Evaluation of the trade-off between water use efficiency and nutrient use efficiency in two semiarid coniferous tree species growing on an organic amended metalliferous mine tailing substrate.

We evaluated the ecophysiological responses of two semiarid coniferous tree species, Pinus halepensis and Tetraclinis articulata, growing on a nutrient-poor metalliferous mine tailings substrate to organic amendments (biochar and/or organic municipal waste). The trees were grown in mesocosms under irrigated conditions for 20 months. Then, a comprehensive characterization of soil and plant parameters (including stable isotopes) was carried out. Treatments containing municipal waste showed better soil fertility indicators (approximately 2-fold higher organic carbon and total nitrogen concentrations) and higher plant biomass (up to 5-fold higher) than unamended and only biochar treatments. Trees in most of the treatments exhibited leaf N/P ratios <14 indicating severe N limitation of plant growth. Metal uptake was below phytotoxic levels across all the treatments. Leaf δ13C values correlated positively with δ18O across treatments for both species indicating increasing water use efficiency with tighter stomatal regulation of water flux, and with T. articulata exhibiting tighter stomatal control (higher δ18O values) than P. halepensis. Trees in treatments containing only biochar did not differ in ecophysiological performance from those in the unamended treatments. In contrast, leaf stable isotopes revealed sharply increased of time-integrated photosynthetic activity (favoured by higher leaf N concentrations) combined with lower time-integrated stomatal conductance in the treatments containing municipal waste, indicating greatly enhanced water use efficiency in better nourished plants. Trade-offs between water use efficiency and nutrient (N and P) use efficiency were evident across treatments, with higher leaf nutrient concentrations associated with higher water use efficiency, at the cost of a lower nutrient use efficiency. These trade-offs were not impaired by the high metal concentrations of the tailings substrate, indicating that ecophysiological adjustments in response to changes in plant nutrient status promoted by the addition of organic amendments are critical for the adaptability of native tree species employed in the phytostabilisation of mine tailings.

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The radial growth of trees plays a crucial role in determining forest carbon sequestration capacity. Understanding the growth dynamics of trees and their response to environmental factors is essential for predicting forest's carbon sink potential under future climate change. Coniferous forest trees are particularly sensitive to climate change, with growth dynamics responding rapidly to environmental shifts. We collected and analyzed data from 99 papers published between 1975 and 2023, and examined the effects of exogenous factors (such as temperature, water, and photoperiod) and endogenous factors (including tree age and species) on cambial activity and radial growth in conifers. We further explored the mechanisms underlying these effects. The results showed that climate warming had the potential to advance the onset while delayed the end of xylem differentiation stages in conifers in temperate and boreal regions. Water availability played a crucial role in regulating the timing of cambial phenology and wood formation by influencing water potential and cell turgor. Additionally, the photoperiod not only participated in regulating the start and end times of growth, but also influenced the timing of maximum growth rate occurrence. Future climate warming was expected to extend the growing season, leading to increase in growth of conifers in boreal regions and expanding forests to higher altitudes or latitudes. However, changes in precipitation patterns and increased evapotranspiration resulting from temperature increases might advance the end of growing season and reduce growth rate in arid areas. To gain a more comprehensive understanding of the relationship between radial growth and climatic factors, it is necessary to develop process-based models to elucidate the physiological mechanisms underlying wood formation and the response of trees to climatic factors.

Mechanisms of photoprotection in overwintering evergreen conifers: Sustained quenching of chlorophyll fluorescence.

Evergreen conifers growing in high-latitude regions must endure prolonged winters that are characterized by sub-zero temperatures combined with light, conditions that can cause significant photooxidative stress. Understanding overwintering mechanisms is crucial for addressing winter adversity in temperate forest ecosystems and enhancing the ability of conifers to adapt to climate change. This review synthesizes the current understanding of the photoprotective mechanisms that conifers employ to mitigate photooxidative stress, particularly non-photochemical "sustained quenching", the mechanism of which is hypothesized to be a recombination or deformation of the original mechanism employed by conifers in response to short-term low temperature and intense light stress in the past. Based on this hypothesis, scattered studies in this field are assembled and integrated into a complete mechanism of sustained quenching embedded in the adaptation process of plant physiology. It also reveals which parts of the whole system have been verified in conifers and which have only been verified in non-conifers, and proposes specific directions for future research. The functional implications of studies of non-coniferous plant species for the study of coniferous trees are also considered, as a wide range of plant responses lead to sustained quenching, even among different conifer species. In addition, the review highlights the challenges of measuring sustained quenching and discusses the application of ultrafast-time-resolved fluorescence and decay-associated spectra for the elucidation of photosynthetic principles.

Contrasting coordination of non-structural carbohydrates with leaf and root economic strategies of alpine coniferous forests.

Non-structural carbohydrates (NSCs), as the labile fraction and dominant carbon currency, are essential mediators of plant adaptation to environments. However, whether and how NSC coordinates with plant economic strategy frameworks, particularly the well-recognized leaf economics spectrums (LES) and root economics space (RES), remains unclear. We examined the relationships between NSC and key plant economics traits in leaves and fine roots across 90 alpine coniferous populations on the Tibetan Plateau, China. We observed contrasting coordination of NSC with economics traits in leaves and roots. Leaf total NSC and soluble sugar aligned with the leaf economic spectrum, conveying a trade-off between growth and storage in leaves. However, NSC in roots was independent of the root economic spectrum, but highly coordinated with root foraging, with more starch and less sugar in forage-efficient, thinner roots. Further, NSC-trait coordination in leaves and roots was, respectively, driven by local temperature and precipitation. These findings highlight distinct roles of NSC in shaping the above- and belowground multidimensional economics trait space, and NSC-based carbon economics provides a mechanistic understanding of how plants adapt to heterogeneous habitats and respond to environmental changes.

Plant periderm as a continuum in structural organisation: a tracheophyte-wide survey and hypotheses on evolution.

Periderm is a well-known structural feature with vital roles in protection of inner plant tissues and wound healing. Despite its importance to plant survival, knowledge of periderm occurrences outside the seed plants is limited and the evolutionary origins of periderm remain poorly explored. Here, we review the current knowledge of the taxonomic distribution of periderm in its two main forms - canonical periderm (periderm formed as a typical ontogenetic stage) and wound periderm (periderm produced as a self-repair mechanism) - with a focus on major plant lineages, living and extinct. We supplement the published occurrences with data based on our own observations and experiments. This updated body of data reveals that the distribution of wound periderm is more widespread taxonomically than previously recognized and some living and extinct groups are capable of producing wound periderm, despite canonical periderm being absent from their normal developmental program. A critical review of canonical and wound periderms in extant and fossil lineages indicates that not all periderms are created equal. Their organisation is widely variable and the differences can be characterised in terms of variations in three structural features: (i) the consistency in orientation of periclinal walls within individual files of periderm cells; (ii) the lateral coordination of periclinal walls between adjacent cell files; and (iii) whether a cambial layer and conspicuous layering of inward and outward derivatives can be distinguished. Using a new system of scoring periderm structure based on these criteria, we characterise the level of organisation of canonical and wound periderms in different lineages. Looking at periderms through the lens provided by their level of organisation reveals that the traditional image of periderm as a single generalised feature, is best viewed as a continuum of structural configurations that are all predicated by the same basic process (periclinal divisions), but can fall anywhere between very loosely organized (diffuse periclinal growth) to very tightly coordinated (organized periclinal growth). Overall, wound periderms in both seed plants and seed-free plants have lower degrees of organisation than canonical periderms, which may be due to their initiation in response to inherently disruptive traumatic events. Wound and canonical periderms of seed plants have higher degrees of organisation than those of seed-free plants, possibly due to co-option of the programs responsible for organizing their vascular cambial growth. Given the importance of wound periderm to plant survival, its widespread taxonomic distribution, and its early occurrence in the fossil record, we hypothesise that wound periderm may have had a single origin in euphyllophytes and canonical periderm may have originated separately in different lineages by co-option of the basic regulatory toolkit of wound periderm formation. In one evolutionary scenario, wound periderm regulators activated initially by tissue tearing due to tensional stresses elicited by woody growth underwent heterochronic change that switched their activation trigger from tissue tearing to the tensional stresses that precede it, with corresponding changes in the signalling that triggered the regulatory cascade of periderm development from tearing-induced signals to signalling induced by tension in cells.

Towards multivariate functional trait syndromes: Predicting foliar water uptake in trees.

Analysis of functional traits is a cornerstone of ecology, yet individual traits seldom explain useful amounts of variation in species distribution or climatic tolerance, and their functional significance is rarely validated experimentally. Multivariate suites of interacting traits could build an understanding of ecological processes and improve our ability to make sound predictions of species success in our rapidly changing world. We use foliar water uptake capacity as a case study because it is increasingly considered to be a key functional trait in plant ecology due to its importance for stress-tolerance physiology. However, the traits behind the trait, that is, the features of leaves that determine variation in foliar water uptake rates, have not been assembled into a widely applicable framework for uptake prediction. Focusing on trees, we investigated relationships among 25 structural traits, leaf osmotic potential (a source of free energy to draw water into leaves), and foliar water uptake in 10 diverse angiosperm and conifer species. We identified consistent, multitrait "uptake syndromes" for both angiosperm and conifer trees, with differences in key traits revealing suspected differences in the water entry route between these two clades and an evolutionarily significant divergence in the function of homologous structures. A literature review of uptake-associated functional traits, which largely documents similar univariate relationships, provides additional support for our proposed "uptake syndrome." Importantly, more than half of shared traits had opposite-direction influences on the capacity of leaves to absorb water in angiosperms and conifers. Taxonomically targeted multivariate trait syndromes provide a useful tool for trait selection in ecological research, while highlighting the importance of micro-traits and the physiological verification of their function for advancing trait-based ecology.

Multi-centennial phase-locking between reproduction of a South American conifer and large-scale drivers of climate.

Climate forcings determine the episodic occurrence of local climate anomalies that trigger the occurrence of masting events (massive, synchronized and intermittent seed production by perennial plants). This suggests some kind of phase-locking of the reproductive cycles of individual plants to the climatological cycle, thus further reinforcing reproductive synchrony and the Moran effect. We propose a dendrochronological approach to filter out the long-term direct effects of climate on tree radial growth and temporal reproductive effort by sex by using actual trees as climatic controls to reconstruct masting events in Araucaria araucana, a long-lived dioecious masting conifer. In this way, we developed a multi-century-long tree masting reconstruction for South America using female-male radial growth determined by differences in timing and magnitude of the reproductive effort between sexes. We provide evidence for a regional synchronizing mechanism of masting which is drought induced by strong cold La Niña phases of El Niño/Southern Oscillation (ENSO) amplified by the positive phases of the Southern Annular Mode (SAM) that activate both female and male cone bud formation during year -2 before seed fall; that is, a long-term phase-locking between the ENSO cycle and the reproductive cycle modulated by the strength of SAM. In addition, our regional index of masting frequency showed its maximum during the late twentieth century relative to the previous centuries, suggesting that the species is currently at its maximum masting frequency concurrent with a period of enhanced temperature and drought conditions in Patagonia, probably driven by the positive phase of the SAM.

Flow resistance characteristics of the stem and root from conifer (Sabina chinensis) xylem tracheid.

Xylem tracheids are the channels for water transport in conifer. Tracheid flow resistance is composed of tracheid lumen resistance and pit resistance. The single tracheid structure parameters in the stem and root of Sabina chinensis were obtained by dissociation and slicing, combined with numerical simulation to analyze the tracheid flow resistance characteristics. The results showed that the tracheid lumen resistance was determined by the tracheid width and tracheid length. The pit resistance was determined by the number of pits and single pit resistance. The single pit resistance was composed of four elements: the secondary cell wall, the border, the margo and the torus. The margo contributed a relatively large fraction of flow resistance, while the torus, the border and the secondary cell wall formed a small fraction. The size and position of the pores in the margo had a significant effect on the fluid velocity. The number of pits were proportional to tracheid length. The power curve, S-curve and inverse curve were fitted the scatter plot of total pit resistance, total resistance, total resistivity, which was found that there were the negative correlation between them. The three scatter plot values were larger in the stem than in the root, indicating that the tracheid structure in the root was more conducive to water transport than the stem. The ratio of tracheid lumen resistance to pit resistance mainly was less than 0.6 in the stem and less than 1 in the root, indicating that the pit resistance was dominant in the total resistance of the stem and root.

The effect of host community functional traits on plant disease risk varies along an elevational gradient.

Quantifying the relative impact of environmental conditions and host community structure on disease is one of the greatest challenges of the 21st century, as both climate and biodiversity are changing at unprecedented rates. Both increasing temperature and shifting host communities toward more fast-paced life-history strategies are predicted to increase disease, yet their independent and interactive effects on disease in natural communities remain unknown. Here, we address this challenge by surveying foliar disease symptoms in 220, 0.5 m-diameter herbaceous plant communities along a 1100-m elevational gradient. We find that increasing temperature associated with lower elevation can increase disease by (1) relaxing constraints on parasite growth and reproduction, (2) determining which host species are present in a given location, and (3) strengthening the positive effect of host community pace-of-life on disease. These results provide the first field evidence, under natural conditions, that environmental gradients can alter how host community structure affects disease.

Climate change is causing shifts in the ecology and biodiversity of different world regions at unprecedented rates. Global warming is also linked with changes in the risk for certain infectious diseases in humans, but also in animals and plants. There are several possible mechanisms for this. For one thing, changing weather patterns may affect how pathogens grow and reproduce. For another, the distribution ranges of animal and plant hosts of certain disease-causing pathogens are changing because of global warming. This means that the distributions of pathogens are also changing, and so is the severity of the diseases that they cause. Increasing temperatures may also influence the physiological traits that make host species suitable for pathogens. This is because the traits that allow species to survive or adapt to changes in their environment may also make them better at hosting and transmitting the pathogens that cause disease. For example, in plant communities, rising temperatures could favor species with faster growth rates, quicker reproduction and high dispersal, and these traits are often associated with more efficient spread of disease. Despite a lot of research into the effects of climate, it remains unclear how temperature, pathogen growth and reproduction, and host species' traits and distributions combine and interact to alter infectious disease risk, especially in wild plant communities. To investigate this, Halliday, Jalo and Laine studied an area in southeast Switzerland where natural temperature and biodiversity change gradually through the region. The aim was to explore how relationships between plant biodiversity, pathogens and disease risk change with temperature, and to understand whether environmental or biological factors influence infectious disease risk more. Halliday, Jalo and Laine measured the levels of fungal diseases found in the leaves of plant communities spanning 1,100 meters of elevation, showing that higher temperatures increase disease risk both directly and indirectly. Directly, higher temperatures increased pathogen growth and reproduction, and indirectly, they influenced which plants were present and therefore able to act as disease hosts. The results also indicated that temperature can affect how the traits of plants drive the transmission rates of fungal pathogens. Important predictors of disease risk were traits relating to the growth rate of host plants, which tended to increase in areas with low elevation where the surface of the soil was warm. This study represents the first analysis, in wild plants, of how changing temperatures, the traits of shifting host species, and resident parasite populations interact to impact infectious disease risk. The insights Halliday, Jalo and Laine provided could aid in predicting how global climate change will influence infectious disease risk.

In Vitro Plant Regeneration in Conifers: The Role of WOX and KNOX Gene Families.

Conifers are a group of woody plants with an enormous economic and ecological importance. Breeding programs are necessary to select superior varieties for planting, but they have many limitations due to the biological characteristics of conifers. Somatic embryogenesis (SE) and de novo organogenesis (DNO) from in vitro cultured tissues are two ways of plant mass propagation that help to overcome this problem. Although both processes are difficult to achieve in conifers, they offer advantages like a great efficiency, the possibilities to cryopreserve the embryogenic lines, and the ability of multiplying adult trees (the main bottleneck in conifer cloning) through DNO. Moreover, SE and DNO represent appropriate experimental systems to study the molecular bases of developmental processes in conifers such as embryogenesis and shoot apical meristem (SAM) establishment. Some of the key genes regulating these processes belong to the WOX and KNOX homeobox gene families, whose function has been widely described in Arabidopsis thaliana. The sequences and roles of these genes in conifers are similar to those found in angiosperms, but some particularities exist, like the presence of WOXX, a gene that putatively participates in the establishment of SAM in somatic embryos and plantlets of Pinus pinaster.

The capacity of ion adsorption and purification for coniferous forests is stronger than that of broad-leaved forests.

In the past few decades, industrialization has caused a large number of pollutants to be released into the atmosphere. Forest ecosystems play an important function in regulating the biogeochemistry and the circulation of metal ions pollutants. Forest ecosystems affect the absorption of pollutants and dissolution of nutrients from the atmosphere and vegetation canopy, thereby influencing the content and composition of forest floor leachate and soil solution. This study examined changes in acid anions (NO3-, SO42-, Cl-) and metal cations (K+, Ca2+, Na2+, Mg2+, Fe3+, Pb2+, Cu2+, Cd2+) in rainfall, throughfall, stemflow, and forest floor leachate for five different forests (Larix principis-rupprechtii, Picea wilsonii, Picea crassifolia, Betula platyphylla and Rhododendron communities). The results showed that the enrichment capacity of acid anions and metal cations in the vegetation canopy of the coniferous forests (L. principis-rupprechtii, P. wilsonii, P. crassifolia) was stronger than that of the broad-leaved forests (B. platyphylla and Rhododendron communities). The content of acid anions and metal cations in stemflow of coniferous forests were 3.7-5.6 times and 0-9.3 times higher than those of broad-leaved forests, respectively. Corresponding values in throughfall were 1-1.4 times and 0.3-2.4 times, respectively. The contents of NO3-, Cl-, K+, Mg2+, Fe3+, Pb2+, Cu2+, and Cd2+ in leachate filtered from the soil layers that are deepening gradually showed consistent decreasing trend for all the forest stands. In addition, NO3-, Cl-, K+, Mg2+, Fe3+, and Pb2+ were also concentrated in the topsoil, except for Cu2+ and Cd2+. Nevertheless, SO42- and Na+ were concentrated in the subsoil, whereas Ca2+ was concentrated in the upper soil layers. Soil organic carbon (SOC) and total nitrogen (TN) contents in coniferous forest stands were 20-37% and 34-63% higher than those in broad-leaved forest stands, respectively. This results also shown that the contents of OC and TN has a strong correlation with the content of partial metal cations in soil and litter, indicating that coniferous forest stands had stronger ion scavenging and adsorption capacity in soil layer and litter layer than broad-leaved forest stands. Therefore, L. principis-rupprechtii, P. wilsonii, P. crassifolia had higher air pollutant adsorption and soil pollution remediation capacities than the other two forests. Thus, we recommend planting coniferous tree species (L. principis-rupprechtii, P. wilsonii and P. crassifolia) for eco-rehabilitation and water purification to improve the ecological service function of forest ecosystems.

Individuality, self and sociality of vascular plants.

Vascular plants are integrated into coherent bodies via plant-specific synaptic adhesion domains, action potentials (APs) and other means of long-distance signalling running throughout the plant bodies. Plant-specific synapses and APs are proposed to allow plants to generate their self identities having unique ways of sensing and acting as agents with their own goals guiding their future activities. Plants move their organs with a purpose and with obvious awareness of their surroundings and require APs to perform and control these movements. Self-identities allow vascular plants to act as individuals enjoying sociality via their self/non-self-recognition and kin recognition. Flowering plants emerge as cognitive and intelligent organisms when the major strategy is to attract and control their animal pollinators as well as seed dispersers by providing them with food enriched with nutritive and manipulative/addictive compounds. Their goal in interactions with animals is manipulation for reproduction, dispersal and defence. This article is part of the theme issue 'Basal cognition: multicellularity, neurons and the cognitive lens'.

Tight association of genome rearrangements with gene expression in conifer plastomes.

BACKGROUND: Our understanding of plastid transcriptomes is limited to a few model plants whose plastid genomes (plastomes) have a highly conserved gene order. Consequently, little is known about how gene expression changes in response to genomic rearrangements in plastids. This is particularly important in the highly rearranged conifer plastomes. RESULTS: We sequenced and reported the plastomes and plastid transcriptomes of six conifer species, representing all six extant families. Strand-specific RNAseq data show a nearly full transcription of both plastomic strands and detect C-to-U RNA-editing sites at both sense and antisense transcripts. We demonstrate that the expression of plastid coding genes is strongly functionally dependent among conifer species. However, the strength of this association declines as the number of plastomic rearrangements increases. This finding indicates that plastomic rearrangement influences gene expression. CONCLUSIONS: Our data provide the first line of evidence that plastomic rearrangements not only complicate the plastomic architecture but also drive the dynamics of plastid transcriptomes in conifers.

Active layer depth and soil properties impact specific leaf area variation and ecosystem productivity in a boreal forest.

Specific leaf area (SLA, leaf area per unit dry mass) is a key canopy structural characteristic, a measure of photosynthetic capacity, and an important input into many terrestrial process models. Although many studies have examined SLA variation, relatively few data exist from high latitude, climate-sensitive permafrost regions. We measured SLA and soil and topographic properties across a boreal forest permafrost transition, in which dominant tree species changed as permafrost deepened from 54 to >150 cm over 75 m hillslope transects in Caribou-Poker Creeks Research Watershed, Alaska. We characterized both linear and threshold relationships between topographic and edaphic variables and SLA and developed a conceptual model of these relationships. We found that the depth of the soil active layer above permafrost was significantly and positively correlated with SLA for both coniferous and deciduous boreal tree species. Intraspecific SLA variation was associated with a fivefold increase in net primary production, suggesting that changes in active layer depth due to permafrost thaw could strongly influence ecosystem productivity. While this is an exploratory study to begin understanding SLA variation in a non-contiguous permafrost system, our results indicate the need for more extensive evaluation across larger spatial domains. These empirical relationships and associated uncertainty can be incorporated into ecosystem models that use dynamic traits, improving our ability to predict ecosystem-level carbon cycling responses to ongoing climate change.

Persistent biotic interactions of a Gondwanan conifer from Cretaceous Patagonia to modern Malesia.

Many plant genera in the tropical West Pacific are survivors from the paleo-rainforests of Gondwana. For example, the oldest fossils of the Malesian and Australasian conifer Agathis (Araucariaceae) come from the early Paleocene and possibly latest Cretaceous of Patagonia, Argentina (West Gondwana). However, it is unknown whether dependent ecological guilds or lineages of associated insects and fungi persisted on Gondwanan host plants like Agathis through time and space. We report insect-feeding and fungal damage on Patagonian Agathis fossils from four latest Cretaceous to middle Eocene floras spanning ca. 18 Myr and compare it with damage on extant Agathis. Very similar damage was found on fossil and modern Agathis, including blotch mines representing the first known Cretaceous-Paleogene boundary crossing leaf-mine association, external foliage feeding, galls, possible armored scale insect (Diaspididae) covers, and a rust fungus (Pucciniales). The similar suite of damage, unique to fossil and extant Agathis, suggests persistence of ecological guilds and possibly the component communities associated with Agathis since the late Mesozoic, implying host tracking of the genus across major plate movements that led to survival at great distances. The living associations, mostly made by still-unknown culprits, point to previously unrecognized biodiversity and evolutionary history in threatened rainforest ecosystems.

Large-Scale Green Liver System for Sustainable Purification of Aquacultural Wastewater: Construction and Case Study in a Semiarid Area of Brazil (Itacuruba, Pernambuco) Using the Naturally Occurring Cyanotoxin Microcystin as Efficiency Indicator.

The aquaculture industry in Brazil has grown immensely resulting in the production of inefficiently discarded wastewater, which causes adverse effects on the aquatic ecosystem. The efficient treatment of aquaculture wastewater is vital in reaching a sustainable and ecological way of fish farming. Bioremediation in the form of the Green Liver System employing macrophytes was considered as wastewater treatment for a tilapia farm, COOPVALE, in Itacuruba, Brazil, based on previously demonstrated success. A large-scale system was constructed, and the macrophytes Azolla caroliniana, Egeria densa, Myriophyllum aquaticum, and Eichhornia crassipes were selected for phytoremediation. As cyanobacterial blooms persisted in the eutrophic wastewater, two microcystin congeners (MC-LR and -RR) were used as indicator contaminants for system efficiency and monitored by liquid-chromatography-tandem-mass-spectrometry. Two trial studies were conducted to decide on the final macrophyte selection and layout of the Green Liver System. In the first trial, 58% MC-LR and 66% MC-RR were removed and up to 32% MC-LR and 100% MC-RR were removed in the second trial. Additional risks that were overcome included animals grazing on the macrophytes and tilapia were spilling over from the hatchery. The implementation of the Green Liver System significantly contributed to the bioremediation of contaminants from the fish farm.

Synergetic enhancement toxicity of copper, cadmium and microcystin-LR to the Ceratophyllum demersum L.

Heavy metals and microcystins commonly co-exist in water bodies with cyanobacteria, and have been shown to affect aquatic plants. However, their combined effects remain largely unknown. In this study, the toxic effects of copper (Cu) and cadmium (Cd) on Ceratophyllum demersum L. were characterized in the presence of microcystin-LR (MC-LR). The results showed that the bioaccumulation of MC-LR and Cu/Cd in C. demersum was significantly increased by the interaction between MC-LR and Cu/Cd. The combined toxicity assessment results suggested that the toxicities of Cu or Cd to C. demersum would be largely exacerbated by MC-LR, which could be the results of increased bioaccumulation of the pollutants. Cu, Cd and MC-LR, as well as their mixture, significantly decreased plant fresh weight and total chlorophyll content of C. demersum, especially at their high concentrations. The antioxidative system was activated to cope with the adverse effects of oxidative stress. Antioxidant enzyme activities were significantly stimulated by Cu, Cd and MC-LR, as well as their mixture. However, the decreased superoxide dismutase (SOD) and glutathione reductase (GR) activities were observed when exposed to relative high concentrations of Cu or Cd together with MC-LR of 5 µg L-1. MC-LR brought more stress to the antioxidative system, which is another possible explanation for the synergistic effect. Our findings highlight increased ecological risks of the co-contamination of heavy metals and harmful cyanobacteria.

Driving factors of conifer regeneration dynamics in eastern Canadian boreal old-growth forests.

Old-growth forests play a major role in conserving biodiversity, protecting water resources, and sequestrating carbon, as well as serving as indispensable resources for indigenous societies. Novel silvicultural practices must be developed to emulate the natural dynamics and structural attributes of old-growth forests and preserve the ecosystem services provided by these boreal ecosystems. The success of these forest management strategies depends on developing an accurate understanding of natural regeneration dynamics. Our goal was therefore to identify the main patterns and drivers involved in the regeneration dynamics of old-growth forests with a focus on boreal stands dominated by black spruce (Picea mariana (L.) Mill.) and balsam fir (Abies balsamea (L.) Mill.) in eastern Canada. We sampled 71 stands in a 2 200 km2 study area located within Quebec's boreal region. For each stand, we noted tree regeneration (seedlings and saplings), structural attributes (diameter distribution, deadwood volume, etc.), and abiotic (slope and soil) factors. The presence of seed-trees located nearby and slopes having moderate to high angles most influenced balsam fir regeneration. In contrast, the indirect indices of recent secondary disturbances (e.g., insect outbreaks or windthrows) and topographic constraints (slope and drainage) most influenced black spruce regeneration. We propose that black spruce regeneration dynamics can be separated into distinct phases: (i) layering within the understory, (ii) seedling growth when gaps open in the canopy, (iii) gradual canopy closure, and (iv) production of new layers once the canopy is closed. These dynamics are not observed in paludified stands or stands where balsam fir is more competitive than black spruce. Overall, this research helps explain the complexity of old-growth forest dynamics, where many ecological factors interact at multiple temporal and spatial scales. This study also improves our understanding of ecological processes within primary old-growth forests and identifies the key factors to consider when ensuring the sustainable management of old-growth boreal stands.

Physiological mechanisms and phytoremediation potential of the macrophyte Salvinia biloba towards a commercial formulation and an analytical standard of glyphosate.

Glyphosate (Gly) is the most widely used herbicide in the world and has broad-spectrum and non-selective activity. Its indiscriminate use hence risks contamination of water bodies and can affect living organisms, especially sensitive or resistant non-target plants. Despite this, studies on physiological mechanisms and Gly remediation in Neotropical aquatic plants remain limited. This study aims to evaluate the physiological mechanisms of the aquatic macrophyte Salvinia biloba on exposure to different concentrations of a Gly commercial formulation (Gly-CF) and a Gly analytical standard (Gly-AS). Furthermore, using square-wave voltammetry (SWV), we determined whether the studied plant could remove Gly from water. Our data suggest that Gly-AS and Gly-CF induce similar physiological responses in S. biloba. However, Gly-CF was more phytotoxic. Depending on the concentration, the two forms of Gly affected the plants, decreasing the chlorophyll a and b contents and the photosystem II (PSII) photochemical activity. The data also revealed that Gly promoted oxidative stress and increased the shikimic acid concentration. At the same time, the plants removed Gly from water, with 100% removal for 1 mg L-1 Gly and above 60% removal for the other concentrations studied. Therefore, our results suggest that S. biloba may be a potential phytoremediation agent for low Gly concentrations, since 1 mg L-1 Gly was completely removed and exhibited low phytotoxicity. This study deepens our scientific understanding of the Gly impact on and the phytoremediation potential of S. biloba.