Studies on Andropogon gayanus Kunth

Nectar secretion by grasses is rare. Andropogon gayanus var. bisquamulatus has been observed to secrete nectar from two localized areas: (a) near the sheath margin immediately below the pseudopetiole; (b) the pseudopetiolar ridges adjacent to the ligule. Microchemical tests with Fehlings solution revealed high concentrations of reducing sugars at these two sites. Some evidence is given for supposing that the macrohair basal cells may secrete the nectar.     

Factors Affecting the Flowering of Andropogon gayanus Kunth. Responses to Photoperiod, Temperature and Growth Regulators

Andropogon gayanus is a short-day plant with a critical daylengthfor flowering between 12 and 14 h. Flowering is more intenseas the daylength is shortened from 12 h to 8 h, initiation isalso accelerated by increasing durations of short-day treatment.Plants flower more readily with increasing age. The maximumflowering response can be induced by short-day exposure of onlyone expanding leaf. A fixed number of short days distributedamong different groups of leaves on the plant gave less floweringthan the same number given to only one group. Approximately25°C was optimal for flowering. Root removal treatmentsin short day reduced both growth and flowering responses. Application of the growth regulators indol 3yl-acetic acid,abscisic acid, gibberellic acid or dimethylaminosuccinamic acid(B9) was inhibitory to flowering in all cases but gibberellicacid and B9 applied simultaneously had no inhibitory effect.Growth hormone treatments failed to stimulate flower developmentin long day. These results are discussed in relation to the internal mechanismscontrolling growth and flowering.     

Triglyceride metabolism in germinating Andropogon gayanus seeds

Seed triglycerides of Andropogon gayanus contained 17 fatty acid moieties, principally palmitic, oleic and linoleic acids. These were distributed in an essentially random manner amongst the triglycerides to form the following main types: POL, PLL, OOL, LLO and LLL. Triglycerides decreased during both light and dark germination but there was no evidence for selective hydrolysis. Free fatty acids appear to be derived from triglyceride hydrolysis but the free and triglyceride fatty acid composition differed. Less palmitic, oleic and linoleic acids and more stearic, linolenic and C₂₀-acids were found in the free state than combined in the triglycerides. Free fatty acids did not accumulate during germination.     

Anti-tick effects of Melinis minutiflora and Andropogon gayanus grasses on plots experimentally infested with Boophilus microplus larvae

Our objective in this trial was to investigate the anti-tick effects of molasses grass (Melinis minutiflora) and gamba grass (Andropogon gayanus) against Boophilus microplus, using buffel grass (Cenchrus ciliaris) as a control. During a 3-year-period fieldwork was carried out in the tropical, subhumid climate at Progreso, Municipality of Jiutepec, Morelos, Mexico. Experimental plots were established for three treatments with six replicates under a random factorial design in order to evaluate each of the four seasons. Additional work was developed for two more consecutive autumn seasons to evaluate the anti-tick effects of these grasses. Once the plots were established they were infested with 5000 B. microplus larvae and sampled by dragging flannel cloths. The anti-tick effects were measured by counting the number of larvae recovered from each of the experimental plots. Both grasses, M. minutiflora and A. gayanus, demonstrated anti-tick effects; however, M. minutiflora grass had the greatest anti-tick effects through the seasons studied and in the three consecutive autumns evaluated.     

Residual herbicide treatments reduce Andropogon gayanus (Gamba Grass) recruitment for mine site restoration in northern Australia

Weed invasion is a major threat to Australian tropical savannas, and controlling weeds is essential for successful re‐establishment of native species on disturbed sites. Gamba Grass (Andropogon gayanus) is an African grass which has invaded large areas of tropical savanna across northern Australia. Current management strategies in northern Australia focus on fire and glyphosate to effectively control mature plants; however, re‐establishment of infestations from the soil seed bank remains a major challenge to eradication efforts. This study focused on the effects of soil seed bank treatments on Gamba Grass recruitment on a mine site in northern Australia. Adult Gamba Grass plants within test plots were killed with glyphosate to exclude resource competition. Chemical, physical and biological treatments were then applied, and the treatment effects on subsequent Gamba Grass seedling emergence and survival quantified. Seedling emergence was significantly reduced by three of the four residual herbicide treatments tested. The most effective herbicide treatments, dalapon and sulfometuron, reduced emergence by 90% compared to the standard glyphosate treatment alone. This equated to a reduction in Gamba Grass seedling emergence from 1 seedling/m² to 1 seedling 10 m^?2, a major improvement for Gamba Grass management. These residual herbicide treatments significantly reduced the population density of Gamba Grass for at least 5 months after emergence. The physical and biological treatments did not have a significant effect on seedling emergence. This significant reduction in Gamba Grass seedling emergence and survival can substantially improve Gamba Grass management. Reducing re‐colonisation from the soil seed bank using residual herbicides provides a valuable management tool for land managers, integrating readily with established strategies for controlling the mature plants.     

Andropogon gayanus (Gamba Grass) Invasion Increases Fire-mediated Nitrogen Losses in the Tropical Savannas of Northern Australia

Invasive alien grasses can substantially alter fuel loads and fire regimes which could have significant consequences for fire-mediated nutrient losses. The effects of the alien grass Andropogon gayanus Kunth. (Gamba grass) on fire-mediated nutrient losses was evaluated in Australia’s tropical savannas. Losses of macronutrients during fire were determined by comparing the nutrient pools contained in the fine fuel before fire and in the ash after fire. Pre-fire grass nutrient pools were significantly higher in A. gayanus plots than in native grass plots for all nutrients measured (N, P, K, S, Ca, and Mg). Nutrient losses were substantially higher in A. gayanus plots, with 113% higher losses for N, 80% for P, 56% for K, 63 for S, 355% for Ca, and 345% for Mg. However, only losses of N and Mg varied significantly between grass types. A simplified savanna ecosystem nutrient budget estimated that A. gayanus fires led to the net N loss of 20 kg ha⁻¹ y⁻¹. This is a conservative estimate because total fuel loads were relatively low (7.85 t ha⁻¹) for A. gayanus invaded plots leading to a relatively moderate intensity fire (6,408 kW m⁻¹). Higher A. gayanus fuel loads and fire intensities could potentially lead to losses of up to 61.5 kg N ha⁻¹ from the grass fuel. Over the long term, this is likely to lead to depletion of soil nutrients, particularly N, in the already low-fertility tropical savanna soils.     

Habitat Complexity and Invasive Species: The Impacts of Gamba Grass (Andropogon gayanus) on Invertebrates in an Australian Tropical Savanna

Habitat complexity is an important factor structuring local faunal assemblages. Many invasive plant species alter vegetation complexity because they are both functionally and structurally different from native flora. This study investigated the effects of an invasive grass (Andropogon gayanus Kunth.), which is invading undisturbed savannas in northern Australia. Although A. gayanus is a similar lifeform to that dominant in the native understory (i.e., a C4 grass), it is structurally different and significantly alters habitat complexity. We, therefore, hypothesized that there would be a substantial effect of the invasive grass on ant, spider, and other invertebrate assemblages. Contrary to our hypothesis, there was no effect of A. gayanus on ant species richness, abundance, or composition, nor were spiders or other invertebrates affected. Instead the change in weather conditions with season was more important in structuring the local invertebrate assemblages. Change in habitat complexity was most pronounced vertically, rather than horizontally at ground level, thus although there was a clear difference in the vertical structure between invaded and noninvaded habitats, the limited invertebrate response to different A. gayanus densities suggests some invertebrates are less sensitive to vertical changes in vegetation structure.     

Studies on antihypertensive and antispasmodic activities of Andropogon muricatus Retz

The aqueous-methanolic crude extract of Andropogon muricatus (Am.Cr) was investigated pharmacologically to determine some of its medicinal uses in cardiovascular and gastrointestinal disorders. A series of in vivo and in vitro studies were conducted to evaluate dose-dependent effects of Am.Cr on mean arterial pressure (MAP), cardiac and vascular contractions, and to further investigate the potential mechanism of action. Intravenous administration of Am.Cr (10-50 mg/kg) caused a fall (18%-56%) in MAP in normotensive rats under anesthesia. When tested in isolated guinea pig atria, Am.Cr (0.03-5.0 mg/mL) exhibited a cardiodepressant effect on the rate and force of spontaneous contractions. In isolated rabbit aorta, Am.Cr caused inhibition of K+ (80 mmol/L)-induced contractions at a lower concentration than of phenylephrine. In isolated rabbit jejunum preparations, Am.Cr (0.01-0.10 mg/mL) caused relaxation of spontaneous and high K+ (80 mmol/L)-induced contractions, suggesting that the spasmolytic effect is mediated possibly through calcium channel blockade (CCB). The CCB activity was confirmed when pretreatment of the tissue with Am.Cr (0.03-0.1 mg/mL) shifted the Ca2+ dose-response curves to the right, similar to that caused by verapamil. These data indicate that the blood pressure-lowering and spasmolytic effects of Am.Cr are mediated possibly through a calcium channel blocking activity. Phytochemical screening of Am.Cr revealed the presence of phenols, saponins, tannins, and terpenes, which may be responsible for the observed vasodilator, cardiodepressant, and antispasmodic activities. This study shows potential with respect to its medicinal use in cardiovascular and gut disorders.     

Effect of fibrolytic enzymes added to a Andropogon gayanus grass silage-concentrate diet on rumen fermentation in batch cultures and the artificial rumen (Rusitec)

In vitro batch cultures were used to screen four fibrolytic enzyme mixtures at two dosages added to a 60 : 40 silage : concentrate diet containing the C₄ tropical grass Andropogon gayanus grass ensiled at two maturities – vegetative stage (VS) and flowering stage (FS). Based on these studies, one enzyme mixture was selected to treat the same diets and evaluate its impact on fermentation using an artificial rumen (Rusitec). In vitro batch cultures were conducted as a completely randomized design with two runs, four replicates per run and 12 treatments in a factorial arrangement (four enzyme mixtures×three doses). Enzyme additives (E1, E2, E3 and E4) were commercial products and contained a range of endoglucanase, exoglucanase and xylanase activities. Enzymes were added to the complete diet 2 h before incubation at 0, 2 and 4 μl/g of dry matter (DM). Gas production (GP) was measured after 3, 6, 12, 24 and 48 h of incubation. Disappearance of DM (DMD), NDF (NDFD) and ADF (ADFD) were determined after 24 and 48 h. For all four enzyme mixtures, a dosage effect (P<0.05) was observed for NDFD and ADFD after 24 h and for DMD, NDFD and ADFD after 48 h of incubation of the VS diet. For the FS diet, a dosage effect was observed for GP and NDFD after 24 h and for GP, DMD, NDFD and ADFD after 48 h of incubation. There was no difference among enzyme mixtures nor was there an enzyme×dose interaction for the studied parameters. Because of the greatest numerical effect on NDF disappearance and the least cost price, enzyme mixture E2 at 4 µl/g of diet DM was selected for the Rusitec experiment. The enzyme did not impact (P>0.05) DM, N, NDF or ADF disappearance after 48 h of incubation nor daily ammonia-N, volatile fatty acids or CH₄ production. However, enzyme application increased (P<0.05) microbial N production in feed particle-associated (loosely-associated) and silage feed particle-bound (firmly associated) fractions. With A. gayanus silage diets, degradation may not be limited by microbial colonization, but rather by the ability of fibrolytic enzymes to degrade plant cell walls within this recalcitrant forage.     

BIODIVERSITY RESEARCH: Turning up the heat: the impacts of Andropogon gayanus (gamba grass) invasion on fire behaviour in northern Australian savannas

Aim This study aimed to quantify changes in fire severity resulting from the invasion of Australia’s tropical savannas by the African grass Andropogon gayanus Kunth. (gamba grass). Location Mesic savannas of the Northern Territory, Australia. Method Byram’s fire‐line intensity (I_f), fuel load and architecture, and two post‐fire indicators of fire intensity – scorch height (SH) and char height (CH) of woody vegetation – were determined for fires in native grass savanna and A. gayanus invaded savanna. Leaf scorch is the height at which the fire’s radiant heat browns leaf tissue, and leaf char is the height that radiant heat blackens or consumes leaf tissue and provides an indirect measure of flame height. These data, and 5 years of similar data collected from the Kapalga Fire Project in Kakadu National Park, were used to develop empirical relationships between I_f and the post‐fire indices of fire intensity. Results A relationship between A. gayanus I_f and SH could not be developed because complete canopy scorch occurred in most A. gayanus fires, even at low I_f. In contrast, A. gayanus I_f was strongly correlated with CH. This empirical relationship was substantially different from that for native grass fires. For a given I_f, there was a significantly greater CH in invaded sites. This increase in radiant heat is attributable to the increased biomass (mean 3.6 t ha^?1 in native grasses compared to 11.6 t ha^?1 in A. gayanus) and height (approximately 0.5 m in native grasses compared to 4 m in A. gayanus) of the standing fine fuel. Main conclusion Andropogon gayanus invasion resulted in substantial changes in fire behaviour. This has important regional implications owing to the current (10,000–15,000 km²) and predicted (380,000 km²) area of invasion and the negative consequences for the native savanna biota that has evolved with frequent but relatively low‐intensity fire.     

UeberAnthurium Hookeri,Kunth

Ohne Zusammenfassung     

Studies on N2-fixing bacteria associated with the salt-tolerant grass,Leptochloa fusca (L.) Kunth

Summary N₂-fixing bacteria were isolated from the rhizosphere of naturally grown salt tolerant grass (Leptochloa fusca). A broad spectrum of diazotrophs was found to be associated with the roots ofL. fusca. the systematic position of the three isolates, NIAB-1, C-2 and Iso-2 was determined by morphological, biochemical and mol % (G+C) DNA contents. Two isolates were identified asKlebsiella pneumoniae (NIAB-1) andBeijerinckia sp. (Iso-2).¹⁵N enrichment studies confirmed the nitrogen fixing ability of the isolates. The effects of different levels of combined nitrogen (NO ₃ ^– & NH ₄ ⁺ ), pH (5.5–9.0) and salt (NaCl) on nitrogenase activity of the isolates were determined at various time intervals. All isolates exhibited nitrogenase activity even in the presence of 5 mmol/l NO ₃ ^– or NH ₄ ⁺ in a semi-solid medium after 24 h of growth. Maximum nitrogenase activity was observed at alkaline pH and all isolates were able to tolerate up to 3% NaCl in the medium.

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Resumen Se han aíslado bacterias fijadoras de N₂ en la rizosfera del hábitat natural de la graminea halófilaLeptochloa fusca. Un amplio espectro de diazotrofos se encontró asociado con las raíces deL. fusca. La posición sistemática de tres aíslados: NIAB-1, C-2 y Iso-2 se determinó utilizando sus características morfológicas, bioquímicas y el % (G+C) molar del ADN. El aíslado NIAB-1 se identificó comoKlebsiella pneumoniae y el aíslado Iso-2 comoBeijerinckia. sp. Estudios mediante¹⁵N confirmaron la habilidad fijadora de N₂ de los aíslados. Se determinaron periodicamente los efectos de distintos niveles de nitrógeno combinado (NO₃ ^– y NH₄ ⁺), pH (5.5–9.0) y sal (NaCl) en la actividad nitrogenásica de los aíslados. Todas las cepas aísladas mostraron actividad nitrogenásica incluso en presencia de 5mmol/l de NO₃ ^– y NH₄ ⁺ en un medio semisólido desqués de 24 h. de crecimiento. La actividad nitrogenásica máxima se observó a pH alcalino y todos loa aíslados eran capaces de tolerar hasta 3% de NaCl en el medio.

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Résumé Des bactéries fixatrices de l'azote ont été isolées à partir de la rhizosphère de l'herbe halotoléranteLeptochloa fusca développée dans les conditions naturelles. Il a été constaté qu'un large spectre de diazotrophes est associé aux racines de la plante. La position taxonomique de 3 souches isolées, NIAB-1, C-2 et Iso-2, a été déterminée par des critères morphologiques et biochimiques et par le pourcentage de (G+C) de l'ADN. Deux souches on été identifiées commeKlebsiella pneumoniae (NIAB-1) etBeijerinckia sp. (Iso-2). Les études d'enrichissement en¹⁵N ont confirmé l'aptitude des souches à fixer l'azote. les effets de différents niveaux d'azote combiné (NO₃ ^– et NH₄ ⁺), de pH (5.5–9.0) et de sel (NaCl) sur l'activité nitrogénasique des souches ont été déterminés à divers intervalles de temps. Toutes les souches présentent une activité nitrogènase après 24 h de croissance en milieu semi-solide, et cela même en présence de 5 mmol/l de NO₃ ^– ou NH₄ ⁺. L'activité nitrogènase maximum est observée à pH alcalin, et toutes les souches tolèrent jusqu'à 3% de NaCl dans le milieu.

     

Ueber Anthurium Hookeri,Kunth

Ohne Zusammenfassung     

The grass genus Andropogon in the United States

A key is provided for Andropogon and the segregate genera, Schizachyrium, Bothriochloa, and Dichanthium, as represented in the United States. Included also is a listing of the native and introduced species of each: 17 species of Andropogon (all native) ; 11 species of Schizachryium (all native) ; 14 species of Bothriochloa (8 native + 6 introduced) ; 3 species of Dichanthium (all introduced). New combinations are proposed for: Schizachryium niveum; S. rhizomatum; S. sericatum; S. scoparium var. divergens, var. frequens, var. littoralis, var. neomexicanum, and var. virile.     

Embryological studies of Oxalis debilis Kunth

The study of pollen and female gametophyte development of Oxalis debilis was carried out to elucidate the reasons for the absence of seed production in this species. The formation of an incomplete callosic wall separating the microspores of the tetrad was observed; therefore, cytoplasm connections were present between the microspores. Microspores of different sizes and with different grades of vacuolation were observed in the mature anther. Only few microspores divide mitotically and form the generative and vegetative cell. The cytoplasm of the vegetative cell may accumulate different substances in reserve. Pollen grains are 8–12?colpate, and the morphology and electron density of the exine varies. Because flowers in full anthesis have all ovules at the megasporocyte stage with the nucellar epidermis intact, fecundation could not occur. The production of only a few viable pollen grains and the absence of successful megagametophyte development prevent fertilization and account for the absence of fruits and seeds formation.     

Studies in African Cyperaceae 34. New combination in Bulbostylis Kunth ex C. B. Clarke

This paper provides new combinations for 16 species of Bulbostylis Kunth ex C. B. Clarke originally described as Abildgaardia Vahl. The new combinations are: Bulbostylis abbreviata (Lye) Lye, B. acutispicata (Lye) Lye, B. afromicrocephala Lye, B. angustispicata (Lye) Lye, B. capitata (Lye) Lye, B. densiflora (Lye) Lye, B. lacunosa (Lye) Lye, B. laxispicata (Lye) Lye, B. longispicata (Lye) Lye, B. microanthela (Lye) Lye, B. malawiensis (Lye) Lye, B. microrotundata (Lye) Lye, B. nudiuscula (Lye) Lye, B. pluricephala (Lye) Lye, B. scrobiculata (Lye) Lye, B. squarrosa (Lye) Lye.     

Epicuticular waxes of Andropogon hallii and A. Scoparius

Leaf waxes of Andropogon hallii and A. scoparius contain hydrocarbons (2%, 2%), esters (4%, 2%), free acids (3%, 4%), free alcohols (1%, 0.2%, major component dotriacontanol) β-diketones (67%, 80%) and hydroxy β-diketones (16%, 5%). β-Diketones of A. hallii consist mainly of tritriacontane-12,14-dione and hentriacontane-12,14-dione (86:8) and of A. scoparius of tritriacontane-12,14-dione and hentriacontane-10,12-dione (67:29). Hydroxy β-diketones of A. hallii are composed mainly of 5-hydroxytritriacontane-12,14-dione and 5-hydroxy-hentriacontane-12,14-dione (90:8); wax of A. scoparius contains only 5-hydroxytritriacontane-12,14-dione. The hydroxyl group of the major hydroxy β-diketone has the R-configuration opposite to that of all previously described hydroxy β-diketones.     

吉祥草化学成分的研究

为研究吉祥草(Reineckia carnea)的化学成分,运用柱色谱的方法从中分离得到7个化合物,经波谱解析和理化性质分别鉴定为假海马齿醇(1),角鲨烯(2),4′,5,7-三羟基-6,8.二甲基黄酮(3),(R-)-8-甲基柚皮素(4),N-香豆酰酪胺(5),N-香豆酰章鱼胺(6)和胡萝卜苷(7).以上化合物均为首次从该植物中分离得到.     

Comparison of common cytotypesof Andropogon gerardii(Andropogoneae,Poaceae)

Many plant species contain populations with more than one polyploid cytotype, but little is known of the mechanisms maintaining several cytotypes in a population. Andropogon gerardii cytotypes were compared to evaluate different models of autopolyploid cytotype coexistence. The enneaploid (90 chromosome, 9x) cytotype was found to be larger and taller than the hexaploid (60 chromosome, 6x) cytotype. Seed production is significantly more efficient in hexaploids, but seed production per area was not significantly different. The two cytotypes are not exomorphologically separable in the field because of great plasticity in response to environmental variation and wide variation within each cytotype. These data suggest cytotypic variation is maintained by natural selection.