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# Experimental evidence that invasive grasses use allelopathic biochemicals as a potential mechanism for invasion: chemical warfare in nature

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Background and aims Bothriochloa spp. are non-native warm-season grasses invading native grasslands of the southern and central Great Plains, altering ecological services these grasslands supply. Our study investigated potential allelopathic effects of the invasive grass species B. ischaemum on native grass germination, growth, and survival. Methods Leachate or litter from Andropogon gerardii (native) or B. ischaemum were applied to two native grass species (A. gerardii; Schizachyrium scoparium). Leachate and litter were also added to B. ischaemum and a water control was included. Germination, above- and belowground biomass, and survival were determined. Results Application of B. ischaemum leachate or litter significantly reduced the germination, growth, and survival of both A. gerardii and S. scoparium but had no conspecific effects, while A. gerardii treatments had no effect on any species.
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... This perennial, warm-season bunchgrass often escapes cultivation, forming monotypic stands along roadsides and in pastures and rangelands. Bothriochloa ischaemum, a closely related congener of B. bladhii, is known to possess traits that allow them to outcompete native plant species, including but not limited to, drought tolerance (Duell et al. 2016, greater fecundity, and evidence of allelopathic root exudates that inhibit growth and germination of native grasses (Greer et al. 2014). Control and eradication of Bothriochloa spp. is exceedingly difficult for a variety of reasons, including shared functional similarity with native dominant grass species. ...
... Whole soil and steam-pasteurized soil were included as separate treatments to examine the relative roles of beneficial soil microbes and soil alone, as soil alone may act as a buffer against allelopathic compounds exuded by Bothriochloa spp. (Greer et al. 2014). Plots were also established that contained only seed, without soil inoculum, as seeding remains the most common method of grassland restoration (Rinella et al. 2016). ...
Article
... The effect on shoot length (cm) and root length (cm) was also significant (Fig. 2, Fig. 3). inhibition of the root and shoot length is presumably due to the presence of allelochemicals, such as, phenolics, terpenes and other chemical compounds (Batish et al. 2006, Li et al. 2010, Greer et al. 2014, Wardani et al. 2018). Finally, it was concluded that the allelopathic effect was concentration dependent. ...
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The present review discussed that agrotourism is novel centre of research, farm school and agribusiness. It will provide basic and applied research that develop new specific crops.. It will encourage researchers, scientists and professors for specific research and development. It would provide fundamental agriculture and higher education to the candidate. It would offer tangible agriculture training, workshop and demonstration to student and farmer. It will generate revenue with farm linked activities, post harvest production, warehouse and value added products. It will promote sustainable as well as organic agriculture. It will develop each state, district and block. It would generate employment in of research, farm school and agribusiness. It would progress farmer income, farmer livelihood, Gross Domestic Product (GDP) and visitors in India. Key words: Agrotourism, research, farm school and agribusiness
... Correlation analyses, RFA, VPA, and PCA confirmed that seedling biomass is a critical parameter in allelopathy detection ( Figure 6). However, other studies used germination rate [38,39,42] or root length [34,40,55] to describe recipient plant performance. Few studies have also monitored seedling biomass [34,56] to detect allelopathy. ...
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Allelopathy is an important process in plant communities. The effects of allelopathy on seed germination and seedling development have been extensively investigated. However, the influences of extract soaking time and concentration on the foregoing parameters are poorly understood. Here, we conducted a seed germination assay to determine the allelopathic effects of the donor herbs Achnatherum splendens (Trin.) Nevski, Artemisia frigida Willd., and Stellera chamaejasme L., from a degraded grassland ecosystem in northern China, on lettuce (Lactuca sativa L.) seed germination and early seedling growth. Extract soaking times (12 h or 24 h) did not exhibit significantly different effects on lettuce seed germination or seedling development. However, all aqueous herb extracts inhibited lettuce seed germination and root length (RI < 0) and promoted lettuce shoot length, stem length, leaf length, and leaf width (RI > 0) at both low (0.005 g mL−1) and high (0.05 g mL−1) concentrations. Moreover, A. splendens extracts increased seedling biomass (RI > 0) and synthetical allelopathic effect (SE > 0) at both concentrations. In contrast, both A. frigida and S. chamaejasme extracts had hormesis effects, which stimulate at low concentrations (RI > 0) but inhibit at high concentrations (RI < 0) on seedling biomass and synthetical allelopathic effect (SE). The results suggest that allelopathic potential may be an important mechanism driving the dominance of A. frigida and S. chamaejasme in degraded grasslands. Reseeding allelopathy-promoting species such as A. splendens may be beneficial to grassland restoration. The present study also demonstrated that seedling biomass, root and shoot length, and seed germination rate are the optimal bioindicators in allelopathy assays and could be more representative when they are combined with the results of multivariate analyses.
... In the US, Old World Bluestem degrades native grasslands by decreasing native plant diversity, arthropod biomass, grassland bird abundance, and rodent density (Harmoney et al. 2004, Hickman et al. 2006, Mc-Intyre and Thompson 2003, Robertson and Hickman 2012, Sammon and Wilkins 2005. The species changes nutrient cycling and soil microbial composition , Wilson et al. 2012) and is allelopathic (Greer et al. 2014). Old World Bluestem has invaded almost every habitat and soil type in the southern US; only deep shade excludes it (Gabbard and Fowler 2007). ...
Article
Bothriochloa ischaemum (Old World Bluestem) is a problematic invasive grass throughout the southern United States. We measured the long-term effects (12 years) of a single growing-season fire (September 2006) in a grassland dominated by Old World Bluestem. Prescribed fire drastically reduced Old World Bluestem cover (prefire: 76 4% [mean standard error], 2007: 8 2%) and cover remained low (21 6%) in 2018 with no additional management. Surprisingly, Old World Bluestem cover in unburned plots decreased 12% during the same time. After the burn, native graminoid cover peaked after 3 years (29 7%) but decreased to 18 5% by 2018, and native annual forb cover, almost absent before the fire, increased dramatically to 39 7% in 2007, then quickly decreased to pre-burn levels. Native perennial forb cover more than doubled in 2007 and continued to increase to 58 5% in 2018. A single growing-season fire greatly reduced the cover of Old World Bluestem, likely due to high fuel loads, low rainfall, and phenological timing; the fire also allowed perennial forbs to establish. Restoring dominance of native grasses after removal of this invasive species will require additional active restoration such as seeding or planting.
... Alternatively, positive associations that favor invasive species may act by enhancing nutrient acquisition (Tharayil et al., 2009) or decreasing positive microbial associations with other plants (Mummey & Rillig, 2006). Further the release of allelopathic chemicals, known as 'novel 27 weapons' (Callaway & Ridenour, 2004), is an invasive strategy that results in negative effects on native species of terrestrial grasses (Greer et al., 2014). It is also possible that these negative effects release limited resources for natives. ...
Thesis
... A good example of the latter is the suppression of the South American nonnative grass Paspalum notatum by an allelopathic shrub native to Florida, Polygonella myriophylla (Weidenhamer & Romeo 1989; for other examples of native plants allelopathically suppressing nonnative plants, see Zheng et al. 2014 andNing et al. 2016). Additionally, leachates and degraded litter of the nonnative grass Bothriochloa ischaemum reduced germination, growth, and survival of the native grasses Andropogon gerardii and S. scoparium, and leachates and degraded litter of A. gerardii reduced the biomass of B. ischaemum but not of S. scoparium (Greer et al. 2014), again suggesting that evolutionary history matters for the intensity of allelopathic interactions. ...
Article
Allelopathy (i.e., chemical interaction among species) was originally conceived as inclusive of positive and negative effects of plants on other plants, and we adopt this view. Most studies of allelopathy have been phenomenological, but we focus on studies that have explored the ecological significance of this interaction. The literature suggests that studies of allelopathy have been particularly important for three foci in ecology: species distribution, conditionality of interactions, and maintenance of species diversity. There is evidence that allelopathy influences local distributions of plant species around the world. Allelopathic conditionality appears to arise through coevolution, and this is a mechanism for plant invasions. Finally, allelopathy promotes species coexistence via intransitive competition, modifications of direct interactions, and (co)evolution. Recent advances additionally suggest that coexistence might be favored through biochemical recognition. The preponderance of phenomenological studies notwithstanding, allelopathy has broad ecological consequences. Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 52 is November 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... Such variation in SOC mineralization with vegetation patch type may be ascribed to the nature of SOC combined with changes in the chemical composition of plant input in different patches. The latter is particularly marked in the case of grass species; plant residues with high levels of N and soluble organic components but low levels of cellulose and phenolic compounds have been shown to decompose rapidly in grassland soils (Greer et al., 2014;Gupta and Singh, 1981;Redin et al., 2014). In the present study, total SOC mineralization during the incubation period was correlated with soil DOC content across different patch types. ...
Article
Patchy distribution of herbaceous species is common in degraded grasslands on the Qinghai-Tibetan Plateau, but the effects of such a mosaic pattern on soil biochemical properties have rarely been studied. We compared soil organic carbon (SOC) mineralization, nitrogen (N) availability, ammonia oxidation and plant N uptake between the following vegetation patch types (plant communities) in an alpine meadow: grass (dominated by Elymus nutans, Poa crymophila and Leymus secalinus), sedge (Kobresia capillifolia and Kobresia humilis), Polygonum viviparum (P. viviparum only), Artemisia smithii (A. smithii only) and Oxytropis kansuensis (O. kansuensis only). All patches had a diameter ranging from about tens of centimeters to several meters. SOC mineralization was faster in patches beneath grass or A. smithii than in those beneath sedge or O. kansuensis, but the faster SOC mineralization beneath grass and A. smithii patches did not result in a difference in SOC storage in the top 30 cm of soil compared with that in other patches. Greater litter production beneath grasses or belowground carbon input (largest root/shoot ratio) beneath A. smithii may have offset the negative effect of rapid SOC mineralization on SOC storage under grass and A. smithii patches. Productive grasses were associated with the highest level of N availability in the soil, consistent with their greater demands for N uptake. Sedge species and A. smithii inhibited nitrification by decreasing the abundance of ammonia oxidation bacteria in soil, in contrast to grasses. The inhibition of biological nitrification under A. smithii explained the finding that the soil beneath this vegetation patch type had the lowest nitrate content as a percentage of total inorganic N. However, the inhibition of nitrification beneath sedges did not induce a decrease in the nitrate content as a percentage of total inorganic N under sedge patches compared with that under grass patches. This suggests that sedges preferentially use ammonium instead of nitrate as their N source. It is concluded that patchy distribution of herbaceous species in alpine meadows created significant spatial heterogeneity in soil biological and biochemical properties at the field scale. Sampling in ecosystem studies clearly needs to take into account such heterogeneity of soil properties and processes in grasslands with patchily distributed vegetation.
... Further, sideoats grama, which dominates many local grasslands, was uncommon in our study site. Yellow bluestem can also suppress native species through allelopathy ( Greer et al. 2014 ) and altering mycorrhizal interactions ( Wilson et al. 2012 ). In sites long dominated by yellow bluestem, seeding or planting will be necessary to restore native grasses after yellow bluestem is removed. ...
Article
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.
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Allelopathic compounds can inhibit or stimulate the growth of nearby plants. This research examined the allelopathic effects of aqueous stem extract of Euphorbia royleana Boiss on in vitro seed germination in Brassica campestris L., Trifolium repens L. and Trigonella foenum-graecum L. The fresh stem aqueous extract of E. royleana significantly stimulated seed germination with increasing concentration. Germination of seeds, radical and plumule growth were stimulated significantly in the three species tested. It is concluded that the aqueous extract of E. royleana has the potential to be used as a source of organic fertilizer, which could enhance the productivity of some important plants.
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The California chaparral community has a rich flora of species with different mechanisms for cuing germination to postfire conditions. Heat shock triggers germination of certain species but has no stimulatory effect on a great many other postfire species that are chemically stimulated by combustion products. Previous reports have shown that charred wood will induce germination, and here we report that smoke also induces germination in these same species. Smoke is highly effective, often inducing 100% germination in deeply dormant seed populations with 0% control germination. Smoke induces germination both directly and indirectly by aqueous or gaseous transfer from soil to seeds. Neither nitrate nor ammonium ions were effective in stimulating germination of smoke-stimulated species, nor were most of the quantitatively important gases generated by biomass smoke. Nitrogen dioxide, however, was very effective at inducing germination in Caulanthus heterophyllus (Brassicaceae), Emmenanthe penduliflora (Hydrophyllaceae), Phacelia grandiflora (Hydrophyllaceae), and Silene multinervia (Caryophyllaceae). Three species, Dendromecon rigida (Papaveraceae), Dicentra chrysantha, and Trichostema lanatum (Lamiaceae), failed to germinate unless smoke treatment was coupled with prior treatment of 1 yr soil storage. Smoke-stimulated germination was found in 25 chaparral species, representing 11 families, none of which were families known for heat-shock-stimulated germination. Seeds of smoke-stimulated species have many analogous characteristics that separate them from most heat-shock-stimulated seeds, including: (1) outer seed coats that are highly textured, (2) a poorly developed outer cuticle, (3) absence of a dense palisade tissue in the seed coat, and (4) a subdermal membrane that is semipermeable, allowing water passage but blocking entry of large (molecular mass > 500) solutes. Tentative evidence suggests that permeability characteristics of this subdermal layer are altered by smoke. While the mechanism behind smoke-induced germination is not known, it appears that smoke may be involved in overcoming different blocks to germination in different species. For example, in Emmenanthe penduliflora, NO2 in smoke was sufficient to induce germination, and most forms of physical or chemical scarification also induced germination. For Romneya coulteri, NO2 alone failed to induce germination, and scarified seeds required addition of gibberellic acid. In Dicentra chrysantha, none of these treatments, nor smoke alone, induced germination, but germination was triggered by a combination of soil burial followed by smoke treatment. Smoke-stimulated species differed substantially in the duration of smoke exposure required to induce germination, and this was inversely correlated with tolerance to smoke exposure. We suggest that such differences in response may affect postfire community structure.
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Allelopathy may play an important role in the invasion success of alien plant species. In this study, we examined the effects of aqueous extracts from the leaves and roots of the invasive plant species Chromolaena odorata (L.) King and Robinson at different concentrations (control, 1%, 5%, and 10%) on the seed germination and seedling growth (root and shoot length) of 10 herbaceous species using the Petri dish bioassay. The 10 herbaceous species comprised five native and five non-native invasive species all common in most habitats in southern China. C. odorata leaf and root extracts inhibited the seed germination, root length, and shoot length of most target species at different concentration levels. This inhibitory effect generally increased with increased extract concentration, and was more pronounced with the leaf extract than the root extract. There were more obvious inhibitory effects on the five native species than the non-native ones, suggesting that the latter had co-evolved with C. odorata in their native range (South America) and were relatively less susceptible to allelopathic compounds released by C. odorata. These results suggested that allelopathy may contribute to the ability of C. odorata to become dominant in invaded plant communities in southern China.
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Old World bluestems (Bothriochloa spp.) have been seeded on over a million hectares of marginal farmland in Oklahoma and Texas, yet we know little about their regrowth yield and quality. The objective was to determine seasonal pattern of forage regrowth yield and quality of leaves and stems of WW-Iron Master (B. ischaemum [L.] Keng) and Caucasian (B. caucasica [Trin.] C.E. Hubb.) bluestem when 4-week regrowth was harvested at weekly intervals from early May through mid-September. Four plots of each bluestem were established in each of the 4 blocks (32 plots total). Harvesting was rotated so that 4-week regrowth of each bluestem was harvested weekly from 1 of the 4 plots in each block during 1988 and 1989 to determine regrowth yield, in vitro dry matter digestibility (IVDMD), and crude protein (CP) of leaves and stems. Forage regrowth of both species peaked in June both years. Regrowth during August averaged 10 and 35% of June regrowth in 1988 and 1989. WW-Iron Master produced 80 and 45% greater 4-week regrowth than Caucasian in 1988 and 1989. WW-Iron Master produced 75 and 28% greater leaf regrowth than Caucasian in 1988 and 1989 and twice as many stems both years. Leaf and stem IVDMD of WW-Iron Master averaged 2 to 6 percentage units higher than Caucasian. Leaf CP of WW-Iron Master averaged 2 percentage units higher than Caucasian during May and June. However, stem CP of WW-Iron Master averaged 1 percentage unit lower than Caucasian. Grazing management plans need to consider that the majority of bluestem forage production was restricted to a 1 month period in June. This technique of sampling 4-week regrowth every week during the growing season was an effective method for determining the seasonal regrowth pattern.
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What is there about pinyon and juniper trees which reduces growth of blue grama? This study shows that the chief influence is due to tree litter, not canopy.
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Old world bluestem (OWB) grasses (Bothriochloa spp.) have been used for herbage in the southern Great Plains for over 60 years, but release of new, well-adapted cultivars has led to a dramatic increase in use of these grasses in Oklahoma and adjacent areas during the last 15 years. Little information is available on the chemical composition of OWB grasses. The purpose of this study was to obtain information on the chemical composition of OWB grasses as affected by cultivar and maturation. Forage samples for chemical analyses were obtained from a 2-year field experiment conducted on a Kirkland silt loam soil (Udertic Paleustoll). Ten harvest dates (1-week interval between harvests) and 3 plant parts (whole plant, leaf, and stem) were imposed by split-split plot arrangement on established stands of 'Caucasian', 'Ganada', 'Plains', and 'WW-Spar' bluestem. Responses of variables were neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and crude protein (CP). Concentrations of NDF, ADF, and ADL increased in whole plant and stem samples during the 10-week sampling periods of both years. Quadratic equations best described changes in ADF during both years and in NDF and ADL in 1983, whereas linear equations best fitted changes in NDF and ADL in 1982. Concentration of NDF in leaves changed very little with maturation, but its change in whole plant and stems paralleled that described for ADF and ADL. Concentrations of CP decreased in all plant parts through harvest date eight (11-week old growth), with the changes best described by quadratic equations. Changes in all constituents were less affected by advancing maturity in leaves than in stems. Maturity had a much greater effect on concentration of all the chemical constituents than did cultivar. Initial concentrations of NDF in all plant parts exceeded the level (ca 600 ${\rm g}\ {\rm kg}^{-1}$ ) at which intake would likely be affected. Concentrations of CP also declined to levels by the 5th to 6th harvest dates, particularly in whole plant and stem parts, insufficient to supply daily requirements for most classes of mature beef cattle. The results point to the need to maintain and utilize these grasses to the extent possible in a juvenile, actively growing state to provide nutrition for growing livestock.