Native Plant Species Research Articles

Effects of simulated glyphosate drift to native prairie plants and canola-compatible Brassicaceae species of North Dakota, United States

This study evaluated effects to native plant and weedy Brassicaceae species growing in areas potentially affected by drift of glyphosate used with glyphosate-resistant canola (Brassica napus). Ten native grass and forb species were selected based on importance in prairie areas of North Dakota, US; and four introduced Brassicaceae species (Brassica juncea, Brassica nigra, Brassica rapa, and Sinapis arvensis ssp. arvensis) were selected based on their ability to cross with B. napus. Greenhouse-grown seedlings were treated with 0 (carrier control), 0.00056, 0.0032, 0.018 and 0.1 × a field application rate (FAR) of 829 g ha−1 acid glyphosate (g acid equivalent or a.e. ha−1), along with no spray plants; with each treatment repeated in two experiments. Shoot dry weight and height were measured 14 days after treatment, and data were subjected to analysis of variance or covariance followed by a Dunnett's multiple comparison test to obtain No-Observed-Adverse-Effect-Rates (NOAERs) for both parameters. A Weibull regression was used to obtain the rate producing a 25% reduction (ER25) for shoot dry weight or height for a limited number of species and experiment combinations. Based on NOAER values for both shoot dry weight and height, most native species had reductions in growth with 0.1 × FAR resulting in NOAERs of 0.018 × FAR for at least one experiment. Nassella viridula was the most sensitive native species, with a NOAER of 0.0032 × FAR for shoot dry weight and one experiment for height. The Brassicaceae species responded similarly to glyphosate as the native species, with NOAER values ranging from 0.0032 to 0.018 × FAR. Only four species had valid regression analyses for shoot dry weight or height resulting in ER25 values between 0.007 and 0.054 × FAR. Pascopyrum smithii and Schizachyrium scoparium were not affected by glyphosate as indicated by NOAER values. This study indicated that drift concentrations between approximately 0.003, but more commonly ≥0.1 × FAR (2.49 and 82.9 g ha−1 acid glyphosate, respectively) may affect the growth and potential competitiveness of selected native plant species, and Brassicaceae species sexually compatible with glyphosate-resistant B. napus in North Dakota.

Grazing increases the positive feedback of legumes while decreasing the negative feedback of grass

AbstractHerbivore grazing affects plant growth and community structure in grasslands. This effect could be directly through foraging and dung/urine return or indirectly through plant–soil feedbacks (PSFs). Addressing the grazing effect on the feedback of plants can explicate the causes of community changes in the grazing system. However, how grazing and PSF interact to affect plant growth remains unclear. Here, we conducted a classic PSF experiment. In the conditioning stage, two native plant species (a grass Bromus inermis and a legume Medicago sativa) were planted in the field with four simulated grazing treatments (ambient, mowing, dung/urine addition, and mowing + dung/urine addition) in a meadow grassland of northern China. In the feedback stage, B. inermis and M. sativa were planted in the soils (both unsterilized and sterilized) from each treatment in the field experiment. Plant biomass of M. sativa showed positive feedback while B. inermis showed negative feedback across all the simulated grazing treatments. Simulated grazing (mowing and dung/urine addition) increased the positive feedback of M. sativa, while decreasing the negative feedback of B. inermis. The addition of dung/urine to the soil was found to have a significantly stronger impact on plant growth feedback compared to the effect of mowing. Dung/urine addition enriches the soil with higher levels of available nitrogen and phosphorus. Our results suggested that legume plants should have positive PSFs while grass should have negative feedback, which might be amplified by grazing because of the dung/urine fertilization effect. Our study improves the understanding of PSF effects on plant growth and community change in grazed grassland.

Managed honeybee hives negatively affect the reproduction of native plants in a dryland nature reserve

Abstract The honeybee, Apis mellifera, stands out for its positive image due to its contribution to crop pollination and honey production, which facilitated its widespread distribution. However, large apiaries resulting in high honeybee densities could increase pollination frequency while increasing competition for floral resources, ultimately affecting native plant fitness. We studied the impact of managed honeybee hives on pollination and reproductive success of native plants in Villavicencio Nature Reserve, Mendoza, Argentina. During the flowering peak, we studied pollination and reproduction of three native plant species (Larrea divaricata, L. cuneifolia and Zuccagnia punctata) near and far from the hives. We estimated pollen deposition on flower stigmas, pollen tubes developed in flower pistils, fruit set, seed set and seed viability. We found that the honeybee hives had a positive effect on the reproduction of the self‐compatible species, L. divaricata. For the self‐incompatible species, results differed among species: Hives had positive effects on the pollination and negative effects on the reproduction of L. cuneifolia, while they had negative effects on the reproduction of Z. punctata. Synthesis and applications. Beekeeping is increasingly turning to natural areas in search of better quality honey; however, increased honeybee abundance in the field could influence the reproduction of native plants. Our results show that the introduction of managed hives negatively affected the reproduction of self‐incompatible native plants. This result allows us to make several recommendations for conservation and management actions concerning beekeeping in natural areas, regarding the among‐year rotation of the location of hives, the number of hives per site, and the need to monitor the reproduction of self‐incompatible species.

Under Biological Invasion: Impacts of Litter Decomposition Mediated by Invasive Plant Species on Soil Nutrients and Functional Growth Traits of both Invasive and Native Plant Species

Under Biological Invasion: Impacts of Litter Decomposition Mediated by Invasive Plant Species on Soil Nutrients and Functional Growth Traits of both Invasive and Native Plant Species

What is the effectiveness of methods for eradicating or controlling abundance and biomass of invasive aquatic plants in Canada? A systematic review protocol

Abstract Invasive freshwater aquatic plants can have adverse ecological effects on the systems to which they are introduced, changing ecosystem function, threatening native plant species and causing billions of dollars in damage to infrastructure. Additionally, once established, invasive aquatic plants are often difficult to eradicate or control. Given the importance of managing invasive aquatic plants, and the high associated economic costs of doing so, it is essential to determine the relative effectiveness of different control methods. Here, we present a protocol for a systematic review that will estimate the effectiveness of various biological, chemical, habitat manipulations and/or manual/mechanical methods for eradicating or controlling invasive plant abundance and biomass. This systematic review will use published and grey literature, without date restriction, that determines the effectiveness of invasive plant control methods. English‐language searches will be performed using five bibliographic databases, Google Scholar, and networking tools to find relevant literature. Eligibility screening will be conducted at two stages: (1) title and abstract and (2) full text. Studies that evaluate the effectiveness of methods for controlling the abundance or biomass or eradicating invasive plants will be included. A list of plant species currently, or potentially, in Canadian freshwater systems and of management concern will be considered. Included studies will undergo critical appraisal of internal study validity. We will extract information on study characteristics, intervention and comparator details, measured outcomes (abundance and biomass, broadly defined) and effect modifiers (e.g., plant growth pattern or timing of treatments). A narrative synthesis will be used to describe the quantity and characteristics of the evidence base, while quantitative synthesis (i.e., meta‐analysis) will be conducted to estimate an overall mean and variance of effect when sufficient numbers of similar studies are available.

Combining different species in restoration is not always the right decision: Monocultures can provide higher ecological functions than intercropping in a desert ecosystem

Vegetation restoration in deserts is challenging due to these ecosystems' inherent fragility and harsh environmental conditions. One approach for active restoration involves planting native species, which can accelerate the recovery of ecosystem functions. To ensure the effectiveness of this process, carefully selecting species for planting is crucial. Generally, it is expected that a more diverse mix of species in the plantation will lead to the recovery of a greater number of ecosystem functions, especially when the selected species have complementary niche traits that facilitate maximum cooperation and minimize competition among them. In this study, we evaluated the planting of two native species from the hyper-desert of Taklamakan, China, which exhibit marked morpho-physiological differences: a phreatophytic legume (Alhagi sparsifolia) and a halophytic non-legume (Karelinia caspia). These species were grown in both monoculture and intercrop communities. Monoculture of the legume resulted in the highest biomass accumulation. Intercropping improved several ecosystem functions in the 50 cm-upper soil, particularly those related to phosphorus (P), carbon (C), and sulfur (S) concentrations, as well as soil enzyme activities. However, it also increased soil sodium (Na+) concentration and pH. Halophyte monocultures enhanced ecological functions associated with nitrogen concentrations in the upper soil and with P, S, C, and cation concentrations (K+, Ca2+, Mg2+, Cu2+, Fe2+, Zn2+, Co2+, Ni2+), along with enzyme activities in the deep soil. It also maximized Na+ accumulation in plant biomass. In summary, we recommend legume monoculture when the primary goal is to optimize biomass accumulation. Conversely, halophyte monoculture is advisable when the objective is to extract sodium from the soil or enhance ecosystem functions in the deep soil. Intercropping the two species is recommended to maximize the ecosystem functions of the upper soil, provided there is no salinization risk. When planning restoration efforts in desert regions, it is essential to understand the impact of each species on ecosystem function and how complementary species behave when intercropped. However, these interactions are likely species- and system-specific, highlighting the need for more work to optimize solutions for different arid ecosystems.

Dynamic occupancy analyses of native birds in an urban ecological reserve reveal seasonal changes in site occupancy and preference for adjacent urbanized areas

Urban ecological reserves are large green areas immersed within cities where native and exotic species of plants and animals coexist. Here, we examined the environmental features that facilitate the occurrence of nine species of native birds in an urban ecological reserve located within one of the largest cities in the world, Mexico City. We also searched for changes in occupancy rates among the three distinct climatic seasons that occur in central Mexico: warm-dry, rainy, and cold-dry. Using data collected during four years and multi-season occupancy models, we found that most of our study species prefer the urbanized sites that surround the reserve over the core conservation areas. This urban affinity can be explained by the diverse vegetation that prevails in such urban sites, which offers a high habitat heterogeneity that facilitates the presence of bird species with distinct ecological needs. In contrast, the reserve consists of a relatively homogeneous xerophytic scrubland where a few species of shrubs and small trees are dominant. We also detected seasonal changes in five species, with highest occupancy during the warm-dry season of each year, which coincides with both their breeding season and the driest period of the year. This finding indicates that these birds find in the reserve and surrounding urban areas enough food and water during this limiting season as well as safe nesting sites. Our study provides evidence that some native birds can become urban exploiters and that the benefits that they obtain from urban settings are greatest during their breeding season.

Interactions between seed functional traits and environmental factors and their influence on germination performance of Australian native species

Abstract Climate variability is expected to increase due to climate change, with projected increases in temperature and erratic rainfall patterns. These changes will alter the environmental cues sensed by seeds, and therefore will impact plant recruitment. This study investigated the effects of seed functional traits (germinability, germination time, synchrony and seed mass) on germination responses of several sub-tropical native Australian plant species under different environmental factors (water stress, salinity and pH). The effect of a hot water pre-treatment was also tested on Fabaceae seeds with known physical dormancy. Seed traits, environmental factors and seed pre-treatments had significant effects on final germination percentage and germination time. Seed mass and time to 50% germination (t50) were also positively correlated. In contrast, pH did not affect germination and there was no interaction between pH and any of the measured seed functional traits. Some species showed a high thermal tolerance to germination and germination was indifferent to light conditions for all species. Results showed that certain seed functional traits interact with environmental factors to influence germination percentage and time. These findings highlight the importance of considering seed functional traits when determining a species germination response under a changing climate. In addition, the findings provide important knowledge to better guide seed-based land restoration programmes.

Testing prescribed burning to shift an agronomic grass community to a diverse native plant community

Prescribed burning can be an effective land management tool. Here, we study changes in plant diversity and composition following experimental fire disturbance in microcosm units extracted from a twenty-five-year-old historically reclaimed grassland located at Highland Valley Copper mine in British Columbia (B.C.), Canada. Experimental microcosm units were dominated by agronomic grass species Elymus lanceolatus, Thinopyrum intermedium and Bromus inermis. The disturbance treatment was fire intensity, represented by three levels (light, moderate, and heavy), replicated six times per treatment. Fire intensity was controlled by modifying the weight of dried litter applied to each microcosm unit (50 g,150 g, 200g), along with the time each grass turf was burned (10 s, 15 s, 20 s). One day after the fire treatment was applied, microcosm units were seeded with a native species mix consisting of six grassland species common to southern B.C. to examine effectiveness of plant establishment postburn. Disturbance treatments resulted in higher overall alpha diversity, richness, evenness, and beta diversity. Plant community changes included colonization of seeded native forbs, grasses, and legumes in response to disturbance. Aboveground net primary productivity (ANPP) was net neutral within the light and moderate burning disturbance treatments but resulted in increased ANPP with heavy disturbance. Litter mass reduced plant diversity and ANPP, indicating that litter was a major factor in plant community dynamics. These results suggest disturbance by burning leads to short term positive plant community response towards increasing diversity of semi-arid grasslands, and aids in shifting plant communities to higher diversity composed of an increase in native plant species. Our results also suggest that without active management the gains observed in native species establishment might quickly be out shadowed and restricted by the previously dominant agronomic plant community.

Remediation of heavy metals by native plant species grown in Iran’s richest gold mine and study of plants’ pollution tolerance strategies

Mining is defined as an environmentally hazardous activity that releases metals and other elements to the environment. Bioremediation is a natural and sustainable technique for harnessing the potential of microorganisms and plants to remove, degrade, or stabilize pollutants from contaminated sites and enable cleanup and restoration of the environment. In the present study, following the investigation of pollution of heavy metals in soil samples collected from the Zarshuran mining area, the role of twenty native plant species in the bioaccumulation of heavy metals was evaluated. After preparation of soil and plant samples, inductively coupled plasma-mass spectroscopy (ICP-MS) was used to determine the concentrations of elements in the soil and plant samples. It was confirmed that the soil samples were highly contaminated by silver (Ag), zinc (Zn), cadmium (Cd), lead (Pb), and antimony (Sb). High amounts of Pb and Zn were accumulated in Eryngium billardieri and Astragalus rostratus. Further, these two plant species could uptake, transport, and accumulate Ag in their aerial parts and the enrichment coefficient of their shoots was more than 1. Scorzonera latifolia also had good potential to stabilise Ag, Zn, and Pb in its root. As a result, E. billardieri, A. rostratus, and S. latifolia may be suitable candidate species to clean heavy metals from soils in contaminated sites. Overall, augmentation of superoxide dismutase activity and the amounts of total phenols and flavonoids in different parts of E. billardieri and A. rostratus confirmed the induction of antioxidant defense systems in the plants (compared to the control plants) and an attempt by the plants to tolerate heavy metal pollution.

The first record of milk thistle (Silybum marianum, Asteraceae) as an alien invasive weed species in Addis Ababa City, Ethiopia.

Abstract Since 2020, milk thistle Silybum marianum, an invasive weed species, has been widely observed in urban green spaces and roadsides in Addis Ababa city, Ethiopia. To plan future management activities, this study aimed to determine the current distribution status of the weed in urban green areas of Addis Ababa city. Weed surveys were conducted across 42 urban green sites located in Yeka, Lemi Kura, Bole, Nifas Silk-Lafto, Kolfie Keraniyo, Akaky Kality, and Gullele sub-cities during the main rainy season from June to September 2023. Urban green areas were selected using purposive sampling techniques. Field observations confirmed that Silybum marianum can invade and colonize a wide range of habitats and is highly competitive, posing a threat to important native plant species. High weed density rates and dense stands of weeds were recorded in the 34 urban green areas surveyed. The survey results strongly suggest implementing fast integrated weed management options such as mowing/tilling, weeding before the plant goes to seed, cutting (stems and/or seed heads), and burning (collected plant parts and/or seed heads) into a prepared burrow to minimize the spread of the weed and its ecological impacts. The purpose of this survey study is to provide information about Silybum marianum to minimize or avoid its distribution and associated impacts by following sustainable invasive weed management programs in the city before spreading to other cities in the country.

Gardens as drivers of native plant species dispersal and conservation

Abstract Gardens hold untapped potential for participatory biodiversity conservation. Conservation gardening has recently emerged as a way to foster declining native plant species in urban and rural green spaces. But the impact of cultivating these species on population trends in the broader landscape remains underexplored. This study examines the effects of cultivating herbaceous native plants on their long‐term population trends and endangerment, using Rothmaler's ‘Herbaceous Ornamental and Crop Plants’ in Germany, along with the German Red List of 1998 and 2018. It investigates whether native plants under cultivation are less endangered, examines the long‐term population trends relative to cultivation frequency and assesses the potential role of cultivation in improving Red List status. The findings reveal that cultivated species, especially those commonly grown in gardens, were less likely to be endangered. Moreover, commonly cultivated species had fewer declining and more positive long‐term population trends compared to non‐cultivated species. Some evidence suggests that commonly cultivated plants recorded on the 1998 Red List as threatened are more likely to improve their status, yet still a considerable proportion is in decline. These findings hint at a promising role of gardens as a means to support native species populations, but they also underscore the need for a nuanced understanding of which species are most likely to benefit from cultivation. Read the free Plain Language Summary for this article on the Journal blog.

Enhancing Native Plant Establishment in Mine Tailings under Drought Stress Conditions through the Application of Organo-Mineral Amendments and Microbial Inoculants

The implementation of phytoremediation strategies under arid and semiarid climates requires the use of appropriate plant species capable of withstanding multiple abiotic stresses. In this study, we assessed the combined effects of organo-mineral amendments and microbial inoculants on the chemical and biological properties of mine tailings, as well as on the growth of native plant species under drought stress conditions. Plants were cultivated in pots containing 1 kg of a mixture of mine tailings and topsoil (i.e., pre-mined superficial soil) in a 60:40 ratio, 6% marble sludge, and 10% sheep manure. Moreover, a consortium of four drought-resistant plant growth-promoting rhizobacteria (PGPR) was inoculated. Three irrigation levels were applied: well-watered, moderate water deficit, and severe water deficit, corresponding to 80%, 45%, and 30% of field capacity, respectively. The addition of topsoil and organo-mineral amendments to mine tailings significantly improved their chemical and biological properties, which were further enhanced by bacterial inoculation and plants’ establishment. Water stress negatively impacted enzymatic activities in amended tailings, resulting in a significant decrease in acid and alkaline phosphatases, urease, and dehydrogenase activities. Similar results were obtained for bacteria, fungi, and actinomycete abundance. PGPR inoculation positively influenced the availability of phosphorus, total nitrogen, and organic carbon, while it increased alkaline phosphatase, urease (by about 10%), and dehydrogenase activity (by 50%). The rhizosphere of Peganum harmala showed the highest enzymatic activity and number of culturable microorganisms, especially in inoculated treatments. Severe water deficit negatively affected plant growth, leading to a 40% reduction in the shoot biomass of both Atriplex halimus and Pennisetum setaceum compared to well-watered plants. P. harmala showed greater tolerance to water stress, evidenced by lower decreases observed in root and shoot length and dry weight compared to well-watered plants. The use of bioinoculants mitigated the negative effects of drought on P. harmala shoot biomass, resulting in an increase of up to 75% in the aerial biomass in plants exposed to severe water deficit. In conclusion, the results suggest that the combination of organo-mineral amendments, PGPR inoculation, and P. harmala represents a promising approach to enhance the phytoremediation of metal-polluted soils under semiarid conditions.

Lead and Copper Removal from Mine Tailings Using Lycium chilense and Haplopappus foliosus

In Chile, the budget for managing environmental liabilities such as abandoned tailings impoundments is limited. Using native and endemic plant species to remove heavy metals from tailings represents a low-cost alternative. Ex situ phytoremediation experiments were conducted over a period of seven months. The endemic species Lycium chilense and native species Haplopappus foliosus were used to remove copper and lead from mine tailings. The results indicate that both species can concentrate levels of Cu and Pb higher than the toxicity threshold in the roots and aerial parts, and present high removal efficiency for Cu higher than 50%. In both species, the concentrations of the target elements are higher in the roots than in the aerial parts. Haplopappus foliosus presents the best performance, accumulating higher concentrations of Cu and Pb than Lycium chilense, and presenting a bioconcentration of over one for Cu.

A native plant species cover crop positively impacted vineyard water dynamics, soil health, and vine vigor

Cover cropping is associated with multiple ecosystem and agronomic benefits. However, in irrigated orchards and vineyards of the dry, Western United States, cover crop adoption rates are low, often owing to concerns over their uptake of critical soil water. Regional concerns, such as this, must be addressed to identify sustainable agricultural practices that meet unique needs of diverse growing regions. A two-year study was conducted to determine the impacts of cover crops on soil water dynamics, soil health, and crop growth during the establishment of an Autumn King table grape vineyard in a semi-arid, Mediterranean climate, specifically the Central Valley of California. Phacelia (Phacelia tanacetifolia), a plant species native to the region, and an introduced species, rye (Secale cereale L. ‘Merced’), were planted as cool season cover crops in the interrow spaces of the grapevines and compared to a standard management practice of no cover crop interrow spaces. The cover crop treatments differentially impacted soil microbial biomass and soil aggregate stability, with the phacelia treatment enhancing both metrics from the first season. The phacelia treatment plots resulted in higher soil moisture beneath the vines in both years, while the rye treatment showed similar benefits only after two consecutive years of cover cropping. Vine vigor was also higher in the phacelia treatment, which was likely consequential of enhanced soil moisture in the rows. Compared to the rye, the phacelia had lower plant tissue carbon to nitrogen ratio and higher above ground plant biomass, which may underpin the soil health benefits associated with the phacelia, although variances in soil total carbon and nitrogen and ammonium and nitrate were not determined for any treatment. Altogether, we present information on cover crop plant traits that show quicker return on investment with regards to soil health improvements and water savings. Further, we demonstrate that cool season cover crops offered benefits for vineyard water productivity. In summary, for Mediterranean vineyards, cover crops can promote vineyard soil quality and be a component of sustainable water management.

Climate-induced tree-mortality pulses are obscured by broad-scale and long-term greening.

Vegetation greening has been suggested to be a dominant trend over recent decades, but severe pulses of tree mortality in forests after droughts and heatwaves have also been extensively reported. These observations raise the question of to what extent the observed severe pulses of tree mortality induced by climate could affect overall vegetation greenness across spatial grains and temporal extents. To address this issue, here we analyse three satellite-based datasets of detrended growing-season normalized difference vegetation index (NDVIGS) with spatial resolutions ranging from 30 m to 8 km for 1,303 field-documented sites experiencing severe drought- or heat-induced tree-mortality events around the globe. We find that severe tree-mortality events have distinctive but localized imprints on vegetation greenness over annual timescales, which are obscured by broad-scale and long-term greening. Specifically, although anomalies in NDVIGS (ΔNDVI) are negative during tree-mortality years, this reduction diminishes at coarser spatial resolutions (that is, 250 m and 8 km). Notably, tree-mortality-induced reductions in NDVIGS (|ΔNDVI|) at 30-m resolution are negatively related to native plant species richness and forest height, whereas topographic heterogeneity is the major factor affecting ΔNDVI differences across various spatial grain sizes. Over time periods of a decade or longer, greening consistently dominates all spatial resolutions. The findings underscore the fundamental importance of spatio-temporal scales for cohesively understanding the effects of climate change on forest productivity and tree mortality under both gradual and abrupt changes.

Native Plant Species as an Alternative to Rehabilitate Iron Ore Waste Piles in Carajás Mineral Province, Brazil

ABSTRACT The selection of promising and appropriate plant species and knowledge of their effects on the soil are essential for mineland rehabilitation success. The present study evaluated the effects of three different plant seed cocktails on fertility, soil cover, and erosion control in two iron waste piles in the Carajás Mineral Province, Eastern Amazon, Brazil. The three different seed cocktails were: commercial (only commercial species); native (only species native of Carajás); mixed (native and commercial species); and a control treatment (without seed application). Additionally, tillers from native grasses from Carajás were planted in one of the waste piles. The cocktails were applied by hydroseeding together with fertilizer, mulch, organic compost, and a tackifier. Analyses were performed at 12 and 24 months after the seeding in the waste piles. In general, all cocktails contributed to vegetation establishment, organic matter accumulation, and increased soil fertility. The commercial cocktail stands out due to its ability to improve soil fertility. Native species showed the best cover performance, and less soil loss, highlighting their use for effective control of soil erosion. Thus, native species have the potential for use in rehabilitation projects involving iron waste piles in the Amazon. This is especially relevant because the use of native plant species is mandatory and a declared rehabilitation target.

Fine-resolution land cover mapping over large and mountainous areas for Lāna‘i, Hawaii using posterior probabilities, and expert knowledge

ABSTRACT The task of accurately mapping species-specific vegetation cover in remote and topographically complex regions like those found in Hawaiʻi presents unique challenges. This study leverages a machine learning approach to accurately classify vegetation into fine species-specific classes across the island of Lāna‘i, Hawaii, offering a novel methodology for tackling such challenges. Utilizing high-resolution WordView-2 satellite imagery, a neural network classifier and a custom lidar-based geometric correction, we introduced two new approaches to refine our high-resolution land cover classifications. This included the implementation of prior-based adjustments to class posterior probabilities to enhance land cover classification accuracy. Moreover, we developed mixed hierarchical classification maps that use class posterior probabilities to identify, at the pixel level, the finest land cover class that meets a user-defined confidence threshold. The resulting high-resolution land cover map for Lāna‘i captures the rich diversity and distribution of native and invasive plant species with high overall accuracy, generally exceeding 95%, based on independent ground control data. The capacity to produce wall-to-wall species-level vegetation maps provides a new window into monitoring vegetation dynamics on Lāna‘i and similarly remote and topographically complex regions, and contributes to our broader understanding of ecosystem responses to invasive species, climatic changes, and land management practices such as erosion and sediment control planning. Our approach offers a blueprint for similar efforts in other complex and remote ecosystems.

Low Resource Competition, Availability of Nutrients and Water Level Fluctuations Facilitate Invasions of Australian Swamp Stonecrop (Crassula helmsii)

Australian swamp stonecrop (Crassula helmsii (Kirk) Cockayne) is invasive in Western Europe. Its small size and high potential for regeneration make it difficult to eliminate. Short-term experiments have demonstrated that the growth of C. helmsii depends on nutrient availability and resource competition. In order to confirm those mechanisms in the field, we studied the abundance of C. helmsii in Northern Europe over a longer period of time in relation to nutrient availability and co-occurring plant communities and plant species. C. helmsii impacted native species mainly by limiting their abundance. The native plant species present indicated that previous or periodic elevated nutrient availability were likely responsible for the proliferation of C. helmsii. When growing in submerged conditions, the dominance of C. helmsii depended on a high availability of CO2. A series of exceptionally dry summers allowed C. helmsii to increase in cover due to weakened biotic resistance and a loss of carbon limitation. Only Littorella uniflora (L.) Asch. and Juncus effusus L. were able to remain dominant and continue to provide biotic resistance. Based on our findings, minimizing nutrient (C and N) availability and optimizing hydrology provides native species with stable growth conditions. This optimizes resource competition and may prevent the proliferation of C. helmsii.

A metagenomic investigation of phytoplasma diversity in Australian vegetable growing regions.

In this study, metagenomic sequence data was used to investigate the phytoplasma taxonomic diversity in vegetable-growing regions across Australia. Metagenomic sequencing was performed on 195 phytoplasma-positive samples, originating either from historic collections (n=46) or during collection efforts between January 2015 and June 2022 (n=149). The sampled hosts were classified as crop (n=155), weed (n=24), ornamental (n=7), native plant (n=6), and insect (n=3) species. Most samples came from Queensland (n=78), followed by Western Australia (n=46), the Northern Territory (n=32), New South Wales (n=17), and Victoria (n=10). Of the 195 draft phytoplasma genomes, 178 met our genome criteria for comparison using an average nucleotide identity approach. Ten distinct phytoplasma species were identified and could be classified within the 16SrII, 16SrXII (PCR only), 16SrXXV, and 16SrXXXVIII phytoplasma groups, which have all previously been recorded in Australia. The most commonly detected phytoplasma taxa in this study were species and subspecies classified within the 16SrII group (n=153), followed by strains within the 16SrXXXVIII group ('Ca. Phytoplasma stylosanthis'; n=6). Several geographic- and host-range expansions were reported, as well as mixed phytoplasma infections of 16SrII taxa and 'Ca. Phytoplasma stylosanthis'. Additionally, six previously unrecorded 16SrII taxa were identified, including five putative subspecies of 'Ca. Phytoplasma australasiaticum' and a new putative 16SrII species. PCR and sequencing of the 16S rRNA gene was a suitable triage tool for preliminary phytoplasma detection. Metagenomic sequencing, however, allowed for higher-resolution identification of the phytoplasmas, including mixed infections, than was afforded by only direct Sanger sequencing of the 16S rRNA gene. Since the metagenomic approach theoretically obtains sequences of all organisms in a sample, this approach was useful to confirm the host family, genus, and/or species. In addition to improving our understanding of the phytoplasma species that affect crop production in Australia, the study also significantly expands the genomic sequence data available in public sequence repositories to contribute to phytoplasma molecular epidemiology studies, revision of taxonomy, and improved diagnostics.