diameter were not clearly related to growth rate and loaded on a separate principal component from the plant economic spectrum. At the community level, growth rate was positively related to soil fertility, and root tissue density (RTD) and branching were negatively related to soil fertility. SRL was negatively related and root diameter was positively related to soil fertility on the large-scale gradient that included ectomycorrhizal angiosperms. Synthesis. Root, stem and leaf tissue traits of tree seedlings are coordinated and influence fitness along soil fertility gradients. RTD responds in unison with above-ground traits to soil fertility gradients; however, root traits are multidimensional because SRL is orthogonal to the plant economic spectrum. In contrast to leaves, trees are not constrained in the way they construct fine roots: plants can construct high or low SRL roots of any tissue density. High RTD is the most consistent below-ground trait that reflects adaptation to infertile soil.

The growth, morphology and biomass allocation of 11 liana species (six light-demanding and five shade-tolerant) were investigated by growing plants in three contrasting light environments (i.e., field, forest edge and forest interior). Our objectives were to determine: (1) changes in plant traits at the species level; and (2) differences in light-demanding and shade-tolerant species in response to altered light environment. We found that all seedlings of liana species increased in total biomass, total leaf area, relative growth rate (RGR), net assimilation rate (NAR), height, basal diameter, root length, leaf number, root mass/total plant mass (RMR) and root-to-shoot dry biomass (R/S ratio), and decreased in leaf area ratio (LAR), specific leaf area (SLA), leaf size, stem mass-to-total plant mass ratio (SMR) and leaf mass-to-total plant mass ratio (LMR) with increasing light availability. Under the three light environments, the two types of species differed significantly in total biomass, total leaf area, RGR, NAR, LAR, SLA and leaf number, and not in leaf area. Only light-demanding species differed significantly in height, root length, basal diameter, RMR, SMR, LMR and R/S ratio. The mean plasticity index of growth and biomass allocation were relatively higher than the morphological variables, with significant differences between the two groups. Our results showed that liana species respond differently to changing light environments and that light-demanding species exhibit higher plasticity. Such differences may affect the relative success of liana species in forest dynamics.