Echinochloa Polystachya Research Articles

Food Plants Eaten by Amazonian Manatees (Trichechus inunguis, Mammalia : Sirenia)

To determine the feeding habits of the Amazonian manatee Trichechus inunguis in some Central Amazonian rivers and lakes, we compared plant epidermis found in the stomach contents and/or faeces of animals with a reference collection of plants present in the studied areas. Twenty five samples from digestive tracts of animals found dead and 25 faeces samples found floating were analyzed. From these samples, 24 aquatic macrophytes were identified. The Gramineae family was identified in 96% of the samples, Paspalum repens and Echinochloa polystachya being the most abundant in the samples. The second most frequent family was the Pontederiaceae primarily Eichhornia crassipes. During the high water period, the animals showed a more selective diet (eight identified species). In the low water period, when food was more scarce, the animals showed a larger diversity of species in their diet (21 species of plants). Differences in the diet among the two studied areas reflected the physiographics characteristics of the region. Amazonian manatees fed mostly on emergent plants.

Decomposition of Echinochloa polystachya and its contribution to nutrient cycling in a Central Amazonian floodplain lake

Decomposition of <i>Echinochloa polystachya</i> and its contribution to nutrient cycling in a Central Amazonian floodplain lake

Very high productivity of the C4 aquatic grass Echinochloa polystachya in the Amazon floodplain confirmed by net ecosystem CO2 flux measurements.

Fluxes of CO2 and H2O vapour from dense stands of the C4 emergent macrophyte grass Echinochloa polystachya were measured by eddy covariance in both the low water (LW) and high water (HW, flooded) phases of the annual Amazon river cycle at Manaus, Brazil. Typical clear-sky midday CO2 uptake rates by the vegetation stand (including detritus, sediment or water surface) were 30 and 35µmolCO2(ground)m-2s-1 in the LW and HW periods, respectively. A rectangular hyperbola model fitted the responses of "instantaneous" (20- or 30-min average) net CO2 exchange rates to incident photosynthetic photon flux densities (PFD) well. Stand evaporation rates were linearly related to PFD. The major difference in CO2 uptake rates between the two periods was the larger respiration flux during LW due to the CO2 efflux from sediment, roots and litter. Integrated 20- or 30-min fluxes were used to derive relationships between daily CO2 and H2O vapour fluxes and incident radiation. The daily CO2 fluxes were almost linearly related to incident radiation, but there was evidence of saturation at the highest daily radiation totals. Annual productivity estimated from the daily model in 1996-1997 agreed closely with that previously estimated for 1985-1986 from a leaf-scale photosynthetic model, but were some 15% less than those derived at that time from biomass harvests. Both CO2 uptake and water use efficiency were comparable with those found in fertilised maize fields in warm temperate conditions.

Biological control of neotropical aquatic weeds with fungi

Many of the world's worst tropical aquatic weeds are native to the Neotropics. Besides, the majority of the most aggressive aquatic weeds in that vast region of the world are endemic and therefore there is a need for exploration for biological control agents in that area. Entomologists had an early lead on this search. Only in the late 1970s did plant pathologists started sporadic collections of fungal pathogens of aquatic weeds in the Neotropics for evaluation and use as classical biocontrol agents or as mycoherbicides. Although intensive search of the mycobiota of water hyacinth and other plant species are recent, they have already yielded a range of new potential biocontrol agents. A discussion on the status of studies of the mycobiota of the following selected Neotropical species is presented: Alternanthera philoxeroides, Azolla filiculoides, Echinochloa polystachya, Eichhornia azurea, Eichhornia crassipes, Egeria densa, Myriophyllum aquaticum, Paspalum repens, Pistia stratiotes, Polygonum spectabile, Salvinia auriculata, Salvinia molesta and Typha domingensis.

Zea nicaraguensis (Poaceae), a New Teosinte from Pacific Coastal Nicaragua

Zea nicaraguensis (Poaceae), a New Teosinte from Pacific Coastal Nicaragua

Periphyton biomass on Echinochloa polystachya (H.B.K.) Hitch. of a lake of the Lower Paraná River floodplain, Argentina

Spatial and temporal variation of periphyton biomass on Echinochloa polystachya (H.B.K.) Hitch. was studied monthly in a turbid lake of the Lower Parana River floodplain from May 1995 to May 1996. Measures of chlorophyll a, dry weight and ash free dry weight were obtained from material scraped off the stems of the plant. Two sampling sites with different macrophyte cover were selected: Montiel (littoral area of lake Montiel) and Ciego (littoral area of a vegetated environment connected to the lake). Physical and chemical variables were measured at each sampling site in order to characterize the environments. The sampling sites differed: Montiel appeared influenced by inputs from the Parana River, while Ciego was less affected due to the effect of the macrophytes. The influence of the substrata on the periphyton dynamics was evident at both sampling sites. The values of periphytic biomass variables were lower at Ciego station where macrophyte development was more important. Multiple regression analyses performed with the different biomass variables, revealed that a combination of physical-chemical variables could explain the variability of the biomass, both at Ciego and Montiel, confirming that it is difficult to detect a single factor affecting the periphytic community in natural systems.

Chemical composition of tropical macrophyte Echinochloa polystachya (H.B.K.) Hitchcock in Jurumirim Reservoir (São Paulo, Brazil)

Seasonal variations of C, N and P concentrations and stocks in the emergent macrophyte Echinochloa polystachya (H.B.K.) Hitchcock, of the Paranapanema River mouth zone at Jurumirim Reservoir (SP, Brazil), were examined. Marked variation in nutrient concentrations (from 287.6 to 463.2 mg C g DW-1; 3.4 to 37.8 mg N g DW-1; 0.13 to 2.31 mg P g DW-1) and stocks (from 3.8 to 11.9 t C ha-1; 96.3 to 400.6 kg N ha-1, 3.6 to 44.3 kg P ha-1) were observed along the year (August 1993 – July 1994). Peaks in concentrations and stocks were observed in January, February and March 1994. As nutrient concentrations in water and sediments are low and stocks in the plant high, the local nutrient dynamics seem to be controlled by this macrophyte. Leaf blades and sheaths participate most in recycling, while stems contain the principal nutrient stock.

Temporal Variation in C, N and P of the Periphyton on the Tropical Aquatic Macrophyte Echinochloa polystachya (H.B.K.) HITCH. in Jurumirim Reservoir (São Paulo, Brazil)

The temporal variations in C, N and P concentrations of the periphyton on the natural substratum (Echinochloa polystachya) and its relationships to the water's climatological (air temperature and precipitation), hydrodynamic (water discharge and water level), physical (temperature, transparency) and chemical variables (conductivity, total suspended solids, nitrate, nitrite, ammonia, silica, total phosphorus and orthophosphate) were evaluated in a lagoon at the Par-anapanema River mouth into the Jurumirim Reservoir (São Paulo, Brazil) from August 1993 to July 1994. An amplitude variation of 2.0 m in water level was observed. Depending on to the hydrologic conditions, the lagoon presents intermediate conditions of lentic and lotic environments. The amplitude variations in C, N and P were 14.5-52.1% C DW-1, 0.5-3.2% N DW-1, and 0.03-0.4% P DW-1, respectively. The periphyton presented a decreased protein content. The environmental trophic degree appears to be decisive in chemical periphyton composition.

Evaluation of Allorhogas pyralophagus Marsh (Hymenoptera: Braconidae) for the biological control of Diatraea spp. (Lepidoptera: Pyralidae) in sugar-cane in Guyana

In 1989, a mass production and field release programme of Allorhogas pyralophagus Marsh (Hymenoptera: Braconidae) for the control of the Diatraea spp., particularly D. centrella (Möschler) (Lepidoptera: Pyralidae) in sugar-cane, was initiated by the Guyana Sugar Corporation. The programme was terminated in 1995 after the release of approximately two million adult parasites resulted in a mean field parasitism in Diatraea spp. larvae of only 0.22%. In contrast, 62% of Diatraea spp. larvae were parasitised in vitro as were 32% of larvae in young cane shoots exposed to A. pyralophagus in the laboratory. Neither Diatraea larvae in young cane plants caged in the field nor those recovered from Echinochloa polystachya (Kunth) Hitchc. and Paspalum virgatum L. around release fields showed any parasitism by A. pyralophagus. The reasons for the low rate of host acquisition outside the laboratory are not known, but it is clear that A. pyralophagus offers little prospect for significant control of Diatraea spp., particularly D. centrella in sugar-cane in Guyana.

Nutrient dynamics of the highly productive C4 macrophyte Echinochloa polystachya on the Amazon floodplain

1. Echinochloa polystachya forms extensive monotypic stands on the lower levels of the Amazon floodplains. During its annual growth cycle c. 100t (dry mass) ha–1 of biomass is formed as the floodplain is being submerged (December–September) and a phase of death and decomposition occurs when the water has retreated (October–November). This study examines the mineral nutrient dynamics of this plant and its potential significance to the nutrient status of the floodplain. 2. Echinochloa polystachya was sampled monthly from a study site in the central Amazon. N, P and K contents for different plant organs were determined and net uptake calculated from concurrent measurements of dry matter production and turnover. 3. Leaf N, P and K contents were c. 20, 1·7 and 19gkg–1, values typical of nutrient‐replete stands of C4 plants. Stem concentrations were c. 12% of those of the leaves. Net N and P uptake followed the rise in the river level, whilst K appeared independent of water level. 4. The vegetation accumulated 377, 51 and 1136kgha–2 of N, P and K, respectively, during the growth phase. Over a possible 5000km2 of these stands in the Várzea, this represents a massive sequestration of nutrients in the flood phase and a high release during the following low‐water period. It is suggested that the E. polystachya stands could have a role in maintaining the nutrient status of the Amazon floodplain.

Effects of Drought and Flooding on Root Anatomy in Four Tropical Forage Grasses

Seasonal drought and flooding severely limit pasture growth in savannas, although tropical grasses show broad variation in their tolerance to these water stresses. In this study we analyzed and compared the responses in morphology and anatomy of the roots of four important perennial C4 forage grass species to short-term flooding and moderate drought under controlled conditions. The plants studied were the dryland bunchgrasses Andropogon gayanus and Hyparrhenia rufa and the wetland stoloniferous Echinochloa polystachya and Brachiaria mutica. The responses to flooding were more conspicuous than those to drought, and all species were able to alter their root form and structure under flooding. The most evident response was the development of aerenchymatous tissue in the root cortex, which was proportionally highest in H. rufa. The wetland grasses already had constitutively high proportions of aerenchyma tissue in the cortex, which changed little with waterlogging, up to 40%-49% of total transverse root area. Andropogon gayanus developed the least aerenchyma space in the cortex and was the most affected by flooding. Other effects of flooding included root dimorphism and suberization of both exodermis and endodermis cells in all grasses.

Role of N 2-fixation in the sustainability of the ponded grass pasture system

Ponded pastures in northern Australia produce green fodder in the seasonally dry winter period and may be employed to reduce grazing pressure on dryland pastures. The soils under ponded pasture, currently 26,000 ha in Queensland, are inherently infertile. This study was conducted to determine if a non-symbiotic association between bacteria and grass roots was responsible for the supply of N to ponded grasses. Intact soil-plant cores were obtained from a new ponded pasture of Aleman ( Echinochloa polystachya) and an 8-year-old pasture of Hymenachne ( Hymenachne amplexicaulis). Nitrogenase (N 2-ase) activity was measured using the acetylene reduction assay and bacteria were selectively isolated to N-free malate medium from root segments of the most active plants. N 2-ase activity of the intact soil-plant cores ranged from 76 to 380 g N ha −1 d −1 for the Aleman pasture and from 5 to 179 g N ha −1 d −1 for the Hymenachne pasture. Assays on excised roots showed the greatest activity on adventitious roots formed on the submerged nodes of Hymenachne stems. No major differences in colony morphology were detected in N 2-fixing bacteria isolated from the roots of the two grasses. An association appeared to exist between bacteria and the roots of both grasses with most of the N for the young Aleman pasture being fixed N, whereas the fixed N supply for the older Hymenachne pasture was supplemented by the mineralization of organic N.

Responses to drought and flooding in tropical forage grasses

Long dry seasons or permanent flooding, typical of tropical savannas, severely limit the growth of pasture plants. This study compares the responses of water relations, carbon assimilation and alcohol dehydrogenase (ADH) activity to drought and flooding in four perennial Ca grasses: the tufted or caespitose Hyparrhenia rufa and Andropogon gayanus (CIAT 621) and the stoloniferous Brachiaria mutica and Echinochloa polystachya. Plants of the four species were subjected to medium term flooding (20-25 days) and moderate drought in a greenhouse. Leaf water potential (W), stomatal conductance (Gs) and photosynthesis rate (Pn) were measured throughout the experiment and ADH activity was measured in flooded and control plants. Moderate drought produced similar effects in all grasses reducing Gs which caused reduced Pn. Net photosynthesis compensation point was reached at the lowest W in A. gayanus which was considered as the most drought tolerant. The responses to flooding varied across species. Andropogon gayanus and H. rufa showed early stomatal closure without concurrent decrease in W and leaf turgor. This low Gs was responsible of reduced Pn and growth rate. There was a slight increase of Gs in the middle of the flooding period and both grasses recovered pre-stress Gs and Pn after drainage. ADH activity increased markedly only in A. gayanus under flooding suggesting that this grass was the most flood-sensitive. Stomatal aperture, Pn and ADH activity in B. mutica and E. polystachya were not affected by flooding. The higher flood-tolerance in these grasses might be attributed to enhanced oxygen diffusion to the roots through the hollow stolons, development of adventitious rootlets and large aerenchyma in the roots which compensate for the reduction of soil oxygen and permit the maintenance of root activity.

Responses to drought and flooding in tropical forage grasses

Seasonal drought and flooding severely limit pasture growth in tropical savannas. The objective of this study is to analyze and compare yield, biomass allocation, leaf growth rate and nutrient concentration of four important perennial C4 forage grasses to short term flooding and moderate drought under controlled conditions. The grasses studied were the tufted Andropogon gayanus (CIAT 621) and Hyparrhenia rufa and the stoloniferous Echinochloa polystachya and Brachiaria mutica.

Leaf and canopy photosynthetic CO2 uptake of a stand of Echinochloa polystachya on the Central Amazon floodplain : Are the high potential rates associated with the C4 syndrome realized under the near-optimal conditions provided by this exceptional natural habitat?

The C4 grass Echinochloa polystachya, which forms dense and extensive monotypic stands on the Varzea floodplains of the Amazon region, provides the most productive natural higher plant communities known. The seasonal cycle of growth of this plant is closely linked to the annual rise and fall of water level over the floodplain surface. Diurnal cycles of leaf photosynthesis and transpiration were measured at monthly intervals, in parallel with measurements of leaf area index, canopy light interception and biomass. By artificial manipulation of the light flux incident on leaves in the field light-response curves of photosynthesis at the top and near to the base of the canopy were generated. Fitted light-response curves of CO2 uptake were combined with information of leaf area index, incident light and light penetration of the canopy to estimate canopy rates of photosynthesis. Throughout the period in which the floodplains were submerged photosynthetic rates of CO2 uptake (A) for the emergent leaves were high with a mean of c. 30 μmol m-2 s-1 at mid-day and occasional values of 40 μmol m-2 s-1. During the brief dry phase, when the floodplain surface is uncovered, there was a significant depression of A, with mid-day mean values of c. 17 μmol m-2 s-1. This corresponded with a c. 50% decrease in stomatal conductance, and a c. 35% depression in the ratio of the leaf inter-cellular to external CO2 concentration (c i/c a). During the dry phase, a midday depression of rates of CO2 assimilation was observed. The lowest leaf area index (F) was c. 2 in November-December, when the flood plain was dry, and again in May, when the rising floodwaters were submerging leaves faster than they were replaced. The maximum F of c. 5 was in August when the floodwaters were receding rapidly. Canopy light interception efficiency varied from 0.90 to 0.98. Calculated rates of canopy photosynthesis exceeded 18 mol C m-2 mo-1 throughout the period of flooding, with a peak of 37 mol C m-2 mo-1 in August, but declined to 13 mol C m-2 mo-1 in November during the dry phase. Estimated uptake of carbon by the canopy from the atmosphere, over 12 months, was 3.57 kg C m-2. This was insufficient to account for the 3.99 kg C m-2 of net primary production, measured simultaneously by destructive harvesting. It is postulated that this discrepancy might be accounted for by internal diffusion of CO2 from the CO2-rich waters and sediments via the roots and stems to the sites of assimilation in the leaves.

Primary Productivity of Grass Ecosystems of the Tropics and Sub-Tropics.

Aims, goals and general methods, S.P.Long and M.B.Jones the primary productivity and photosynthesis of savanna grasses in Kenya - studies at Nairobi National Park, J.I.Kinyamario and S.K.Imbamba saline grassland near Mexico City, E.Garcie-Moya and P.Montanez Castro moist savannas of Thailand, A.Kamnalrut and J.Evenson the productivity of echinochloa polystachya, a semiaquatic grass in the Amazonian floodplain, M.T.F.Piedade et al the productivity and photosynthesis of bamboo with reference to phyllostachya pubescens forest in subtropical China, C-X.Qiu et al remote sensing of primary producation in natural tropical grasslands and articifial mixed-species canopies, J.M.O.Scurlock synthesis and conclusions, M.B.Jones and S.P.Long UNEP epilogue, R.J.Olembo.

The Productivity of the C_4 Grass Echinochloa Polystachya on the Amazon Floodplain

Plants utilizing the C4 photosynthetic pathway show higher potential efficiencies in the use of intercepted radiation, water, and nitrogen for the production of dry matter than do other photosynthetic types. C4 species are most numerous in tropical and warm, temperature semi—arid zones, where their greater water—use efficiency appears to be a key selective advantage. This fails to explain the dominance of a few C4 grasses in floodplain communities of the wet tropics. One such species, Echinochloa polystachya, occurs along the fertile white waters of the Amazon region. In this habitat, where neither water nor nitrogen supply are likely to be limiting to production or survival, a C4 species may realize its high productivity potential. This possibility was examined by monthly measurements of stand demography, biomass, and radiation interception at a site in the central Amazon. The maximum standing crop of 80 Mg/ha and annual net primary production of 99 Mg/ha of dry matter are among the highest values recorded for natural vegetation. The mean rate of dry—matter production per unit of solar radiation intercepted by the stand was 2.3g/MJ, an efficiency close to the considered maximum for C4 species. The significance of this high productivity to the carbon budget of the region is discussed. Despite the investment of most of its high productivity into stem material, growth of E. polystachya was only just sufficient to keep pace with the 8 m rise in water level that occurs as part of the annual cycle in river discharge. In this unusual environment, the high productivity potential conferred by C4 photosynthesis may be essential, in allowing this rooted macrophyte to produce a stem which is of sufficient rigidity and length to hold the canopy above the rising flood waters.

Productivity of Clay Tailings from Phosphate Mining: I. Biomass Crops

AbstractPhosphate mining in Florida yields waste products of phosphatic clay and quartz sand tailings, each making up about one‐third of the original matrix (PO4 ore, sand, and clay). Phosphatic clay ponds typically occupy about 50% of the mined sites and normally require 10 to 15 yr before 40 to 50% solids are obtained. These clays contain no phytotoxic materials and are high in most plant nutrients. When surface water has disappeared, these clays are classified as clayey Haplaquents. A split‐plot field experiment was conducted to study biomass yield, quality, plant nutrient concentrations, changes in soil nutrients, and 226Ra. Seven biomass crops—(i) elephantgrass (Pennisetum purpureum L. ‘PI 300086’), (ii) leucaena [Leucaena leucocephala (Lam.) De Wet], (iii) alemangrass [Echinochloa polystachya (H.B.K) Hitche], (iv) erianthus [Erianthus arundinaceum (Retz) Jesw ‘IK 76‐63’], (v) desmodium (Desmodium cinerascens A. Gray), (vi) sweet sorghum [Sorghum bicolor (L.) Moench ‘USDA M 8IE’], and (vii) forage sorghum] Sorghum bicolor (L.) Moench ‘Pioneer 931’]—were grown on the phosphatic clay with and without a 5‐cm surface layer of quartz sand tailings. Nitrogen was the only fertilizer element applied for grass species and no fertilizer was applied for legumes during the 4‐yr period. Dry biomass yield averaged over 4 yr for erianthus, leucaena, and elephantgrass averaged 139.6, 58.5, and 56.5 Mg ha−1 yr−1, respectively. Crude protein and digestibility were low in mature, whole‐plant samples except for leucaena (122.0 g kg−1). Generally, all whole plants contained adequate concentrations of nutrients averaging (g kg−1) P, 2.05; K, 11.5; Ca, 4.3; Mg, 2.77 and (mg kg−1) Cu, 4.0; Zn, 26; Fe, 68; and Mn, 35. Mehlich‐I‐extractable soil nutrient concentrations changed little over the 4‐yr period. Radium‐226 concentration in plant tissue (0.23 pCi g−1) was nearly six times higher than the concentration measured in plants from an unmined surface Spodosol (0.04 pCi g−1). Data indicate that these present‐day waste lands can be a valuable resource for biomass production.

The Ecological Distribution of some South American Grass and Sugar-cane Borers (Diatraea spp., Lep., Pyralidae)

1. The survey of Diatraea spp. in their primitive habitats has been extended to cover the interior Guiana plateau, the Rio Branco, the lower Rio Negro and the lower Amazon.2. The greatest practical result has been the discovery and introduction into British Guiana of the Amazon fly parasite (Metagonistylum minense) of D. saccharalis.3. The most interesting ecological result was the finding of several Diatraea spp. as original members of a true savannah association.4. The twelve species considered are grouped as forest, riparian, savannah and domestic species.5. The two forest species are D. bellifactella and D. brunnescens.6. Riparian grass associations are developed over huge areas on the lower Amazon, where they may be divided roughly into three main zones, dominated by Paspalum repens, Echinochloa polystachya and Paspalum fasciculatum, respectively.7. The chief, and in fact only Diatraea of the first and second zones, is D. saccharalis, which is occasionally abundant.8. The P. fasciculatum zone is colonised by D. amazonica and D. myersi.9. The pure savannah species are D. canella, D. impersonatella, D. savannarum and D. cayennella.10. D. lineolata is practically confined to maize, and no wild host-plants, either naturalised or indigenous, are known.11. Five species attack cane, namely, saccharalis, busckella, impersonatella, canella and albicrinella, and all except the latter are major pests over considerable areas.