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The genus Avena (oats) contains diploid, tetraploid and hexaploid species that evolved through hybridization and polyploidization. Four genome types (named A through D) are generally recognized. We used GBS markers to construct linkage maps of A genome diploid ( Avena strigosa x A . wiestii , 2n = 14), and AB genome tetraploid ( A . barbata 2n = 28) oats. These maps greatly improve coverage from older marker systems. Seven linkage groups in the tetraploid showed much stronger homology and synteny with the A genome diploids than did the other seven, implying an allopolyploid hybrid origin of A . barbata from distinct A and B genome diploid ancestors. Inferred homeologies within A . barbata revealed that the A and B genomes are differentiated by several translocations between chromosomes within each subgenome. However, no translocation exchanges were observed between A and B genomes. Comparison to a consensus map of ACD hexaploid A . sativa (2n = 42) revealed that the A and D genomes of A . sativa show parallel rearrangements when compared to the A genomes of the diploids and tetraploids. While intergenomic translocations are well known in polyploid Avena , our results are most parsimoniously explained if translocations also occurred in the A, B and D genome diploid ancestors of polyploid Avena .

The slender wild oat (Avena barbata) was widely studied in California using allozymes in the 1970s and interpreted as a case of ecotypic adaptation to contrasting moisture environments. However, common garden studies suggested that the moist-associated (“mesic”) ecotype had high fitness in both moist and dry habitats, thus predicting an adaptive spread into areas occupied by the dry associated (“xeric”) ecotype. To test this prediction, we revisited 100 populations of A. barbata that were screened genetically 40 y ago. As expected, mesic allozyme and morphological markers are much more common than in the 1970s. The less-fit xeric ecotype, while still widespread, has declined markedly in range and frequency. Genotyping by sequencing of modern populations reveals striking genetic uniformity within each of the two ecotypes. In recombinants between the two ecotypes, the mesic allele at a major fitness quantitative trait locus (QTL) shows a high frequency but so do many other genomic regions not identified as fitness QTL. Additional introduced genotypes are diverse and more widespread than in the past, and our results show that these have spread into the former range of the xeric ecotype to an even greater extent than the mesic ecotype has. While these results confirm the prediction of contemporary evolution from common gardens, they also suggest that much of the change has been driven by additional waves of introduced genotypes.

Non-native, invasive plants are projected to shift their ranges with climate change, creating hotspots of risk where a multitude of novel species may soon establish and spread. The Northeast U.S. is one such hotspot. However, because monitoring for novel species is costly, these range-shifting invasive plants need to be prioritized. Preventing negative impacts is a key goal of management, thus, comparing the potential impacts of range-shifting invasive species could inform this prioritization. Here, we adapted the environmental impacts classification for alien taxa protocol to evaluate potential impacts of 100 invasive plants that could establish either currently or by 2050 in the states of New York, Massachusetts, Connecticut, or Rhode Island. We searched Web of Science for each species and identified papers reporting ecological, economic, human health, or agricultural impacts. We scored ecological impacts from 1 (‘minimal concern’) to 4 (‘major’) and socio-ecological impacts as present or absent. We evaluated 865 impact studies and categorized 20 species as high-impact, 36 as medium-impact, and 26 as low-impact. We further refined high-impact invasive species based on whether major impacts affect ecosystems found in Northeast U.S. and identified five high-priority species: Anthriscus caucalis, Arundo donax, Avena barbata, Ludwigia grandiflora, and Rubus ulmifolius. Additional research is needed for 18 data-deficient species, which had no studies reporting impacts. Identifying and prioritizing range-shifting invasive plants provides a unique opportunity for early detection and rapid response that targets future problem species before they can establish and spread. This research illustrates the feasibility of using impacts assessments on range-shifting invasive species in order to inform proactive policy and management.

Weed resistance is highly desirable in seed used for restoration. Therefore, assessing the competitiveness of target species during germination and establishment stages would help to plan effective restoration projects. Our study aims to assess the impact of competition in seedling establishment, height, leaf number, and aerial biomass of three native perennial forage grasses with different seed sizes. We conducted a competition experiment under greenhouse conditions with three native species Nassella longiglumis , N. tenuis and Piptochaetium napostaense ), and one exotic annual species ( Avena barbata ). Two competition levels were established (with and without A. barbata ) and two seeding densities for the perennial species were defined (15 and 30 seeds per pot). Established seedlings, leaf number, height and aerial biomass were measured. Seedling establishment was affected by competition only for N. tenuis . For all three species, N. longiglumis , with the larger seed size, was the least affected by competition. Competition reduced seedling biomass for all three species, with N. longiglumis , with the larger seed size, being the least affected. Increasing seeding density has little effect on the aerial biomass of the weed. The co-occurrence of native perennial species and the annual species A. barbata severely reduces growth, therefore it is important to implement management practices to control annual exotic species and effectively restore grassland ecosystems.

Background and aims The importance of plant-soil feedback is becoming widely acknowledged; however, how different soil conditions influence these interactions is still relatively unknown. Using soil from a degraded old-field and a remnant grassland, we aimed to explore home-field advantages in plant-soil feedbacks and plant responses to the abiotic and biotic soil conditions. We quantified the soil bacterial and fungal community from these sites and their responses to soil conditions and plant species. Methods Sterilized old-field and remnant-grassland soil was inoculated with home or away soil in a reciprocal transplant experiment using a native grass, Rytidosperma auriculatum, and an invasive grass, Avena barbata, as test species. The soil fungal and bacterial communities were characterised using high throughput sequencing. Results Plants had a greater growth response to microbes when an inoculant was added to its home soil. However, this relationship is complex, with microbial communities changing in response to the plant species and soil type. Conclusion The apparent home-field advantage of the soil microbes shown in this study may restrict the utility of inoculants as a management tool. However, since we inoculated sterile soil, future work should focus on understanding how the inoculated microbial community interacts and competes with resident communities.

Pathogen infection is common in wild plants and animals, and may regulate their populations. If pathogens have narrow host ranges and increase with the density of their favored hosts, they may promote host species diversity by suppressing common species to the benefit of rare species. Yet, because many pathogens infect multiple co-occurring hosts, they may not strongly respond to the relative abundance of a single host species. Are natural communities dominated by specialized pathogens that respond to the relative abundance of a specific host or by pathogens with broad host ranges and limited responses to the relative abundance of single host? The answer determines the potential for pathogens to promote host coexistence, as often hypothesized, or to have negligible or even negative effects on host coexistence. We lack a systematic understanding of the impacts, identities, and host ranges of pathogens in natural communities. Here we characterize a community of foliar fungal pathogens and evaluate their host specificity and fitness impacts in a California grassland community of native and exotic species. We found that most of the commonly isolated fungal pathogens were multi-host, with intermediate to low specialization. The amount of pathogen damage each host experienced was independent of host species local relative abundance. Despite pathogen sharing among the host species, fungal communities slightly differed in composition across host species. Plants with high pathogen damage tended to have lower seed production but the relationship was weak, suggesting limited fitness impacts. Moreover, seed production was not dependent on the local relative abundance of each plant species, suggesting that stabilizing coexistence mechanisms may operate at larger spatial scales in this community. Because foliar pathogens in this grassland community are multi-host and have small fitness impacts, they are unlikely to promote negative frequency dependence or plant species coexistence in this system. Still, given that pathogen community composition differentiates across host species, some more subtle feedbacks between host relative abundance and pathogen community composition, damage, and fitness impacts are possible, which could, in turn, promote either coexistence or competitive exclusion.

Aims Invasion by exotic species commonly influences the structure and diversity of natural grasslands particularly in fertile soils. This study examined the effect of resource availability on intra- and interspecific competition between a native and an exotic grass, and provides mechanistic explanations for the successful invasion of exotic species in temperate grasslands of southern Australia. Methods Frequently co-occurring exotic Avena barbata (wild oat) and native Rytidosperma caespitosum (wallaby grass) of temperate grasslands in southern Australia were grown with and without competition across a soil nutrient and moisture gradient in a glasshouse experiment. Results Wallaby grass and wild oat showed similar growth responses to soil nutrient levels: both performed better at lower levels. Intra- and interspecific competition significantly reduced plant biomass and relative growth rate, but their effects depended on resource availability. Higher soil nutrient availability promoted the performance of the exotic grass and strengthened its competitive advantage over the native grass because of their different responses to the interaction of competition, soil nutrient and moisture. Moreover, changes in relative competition intensity suggested wallaby grass experienced stronger suppression from interspecific competition than wild oat in mixture which led to its decreasing abundance. Conclusions Nutrient accumulation due to management for grazing combined with high rainfall during the wet season can reduce the interspecific competitive ability of native grass and favors exotic invasion in temperate grasslands of southern Australia. The ongoing climate changes may dramatically increase wild oat's prevalence and pose a great challenge on the restoration of native temperate grasslands in Australia.

Arbuscular mycorrhizal fungi (AMF) are important root symbionts that can provide benefits to plant hosts, yet we understand little about how neighboring hosts in a plant community contribute to the composition of the AMF community. We hypothesized that the composition of the plant neighborhood, including the identities of both host and neighbor, would alter AMF community composition. We tested this in a glasshouse experiment in which a native perennial grass (Nassella pulchra) and three annual grasses (Avena barbata, Bromus hordeaceaous and Vulpia microstachys) were grown in two neighborhoods: conspecific monocultures and heterospecific perennial-annual mixtures. To identify AMF taxa colonizing plant roots, we used a combination of terminal restriction fragment length polymorphism and cloning. Both host and neighbor were important in structuring AMF communities. Unique AMF communities were associated with each plant host in monoculture. In heterospecific neighborhoods, the annual neighbors V. microstachys, A. barbata, and B. hordeaceus influenced N. pulchra AMF in different ways (synergistic, controlling, or neutral) and the reciprocal effect was not always symmetric. Our findings support a community approach to AMF studies, which can be used to increase our understanding of processes such as invasion and succession.

Global climate models suggest that many ecosystems will experience reduced precipitation over the next century and the consequences for invasive plant performance are largely unknown. Annual invasive species may be able to quickly evolve traits associated with drought escape or tolerance through rapid genetic changes. We investigated the influence of 5 years of water and nitrogen manipulations on trait values in a southern California grassland system. Seeds from two annual grass species (Avena barbata and Bromus madritensis) were collected from experimental plots and grown in a common environment over two generations. We measured 14 physiological, morphological, phenological and reproductive traits. Both species displayed phenotypic differences depending on the water treatment from which they were collected, but not depending on the nitrogen treatment. Both species displayed trait values characteristic of drought escape (e.g. earlier flowering in A. barbata and B. madritensis, lower water‐use efficiency in B. madritensis) when grown from the seeds collected from plots that experienced five years of reduced precipitation. Furthermore, A. barbata individuals grown from the seeds collected from drought plots had higher reproductive output and higher photosynthetic performance than individuals grown from water addition plots, with individuals grown from ambient plots displaying intermediate trait values. Notably, we found no phenotypic variation among treatments for six root traits. Synthesis. Trait differences were observed following two generations in a common garden, suggesting that treatment differences were genetically based. This suggests that populations were responding to selection over the 5 years of water manipulations, a remarkably short time period. The rapid evolutionary responses observed here may help these two widespread invasive grass species thrive under reduced precipitation scenarios, which could have important implications for fire dynamics, invasive species management and native plant restoration in communities invaded by annual grasses.

Global atmospheric CO₂ is increasing at a rate of 1.5-2 ppm per year and is predicted to double by the end of the next century. Understanding how terrestrial ecosystems will respond in this changing environment is an important goal of current research. Here we present results from a field study of elevated CO₂ in a California annual grassland. Elevated CO₂ led to lower leaf-level stomatal conductance and transpiration (approximately 50%) and higher mid-day leaf water potentials (30-35%) in the most abundant species of the grassland, Avena barbata Brot. Higher CO₂ concentrations also resulted in greater midday photosynthetic rates (70% on average). The effects of CO₂ on stomatal conductance and leaf water potential decreased towards the end of the growing season, when Avena began to show signs of senescence. Water-use efficiency was approximately doubled in elevated CO₂, as estimated by instantaneous gas-exchange measurements and seasonal carbon isotope discrimination. Increases in CO₂ and photosynthesis resulted in more seeds per plant (30%) and taller and heavier plants (27% and 41%, respectively). Elevated CO₂ also reduced seed N concentrations (9%).