Parasitic plants can inflict significant damage to invasive plants and are considered biocontrol agents. Climate warming can affect the fitness of invasive plants and the efficacy of their biocontrol agents. However, the impact of climate warming on the responses of invasive plants to parasitism remains inadequately explored. To investigate this critical issue, we conducted a controlled warming experiment to assess the impact of a constant, continuous +2 °C temperature increase, consistent with projected global warming scenarios reported by the Intergovernmental Panel on Climate Change, on the responses of two common invasive plants in China, Solidago canadensis and Bidens pilosa to the parasitic plant Cuscuta gronovii. Our findings indicate that parasitism significantly reduces the growth of both invasive species irrespective of temperature increases. A significant interaction was observed between Cuscuta parasitism and the different host species, particularly affecting stem diameter, plant height, and root-to-shoot ratio of the host plants. Interestingly, while increased temperature independently did not significantly impact total biomass, aboveground biomass, or leaf number of the host plants, it exhibited marginal interactions with parasitism and the different hosts regarding belowground biomass of the hosts. Moreover, C. gronovii biomass was significantly influenced by host type; however, increased temperatures did not significantly affect the biomass of C. gronovii or its deleterious effects on host plants. Overall, these findings highlight the complex interplay among parasitism, host species, and environmental factors, which are crucial for comprehensively understanding invasive species dynamics and their ecological implications.
Plant-plant interactions play a crucial role in shaping the growth environment for crops, impacting their productivity and resilience to stress. Interactions between plants have been incorporated into breeding programmes by selecting new target traits that will advance plants' abilities to produce in high densities. The study of plant-plant interactions belowground promises new pathways and traits for crop improvement. This study focuses on the developmental and physiological responses of sorghum (Sorghum bicolor L.) genotypes to neighbouring sorghum plants. In this study, we used two growing methods: (i) a focal plant surrounded by neighbouring plants in the same pot but without shading, and (ii) a focal plant grown either alone or surrounded by neighbours, irrigated with nutrient solution that was passed through pots (leachates) with or without plants. Our results show that the presence of neighbours in the same pot led to reduced dry weight, plant height, and leaf area of the focal plant. In addition, the presence of neighbours reduced stomatal conductance and photosystem II quantum yield. While the response direction was similar across tested genotypes, the magnitude varied. The results were repeated when neighbouring plants were not grown in the same pot, but a nutrient solution was passed through the root systems of other plants into a separate pot containing another plant. Furthermore, we saw a reduction in assimilation rate and stomatal conductance when plants were exposed to either the physical presence of neighbours or leachate. We did not find differences in root architecture in either treatment. These results show that plants change their growth in response to neighbours and that the signal is carried through the liquid phase of the soil. Our findings provide insights into sorghum plants' responses to belowground signalling from neighbouring plants and lay the foundation for future studies enabling increased crop performance under high-density planting conditions.
While mobile apps are becoming more accurate at identifying vascular plants, it is unclear whether accuracy is maintained when doing plot-based surveys, where image acquisition is limited to a small pool of individuals that often lack ideal identification features. We evaluated two free plant identification apps, Flora Incognita and iNaturalist, using 5291 field images of 119 species from 54 plots of 0.8 m2, from graminoid-dominated grassland and forested sites. We examined the top-1 identification (ID) accuracy as a function of botanical (growth form and reproductive state) and photographic (image quality and background) parameters. We used score fusion to test whether combining multiple images of the same individual (perspective combination) improved ID accuracy. Top-1 ID accuracy was consistently higher in Flora Incognita (79.2% overall) as compared to 66.5% in iNaturalist. No groups reached the reference expert accuracy of plot-based surveys (90%-95%). Images featuring reproductive structures significantly improved ID accuracy, particularly for graminoids (overall +8.9% in Flora Incognita, +17.1% in iNaturalist), and high-quality images increased accuracy significantly for graminoids and herbs in iNaturalist. Combining multiple images improved the overall ID accuracy of vascular plants in iNaturalist by 6% and 1.7% in Flora Incognita, with significant improvement for herbs and shrubs in iNaturalist. We provide recommendations for ID success in the field for app users as well as app developers to optimize image acquisition for species identification in surveying and monitoring efforts.
Iron is essential for biological nitrogen removal in wastewater treatment plants (WWTPs), as a significant portion of microbial nitrogen-transforming enzymes require iron. However, iron bioavailability is a global challenge for nitrogen removal microbes in WWTPs, where it often exists in insoluble forms due to its complexation with various wastewater constituents. Combined laboratory experiment and metagenomic analysis of 52 global WWTPs, we found that siderophore-producing bacteria (SPB) were previously uncharacterized dominant members in activated sludge. SPB enhance the iron uptake of activated sludge microbial communities by facilitating the transport of iron ions from insoluble sources into the cells. Of the 1328 total recovered metagenome-assembled genomes (MAGs) from global WWTPs, 6.2% were identified as SPB, while 79.3% of MAGs could utilize siderophores, indicating widespread sharing of siderophores in WWTPs. Interestingly, nearly all ammonium-oxidizing bacteria (AOB) from WWTPs lacked siderophore-producing capacity, and exogenous siderophore (20 µM pyochelin) addition boosted ammonium oxidation rates by 28.2%. Moreover, strong indications were found for an association between AOB and the SPB in global WWTPs, suggesting their symbiotic interaction is a common and critical process to maintain ammonium oxidation performance. SPB in WWTPs were predominantly aerobic or facultative anaerobic heterotrophic bacteria, exhibiting low taxonomic diversity but high abundance. This study reveals SPB as previously overlooked but crucial contributors to biological nitrogen removal in global WWTPs, providing foundational insights into iron-based microbial cooperation within engineered systems. Modulating SPB activity based on their metabolic characteristics is a promising strategy to cope with low iron bioavailability issue for biological processes in WWTPs. Video Abstract.
Coastal wetland plants are adapted to fluctuating and often harsh environmental conditions. In urban wetlands, plant functional groups display a range of physiological and morphological strategies in response to abiotic stress. However, differences amongst functional groups and the coordination between leaf traits, nutrient status, and environmental variation remain poorly understood in these systems. This study evaluates trait-environment relationships in three dominant species-Acrostichum danaeifolium (fern), Dalbergia ecastaphyllum (nitrogen-fixer shrub), and Laguncularia racemosa (halophytic tree)-across contrasting wetland soils and seasonal periods in a tropical urban reserve. We measured leaf gas exchange, specific leaf area (SLA), nutrient content, and photosynthetic nitrogen use efficiency (PNUE) across wet and dry periods on two soils in the Ciénaga Las Cucharillas Natural Reserve, Puerto Rico. Soil bulk density, salinity, and bioavailable nutrients were also quantified. Multivariate analyses (principal component analysis) were used to assess trait covariation. Species differed significantly in morphological and physiological traits. L. racemosa exhibited the highest assimilation rates, PNUE, and succulence, consistent with an acquisitive resource-use strategy. In contrast, A. danaeifolium showed high SLA and water content but conservative stomatal behaviour and lower PNUE, indicative of a shade-tolerant strategy. Dalbergia ecastaphyllum maintained high water-use efficiency during the dry period and exhibited adaptive responses to slightly and moderate saline soils, indicative of a nutrient acquisitive strategy. Soil type influenced elemental availability but had limited effects on photosynthetic rates. Trait differentiation amongst coexisting wetland species reflects contrasting resource-use strategies shaped by both seasonality and soil environment. These findings underscore the functional diversity and adaptive capacity of tropical wetland vegetation under urban and hydrological pressures.
Granule detachment in aerobic granular sludge (AGS) systems is considered an important aspect for both granulation and nitrification performance, yet it has received little attention. This study aimed to identify the dominant detachment mechanisms (erosion, abrasion, sloughing, breakage) and quantify their respective kinetics under operational shear conditions. Ultimately, the impact of detachment on nitrifier migration and growth conditions in flocs was also investigated. Granules from two full-scale AGS wastewater treatment plants (WWTP) were exposed to operational shear (157 s-1) for up to one week in a Couette-Taylor reactor. The distribution of size-classes in terms of total suspended solids (TSS) and nitrifiers was measured, and detachment kinetics and solids retention time (SRT) in flocs, accounting for detachment, were estimated. Under the tested shear rate, shear-induced erosion from the granule surface was the main detachment mechanism with a median detachment rate of 0.017 gTSSdetach gTSSgranule-1 d-1 (25th-75th percentile: 0.014-0.027 gTSSdetach gTSSgranule-1 d-1). In contrast, granule breakage was not observed within 15 detachment tests and therefore does not appear to be a continuous process, indicating that re-growth on breakage debris is not a main driver of granulation as previously proposed in literature. Nitrifiers were found to migrate almost exclusively to biomass <0.2 mm, i.e., flocs. While the migration rates of ammonia- and nitrite-oxidizing bacteria (AOB and NOB) were similar in autumn, distinct values were quantified in winter, with two to six-fold lower NOB migration rates, likely reflecting a temperature-dependent stratification of nitrifiers within granules. Consequently, the influence of nitrifier migration on the growth conditions in flocs varies across nitrifying groups and seasons. The floc SRT of AOB was estimated to be above their minimum SRT throughout the year, indicating migration is not critical for AOB to persist in flocs. In contrast, the minimum SRT of NOB increases significantly at low temperature, such that migration becomes crucial to prevent NOB washout. Migration of NOB from granules to flocs may sufficiently increase the SRT of NOB in flocs, if they are predominantly enriched in granules rather than in flocs. Overall, flocs provide favourable growth conditions for AOB throughout the year, whereas this is only intermittently the case for NOB, which ultimately rely on migration from granules, particularly during cold winter months.
Clonal reproduction is often considered advantageous in stressful environments. While considerable research has explored how clonality supports plant survival in wet and cold conditions, its role in arid and semi-arid conditions remains underexplored. To address this gap, this study examines the distribution and diversity of clonality as a key component of belowground growth form (BGF) along aridity gradients across SW and Central Asia using the species-rich Lamiaceae family as a model. Data were collected from 281 species with a variety of BGFs occurring in a broad range of habitats. Data on BGFs were collected primarily in the field, with additional data from herbarium records and digital databases. BGFs were categorized into hypogeogenous rhizomes, epigeogenous rhizomes, stolons, and non-clonal types. Species distribution data were obtained from regional floras and the Global Biodiversity Information Facility (GBIF) and analysed using precipitation-related bioclimatic variables. Clonal species of the Lamiaceae family, particularly those with hypogeogenous and epigeogenous rhizomes, were more prevalent in extreme environments, both water-limited and moisture-rich, highlighting their adaptation to stressful conditions. They thrived in arid habitats like deserts and semi-deserts as well as wet habitats such as forests or wetlands. Non-clonal species were concentrated in the centre of the gradient, dominating montane steppe shrublands where water availability was moderate and seasonally variable. Clonal plants are not avoiding arid environment. This is particularly noteworthy for species with hypogeogenous rhizomes that have been shown to prefer wet conditions in temperate regions. The exact mechanisms that permit their specialization to wet or dry conditions is to be further studied experimentally. These findings highlight how climate change may differentially affect species based on their BGFs.
Biological nitrification inhibitors (BNIs) present an environmentally friendly approach to reduce nitrogen losses and enhance nitrogen use efficiency, with plant-derived triterpenoids emerging as promising candidates. We evaluated 18 triterpenoids as BNIs using in vitro assays with soil ammonia-oxidizing bacteria (AOB) (Nitrosospira multiformis, Nitrosomonas ureae) and archaea (AOA) (Nitrososphaera viennensis, Nitrosotalea sinensis) at high and low concentrations. A Graph Neural Network framework was applied to predict nitrification inhibition (NI) and identify structural features, including key functional groups, linked to inhibitory patterns. Triterpenoids were more active on AOA, demonstrating higher efficacy than sakuranetin (a known BNI), but did not inhibit AOB. Six triterpenoids showed inhibitory activity on AOA (29-100%), with 3-O-acetyl-11-keto-beta boswellic acid and 11-keto-beta boswellic acid as the most potent inhibitors (ammonia oxidation inhibition > 94%), followed by echinocystic acid (> 87%), ursolic acid (> 74%), asiatic acid (> 65%), and echinocystic acid-3-O-glucoside (29-94%). In silico analyses predicted accurately the activity of model inhibitors such as DMPP, MHPP, and ethoxyquin on AOB and AOA, respectively, and the limited activity of triterpenoids on AOB, but did not predict their strong inhibitory effects on AOA, underscoring the need for expanded datasets for model refinement. The selective activity of some triterpenoids on AOA is hypothesized to involve interference with 3-hydroxy-3-methylglutaryl-CoA reductase, a key enzyme in archaeal membrane biosynthesis, although this requires experimental validation. Still, strain-specific responses suggest the involvement of additional mechanisms. This study provides the first experimental evidence for the potential of plant-derived triterpenoids as BNIs, supporting their relevance for sustainable agriculture. KEY POINTS: • Triterpenoids strongly inhibited AOA but had no effect on AOB nitrification activity. • Six ursane/oleanane-type triterpenoids showed strong AOA inhibition beyond known BNIs. • Inhibition patterns suggest triterpenoid structure relates to AOA selectivity.
Herbivory is particularly threatening to young plants that lack the resources needed to survive an attack. Seeds and seedlings should thus benefit greatly from using pre-attack cues to induce defence before damage. Locomotion mucus from slugs, generalist herbivores that consume young plants, has been shown to speed germination, slow growth, and increase both chemical defences and resistance to herbivores in several herbaceous plants. Whether woody species exhibit similar responses has not been tested. Arion subfuscus, an invasive slug in the eastern USA, is a major herbivore of young sugar maples (Acer saccharum); we explored the effect of its locomotion mucus on Ac. saccharum seeds and seedlings. We exposed sugar maple seeds and seedlings to mucus and measured germination speed and rate, seed susceptibility to slugs, seedling emergence, growth, chemical defences, and foliar susceptibility to Lymantria dispar and Ar. subfuscus. Contrary to our expectations and previous findings with herbaceous species, we found that mucus had no effect on these performance or resistance traits. Habituation to repeated cue exposure or the limited coevolutionary history between Ac. saccharum and Ar. subfuscus could be the reason for the lack of an observed response by the plants. Further studies should investigate the effects of kairomones using a short-term cue exposure procedure or by using a woody plant species and native slug herbivore with a coevolutionary history. Understanding how woody plants respond to kairomones would provide insight into the risk and defence strategies used by long-lived species in crucial early life stages.
Plant-induced defences against herbivores have the potential to modify plant growth, fitness, and the outcome of plant-herbivore interactions. Plants use a variety of cues to initiate the induction of defences, including physical tissue damage, cues released by damaged plant tissues of neighbouring plants (e.g. methyl jasmonate, MeJA), and cues that indicate herbivore presence but are not associated with herbivore damage (e.g. locomotion mucus of herbivorous molluscs). Evidence shows that both herbivore-damage and herbivore-presence cues can generate induced defences in herbaceous plants over relatively short time periods. However, the immediate and long-term effects of these cues on seedlings of deciduous broad-leaved woody plants remain poorly understood. Here, we compare the effects of two cues, MeJA and locomotion mucus of the dusky slug Arion subfuscus, on the growth and defence traits of sugar maple, Acer saccharum, seedlings at multiple timepoints. Specifically, we exposed 4-week-old seedlings to these cues in a greenhouse experiment and quantified their effects on seedling growth, total phenolics, and growth of spongy moth Lymantria dispar across the seedlings' growing season. As expected, MeJA had a negative effect on seedling growth, a positive effect on total phenolics, and no effect on the growth of L. dispar. In contrast, the slug locomotion mucus did not negatively affect growth or change total phenolic levels. Our results highlight that herbivore cues can induce responses in seedling growth and defence in deciduous broad-leaved woody plant seedlings; however, these responses vary with cue type and the induced responses decay for some seedling traits but not others.
Amid growing concerns over water pollution, the secondary effluent from wastewater treatment plants poses significant threats to aquatic ecosystems with limited self-purification capacity. Secondary effluent-constructed wetlands (SECWs) offer a sustainable solution for advanced nitrogen removal from this low-ammonia effluent, yet the functional role of comammox bacteria remains largely unexplored in such habitats. This study investigated the abundance, activity, kinetics, and ecological adaptations of comammox in typical SECWs. Quantitative PCR and amplicon sequencing revealed that comammox Nitrospira ubiquitously presented across all samples, even numerically dominated over ammonia-oxidizing bacteria/archaea (AOB/AOA). Consistent results from double-inhibition assays and DNA-stable isotope probing microcosm experiments indicated that comammox actively participated in nitrification, contributing 2.03-3.89 times those of canonical nitrifiers. Substrate kinetic and metagenomic analyses identified the Nitrospira nitrosa cluster as the sole active comammox population in SECWs, which exhibited relatively lower ammonia affinity (Km(app) = 0.055 ± 0.007 mg N/L) than other comammox species and distinct genomic adaptations to SECW-specific stressors, potentially explaining its dominance. Compared to AOB, comammox combines high substrate affinity with environmental resilience, aligning with K-strategist traits that enable it to outperform r-strategist AOB in SECWs. Overall, it is within this niche differentiation among comammox species and nitrifiers that the N. nitrosa cluster numerically and functionally dominated the nitrification process in SECWs, positioning comammox Nitrospira as pivotal biocatalysts for advanced nitrogen removal in engineered ecosystems.
Herbarium specimens have proven useful for assessing phenological responses to climate change. Using preserved specimens, we analysed the changes in day of year (DOY) for four phenophases: three reproductive (preflowering, flowering, fruiting) and one vegetative (growth). We conducted phenological analysis across bioclimatic belts (thermotypes) from the Rivas-Martinez classification and across 77 taxa present in the Baetic Ranges of the southern Iberian Peninsula. Taxa were characteristic, common, or endemic species from Habitats of Community Interest (HCI) under the European Directive 92/43/EEC. Phenological shifts were assessed using two approaches: long-term trends in DOY with time and relationships with historical climate variables related to temperature and precipitation. At the thermotypes level, flowering advanced consistently over time and with increasing temperatures, showing homogeneous responses and suggesting a weakening of altitudinal differentiation. In contrast, growth exhibited thermotype-specific trends, with stronger advances at high elevations, while preflowering and fruiting showed little or no sensitivity to time or climate variables. At the species level, 31% of taxa showed phenological changes over time in the Baetic Ranges (-3.6 days/decade for reproductive and -5.6 days/decade for vegetative phenophases). However, 97% of taxa showed significant relationships with increasing temperatures and decreasing precipitation, particularly with mean annual temperature (-12.7 days for reproductive and -14.3 days for vegetative phenophases per increased °C). These phenological changes could hinder reproductive and vegetative success by causing mismatches with other ecosystem role-players. As the Mediterranean is expected to become warmer and drier, our findings indicate a potential threat to HCI in the southern Mediterranean.
Transformation of bisphenol compounds during nitrogen removal processes in wastewater treatment plants, along with the key microbial taxa associated with this transformation, remains poorly understood. In this study, we examined the transformation of a series of alkylbisphenols (ABPs; bisphenol A, bisphenol E, and bisphenol F) and sulfonylbisphenol (bisphenol S) in an enriched nitrifying activated sludge (NAS). While bisphenol S was persistent in the NAS, the ABPs were effectively transformed; however, 14C-isotope tracing revealed that the majority of BPA (presumably also other ABPs) was retained in the NAS as transformable intermediates and potentially toxic nitroaromatic compounds, with minor mineralization (< 1 %). In total, nine transformation products were identified, including nitrated aromatic compounds and single-ring phenolic compounds. Ammonia‑oxidizing bacteria (AOB), primarily Nitrosomonas, drove abiotic ABP transformation to persistent nitroaromatic products. Heterotrophic bacteria, such as Sphingomonas, Methyloterena, and Comamonas, initiated ABP transformation via type II ipso-hydroxylation and oxidative cleavage, and also mineralized the intermediates formed through the AOB-mediated dealkylative nitration. By integrating batch experiments, HPLC-QTOF-MS/MS, 14C-tracing, and 16S rRNA gene sequencing, we provide a comprehensive understanding of these complementary transformation pathways and the key microbial taxa involved. Our findings highlight the significant role of AOB-mediated abiotic reactions in ABP transformation, and alarmingly revealed that the traditional nitrogen removal processes using NAS may produce toxic persistent nitroaromatic compounds, thereby leading to unexpected environmental risks.
Plant species interactions in woodlands help maintain the coexistence of trees and groundcover, contributing to high plant diversity. Interactions can be either positive or negative and take place both above and below ground. Both competitive and facilitative interactions have been documented in longleaf pine woodlands, but the dynamics of these interactions and their effects on plant physiology are poorly understood. Our objective was to quantify the impact of tree root exclusion on physiology and growth of understory plant functional types (PFTs) that represent the diversity of longleaf pine woodlands. We used trenching to isolate understory plants from tree roots and compared soil moisture, leaf water potential (Ψ), leaf-level gas exchange, and plant growth for four understory species representing different PFTs in trenched root exclusion plots and untrenched control plots. We hypothesized that root exclusion would reduce understory plant performance compared to untrenched control plots by isolating plants from facilitative effects of canopy trees, but our hypothesis was not supported. We observed better plant performance in trenched plots for some PFTs, and no differences in plant growth for any PFT. These data suggest competitive effects of tree root presence, but results varied among PFT. The study period was unusually wet, with rainfall 53% above normal. In the context of previous studies, these results suggest that belowground competition is more important than facilitation during a wet year, and the relationship between longleaf pines and understory plants shifts from facilitation to competition depending on rainfall.
Previous research has demonstrated the negative impacts Centaurea stoebe has on both carbon and nitrogen availability in soils. However, its impact on nitrogen cycling remains poorly understood. This project investigates the effects of C. stoebe on genes associated with nitrogen cycling in grasslands, where soil nitrogen is limited. Uninvaded soil - free of any invasive plant species - was collected from the upper elevation grasslands of the Lac du Bois Grasslands Protected Area, British Columbia, Canada, and used to set up a microcosm experiment with four treatments. Each treatment consisted of planting with either spotted knapweed (C. stoebe), yarrow (Achillea millefolium), hairy vetch (Vicia villosa), or no treatment (control). All treatments were replicated nine times for a total of 36 microcosm units. Plants were grown for six months before the soil samples were collected for analysis. Soil and plant nitrogen content were quantified at the end of the experiment. The abundance of seven key nitrogen-cycling functional genes, including nitrogen fixation genes (nifH), nitrification genes (AOB-amoA, AOA-amoA), and denitrification genes (narG, nirK, nosZ, and nirS) was assessed using quantitative PCR (qPCR) to determine how C. stoebe influences the quantities of these genes compared to uninvaded soils and other plant species. In addition, nitrogen cycling-related soil enzyme activities were measured by quantifying leucine-aminopeptidase (LAP) and N-acetyl-β-glucosaminidase (NAG) activities. The results indicate that C. stoebe invasion significantly impacted the soil nitrogen content. C. stoebe invasion was associated with a broad suppression of nitrogen-cycling genes, including nifH, AOB-amoA, nirK, and nirS, as well as elevated NAG activity, an N-acquiring enzyme. Further, its nitrogen requirements and uptake efficiency are higher than those of a non-leguminous plant (A. millefolium), while suppressing nitrogen fixation, resulting in a decline in soil nitrogen content. Overall, our results show that C. stoebe disrupts soil nitrogen cycling, likely increasing nitrogen availability for itself and enabling C. stoebe to efficiently uptake the labile nitrogen. These findings highlight the need for early management interventions to control the spread of C. stoebe.
Aniline is a prevalent contaminant in wastewater treatment plants (WWTPs) affected by industrial discharges. However, its impact on nitrous oxide (N2O) emissions during biological nitrogen removal (BNR) is not well understood. In this study, two sequencing batch reactors (SBRs) were operated under identical conditions, with the only difference being continuous addition of 20 mg/L aniline to the experimental reactor (SBR-A). SBR-A exhibited an N2O emission factor of 1.13 ± 0.10%, 43% lower than that of the control reactor (SBR-C), and N2O emission during aerobic nitrification was clearly delayed. Batch tests were performed to elucidate the underlying mechanisms. Despite similar nitrifier abundances, SBR-A exhibited a 30% lower maximum ammonia oxidation rate than SBR-C, indicating metabolic suppression rather than biomass loss. During nitrification, oxygen competition and aniline toxicity further constrained AOB activity, with negligible N2O emission detected prior to the complete degradation of aniline. Across a dissolved oxygen range of 0.3-2.0 mg/L, N2O production during nitrification decreased by 37-57%, consistent with inhibition of the AOB denitrification pathway. Conversely, the maximum heterotrophic N2O reduction rate in SBR-A increased 2.28-fold, which was higher than the enhancement for NO2- reduction. This resulted in lower N2O accumulation, indicating preferential stimulation of nitrogen removal. Microbial community analysis further demonstrated significant enrichment of denitrification in SBR-A, particularly Thauera, whose relative abundance was 1.45 times that in SBR-C. Overall, sustained aniline loading reduced nitrification-derived N2O production and strengthened its reduction, providing new insight into how industrial co-contaminants affect N2O emissions in conventional BNR systems.
Parasitic organisms are of interest in evolutionary biology, often displaying drastic modifications in morphology, physiology, genomes, and ecology. These properties, however, make them challenging from a systematics perspective. Mycoheterotrophy, in which plants become non-photosynthetic parasites on fungi, is an excellent example, and this unique life history has evolved numerous times in the orchid family. Here, we focused on Stereosandra, a genus of mycoheterotrophic orchid comprising a single species, S. javanica, about which little is known. Stereosandra has been placed in the orchid tribe Nervilieae, along with the leafy, autotrophic Nervilia, and the leafless, mycoheterotrophic Epipogium. We characterized the first complete plastid genome for Stereosandra and used nuclear sequence capture to determine its relationships within Nervilieae. This study presents the first genetic data ever produced for Stereosandra. The plastid genome exhibits rampant gene losses, pseudogenes, and reduced size relative to Nervilia but not to the extent seen in Epipogium. There is evidence of relaxed negative selection in six genes in Stereosandra, including matK, which functions in Group IIA intron removal of seven plastid genes, four of which have been lost or pseudogenized in this species. Applying mixture models, plastid genomes provided weak support for a sister position of Stereosandra to a clade of Epipogium + Nervilia. Nuclear phylogenomic analyses provided strong support for the same relationships. Ancestral state reconstruction revealed clear evidence that mycoheterotrophy evolved multiple times in the tribe from leafy ancestors. This study provides a previously unidentified, convergent instance of the evolution of full mycoheterotrophy in plants. We discuss the results in the context of proposed models of reductive plastid genome evolution and the genomic and evolutionary consequences of radical life history shifts in heterotrophic plants.
Most species of orchids become autotrophic after the formation of the first leaf develops; however, some mycoheterotrophic species remain achlorophyllous at maturity and non-photosynthetic throughout their entire life cycles, depending on fungal associations for survival. However, the mechanisms governing carbon and nitrogen exchange between mycoheterotrophic plants and their associated fungi remain largely unexplored in neotropical regions. Studies with mycoheterotrophic orchids from tropical regions and different subfamilies contribute to a better understanding of the nutrition mode of these plants, and allow evaluation of the role that morphological and anatomical characteristics play in the mycoheterotrophic way of life. Samples of different individuals of Pogoniopsis schenckii were fixed and subjected to standard anatomical techniques for light microscopy, histochemical tests, transmission and scanning electron microscopy and stable isotope analysis. Pogoniopsis schenckii exhibits two distinct root types: one with acute apex and another with a rounded apex. Fungal hyphae were found in all roots but were not organized into typical pelotons; instead, they were distributed throughout the epidermis and cortex, including within cells associated with starch storage. Our isotopic results suggest that P. schenckii acquires carbon and nitrogen through its symbiotic fungi from the soil. The root system of P. schenckii exhibits two root morphotypes that differ in size, apex shape, and anatomy. The observed patterns of 13C and 15N abundances in P. schenckii suggest that this mycoheterotrophic orchid is associated with ectomycorrhizal fungi. Additionally, we described two trends in the degradation of the semi-coiled hyphae found within the epidermal and cortical cells of the two root morphotypes of this mycoheterotrophic species.
Rhododendron, an important acidophilic plant, often faces challenges in urban soils that typically have an alkaline reaction and high bulk density due to low organic matter. Understanding how biochar alleviates urban soil stresses, promotes plant growth, and enhances nitrogen use efficiency (NUE) is crucial for advancing urban landscaping. A pot experiment was conducted to investigate the effects of different doses of biochar (0%-8% w/w) on the root development and NUE of Rhododendron, with a focus on the underlying micro-ecological mechanisms. Biochar amendment dose-dependently enhanced total fine root length (57.2-85.4%) and plant NUE (94.2-199%), along with increases in the fungal-to-bacterial ratio and mycorrhizal colonization. Illumina HiSeq sequencing revealed that biochar reshaped the soil microbial community by not only suppressing N-competing bacteria (e.g., Lysobacter) and pathogenic fungi (e.g., Dactylonectria) but also enriching beneficial fungi (e.g., Condenascus) and copiotrophic bacteria (e.g., Pseudomonas). These shifts likely influenced soil N transformations. Relevantly, biochar enhanced ammonia-oxidizing bacteria (AOB) abundance but reduced nirS abundance, with concurrent increases in potential nitrification and decreases in denitrification activity. At higher application rates (4%-8%), the decreased (nirS + nirK)/nosZ ratio indicated a potential reduction in N2O emissions. Partial least squares path modeling confirmed that AOB abundance was associated with soil fertility, while nirS was linked to soil pH, with both pathways ultimately governing NUE. Overall, this study demonstrated that weakly acidic biochar could enhance the growth and NUE of acidophilic plants by selectively reshaping functional microbial communities and steering inorganic N transformation toward more efficient pathways.
Extreme events (e.g. severe drought) can hinder the establishment of saplings in tropical forest plantations. To assess the resistance and recovery of three commercially important Amazonian tree species under drought conditions and to identify their key functional strategies for drought response, we conducted a controlled drought experiment exposing saplings of Bertholletia excelsa, Dipteryx odorata, and Tachigali vulgaris to water deficit followed by recovery. Tachigali vulgaris (fast-growing species) was more vulnerable to drought, as 80% of the drought-treated plants died. Nevertheless, the individuals who survived demonstrated a rapid recovery of physiological performance following rewatering. Bertholletia excelsa and D. odorata (slow-growing species) were more resistant to drought stress, as evidenced by lack of mortality in these species. Drought-stressed plants had the lowest growth rates, more biomass allocated to roots and less leaf biomass. The greater biomass allocation to roots in B. excelsa and D. odorata, together with their more conservative functional traits compared to T. vulgaris, appears to play an important role in their lower sensitivity to drought. These species exhibited strategies consistent with drought avoidance. Our results highlight the specific strategies of these species under water-deficit conditions and can help guide decisions on species selection and plantation management for reforestation under climate change scenarios.