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Invasive plants can influence ecosystem processes such as greenhouse gas (GHG) emissions from wetland systems directly through plant-mediated transfer of GHGs to the atmosphere or through indirect modification of the environment. However, patterns of plant invasion often co-vary with other environmental gradients, so attributing ecosystem effects to invasion can be difficult in observational studies. Here, we assessed the impact of Phragmites australis invasion into native shortgrass communities on methane (CH sub(4)) emissions by conducting field measurements of CH sub(4) emissions along transects of invasion by Phragmites in two neighboring brackish marsh sites and compared these findings to those from a field-based mesocosm experiment. We found remarkable differences in CH sub(4) emissions and the influence of Phragmites on CH sub(4) emissions between the two neighboring marsh sites. While Phragmites consistently increased CH sub(4) emissions dramatically by 10.4 plus or minus 3.7 mu mol m super(-2) min super(-1) (mean plus or minus SE) in our high-porewater CH sub(4) site, increases in CH sub(4) emissions were much smaller (1.4 plus or minus 0.5 mu mol m super(-2) min super(-1)) and rarely significant in our low-porewater CH sub(4) site. While CH sub(4) emissions in Phragmites-invaded zones of both marsh sites increased significantly, the presence of Phragmites did not alter emissions in a complementary mesocosm experiment. Seasonality and changes in temperature and light availability caused contrasting responses of CH sub(4) emissions from Phragmites- versus native zones. Our data suggest that Phragmites-mediated CH sub(4) emissions are particularly profound in soils with innately high rates of CH sub(4) production. We demonstrate that the effects of invasive species on ecosystem processes such as GHG emissions may be predictable qualitatively but highly variable quantitatively. Therefore, generalizations cannot be made with respect to invader-ecosystem processes, as interactions between the invader and local abiotic conditions that vary both spatially and temporally on the order of meters and hours, respectively, can have a stronger impact on GHG emissions than the invader itself.

Introduced Phragmites (Phragmites australis ssp. australis) forms part of an invasion assemblage in North America that includes non-native insect herbivores and parasitoids, some of which are now found on both the introduced and native subspecies of Phragmites (P. australis ssp. americanus). This insect assemblage is key to understanding the impact of P. australis invasion and interpreting the efficacy of biological control used against introduced P. australis. Our study provides the first dedicated comparison of insect assemblages associated with native and introduced P. australis in Canada. From a 2016 to 2017 survey of 28 geographically paired sites across Ontario, Canada, fourteen insect taxa were recorded from both subspecies. Genotype had no effect on α-diversity but stem attack rates from at least one herbivore were higher on native populations than on paired introduced populations (+ 18.6%). We report the first record of Chaetococcus phragmitis (Homoptera: Pseudococcidae) and Rhizedra lutosa (Lepidoptera: Noctuidae) in Canada and of R. lutosa and Lasioptera hungarica (Diptera: Cecidomyiidae) on native P. australis in North America.

Common reed ( Phragmites australis ) is a cosmopolitan species, though its dieback is a worldwide phenomenon. In order to assess the evolutionary role of phenotypic plasticity in a successful plant, the values and plasticity of photophysiological traits of Phragmites australis were investigated in the Lake Fertő wetlands at 5 sites with different degrees of reed degradation and along a seasonal sequence. On the one hand, along the established ecological degradation gradient, photophysiological traits of Phragmites changed significantly, affecting plant productivity, although no consistent gradient-type trends were observed. Gradual changes within a season in the values of photosynthetic traits were observed that were recorded in both degraded and stable stands, suggesting a universal response to seasonally changing environmental conditions that could not be overridden by the ecological gradient. On the other hand, reed plants exposed to different levels of degradation showed comparable physiological plasticity; there was no difference in trait variability between stable and degraded stands. This relatively uniform plasticity is likely to contribute to the resilience of reed plants by providing a wider range of adaptive traits under different conditions. In contrast, the 150-200% gradual change in photophysiological trait plasticity with senescence in Phragmites was also demonstrated, reflecting a more dynamic response of the photosynthetic apparatus to seasonal changes. Senescence affected the plasticity of plant traits independently of their degradation status, suggesting a more universal nature of seasonal changes. This research shows that under conditions of conservative resource use determined by stressful habitats, trait values respond to conditions, while trait plasticity shows minimal changes. Furthermore, phenological sequence significantly influenced both the values and the plasticity of the photosynthetic traits studied. Our results underline the impact of ecological degradation on reed physiology and highlight the importance of understanding both trait values and plasticity in plant responses to environmental and seasonal change.

Emissions of nitrous oxide (N sub(2)O) from wetland ecosystems are globally significant and have recently received increased attention. However, relatively few direct studies of these emissions in response to water depth-related changes in sediment ecosystems have been conducted, despite the likely role they play as hotspots of N sub(2)O production. We investigated depth-related differential responses of the dissolved inorganic nitrogen distribution in Phragmites australis (Cav.) Trin. ex Steud. rhizosphere versus non-rhizosphere sediments to determine if they accelerated N sub(2)O emissions and the release of inorganic nitrogen. Changes in static water depth and P. australis growth both had the potential to disrupt the distribution of porewater dissolved NH sub(4) super(+), NO sub(3) super(-), and NO sub(2) super(-) in profiles, and NO sub(3) super(-) had strong surface aggregation tendency and decreased significantly with depth. Conversely, the highest NO sub(2) super(-) contents were observed in deep water and the lowest in shallow water in the P. australis rhizosphere. When compared with NO sub(3) super(-), NH sub(4) super(+), and NO sub(2) super(-), fluxes from the rhizosphere were more sensitive to the effects of water depth, and both fluxes increased significantly at a depth of more than 1 m. Similarly, N sub(2)O emissions were obviously accelerated with increasing depth, although those from the rhizosphere were more readily controlled by P. australis. Pearson's correlation analysis showed that water depth was significantly related to N sub(2)O emission and NO sub(2) super(-) fluxes, and N sub(2)O emissions were also strongly dependent on NO sub(2) super(-) fluxes (r=0.491, p<0.05). The results presented herein provide new insights into inorganic nitrogen biogeochemical cycles in freshwater sediment ecosystems.

Common reed, Phragmites australis (Cav.) Trin. Ex Steud., is the dominant emergent vegetation in the lower Mississippi River Delta (MRD), Louisiana, USA and is comprised primarily of introduced lineages of different phylogeographic origins. Dense stands of P. australis are important for protecting marsh soils from wave action and storm surges. In the Fall of 2016, while investigating symptoms of die-back of Phragmites stands in the lower marsh, a non-native scale was found infesting affected stands in high densities. Identified as Nipponaclerda biwakoensis (Kuwana) (Hemiptera: Aclerdidae), the scale was well established across the lower MRD. This report represents the first recorded population of Nipponaclerda biwakoensis in North America. Intriguingly, there are noticeable differences in die-back symptoms and in scale densities among different lineages of Phragmites in the MRD, with stands of the well-known European invasive lineage appearing healthier and having lower scale densities than other Phragmites lineages. Given its apparent relationship with the die-back syndrome, the scale may have serious implications for the health and stability of Phragmites marsh communities across coastal Louisiana. Efforts are currently underway to investigate the role of the scale and other abiotic stressors in the die-backs and potential management solutions.

Isoprene reduces visible damage (necrosis) of leaves caused by exposure to ozone but the mechanism is not known. Here we show that in Phragmites leaves isoprene emission was stimulated after a 3-h exposure to high ozone levels. The photosynthetic apparatus of leaves in which isoprene emission was inhibited by fosmidomycin became more susceptible to damage by ozone than in isoprene-emitting leaves. Three days after ozone fumigation, the necrotic leaf area was significantly higher in isoprene-inhibited leaves than in isoprene-emitting leaves. Isoprene-inhibited leaves also accumulated high amounts of nitric oxide (NO), as detected by epifluorescence light microscopy. Our results confirm that oxidative stresses activate biosynthesis and emission of chloroplastic isoprenoid, bringing further evidence in support of an antioxidant role for these compounds. It is suggested that, in nature, the simultaneous quenching of NO and reactive oxygen species by isoprene may be a very effective mechanism to control dangerous compounds formed under abiotic stress conditions, while simultaneously attenuating the induction of the hypersensitive response leading to cellular damage and death.

Premise of the study: Long-distance dispersal can affect speciation processes in two opposing ways. Dispersal can promote geographic isolation or it can bring together geographically distant and distantly related genotypes, thus counteracting local differentiation. We used the Gulf Coast of North America (GC), a \"hot spot\" of reed diversity and evolutionary dynamics, as a model system to study the diversification processes within the invasive, cosmopolitan, polyploid grass Phragmites. Methods: Genetic diversity was studied using collections representing all species of the genus and from all continents (except Antarctica). A range of molecular markers, including chloroplast and nuclear sequences, microsatellites, and AFLPs, was analyzed to detect DNA variation from the population to the species level and to infer phylogenetic relationships across continents. Key results: An interspecific hybrid, Phragmites mauritianus × P. australis, and four P. australis cp-DNA haplotypes from Africa, Europe, and North America have been dispersed to the GC and interbreed with each other. Conclusions: Long-distance dispersal and weak breeding barriers appear to be recurring phenomena, not only in the GC, but worldwide. We present data strongly suggesting that interspecific hybridization and introgression among different Phragmites species take place and appear to have contributed significantly to the diversification processes within the genus. Hence, the application of traditional species concepts within Phragmites might be inappropriate.

The genus Phragmites includes several species, of which only Phragmites australis has a worldwide distribution. It has been several decades since the last formal taxonomic examination of the genus and a number of recent genetic studies have revealed novel diversity and unique lineages within the genus. In my initial work on genetic variation in Phragmites (Saltonstall in Proc Nat Acad Sci 99:2445–2449, 2002 ), I came up with a naming scheme for identifying chloroplast DNA haplotypes which combined unique sequences at two loci, designated by numbers, to form haplotypes, designated by letters. Here I describe this naming system in more detail, explain how it has evolved over time as more genetic data has become available, provide a summary of all haplotypes currently available on GenBank, and address some common misunderstandings about how the haplotypes are named.

Abiotic global change factors, such as rising atmospheric CO 2 , and biotic factors, such as exotic plant invasion, interact to alter the function of terrestrial ecosystems. An invasive lineage of the common reed, Phragmites australis, was introduced to North America over a century ago, but the belowground mechanisms underlying Phragmites invasion and persistence in natural systems remain poorly studied. For instance, Phragmites has a nitrogen (N) demand higher than native plant communities in many of the ecosystems it invades, but the source of the additional N is not clear. We exposed introduced Phragmites and native plant assemblages, containing Spartina patens and Schoenoplectus americanus, to factorial treatments of CO 2 (ambient or +300 ppm), N (0 or 25 g m −2  year −1 ), and hydroperiod (4 levels), and focused our analysis on changes in root productivity as a function of depth and evaluated the effects of introduced Phragmites on soil organic matter mineralization. We report that non-native invasive Phragmites exhibited a deeper rooting profile than native marsh species under all experimental treatments, and also enhanced soil organic matter decomposition. Moreover, exposure to elevated atmospheric CO 2 induced a sharp increase in deep root production in the invasive plant. We propose that niche separation accomplished through deeper rooting profiles circumvents nutrient competition where native species have relatively shallow root depth distributions; deep roots provide access to nutrient-rich porewater; and deep roots further increase nutrient availability by enhancing soil organic matter decomposition. We expect that rising CO 2 will magnify these effects in deep-rooting invasive plants that compete using a tree-like strategy against native herbaceous plants, promoting establishment and invasion through niche separation.

Aim In agricultural basins, riparian buffers maintained along stream channels reduce nitrogen (N) concentrations in agricultural runoff, thereby improving water quality. Investigating the role of riparian vegetation in the related processes will provide insights into the mechanisms by which riparian zones retain soil N. Methods In our study, the proportion of plant N uptake, fine root (diameter < 1mm) biomass and fine root morphology at five soil depths (0-15, 15-30, 30-45, 45-60, and 60-75 cm) for Acorus calamus , Canna indica and Phragmites communis were measured in Taihu Lake Basin. Results The soil layer from which the majority of N was absorbed was 0-15 cm (50.8±1.0, 56.0±1.4 and 37.5±3.2% for A. calamus , C. indica, and P. communis , respectively). The N uptake from 45 to 75 cm for P. communis (21.2±2.2%) was significantly higher than A. calamus (14.9±0.7%) and C. indica (9.2±1.5%) ( P < 0.05). Our results showed that N uptake was directly proportional to root morphological characteristics such as specific root surface area (SRA, P < 0.05) and specific root length (SRL, P < 0.01), but the relationships varied among species. Changes in environmental factors caused by soil depth strongly influenced some of the root morphological indicators (e.g., fine root biomass, mean diameter (D)). Conclusions Soil environmental factors and plant root morphology jointly influenced plant N uptake. During vegetation selections of the riparian restoration projects, plants with high SRL or SRA should be given priority due to their expected high capacity in N uptake. But cautions need to be taken as the positive relationships between SRL and SRA and plant N uptake may vary between plant species. Optimal selection of diverse species with complementary nutrient uptake strategies could maximize N uptake at various soil depths and overall N removal from agricultural runoff.