Invasive Perennial Grass Research Articles

Belowground growth strategies of native and invasive rhizomatous perennial grasses in response to precipitation variability, clipping, and competition

Invasive clonal species may exhibit different growth strategies than their native clonal competitors. In this study, we examined the spatial distribution of tiller outgrowth and the bud bank by comparing the investment in phalanx versus guerilla growth of a native and invasive perennial grass in North America. We also examined the effect of altered precipitation frequency, clipping, and competition on their clonal growth strategies. Investment in phalanx and guerilla growth was assessed by examining live propagule and tiller production from the plant crown versus its rhizomes. Although invasive Bromus inermis and native Pascopyrum smithii exhibited similar clonal growth strategies as young seedlings, their clonal growth strategies significantly differed by the end of their first growing season. Pascopyrum smithii invested in dual phalanx and guerilla tiller outgrowth and bud placement, and B. inermis primarily invested in phalanx tiller outgrowth and bud placement. Competition rather than intra-annual precipitation variability and clipping altered the clonal growth strategy of these species. Intra- and inter- specific competition did not alter tiller outgrowth for either species. However, inter-specific competition caused both species to alter their bud placement. Bromus inermis shifted more buds from phalanx to guerilla positions while P. smithii shifted in the opposite direction. This may enable invasive B. inermis to expand while confining native P. smithii to more localized areas in the future. Clonal growth strategies appear to be species specific and responsive to inter-specific competition. Investigating the belowground bud aspect of clonal growth can reveal the mechanism driving the future aboveground clonal growth strategy of native and invasive rhizomatous grasses and help inform the patterns of invasion within a plant community.

Connecting dryland fine-fuel assessments to wildfire exposure and natural resource values at risk

BackgroundWildland fire in arid and semi-arid (dryland) regions can intensify when climatic, biophysical, and land-use factors increase fuel load and continuity. To inform wildland fire management under these conditions, we developed high-resolution (10-m) estimates of fine fuel across the Altar Valley in southern Arizona, USA, which spans dryland, grass-dominated ecosystems that are administered by multiple land managers and owners. We coupled field measurements at the end of the 2021 growing season with Sentinel-2 satellite imagery and vegetation indices acquired during and after the growing season to develop predictions of fine fuel across the entire valley. We then assessed how climate, soil, vegetation, and land-use factors influenced the amount and distribution of fine fuels. We connected fine fuels to fire management points, past ignition history, and socio-economic vulnerability to evaluate wildfire exposure and assessed how fuel related to habitat of the endangered masked bobwhite quail (Colinus virginianus ridgwayi).ResultsThe high amount of fine fuel (400–3600 kg/ha; mean = 1392 kg/ha) predicted by our remote sensing model (R2 = 0.63) for 2021 compared to previous years in the valley was stimulated by near-record high growing season precipitation that was 177% of the 1990–2020 mean. Fine fuel increased across the valley if it was contained within the wildlife refuge boundary and had lower temperature and vapor pressure deficit, higher soil organic content, and abundant annual plants and an invasive perennial grass (R2 = 0.24). The index of potential exposure to wildfire showed a clustering of high exposure centered around roads and low-density housing development distant from fire management points and extending into the upper elevations flanking the valley. Within the Buenos Aires National Wildlife Refuge, fine fuel increased with habitat suitability for the masked bobwhite quail within and adjacent to core habitat areas, representing a natural resource value at risk, accompanied with higher overall mean fine fuel (1672 kg/ha) in relation to 2015 (1347 kg/ha) and 2020 (1363 kg/ha) means.ConclusionsBy connecting high-resolution estimates of fine fuel to climatic, biophysical and land-use factors, wildfire exposure, and a natural resource value at risk, we provide a pro-active and adaptive framework for fire risk management within highly variable and rapidly changing dryland landscapes.

The ‘lawnification’ of Australia’s eastern grassy woodlands: the past, current and likely future spread of an invasive perennial grass, Bothriochloa pertusa

Many of today’s damaging invasive plants were intentionally introduced for pasture development and amenity. By examining the introduction history and consequent spread of these species, we can identify factors associated with their successful establishment and dominance. Using collated presence/absence and cover data, alongside a review of the literature and discussions with land managers, we present a comprehensive analysis of the introduction history and spread of the environmental and agricultural grassy weed, Bothriochloa pertusa (L.) A.Camus (Indian couch) throughout Queensland, Australia. Using this data, we also perform habitat suitability models to predict its potential distribution and local-scale cover across Queensland in relation to key environmental variables. We found that B. pertusa was introduced on multiple occasions and across a large area of Queensland, despite re-occurring doubts and poor evidence for its benefit to livestock production. Livestock grazing, associated disturbances (i.e. land clearing, soil erosion) and climatic extremes were commonly associated with its spread throughout the landscape. In 2020 the main area of B. pertusa invasion as indicated by occurrence records spanned 28,537,600 ha. Results from the habitat suitability models suggest the occurrence and local-scale cover of B. pertusa is largely determined by climate variables and the foliage projective cover of trees. Based on these results B. pertusa still has considerable capacity to spread and increase in dominance across many areas of Queensland, particularly further west and south of its current range. The introduction and spread history of B. pertusa suggests propagule pressure, traits, climate, land management and cultural perceptions are all key factors implicated in the spread of B. pertusa. Where B. pertusa has become dominant there has been a major shift in lifeform from native perennial tussock species to a grazing tolerant stoloniferous species. To slow this process of ‘lawnification’ we recommend more conservative grazing strategies and strategically selected protected areas to maintain cover of grazing sensitive native tussock grass species.

Early invasion of common cordgrass (Spartina anglica) increases belowground biomass and decreases macrofaunal density and diversity in a tidal flat marsh

Spartina anglica (hereafter Spartina) is an invasive perennial marsh grass shifting hydrodynamic regime and sediment characteristics in invaded area, thereby reducing macrobenthic diversity. There have been only a few studies focusing on the patch structure of Spartina according to size and its effects on macrofauna. A field experiment was conducted to identify effects of Spartina patches where they have been introduced no later than 5 years after invasion occurred on macrofauna assemblages in Ganghwa Island, South Korea. The survey area was divided into two sections according to vegetation: (1) Suaeda japonica vegetation from 0 to 60 m away from the levee, and (2) bare mudflat from 60 to 90 m away from the levee. The patch sizes of Spartina were categorized into small (1–4 m2), medium (5–11 m2), and large (13–40 m2) in area with four replicates for each section. The biomass ratio of the belowground and aboveground in the small size patch of Spartina was significantly higher than those in the medium and large size patch of Spartina. It indicated that more resource was allocated to rhizomes in small size patch with short invasion history (1 ~ 2 years). After Spartina invaded, macrofauna richness (70%), Shannon–Wiener diversity (80%), and density (67%) were decreased. However, infaunal deposit-feeding polychaete Perinereis linea and epifaunal gastropods Batillaria cumingi and Lactiforis takii increased by Spartina. Ordination of macroinvertebrate assemblages separated the habitat with Spartina invasion from the adjacent uninvaded tidal flat and Suaeda japonica habitats. This study offers a significant insight into early invasion strategies of an aggressive plant invader, Spartina for management of coastal wetlands and its impacts on macrofaunal assemblages.

Simulated distribution of Eragrostis lehmanniana (Lehmann lovegrass): Soil–climate interactions complicate predictions

AbstractThe invasive perennial grass Eragrostis lehmanniana has expanded rapidly throughout the Sonoran Desert (SD) while remaining sparse and patchily distributed in the neighboring Chihuahuan Desert (CD). As temperatures and patterns in precipitation change, identifying the drivers limiting spread in the CD is needed. Our objectives were (1) to identify the climatic and edaphic factors limiting recruitment of E. lehmanniana throughout the CD and (2) to predict the edaphic and climatic locations in the CD where this species is expected to have higher probabilities of recruitment under future climatic conditions. Recruitment was simulated at 57 locations throughout the CD with a daily, multilayer soil water model (SOILWAT) that was parameterized and tested to develop recruitment parameters for E. lehmanniana using long‐term data from research stations in the SD and CD. Logistic regression was used to predict recruitment across the CD using climate and soil factors to create a map of simulated recruitment under current and alternative climate scenarios. Simulated recruitment under current climate was low for most of the CD. However, localized areas with high probabilities (>0.8) occurred along the western transition between the CD and the SD, and in the southern extent of the CD. In general, the CD climate is too cool and dry for rapid and widespread invasion. However, increases to temperature and precipitation are likely to increase recruitment success. Interactions among soil, temperature, and precipitation were important to increases in recruitment of E. lehmanniana and are expected to lead to heterogeneous increases in abundance as climate continues to change. This patchy increase in abundance will result in changes in its geographic distribution that will make predictions in the future challenging.

Plant growth promoting strain Bacillus cereus (RCS-4 MZ520573.1) enhances phytoremediation potential of Cynodon dactylon L. in distillery sludge

Elevated levels of physico-chemical pollution including organic pollutants, metals and metalloids were detected in distillery sludges despite of the anaerobic digestion treatment prior to disposal. The concentrations of the metals were (in mg kg−1): Fe (400.98 ± 3.11), Zn (17.21 ± 0.54), Mn (8.32 ± 0.42), Ni (8.00 ± 0.98), Pb (5.09 ± 0.43), Cr (4.00 ± 0.98), and Cu (3.00 ± 0.10). An invasive grass species, Cynodon dactylon L., demonstrated its ability to remediate the distillery waste sludge (DWS) in the field study. All the physico-chemical parameters of the sludge significantly improved (up to 70–75%) in the presence of Cynodon dactylon L. (p < 0.001) than the control with no plant growth. The highest phytoremediation capacity was associated with the uptake of Fe in the root and shoot. Sludge samples collected near the rhizosphere also showed lower amount of organic compounds compared to control sludge samples. Metal resistant Bacillus cereus (RCS-4 MZ520573.1) was isolated from the rhizosphere of Cynodon dactylon L. and showed potential to enhance the process of phytoremediation via plant growth promoting activities such as production of high level of ligninolytic enzymes: manganese peroxidase (35.98 U), lignin peroxidase (23.98 U) and laccase (12.78 U), indole acetic acid (45.87(mgL−1), phosphatase activity (25.76 mg L−1) and siderophore production (23.09 mg L−1). This study presents information on the performance of Cynodon dactylon L., an abundant invasive perennial grass species and its associated plant growth promoting rhizobacteria demonstrated good capacity to remediate and restore contaminated soil contained complex organic and inorganic pollutants, they could be integrated into the disposal system of distillery sludge to improve the treatment efficiency.

Soil properties are resilient despite grass invasion, fire, and grazing

AbstractKentucky bluegrass (Poa pratensisL.; hereafter referred to as bluegrass) is an invasive perennial grass that has become naturalized throughout the entire United States. This species is an effective competitor and produces abundant litter, which in turn creates a thick thatch layer. In the northern Great Plains, fire and grazing are effective management tools for reducing the thatch layer, promoting expression of native grasses and forbs, and improving forage quality. The overall objective of this research was to examine belowground characteristics under accumulated thatch in response to management with fire and grazing. Soil samples were collected from plots dominated by bluegrass with thatch and from plots one year after management with fire and season‐long grazing. Additionally, to understand immediate and in‐season effects of fire and grazing on soil properties, we sampled soil immediately before and at increasing time steps after spring fires and exposure to grazing. All soils were analyzed for carbon and nitrogen pools, microbial abundance and community structure, and decomposition rates. In general, belowground pools of carbon, nitrogen, and microbial communities were stable despite vegetation management treatments. However, prescribed burning caused a brief decline of labile carbon and decomposition rates in shallow soil, but both properties returned to prefire levels within one year after burning. Our observations indicate that the combination of fire and grazing has minimal effect on the soil and is effective at removing thatch and reducing bluegrass.

Biology and Management of Torpedograss (Panicum repens) in Ornamental Landscape Planting Beds

Torpedograss is one of the most invasive perennial grass species in Florida landscapes. This new 5-page publication of the UF/IFAS Environmental Horticulture Department was written for green industry professionals and others to aid in the identification and management of torpedograss in landscape planting beds. Written by Yuvraj Khamare, Candice Prince, and Chris Marble.https://edis.ifas.ufl.edu/ep615

‘Invasion debt’ after extensive land-use change: An example from eastern Australia

Land-use change, and associated land clearing/conversion and fragmentation are major drivers of biodiversity decline across the globe. The spread of invasive species is a well-recognised consequence of land-use change. The extent and intensity of invasion however is often difficult to assess due to a lack of temporal data. Using detailed mapping information for 130, 950 km2 of sub-coastal Queensland, Australia and results from field surveys we investigated changes to land-use, the extent of remnant (intact) vegetation and the spread of prominent invasive plant species over time (1997–2018). In the 50 years prior to 1997 the area underwent significant land development (mostly for livestock grazing and crops), resulting in a reduction of 45% of its remnant vegetation. Despite key policy developments aimed at protecting the remaining vegetation and species, 7392 km2 was cleared/converted between 1997 and 2017, mainly for the expansion of grazing and cropping lands. Vegetation types specifically listed for national protection under these policies were some of the greatest affected, highlighting the need for improved implementation and regulation of these control measures. Within remaining fragments of remnant vegetation, the cover and presence of two invasive perennial grass species indian couch (Bothriochloa pertusa) and buffel grass (Cenchrus ciliaris) increased significantly during this time period. There was also a moderate increase in the cover and presence of the annual herb Parthenium weed (Parthenium hysterophorus). The spread of these species within the landscape likely reflects an ‘invasion debt’, incurred from an intense history of land-use within the region and we predict this trend will continue to threaten remnant ecosystems.

Effects of buffelgrass removal and nitrogen addition on soil microbial communities during an extreme drought in the Sonoran Desert

Buffelgrass (Cenchrus ciliaris), an invasive perennial grass in arid regions of the United States, has drastically modified natural ecosystems. Understanding the aboveground–belowground links between buffelgrass invasion and soil microbial communities will be critical for developing a comprehensive understanding of arid ecosystems and for deploying successful control strategies. In a randomized block‐field experiment located in Tucson, AZ, U.S.A., we investigated the effects of buffelgrass removal via hand pulling and nitrogen addition (and their interaction) on soil microbial communities during an extreme drought (summer 2020). We found that experimental treatments did not significantly impact bacterial and archaeal community diversity and composition, while plant removal affected fungal community diversity and composition. In addition, the removal treatment increased the proportion of putative chitinolytic bacteria (genus Lysobacter) and decreased the proportion of putative fungal endophytes (genus Darksidea). Buffelgrass manual removal appeared to favor fungal endophyte death around and inside of leftover intact roots, which may result in an increase of chitinolytic bacteria thriving on the degradation of fungal cell walls. Overall, our results suggest that hand removal—which is a common type of buffelgrass control—can alter soil fungal communities and the proportion of certain microbial functional groups. As these changes could subsequently affect native plants, more research is needed to develop a comprehensive understanding of the effect of buffelgrass control efforts on target plants as well as surrounding ecosystem dynamics.

Grubbing and biological control strategies for Nassella trichotoma evaluated using a matrix population model

AbstractA stage‐structured matrix population model for the invasive perennial grass Nassella trichotoma (nassella tussock) was used to compare a wide range of hypothetical grubbing and biocontrol management options in a population of 19 visible plants ha−1 on a typical sheep and beef cattle‐grazed farm in North Canterbury, New Zealand. The model has two soil seed banks (ephemeral and persistent), five plant size classes, seed production and ground cover‐dependent population growth reaching a carrying capacity of 35,000 plants ha−1 (80% ground cover) in the absence of management. Elasticity analyses showed that population growth (λ) was most sensitive to plant size class transitions and relatively insensitive to the soil seed bank transitions, seedling recruitment and seed production, implying management targeting the growth and/or survival of plants will be most effective. This conclusion was supported by population trajectory simulations which revealed that a biological control agent attacking seeds or seedlings would need to be 99.8% effective to achieve the population stability achieved under current management where 34.4% of the plants are grubbed annually. By contrast, a biological control agent attacking tillers and reducing plant transitions (growth) across all size classes by 30% annually gave a population trajectory equivalent to that achieved by annual grubbing. In the presence of annual grubbing, a combination of seed‐ and tiller‐feeding agents giving 10% reductions in fecundity and plant growth, respectively, reduced the population density by 60%. Overall, the modelling shows that relaxing the current practice of annual grubbing (by reducing the rate or frequency of grubbing) whether in spring or autumn will result in the growth of N. trichotoma populations in North Canterbury. It also indicates that a biocontrol agent that impedes tiller production in N. trichotoma plants could potentially be an effective replacement for, or adjunct to, annual grubbing.

First report of Bipolaris yamadae leaf spot disease on Guinea grass (Panicum maximum) in Florida.

Guinea grass is an invasive perennial C4 grass and is a common weed around agricultural crops in Louisiana, Texas, and Hawaii, USA (Overholt and Franck 2019). In November 2018, leaf spots were observed on Guinea grass occurring in an organic garden located in Gainesville, Florida, USA. Lesions were oblong to irregular, dark grey to brownish center with pale-yellow to brownish black margin. Lesions had coalesced, forming necrotic margins that spread from the leaf tip, resulting in leaf blight and collapse of the canopy. Pieces of symptomatic leaf blades (5 sq cm) were surface sterilized (1 min), washed with sterile distilled water and plated onto water agar media plates. Plates were incubated at 27°C under 12-h light/dark for 3 to 5 days. Grey to black cottony mycelium was consistent on all plates and produced conidia characteristic of Bipolaris spp. Conidia were transferred to potato dextrose agar (PDA) plates with a 0.5 mm diameter sterile needle. Three isolates GG1, GG2 and GG3 were successfully grown on PDA. Conidia were black to brown colored, distoseptate with 3 to 8 septa and measured from (60.6- )70-105(-139.8) × (16.0-)17-23(-25.9) μm (avg: 93.3 μm, n=35, SD = 20.6; avg = 21.3 μm, n = 35, SD = 2.89). Conidiophores were in groups or single, brown, smooth and straight, septate and swollen at upper tip. Sigma Extract-N-Amp was used for genomic DNA extraction. Primers ITS1/ITS4 and GPD1/GPD2 (Berbee et al. 1999) were used to amplify and sequence the internal transcribed spacer region (ITS) and partial glyceraldehyde-3-phosphate dehydrogenase (GPDH) gene, respectively. Sequences were aligned using MUSCLE and alignment was trimmed for length. Maximum likelihood phylogenetic trees were constructed with 1,000 bootstrap samples based on the K2+G substitution model, selected by BIC for these two loci using Mega X (Kumar et al. 2018). The ITS and GPDH sequences of GG1, GG2 and GG3 (Genbank accessions MT514518-20, MT576654-56), grouped with B. yamadae isolates CPC_28807 and CBS_202.29 in phylogenetic trees (Marin-Felix et al. 2017). All three isolates from Guinea grass were inoculated on Sach's agar (Luttrell 1958) at 27°C under 12-h light/dark for a week, but no sexual morph was observed, and consistent for two repeated inoculations. To fulfill Koch's postulates, one isolate, GG1, was used. Conidia were harvested from a one-week-old colony grown on PDA incubated at 27°C and 12-h light/dark cycle. The concentration of the conidial suspension was adjusted to 105 conidia/ml using a hemocytometer. Using a Passche H-202S airbrush sprayer, five-week-old seedlings of Guinea grass were sprayed until runoff with the conidia suspension or 0.5% tween water only. Each treatment included four replicates and the experiment was repeated. Leaf spot symptoms were observed on the seedlings inoculated with conidia, whereas seedlings sprayed with water were asymptomatic. Cultures with the expected morphology were isolated from symptomatic leaf blades and absent from control plants. To our knowledge, this is the first report of leaf spot on Guinea grass caused by B. yamadae in Florida, USA. B. yamadae was previously reported from Guinea grass in India, and from other Panicum species in the northern USA (Farr and Rossman 2019). B. yamadae was also isolated from sugarcane in Cuba and China, and corn in Japan (Manamgoda et al. 2014, Raza et al. 2019), which suggests that it has the potential to impact agronomic crops in Florida, such as sugarcane and corn.

Forb Cover Increases After Solarization and Winter Fire in a Grassland Invaded by Yellow Bluestem

Solarization (covering soil and vegetation with plastic) has long been used in agriculture to control undesirable plants, but solarization of invasive plants in rangelands has shown mixed and species-specific results. Yellow bluestem (Bothriochloa ischaemum (L.) Keng var. songarica (Rupr. ex Fisch & C.A. Mey) Celarier & Harlan), an invasive perennial C4 grass, is common throughout the southern Great Plains and is not controlled by winter prescribed fire. We tested whether solarization (tarping) with black plastic, combined with winter prescribed fire, could control yellow bluestem. We applied three treatments (with four replicates): solarization (August to November 2017) + fire (January 2018), trimming + fire, and fire only. Results after two growing seasons show that total yellow bluestem cover in solarized + fire plots was reduced to 54% ± 10% (mean ± standard error), lower than trimmed + fire (82% ± 5%, p < 0.01) and fire only plots (78% ± 6%, p = 0.01). Forb cover in solarized + fire plots (15% ± 4%) was much higher than trimmed + fire (4% ± 1%, p < 0.01) and fire only plots (3% ± 1%, p < 0.01). Native forb richness was only slightly higher in solarized + fire plots (16 ± 2 species) compared to fire only (10 ± 2 species, p = 0.08) and trimmed + fire plots (10 ± 1 species, p = 0.08). Interestingly, native forb richness in all plots increased compared to pre-treatment values (2 ± 1 species for all treatments, p < 0.01). Solarization + winter fire can slightly decrease yellow bluestem cover and greatly increase native forb cover, creating islands of diversity in otherwise low-diversity grasslands. However, repeated treatments or alternative techniques will be needed for full control of yellow bluestem.

Can Targeted Grazing Reduce Abundance of Invasive Perennial Grass (Kentucky Bluegrass) on Native Mixed-Grass Prairie?

The rapid increase of Poa pratensis L. (Kentucky bluegrass) on North Dakota grasslands during the past 30 yr has negatively impacted ecological services. Kentucky bluegrass grows earlier in the spring than many native grasses, which provides an opportunity to use targeted grazing to reduce Kentucky bluegrass and increase native grasses. A 5 year replicated study used 10 cow-calf pairs or pregnant cows to graze 3-ha paddocks in early to mid-May, early spring, (EARLY) until 30% of the native species were grazed. After 1 June, late spring−early summer, five cow-calf pairs were grazed on 3-ha paddocks (LATE) for twice as long as the EARLY treatment. Biomass was clipped inside and outside of cages after each grazing event and outside cages in the fall. In each paddock, a hundred 10-point frames were taken to determine percent native grass, Kentucky bluegrass, Bromus inermis Leyss. (smooth bromegrass), native forbs, and introduced forbs. After 5 yr, native grass abundance in the EARLY paddocks was 26% greater than in the LATE paddocks. Kentucky bluegrass abundance only differed the second year of the study when the EARLY paddocks had 32% less Kentucky bluegrass than the LATE paddocks. Total biomass was greater in the EARLY paddocks than LATE paddocks in year 2 of the study (886 ± 74 g m−2 vs. 608 ± 28 g m−2 for EARLY and LATE, respectively). Targeted grazing by cattle in early spring can increase native grass abundance and, depending on the year, decrease abundance of Kentucky bluegrass. Early spring targeted grazing should be used as a tool in adaptive management programs focusing on reduction of Kentucky bluegrass.

Effect of Epichloë gansuensis endophyte on rhizosphere bacterial communities and nutrient concentrations and ratios in the perennial grass species Achnatherum inebrians during three growth seasons

Achnatherum inebrians is an invasive perennial grass widespread in natural grasslands of north-west China and plays an important role in grassland ecological restoration. The presence of the seed-borne endophytic fungus Epichloë gansuensis in A. inebrians promotes grass growth, increases resistance to abiotic stress, and affects the rhizosphere microbial community of host plants. However, the relationships among E. gansuensis, rhizosphere bacteria and plant contents of carbon (C), nitrogen (N), phosphorus (P) and potassium (K) during different growing seasons are not clear. We examined changes in the rhizosphere bacterial community and in nutrient contents and ratios in A. inebrians with (E+) and without (E−) E. gansuensis in May, August and December. The Shannon diversity index was higher for rhizosphere bacteria of E+ than E− plants in the three different seasons. Leaf C, N and P contents and root P and K contents were higher in E+ than E− plants in May, and leaf K and root C were higher in E+ than E− plants in August. Leaf C:N ratios were lower in E+ than E− plants in December, and leaf C:K ratios were lower in E+ than E− plants in August and December. In addition, our results indicate significant interactions among rhizosphere bacteria, C, N, P and K contents, and endophyte treatment in three different seasons. In conclusion, E. gansuensis enhanced the C, N, P and K contents of host plants, and affected nutrient ratios of A. inebrians probably by increasing rhizosphere bacterial diversity and altering rhizosphere bacterial community structure. This study provides new findings on the ecological function of the endophyte E. gansuensis, including its potential role in enhancing soil fertility. The improvements in soil fertility were utilised in extrapolating to forage grass–endophyte associations.

Evaluation of the bioenergy potential of invasive Pennisetum purpureum through pyrolysis and thermogravimetric analysis

The use of lignocellulosic biomass in the production of bioenergy is escalating with time due to the increase in energy demand and ecological pollution. The purpose of this study is to examine the opportunities of biofuel production from Pennisetum purpureum which is an invasive perennial grass in Brunei Darussalam. The proximate analysis of the study showed that the proportions of moisture content (MC), volatile matter (VM), fixed carbon (FC), and ash content (AC) were 5.93%, 69.44%, 16.81%, and 7.82%, respectively. Moreover, the ratios of carbon (C), hydrogen (H), nitrogen (N), sulfur (S), and oxygen (O) provided by the ultimate analysis were 43.23%, 5.80%, 1.17%, 0.11%, and 41.76%, respectively. The low moisture content and the higher heating value (18.55 MJ/kg) marked this grass as a potential source of biomass. Fourier transform infrared spectroscopy revealed the strong bonds between O–H, C–H, C–O, C=O, and C=C in the biomass. The thermogravimetric and their derivative results depicted that the highest weight losses occurred at a temperature of 334 °C with a degradation rate of 6.56 °C/min for pyrolysis condition and at a temperature of 312 °C with a degradation rate of 7.66 °C/min in combustion conditions.

Differences in root phenology and water depletion by an invasive grass explains persistence in a Mediterranean ecosystem.

Flexible phenological responses of invasive plants under climate change may increase their ability to establish and persist. A key aspect of plant phenology is the timing of root production, how it coincides with canopy development and subsequent water-use. The timing of these events within species and across communities could influence the invasion process. We examined above- and belowground phenology of two species in southern California, the native shrub, Adenostoma fasciculatum, and the invasive perennial grass, Ehrharta calycina to investigate relative differences in phenology and water use. We used normalized difference vegetation index (NDVI) to track whole-canopy activity across the landscape and sap flux sensors on individual chaparral shrubs to assess differences in aboveground phenology of both species. To determine differences in belowground activity, we used soil moisture sensors, minirhizotron imagery, and stable isotopes. The invasive grass depleted soil moisture earlier in the spring and produced longer roots at multiple depths earlier in the growing season than the native shrub. However, Adenostoma fasciculatum produced longer roots in the top 10 cm of soil profile in May. Aboveground activity of the two species peaked at the same time. The fact that Ehrharta calycina possessed longer roots earlier in the season suggests that invasive plants may gain a competitive edge over native plants through early activity, while also depleting soil moisture earlier in the season. Depletion of soil moisture earlier by E. calycina suggests that invasive grasses could accelerate the onset of the summer drought in chaparral systems, assuring their persistence following invasion.

Propagule pressure and priority seeding effects on the demography of invasive annual and native perennial grass species

ABSTRACTBackground: Annual grass invasion and dominance creates a self-sustaining cycle that promotes wildfires and reduces forage abundance. Restoring native plant species to annual grass-invaded ecosystems is fundamental to fostering self-sustaining native plant communities.Aims: We sought to clarify varying restoration strategies on invasive annual and native perennial grass assembly, including strategically modified seeding times, seeding rates, and added water.Methods: We tested the effects of seeding perennial grasses in autumn, spring, or seeding half in autumn and the remaining half in spring, adding water, and varying annual and perennial grass seeding rates on annual and perennial grass life history.Results: While varying perennial grass seeding times did not affect perennial grass germination rates, annual grass germination rates were highest when perennial grasses were seeded in autumn. Seeding perennial grasses in spring produced the highest adult perennial grass density in the first-growing season, but adult perennial grass density in the second-growing season was greatest when seeding occurred in autumn. Second-growing season perennial grass density was highest where annual grass seeding rates were lowest and perennial grass seeding rates were highest. Adding water in the first-growing season produced almost two-times more second-year adult perennial grasses compared to where water was not added.Conclusions: High water availability during the seeding year appears to be the most important factor for retaining perennial grasses in annual grass-invaded ecosystems.

Comparing the Biomass Yield and Biogas Potential of Phragmites australis with Miscanthus x giganteus and Panicum virgatum Grown in Canada

The production of bioenergy from plant biomass has the potential to reduce fossil fuel use. The number of biogas facilities around the world has risen dramatically, increasing demand for feedstocks. In this study the invasive perennial grass Phragmites australis was evaluated as a biogas feedstock in comparison with Miscanthus x giganteus and Panicum virgatum. Results from three field sites for each species demonstrated that biomass yields for P. australis averaged approximately 1.82 ± 0.9 kg dry matter (DM) m−2, comparable to that of M. x giganteus. Yield of P. australis was greater than P. virgatum, which ranged from 0.49 ± 0.06 to 0.69 ± 0.07 kg DM m−2 in July and October, respectively. In mesophilic bench-top digester experiments, methane yields were greater for July-harvested material than for October, ranging from 172.4 ± 15.3 to 229.8 ± 15.2 L CH4 kg−1 volatile solids (VS) for all perennial grasses. Methane yields per hectare were highest for October-harvested M. x giganteus, followed by July-harvested M. x giganteus and P. australis, whereas methane yield from P. virgatum at both harvest times was lower than the other two species. These results suggest that P. australis is not an economically viable biogas feedstock without pre-treatment to improve methane yield.

Secondary Invasion and Reinvasion after Russian-Olive Removal and Revegetation

Russian-olive is a nitrogen-fixing tree invading riparian corridors in western North America. The premise of revegetation after weed removal is that revegetation is required to return native species to a removal site and that revegetation improves site resistance to invasion or reinvasion via competitive exclusion. Therefore, we expected that revegetation would reduce invasive species cover and increase native species cover compared with non-revegetated controls. Native understory species diversity increased with time since removal. We recorded 18.2 native species in 2012, and 28.2 native species in 2016. Out of 22 planted species, 2 did not establish. Diversity in revegetated plots did not differ from unplanted controls, likely because species spread quickly across plot boundaries. Native perennial grass, seeded species, and annual bromes increased over time, while nonnative forbs and native forbs decreased over time. Only invasive perennial grass cover responded to the revegetation treatment with cover much higher in controls compared with revegetated plots (25.7% vs. 7.7%); this was likely a response to a preplanting herbicide treatment. All categories of species diversity except invasive species diversity increased over time. Only 4% of Russian-olive stumps resprouted in the first year of removal, less than 1% resprouted 2 yr after removal. There was no Russian-olive emergence from seed in the removal year, and seed emergence varied exponentially among following years. Seeded native species did not have trouble establishing once adequate spring moisture occurred in the second growing season after Russian-olive removal, indicating that removal did not present substantial obstacles to successful revegetation. Follow-up control of Russian-olive is critical after initial treatment.