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Duckweeds (Lemnaceae) are representative producers in fresh aquatic ecosystems and also yield sustainable biomass for animal feeds, human foods, and biofuels, and contribute toward effective wastewater treatment; thus, enhancing duckweed productivity is a critical challenge. Plant-growth-promoting bacteria (PGPB) can improve the productivity of terrestrial plants; however, duckweed–PGPB interactions remain unclear and no previous study has investigated the molecular mechanisms underlying duckweed–PGPB interaction. Herein, a PGPB, Ensifer sp. strain SP4, was newly isolated from giant duckweed (Spirodela polyrhiza), and the interactions between S. polyrhiza and SP4 were investigated through physiological, biochemical, and metabolomic analyses. In S. polyrhiza and SP4 coculture, SP4 increased the nitrogen (N), chlorophyll, and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) contents and the photosynthesis rate of S. polyrhiza by 2.5-, 2.5-, 2.7-, and 2.4-fold, respectively. Elevated photosynthesis increased the relative growth rate and biomass productivity of S. polyrhiza by 1.5- and 2.7-fold, respectively. Strain SP4 significantly altered the metabolomic profile of S. polyrhiza, especially its amino acid profile. N stable isotope analysis revealed that organic N compounds were transferred from SP4 to S. polyrhiza. These N compounds, particularly glutamic acid, possibly triggered the increase in photosynthetic and growth activities. Accordingly, we propose a new model for the molecular mechanism underlying S. polyrhiza growth promotion by its associated bacteria Ensifer sp. SP4, which occurs through enhanced N compound metabolism and photosynthesis. Our findings show that Ensifer sp. SP4 is a promising PGPB for increasing biomass yield, wastewater purification activity, and CO2 capture of S. polyrhiza. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Aims: The research aimed to investigate the shade response of E. gracilis Klebs while making the irradiance a crucial factor for photosynthesis based physiological activities and its applicability for industrial level culture conditions. Study Design: Euglena was cultured at three different light intensities of 30, 90, and 210 mol m-2s-1 photoautotrophically and axenically in modified Cramer-Meyer medium at 25 ˚C as batch cultures. Methodology: The photosynthesis O2 evaluation of Euglena cultures was measured under exponential (EP), transitional (TP), and stationary phases (SP). The light compensation point (LCP), light saturation point (LSP), and dark respiration rate (DRR) were obtained. Cell volume and cell number in each culture were measured simultaneously. Cells were collected and obtained dry mass (DM) after drying aliquots at 80˚C. Specific growth rate (SGR) and relative growth rate (RGR) were calculated. Tests for homogeneity of variance were performed on all parameters and LSDs were used for the mean separation. Results: In the TP, the lowest LCP was achieved in the higher light culture. The values of both the DRR and the LSP were the same as in EP. The DRR, LCP and LSP are lower in lower PFD cultures and decreased with increasing cell titers. The cellular growth levels were lower in lower light culture and decreased as each culture grew. Cellular DM was maintained constant in the EP, where SGR almost equaled RGR. In the EP, SGR was maintained constant in each culture, SGR displayed a saturation phenomenon. In the later TP, SGR became equal to RGR and all the cultures revealed constant DM. Conclusion: Euglena photoautotrophic cultures can tolerate low light intensities. With the SGR and RGR behavior under the shade conditions, they can maintain the constant photosynthesis rate and constant dry matter level.

Taxonomy of Azolla was extensively studied, but still its identification based on morphological, physiological, and reproductive structure remains unclear. Hence, an attempt was made to differentiate Azolla strains based on morphological and physiological traits, keeping six known Azolla (Azolla microphylla, Azolla caroliniana, Azolla mexicana, Azolla rubra, Azolla filiculoides, and Azolla pinnata) as reference for this study. The results showed that out of 96, 21 strains were sporulated during December, 2017 to February 2018 along with two known species, i.e., A. microphylla and A. pinnata. All sporulating strains (except GSMI 1) showed morphological-resemblance with A. pinnata, whereas GSMI 1 was resembled with A. microphylla. Biplot principal coordinate analysis (PCoA) based on physiological data revealed that GSMI 1 was significantly resembled with A. microphylla. Moreover, the presence of rounded dorsal leaf lobe in A. caroliniana has made it unique in Euzolla sub-section and hence, differentiated from other four species (A. microphylla, A. mexicana, A. rubra, and A. filiculoides). WinRHIZO-based root-imaging technique showed the presence of thick root hairs in A. pinnata as compared to other Azolla strains, whereas efficiency of photosystem II (Fv /Fm, a chlorophyll fluorescence-imaging derived value) and relative growth rate were found higher in CRRI 4. In conclusion, the present study generated a presumptive classification key of 102 strains of Azolla for the first time, which indicates clearly that taxonomy in Azolla should be reviewed. Validation of these characters through molecular markers will give further insight about their classification.

○ The potential amelioration of Al (Al) toxicity by elevated dissolved inorganic carbon (DIC = CO 2 + HCO 3 - ) in the root medium was investigated in both NH 4 + - and NO 3 - -fed Lycopersicon esculentum (tomato) plants. ○ Hydroponically grown L. esculentum seedlings were intermittently supplied with 50 μM AlCl 3 and the nutrient solutions aerated with either 360 or 5000 ppm CO 2 . Relative growth rate (RGR), nitrogen uptake, root respiration and root incorporation of DI 14 C and subsequent partitioning were measured. ○ Al reduced the RGR of plants grown with 360 ppm root-zone CO 2 . At elevated root-zone CO 2 , Al had no significant effect on the RGR of NO 3 - -fed plants whereas the RGR of the NH 4 + -fed plants was increased by 21 %. Al decreased the respiratory quotient (Rq) by 15% at 360 ppm CO 2 , but had no influence at 2000 ppm CO 2 . Exudation of organic 14 C, especially of [ 14 C]-organic acids derived from root incorporation of DI 14 C, was increased by Al. ○ It is concluded that elevated DIC partially ameliorated Al toxicity by providing anaplerotic carbon for organic acid synthesis.

Gevuina avellana and Lomatia dentata are Proteaceae species from evergreen temperate forests, but only G. avellana can colonize nutrient deprived volcanic depositions. We hypothesized that under nutrient deprivation, G. avellana would present higher survival, physiological performance, and adjustment regarding cluster root (CR) formation and carboxylate exudation rate than L. dentata. We evaluated relative growth rate, maximal photosynthetic rate, photochemical performance, nitrogen (N) and phosphorus (P) leaf concentrations, specific leaf area, photosynthetic P and N use efficiency (PPUE and PNUE), CR formation and carboxylate exudation rate. Plants were grown in a greenhouse, using recent volcanic substrate and watered with different nutrient Hoagland (H) solutions: modified full Hoagland, without P, without N, or tap water. Both species showed high survival. G. avellana exhibited higher growth rates (RGR), and higher CR number and biomass allocation under nutrient deprivation, but lower carboxylate exudation rates than L. dentata. Malate, oxalate and succinate were detected in root exudates of G. avellana but only oxalate in L. dentata. However, PPUE and PNUE were higher in L. dentata than in G. avellana . Our hypothesis was not entirely accepted, CR formation was more “constitutive” in G. avellana, and composition of carboxylates was more diverse, with lower exudation rates than L. dentata. Moreover, L. dentata showed higher PNUE and PPUE, partly explained by thinner leaves. Different responses are related with edaphic conditions, where both species inhabit: more diverse to G. avellana and restricted to developed soils to L. dentata.

The selection of unialgal culture strains suitable as sources of algal hemagglutinins is one of the important factors for success in algal component production. To obtain suitable unialgal culture strains, several Gracilariopsis chorda and Gracilaria vermiculophylla strains were surveyed for hemagglutinating activity, relative growth rates, and fertility difficulty. Fertile tetrasporophyte samples of naturally occurring G. chorda and G. vermiculophylla were collected at each of three different collection sites around Shikoku Island in southwest Japan. Unialgal culture strains were started from isolated tetraspores obtained from each naturally occurring plant. The hemagglutinating activities in algal extracts of the three G. chorda strains (3100–7000 units mg−1) were higher than those of the three G. vermiculophylla strains (920–980 units mg−1). The daily growth rates of the G. chorda strains (8.0–13.8% day−1 at 22 °C) were higher than those of the G. vermiculophylla strains (4.1–4.4% day−1 at 22 °C). Among the unialgal culture strains tested, the one started from isolated tetraspores from G. chorda growing in the Katsuura River had the highest hemagglutinating activity and relative growth rate. This strain also did not become fertile even after a period of 3 years of culture with aeration at 22 °C, in a 14-h light–10-h dark cycle at 60 μmol photons m−2 s−1. Thus, the unialgal culture strain started from isolated tetraspores from G. chorda growing in the Katsuura River seems to be a useful source for hemagglutinin production.

The sexual reproduction period (May–June) of Sargassum fusiformis, an important aquaculture seaweed in China, coincides with a time of high frequency of algal blooms caused by dinoflagellates such as Karenia mikimotoi. We studied the effects of dense K. mikimotoi suspensions on the sexual reproduction and subsequent development of the fertilized eggs of S. fusiformis in the laboratory. The results showed that K. mikimotoi did not inhibit the egg fertilization, but significantly (P

This review focuses on recently characterized traits of the aquatic floating plant Lemna with an emphasis on its capacity to combine rapid growth with the accumulation of high levels of the essential human micronutrient zeaxanthin due to an unusual pigment composition not seen in other fast-growing plants. In addition, Lemna’s response to elevated CO2 was evaluated in the context of the source–sink balance between plant sugar production and consumption. These and other traits of Lemnaceae are compared with those of other floating aquatic plants as well as terrestrial plants adapted to different environments. It was concluded that the unique features of aquatic plants reflect adaptations to the freshwater environment, including rapid growth, high productivity, and exceptionally strong accumulation of high-quality vegetative storage protein and human antioxidant micronutrients. It was further concluded that the insensitivity of growth rate to environmental conditions and plant source–sink imbalance may allow duckweeds to take advantage of elevated atmospheric CO2 levels via particularly strong stimulation of biomass production and only minor declines in the growth of new tissue. It is proposed that declines in nutritional quality under elevated CO2 (due to regulatory adjustments in photosynthetic metabolism) may be mitigated by plant–microbe interaction, for which duckweeds have a high propensity. This work was funded by the Translational Research Institute for Space Health through Cooperative Agreement NNX16AO69A, the National Science Foundation award number IOS-1907338, and the University of Colorado.

An efficient regeneration protocol was applied to regenerate shoots on salt stress-tolerant calli lines of aubergine (Solanum melongena). These NaCl-tolerant cell lines were obtained by two different methods. On the one hand, the developed callus tissue was transferred to a medium with a continuous salt content of 40, 80, 120, or 160 mM NaCl. On the other hand, the callus tissue was subjected to a stepwise increasing salinity to 160 mM NaCl every 30 days. With the second method, calli which could be selected were characterized by compact growth, a greenish color, and absence of necrotic zones. When grown on salt-free medium again, NaCl-tolerant calli showed a decline in relative growth rate and water content in comparison to the control line. This was more obvious in the 120 mM NaCl-tolerant callus. Lipid peroxidase activity increased in 40 and 80 mM NaCl-tolerant calli; yet did not increase further in 120 mM-tolerant callus. An increase in ascorbic acid content was observed in 80 and 120 mM NaCl-tolerant calli compared to the 40 mM NaCl-tolerant lines, in which ascorbic acid content was twice that of the control. All NaCl-tolerant lines showed significantly higher superoxide dismutase (SOD) (208–305–370 µmol min−1 mg−1 FW) and catalase (CAT) (136–211–238 µmol min−1 mg−1 FW) activities compared to control plants (231 and 126 µmol min−1 mg−1 FW). Plants were regenerated on the calli lines that could tolerate up to 120 mM NaCl. From the 32 plants tested in vitro, ten plants with a higher number of leaves and root length could be selected for further evaluation in the field. Their high salt tolerance was evident by their more elevated fresh and dry weight, their more increased relative water content, and a higher number and weight of fruits compared to the wild-type parental control. The presented work shows that somaclonal variation can be efficiently used to develop salt-tolerant mutants.

In order to produce protein-rich duckweed for human and animal consumption, a stable cultivation process, including an optimal nutrient supply for each species, must be implemented. Modified nutrient media, based on the N-medium for duckweed cultivation, were tested on the relative growth rate (RGR) and crude protein content (CPC) of Lemna minor and Wolffiella hyalina, as well as the decrease of nitrate-N and ammonium-N in the media. Five different nitrate-N to ammonium-N molar ratios were diluted to 10% and 50% of the original N-medium concentration. The media mainly consisted of agricultural fertilizers. A ratio of 75% nitrate-N and 25% ammonium-N, with a dilution of 50%, yielded the best results for both species. Based on the dry weight (DW), L. minor achieved a RGR of 0.23 ± 0.009 d−1 and a CPC of 37.8 ± 0.42%, while W. hyalina’s maximum RGR was 0.22 ± 0.017 d−1, with a CPC of 43.9 ± 0.34%. The relative protein yield per week and m2 was highest at this ratio and dilution, as well as the ammonium-N decrease in the corresponding medium. These results could be implemented in duckweed research and applications if a high protein content or protein yield is the aim.

The prevalence of microplastics in marine, terrestrial, and freshwater habitats has raised concerns about their availability and risks to organisms. However, the effects of plastic debris on vascular plants remain largely unknown and have hardly been studied, despite the importance of these plants in freshwater ecosystems. In this study, we exposed the aquatic carnivorous plant Utricularia vulgaris to polystyrene microplastics (10 and 80 mg/L) combined with different nutrient concentrations and then assessed their effects on the growth rate, photosynthesis, oxidative stress, and trap-associated microbial community of U. vulgaris. The impact of microplastic accumulation in the traps (or "bladders") of U. vulgaris was investigated for the first time using confocal microscopy. The results showed that the relative growth rate, shoot length, chlorophyll content, Fv/Fm, and ascorbate peroxidase enzyme activity of U. vulgaris decreased in 80 mg/L microplastics, whereas the superoxide dismutase and peroxidase enzyme activities increased significantly. The presence of microplastics led to higher malondialdehyde and hydrogen peroxide contents. However, high nutrient concentrations can compensate for the reduced growth performance of U. vulgaris in microplastic-exposure treatments. The microplastic treatments significantly altered the trap-associated microbial community structure and diversity. The results of this study revealed that beside adsorption, carnivorous plants can accumulate microplastics in their digestive organs.

Xylem conduit diameter (D max ) of woody angiosperm adults scales with plant size and widens from the stem apex downwards. We hypothesized that, notwithstanding relative growth rate (RGR), growth form or leaf habit, woody seedling conduit D max scales linearly with plant size across species; this scaling should be applicable to all vegetative organs, with consistent conduit widening from leaf via stem to main root and coupling with whole-leaf area and whole-stem xylem area. To test these hypotheses, organ-specific xylem anatomy traits and size-related traits in laboratory-grown seedlings were analyzed across 55 woody European species from cool-temperate and Mediterranean climates. As hypothesized, conduit D max of each organ showed similar scaling with plant size and consistent basipetal widening from the leaf midvein via the stem to the main root across species, independently of growth form, RGR and leaf habit. We also found a strong correlation between D max and average leaf area, and between stem xylem area and whole-plant leaf area. We conclude that seedlings of ecologically wide-ranging woody species converge in their allometric scaling of conduit diameters within and across plant organs. These relationships will contribute to modeling of water transport in woody vegetation that accounts for the whole life history from the trees’ regeneration phase to adulthood.

Rising atmospheric CO2 concentration is one of the most important ways human activity is contributing to global change. It has led to climate-related changes that affect physiological performance, phenology, and distributions of species globally. Elevated [CO2] enhances growth in many plant species through increased photosynthetic rates, improved water and nitrogen use efficiency, and altered functional traits. In this study, we investigated the growth, reproduction and functional trait responses to elevated [CO2] of two free-floating ferns, the native Azolla filiculoides (Azollaceae) and the exotic invasive Salvinia molesta (Salviniaceae), and a submerged native angiosperm, Vallisneria spiralis (Hydrocharitaceae). The species were grown in monocultures under ambient (∼400 ppm) and elevated (∼600 ppm) [CO2] in a greenhouse experiment. We found that A. filiculoides had enhanced relative growth rate and reproduction under elevated [CO2]. However, its root to shoot ratio was unaffected while its specific leaf area was reduced under elevated [CO2]. In contrast, S. molesta and V. spiralis did not differ in their growth, reproduction or functional trait responses between the CO2 treatments. We conclude that freshwater plant responses to elevated [CO2] may vary across species, with functional differences potentially driving differential responses as exemplified by the lack of response of the CAM physiology species Vallisneria spiralis and the strong response of the nitrogen-fixing A. filiculoides compared to the non nitrogen-fixing species in this study. Future work should focus on the impact of elevated CO2 on plant growth in the context of environmental conditions such as pH, temperature and light availability in freshwater systems.

Banksia attenuata is a resprouting species growing in deep sand, while B. sessilis is a fire-killed species occurring in shallow sand over laterite or limestone. We aimed to discover the ecophysiological basis for their different distributions by exploring their investment in deep non-cluster roots and shallow cluster roots, and their cluster-root functioning. Deep-pot (1 m), shallow-pot (400 mm), hydroponic experiments and phosphorus (P)-extraction experiment were carried out. Biomass allocation, cluster-root exudation, plant P and leaf manganese (Mn) concentrations were measured. Banksia attenuata allocated more biomass to deep roots and less biomass to cluster roots than B. sessilis did in deep pots. The two Banksias released similar carboxylates in all experiments, with similar carboxylate-exudation rates in hydroponics. The carboxylate amount per unit cluster root of B. sessilis grown in shallow pots was greater than that of B. attenuata, and B, sessilis acquired more P than B. attenuata did in limestone substrate. Greater investment in deep roots for water uptake accounts for the presence of B. attenuata in deep sand, and vice versa for the absence of B. sessilis. A larger investment in cluster roots, which released greater amounts of carboxylates, likely accounts for B. sessilis occurring over limestone. Trade-offs in investment and cluster-root functioning support the species’ distribution patterns and life histories. Leaf Mn concentration was a good proxy for the plant capacity to acquire P.

Premise of research. Tolerance to herbivory is the capacity of plants to reduce the negative effects of damage on fitness. Increased growth rate and photosynthesis are two important mechanisms behi...

We studied the relative growth rate of seedlings and aboveground and underground organs, as well as functional traits of leaves and absorbing roots in the invasive species Heracleum sosnowskyi and congeneric native species H. sibiricum. The plants were grown in laboratory conditions and the functional plant traits of 21- and 35-day-old seedlings were analyzed. The relative growth rate (RGR) of H. sosnowskyi differed from that of H. sibiricum by 2.5 times, but the growth of plants in height and in area of leaves was similar. Plant biomass and total leaf area were twice as high in 35-day-old seedlings of invasive species. Structural features of the leaves in 35-day-old H. sosnowskyi seedlings were a lower leaf thickness and a higher leaf density. The invasive species had a lower root mass ratio, but the roots were more branched with a greater ratio of absorbing roots and a better development of the root hairs. As a result, H. sosnowskyi had a higher growth rate of absorbing roots (by 2 times) and a larger absorbing surface in relation to the total root surface. We concluded that the structural and functional traits of the leaves and roots provided a 2 times higher net assimilation rate (NAR) and 2.5 times larger RGR in the invasive species H. sosnowskyi.

Summary • Regeneration of the dominant ectomycorrhizal tree Microberlinia bisulcata in groves in Korup, Central Africa, is very poor. The hypothesis was tested that this species is more shade intolerant than other co-occurring species. • In two 1-yr trials, each with M. bisulcata and four other species at a nursery close to Korup, growth was measured under five PAR levels, with ± added P and ± watering in the dry season. In parallel experiments the effects of PAR with two R : FR ratios were investigated. • Increasing PAR had a consistent effect on the rates of increase in plant mass and on changes in the other variables. Doubling soil P, watering and halving the R : FR ratio had almost no effect. However, across species, mass at low PAR and relative growth rate related positively and negatively, respectively, to seed mass. • One contributing factor for the poor recruitment of M. bisulcata is therefore its low survival and slow growth at low PAR, due to its small seed size. The two codominant ectomycorrhizal grove species of Tetraberlinia, with larger seeds, were less affected by low PAR.

summary This paper is the first to report cadmium tolerance in a dicotyledonous species, Silene vulgaris (Moench.) Garcke. The response to cadmium of five populations originating from one uncontaminated and various heavy-metal contaminated sites was examined under standardized conditions for three weeks. The tolerance index (TI), based on the mean relative growth rate (R), was determined. Populations originating from cadmium-contaminated sites showed a distinct tolerance to cadmium. A population from a site enriched only with copper also exhibited a marked co-tolerance to cadmium. A clear difference in biomass production between the sensitive and tolerant populations was attained at 1 μM cadmium. An optimum biomass production in tolerant populations at a metal concentration higher than in the control, as demonstrated for zinc and copper, could not be established for cadmium. The pattern of cadmium uptake and translocation differed between tolerant and sensitive populations. All tolerant populations accumulated cadmium in the roots and showed some degree of restricted transport to the shoots. The effect of cadmium on the elemental distribution in roots and shoots was population-independent for some elements (copper, zinc, potassium) and population-specific for others (phosphorus, magnesium and sodium). The phenomenon of co-tolerance to cadmium is discussed in relation to possible tolerance mechanisms, especially with regard to metal-binding compounds (metallothioneins, phytochelatins).

Summary • Internal conflicts in the allocation of resources lead to trade-offs or compromises that can influence fitness and the evolution of specific life-history traits. • Here, the reproductive schedule of Floerkea proserpinacoides plants, a spring ephemeral annual of the deciduous forests of eastern North America, was manipulated to determine the presence of potential conflicts between growth and reproduction, and the advantage of early reproduction. • Plants on which flowering was delayed had a greater relative growth rate (RGR) and vegetative biomass than control plants after 8 wks (when control plants started to senesce). Delayed-flowering plants took 1 week longer to senesce, which allowed them to mature almost as many seeds as did control plants in 8 wks. • However, late flowering in F. proserpinacoides may be maladaptive. With reduced light availability through canopy closure, early flowering plants can rapidly divert most of the resources accumulated in the stem and leaves to seed maturation. Thus, the advantage of maintaining a higher RGR by delaying flowering is associated with the greater disadvantage of necessitating more time to mature seeds.

SUMMARY Two inbred lines of Plantago major L., differing in relative growth rate (RGR), were studied in order to elucidate physiological factors responsible for this difference. The slow growing inbred line of P. major ssp. major L. (line W9) had a lower specific leaf area (SLA) compared with that of the fast growing P. major ssp. pleiosperma Pilger (line A4). Photosynthetic activity per unit leaf area was higher than that of A4, but expressed per unit leaf dry weight W9 exhibited a lower activity than A4. Photosynthetic capacity (per unit leaf dry weight or nitrogen) was identical for both lines. The amount of chlorophyll a per unit dry weight or leaf area was higher for line W9. Differences in the chemical composition of the leaf dry weight of the two lines did not explain the lower SLA or lower photosynthetic activity per unit leaf dry weight of the slow growing line. The lower SLA of W9 was mainly caused by the lower water content per unit dry weight. A higher amount of cell wall material per unit leaf dry weight was found. We conclude that the lower SLA of W9 resulted in a greater shading within the leaf, a lower light absorption and lower photosynthetic rate per unit leaf dry weight. Consequently, this resulted in a lower RGR. The significance of these characters for growth under trampling and soil compaction is discussed.

Summary • The effects are reported of substrate salinity and light on the relative growth rate of the annual Aster laurentianus, an endangered species of eastern Canadian salt marshes. • The independent and combined effects of photosynthetically active photon flux density and salinity on the relative growth rate (RGR) and overall plant performance were measured in glasshouse and growth-chamber experiments on seedlings of A. laurentianus. • Low light availability decreased RGR through its negative effect on unit leaf rate. However, specific leaf area and leaf mass ratio varied inversely with changes in light, such that leaf area ratio did not differ greatly among light levels. High salinity decreased RGR by reducing unit leaf rate and leaf area ratio; a reduction in the latter was brought about by a lower leaf mass ratio rather than by a lower specific leaf area. Low light availability combined with high substrate salinity affected A. laurentianus in a strictly additive manner; there was no significant interaction between the two factors on overall plant performance. • Light and salinity are important factors controlling growth of A. laurentianus, and might explain the distribution pattern of the species in the field.

Due to their different physiological effects, elevated carbon dioxide and elevated ozone might have interactive impacts on plants, and differentially so on plants differing in photosynthetic pathway and growth rate. To test several hypotheses related to these issues, we examined the physiological, morphological and growth responses of six perennial species grown at various atmospheric concentrations of carbon dioxide and ozone. The species involved (two C3 trees: Populus tremuloides Michx., Quercus rubra L.; two C3 grasses: Agropyron smithii Rybd., Koeleria cristata L.; two C4 grasses: Bouteloua curtipendula Michx., Schizachyrium scoparium Michx.) differed in growth form, stomatal conductance and photosynthetic pathway. In situ photosynthesis, relative growth rate (RGR) and its determinants (leaf area ratio, specific leaf area, leaf weight ratio and root weight ratio) were determined via sequential harvests of seedlings that were grown in all combinations of 366 or 672 μmol mol−1 CO2 and 3 or 95 nmol mol−1 O3 over a 101-d period. Elevated CO2 had minimal effect on either photosynthesis or RGR. By contrast, RGR for all six species was lower in high O3 concentrations at ambient CO2, significantly so in A. smithii and P. tremuloides. Five of the six species also exhibited reductions in in situ photosynthesis at ambient CO2 in high-O3-grown compared with low-O3-grown plants. For all species, these O3-induced reductions in RGR and photosynthesis were absent in the elevated CO2 environment. Root weight ratio was significantly reduced by elevated O3 in A. smithii and P. tremuloides in ambient but not elevated CO2. Species with high stomatal conductance were the most susceptible to oxidant injury, while those with low stomatal conductance, such as the C4 species and Q. rubra, were not as detrimentally affected by O3. Elevated levels of CO2 will reduce stomatal conductance and O3 uptake, and might therefore reduce the potential for oxidant damage. However, there was a stronger relationship of the percent reduction in whole-plant mass due to O3, related to the ratio of photosynthesis to stomatal conductance. In general, results of this study of six functionally diverse plant species suggest that O3 pollution effects on carbon balance and growth are likely to be ameliorated by elevated concentrations of atmospheric CO2.

The effects of ambient and elevated ozone levels on growth and photosynthesis of beech (Fagus sylvatica) were studied by exposing seedlings in open-top chambers for one growing season to three treatments: charcoal-filtered (CF), non-filtered (NF) and non-filtered air with addition of ozone (30 ppb ozone) on clear days for 8–10 h d−1 (NF +). Ambient levels were relatively low and accumulated to an AOT40 (accumulated exposure over a threshold of 40 ppb) of 4055 ppb h (for the period 23 Apr–30 Sept). The NF + chambers received an AOT40 of 8880 ppb h. Throughout the growing season we measured growth and photosynthetic properties. The treatments did not cause strong effects: measurements of gas exchange (light-saturated assimilation rate, CO2 and light-response curves) and chlorophyll fluorescence showed slight and mostly non-significant reductions of several parameters. No significant differences were found for growth, though in the NF + treatment (AOT40 8880 ppb h) the relative growth rate for diameter increment was at times reduced by 12% compared with the control treatment.

summary A range of wetland plant species (44) was screened in solution culture experiments for sensitivity to large concentrations of supplied Fe. Two distinct root precipitates were observed (see ‘Appendix’ for a tabulated summary of symptoms). Energy dispersive spectroscopy showed that an ochreous precipitate was probably a hydrated ferric oxide whilst a pale yellow or yellow-grey one was an Fe-P solid, possibly a ferric phosphate. Ochre precipitates were found almost exclusively cm the roots of Fe-tolerant species and were particularly intense on the most tolerant ones, Monocotyledonous species (generally more Fe-tolerant than dicotyledonous species and with higher root porosities), tended to produce ochre most freely. The Fe-P precipitate was frequently found on roots of the less tolerant species and was particularly abundant on the most sensitive ones. Blackening of roots (with flaccidity I, another common response of roots of Fe-sensitive plants exposed to large Fe concentrations, was not a result of any obvious external precipitate. There was no evidence that differential pH changes induced by roots helped to determine either Fe tolerance or the nature of the root precipitate observed. Roots of all species tested caused the pH of an agar medium to rise. Elevated Ft- supply resulted in greater external acid phosphatase activity in roots of two test species. The increase corresponded with the species' mean relative growth rate (RGR) (and presumed P requirement), and with me fertility of sites in which it grows. Chemical analyses of shoots and roots of four species of differing Fe tolerance showed that, with increasing Fe supply, mean shoot Fe concentrations increased significantly whereas for most other elements (except Na and Zn) a significant reduction in concentrations in the shoot was observed. Mean root concentrations of most elements also fell significantly with increasing Fe supply, though for three of the four test species there was a significant increase in root P concentrations. It is clear that only some wetland plant species form ochreous root precipitates when grown in Fe-rich conditions, and have an effective Fe-exclusion mechanism. Growth of those species that lack this capacity is affected adversely by high Fe concentrations. This might be owing both to direct effects of Fe uptake and to indirect effects, particularly of Fe upon P metabolism. No evidence was found to suggest chat the Fe-tolerant species examined could accommodate higher tissue Fe concentrations than the Fe-sensitive species.

The present study investigated to what extent there is a link between root tissue structure and ecological strategies of plant species; such a link is known for leaf tissue structure. We investigated experimentally root tissue mass density, root diameter and several characteristics of root anatomy in the axile roots of 19 perennial grass species from different habitats and related these parameters to the ecological behaviour of the species. Root characteristics were assessed in new roots produced by mature plants grown under standardized conditions. The ecological behaviour was characterized in terms of relative growth rate (RGR), plant height at maturity and ecological indicator values for nutrients, light and tolerance to mowing according to Ellenberg. We found a striking dichotomy between root anatomical characteristics associated with interspecific variation in RGR and those associated with variation in plant height. RGR correlated with anatomical characteristics that contribute to root robustness, whereas plant height correlated with characteristics associated with axile root hydraulic conductance. RGR correlated negatively with tissue mass density (TMDr ) in roots. Interspecific variation in TMDr was explained by the proportion of stele in the cross-sectional area (CSA) of the axile root and the proportion of cell wall in the CSA of the stele. For a given root diameter, slow growing species had smaller, albeit more numerous, xylem vessels, indicating a higher resistance to cavitation and protection against embolisms. Plant height correlated positively with root CSA, total xylem CSA and mean xylem vessel CSA, indicating a need for a high transport capacity in roots of species that attain a large size at maturity. TMDr correlated positively with dry matter content in leaves. The results emphasize the close relationship between tissue structure and growth characteristics at the whole-plant level.

The tidal estuarine wetlands of China are rich in plant diversity, but several human-driven processes, such as species invasion, can affect the biogeochemical cycles of these ecosystems, and by changing soil conditions can inhibit the regeneration of native vegetation. We seasonally analyzed the carbon (C), nitrogen (N) and phosphorus (P) concentrations in soils and in leaves, stems and roots of the invasive species Spartina alterniflora and of the native species Cyperus malaccensis var. brevifolius Boeckeler. This latter species was analyzed both in natural non-invaded stands and in stands that had been invaded by Spartina but from which it had been removed and replaced by Cyperus. The aim was to investigate the effect of plant invasion, subsequent removal and replanting with a native species on C, N and P stoichiometry of the plant–soil system in the tidal wetlands of the Minjiang River. C and N concentrations averaged across seasons did not differ significantly among the plant species. P concentration was lower in the stems of Spartina than in the stems of the native species Cyperus but was not significantly different in the roots of the two species. The soil C and N concentrations were higher in the Spartina stand than in the Cyperus stand, whereas the soil P concentrations were not significantly different. The invasive species had a higher N-resorption capacity, N:P ratios in stem and roots, biomass, absolute growth and biomass N and had a lower relative growth rate and litter production than the native species. After the removal of the invasive plants, the regenerating native plants have a higher capacity to resorb N and lower relative growth rates. All these traits show that a conservative strategy and a high N-use efficiency and internal plant control of the N in the ecosystem underlie the invasive success of Spartina in this N-limited wetland. Relative growth rate was associated with lower plant N:P ratios, whereas absolute growth rate was associated with higher nutrient-use efficiency and lower C and N turnover and storage capacities in the biomass. Changes in soil properties produced by the establishment of an invasive plant can condition the later regeneration of native plants.

A comprehensive characterization of water stress is needed for the development of automated irrigation protocols aiming to increase olive orchard environmental and economical sustainability. The main aim of this study is to determine whether a combination of continuous leaf turgor, fruit growth, and sap flow responses improves the detection of mild water stress in two olive cultivars characterized by different responses to water stress. The sensitivity of the tested indicators to mild stress depended on the main mechanisms that each cultivar uses to cope with water deficit. One cultivar showed pronounced day to day changes in leaf turgor and fruit relative growth rate in response to water withholding. The other cultivar reduced daily sap flows and showed a pronounced tendency to reach very low values of leaf turgor. Based on these responses, the sensitivity of the selected indicators is discussed in relation to drought response mechanisms, such as stomatal closure, osmotic adjustment, and tissue elasticity. The analysis of the daily dynamics of the monitored parameters highlights the limitation of using non-continuous measurements in drought stress studies, suggesting that the time of the day when data is collected has a great influence on the results and consequent interpretations, particularly when different genotypes are compared. Overall, the results highlight the need to tailor plant-based water management protocols on genotype-specific physiological responses to water deficit and encourage the use of combinations of plant-based continuously monitoring sensors to establish a solid base for irrigation management.

Although the sensitivity of growth and yield to ground-level ozone (O3) has been determined for a variety of agronomic crops and trees, little information is available for weedy species. Common ragweed (Ambrosia artemisiifolia L.) is recognized both as a common agricultural weed and the principle source of pollen for Fall (late August to November) allergies in North America. To quantify the extent to which ambient O3 limits growth and reproduction, ragweed was grown from germination to floral initiation at control [carbon filtered (CF), 15.8� nL� O3� L–1 air] and treatment levels (63.5 nL O3 L–1 air) of tropospheric O3. This 8-h treatment average is similar to the average 1-h O3 peak values from May through September in urban areas of Washington D.C. and Baltimore, MD. By 48 d after sowing, during floral initiation, no significant differences in total plant or floral biomass were observed as a function of O3 concentration, relative to the CF control. Analysis of leaf area ratio, relative growth rate and net assimilation rate at approximately 10-d intervals during early vegetative growth also did not demonstrate any significant effect of O3. Data from this experiment indicate that ragweed is insensitive to O3 levels up to four times that of the CF control, and suggests that O3 levels associated with urban environments may not limit the growth or reproductive development of ragweed.

Four wheat genotypes with contrasting degrees of Na+ exclusion were selected to see if low Na+ uptake had an adverse effect on water relations or growth rates during exposure to saline conditions. Plants were grown in supported hydroponics with and without 150 mM NaCl, and sampled for measurements of water relations, biomass, stomatal conductance, and ion accumulation. After 4 weeks exposure to salt, biomass was reduced in all genotypes to a similar extent (about 50%), with the effect of salinity on relative growth rate confined largely to the first week. There was little difference between genotypes in the effect of salinity on water relations, as indicated by their relative water content and estimated turgor. Osmotic adjustment occurred in all genotypes, with one of the low-Na+ genotypes having the greatest adjustment. In the low-Na+ genotypes, osmotic adjustment depended on higher K+ and high organic solute accumulation. Stomatal conductance of all genotypes was reduced by saline conditions, but the reduction was greater in the low-Na+ genotypes. These genotypes also showed a larger fall in the value of carbon isotope discrimination measured in expanding leaves, indicating a greater transpiration efficiency when exposed to saline conditions. Chlorophyll fluorescence measurements failed to indicate damage to photochemical pathways in either high- or low-Na+ genotypes. These data indicate that selecting lines with low Na+ accumulation for the purpose of improving salt tolerance is unlikely to introduce limitations for osmotic adjustment.

Leaves of Ricinus communis L. show strong nyctinastic movements as well as diurnal variations of growth activity, combined with prominent basipetal gradients of relative growth rate. A novel technique, using digital image sequence processing, is able to resolve such spatio–temporal patterns of leaf growth with high resolution. In this paper we analyse the impact of prevention of nyctinastic movements, and the potential of tensile forces to overcome the retarding effects. Tensile forces affected leaf expansion and tissue expansibility in a dose–response relation. In a comparison with freely-growing leaves, an appropriate, optimal tensile force was identified that rebuilt the natural diurnal course of leaf expansion. With this tensile force, undisturbed patterns of temporal and spatial growth distribution as well as undisturbed concentrations of major cations, amino acids or soluble sugars were observed. However, diurnal fluctuations in starch content of almost fully-grown leaves were affected by the treatment and could not be compensated by tensile forces. This effect might point to a connection between diurnal growth variations of the leaf vein, biomechanical forces that synchronize growth within the vein, and metabolism of carbohydrates as growth substrates of the vein. We therefore hypothesize that interveinal tensions, which are produced during nyctinastic leaf movements, are (i) required for undisturbed leaf growth and (ii) can be simulated by application of adequate tensile forces.

Arbuscular mycorrhizal (AM) fungi are ubiquitous symbionts of most terrestrial plants. These fungi not only provide their host plants with access to nutrients and resources but are known to augment plant defences against insect herbivores. Relatively little is known about the role of AM fungal diversity and community assembly on the expression of plant defence traits. Here, we report how plant (Triticum aestivum) phenolic-based resistance to insect herbivory is differentially affected by different AM fungal communities. An inoculant of four AM fungal species and a field-sourced native AM fungal community increased plant phenolics by 47.9% and 50.2%, respectively, compared to plants inoculated with only one fungal species. Correspondingly, the performance (relative growth rate) of the insect herbivore was 36% and 61.3% lower when feeding on plants associated with these AM fungal communities. Furthermore, there was a negative correlation between foliar phenolics and herbivore growth. We propose that AM fungal community assembly can drive insect herbivore performance by affecting phenolic-based defence mechanisms.

We compared the use of phosphorus (P) and nitrogen (N) in slow-growing Banksia attenuata (Proteaceae), which resprouts after fire and naturally occurs on deep sand, with faster-growing opportunistic B. sessilis, which is killed by fire and occurs on shallow sand over laterite or limestone. We carried out pot experiments with plants on substrates with different P availability. We measured foliar nutrient concentrations, and P allocated to major biochemical fractions. The two species had similar foliar total P concentrations, but distinct patterns of P allocation to P-containing fractions. The foliar total N concentration of B. sessilis was greater than that of B. attenuata on all substrates. The foliar total P and N concentrations in both species decreased with decreasing P availability. The relative growth rate of both species was positively correlated with both foliar nucleic acid P and total N concentrations, but there was no correlation with other P and N fractions. Faster-growing B. sessilis allocated more P to nucleic acids than B. attenuata did, but other fractions were similar. We conclude that the nutrient-allocation patterns in faster-growing opportunistic B. sessilis and slower-growing B. attenuata revealed different strategies in response to soil P availability, which matched their contrasting growth strategy.

Exogenous glycine betaine (GB) or hydrogen peroxide (H2O2) application has not been explored to mitigate waterlogging stress in Andean fruit trees. The objective of this study was to evaluate foliar GB or H2O2 application on the physiological behavior of Cape gooseberry plants under waterlogging. Two separate experiments were carried out. In the first trial, the treatment groups were: (1) plants without waterlogging and with no foliar applications, (2) plants with waterlogging and without foliar applications, and (3) waterlogged plants with 25, 50, or 100 mM of H2O2 or GB, respectively. The treatments in the second trial were: (1) plants without waterlogging and with no foliar applications, (2) plants with waterlogging and without foliar applications, and (3) waterlogged plants with 100 mM of H2O2 or GB, respectively. In the first experiment, plants with waterlogging and with exogenous GB or H2O2 applications at a dose of 100 mM showed higher leaf water potential (&minus, 0.5 Mpa), dry weight (1.0 g), and stomatal conductance (95 mmol&middot, m&minus, 2&middot, s&minus, 1) values. In the second experiment, exogenously supplied GB or H2O2 also increased the relative growth rate, and leaf photosynthesis mitigating waterlogging stress. These results show that short-term GB or H2O2 supply can be a tool in managing waterlogging in Cape gooseberry.