BATHYMETRIC STUDIES ON THE PONGOLO RIVER FLOODPLAIN

SUMMARY

Thirteen of the major pans on the Pongolo river floodplain have been studied. Most are shallow (>2.5 m) and regularly lose up to 70% of their water each year, although few dry out. Floods inundate considerable areas (1000 ha) around pans situated in the flatter parts of the floodplain. Whilst inundated, these areas provide an allochthonous energy and nutrient source for the pan and, as the water levels recede, the exposed Cynodon dactylon (L.) Pers lawns provide grazing for cattle. The suitability of the various pans for fish production is discussed.     

Nitrogen, Phosphorus, and Potassium Nutrition of the Edaphic Ecotypes in Cynodon dactylon (L.) Pers.

A differential response to nitrogen, phosphorus, and potassiumwas observed for the three edaphic ecotypes in Cynodon dactylon(L.) Pers. naturally occurring at Malla, Shiwalik, and Chandigarh.The soils of these sites differ markedly with respect to availablenutrients. The better growth of the Malla population comparedto the Chandigarh population in low potassium and low nitrogenmedia could be related to the low availability of these nutrientsin the calcareous Malla soil. The Shiwalik population tendedto show an intermediate behaviour. Whilst the Malla populationwas susceptible to ‘phosphate toxicity’, the growthyield of the Shiwalik and the Chandigarh populations improvedwith increase in phosphorus in the medium. The three populationsalso differed from each other with respect to the uptake ofvarious nutrients. These results could be correlated with thenatural habitat conditions in which the three ecotypes occur.It was concluded that besides calcium which was shown to bepartly responsible for the restriction of the three ecotypesto their respective habitats, the availability of nitrogen,potassium, and also phosphorus may play an important role.     

Amino Acid and protein metabolism in bermuda grass during water stress

The ability of Arizona Common and Coastal Bermuda grass [Cynodon dactylon (L.) Pers.] to synthesize amino acids and proteins during water stress was investigated. Amino acids were continually synthesized during the water stress treatments, but protein synthesis was inhibited and protein levels decreased.     

Pyruvate Kinase Activity in Crude Extracts of Leaves of Cynodon dactylonand Other C4Plants

A new extraction procedure and an LDH-coupled assay method are presented for the study of pyruvate kinase (PK) in leaf crude extracts from Cynodon dactylon(L.) Pers and other C₄plants. Extraction at pH 6.8 and assay at pH 6.2 facilitated the measuring of PK activity by eliminating phosphoenolpyruvate carboxylase interference more effectively than the thermal inactivation or chemical inhibition previously used. The method suggested did not affect the kinetic properties of PK as compared to the purified enzyme from C. dactylon.     

不同护坡草本植物的根系特征及对土壤渗透性的影响

为明确三峡库区植被边坡植物物种根系特征与土壤渗透性之间的关系,以裸地为对照,应用WinRHIZO(Pro.2004c)根系分析系统对香根草(Vetiveria zizanioides(Lin.) Nash)、百喜草(Paspalum notatum Flugge)、狗牙根(Cynodon dactylon (L) Pers.)和紫花苜蓿(Medicago sativa L.)等4种护坡草本的根系特征进行定量分析.结果表明:(1)紫花苜蓿和香根草的根长密度和根表面积密度显著大于狗牙根和百喜草;(2)不同草本类型和同一草本不同土层之间土壤渗透性存在较大差异,且各草本土壤渗透性随土层深度的增加而降低;相对于裸地而言,4种草本均能显著增强土壤渗透性,其土壤渗透性优劣表现为:香根草＞紫花苜蓿＞百喜草＞狗牙根;(3)土壤的初始入渗率、稳渗率、平均渗透率和渗透总量等各参数均随根长密度和根表面积密度增大而增强,且与直径介于0.5-5 mm不同径级的根系特征之间存在明显的相关性,故根系对土壤渗透性的增强作用主要归功于0.5-5 mm径级的根长密度和根表面积密度;(4)根长密度、根表面积密度对考斯加科夫入渗模型参数K和a有较大影响,随着根长密度和根表面积密度的增加,表征土壤初始入渗率的K值逐渐增大,而表征入渗能力衰减的参数a逐渐减小.     

Interactions between period of exposure,grazing and crop growth rate of Cynodon dactylon (L.) Pers. in seasonally flooded areas of the Pongolo River floodplain

Cynodon dactylon (L.) Pers. forms extensive meadows on seasonally inundated areas of the Pongolo river floodplain. As floodwaters receded during winter, the shoots of C. dactylon which had not decomposed during submergence sprouted. Crop growth rate was high (up to 23 kg/ha/d dry mass) and the meadows were heavily grazed by domestic stock which removed up to 15 kg/ha/d. The high crop growth rate was not maintained because as exposure period increased, soils became dry and water stress conditions developed. This caused the C. dactylon to become less palatable and brought about a shift in grazing which allowed a build-up of the grazeable and ungrazeable fraction standing crop. Maximum standing crop occurred at the onset of the next flood. Grazing is shown to have a net negative effect on production, although at different times during exposure defoliation had either a depressing or stimulating effect on growth. It is postulated that the duration of the inundation period is more significant than the duration of the exposure period in maintaining the C. dactylon meadows.     

Disomic Inheritance and Segregation Distortion of SSR Markers in Two Populations of Cynodon dactylon (L.) Pers. var. dactylon

Common bermudagrass [C. dactylon (L.) Pers. var. dactylon] is economically and environmentally the most important member among Cynodon species because of its extensive use for turf, forage and soil erosion control in the world. However, information regarding the inheritance within the taxon is limited. Accordingly, the objective of this study was to determine qualitative inheritance mode in common bermudagrass. Two tetraploid (2n = 4x = 36), first-generation selfed (S1) populations, 228 progenies of ‘Zebra’ and 273 from A12359, were analyzed for segregation with 21 and 12 simple sequence repeat (SSR) markers, respectively. It is concluded that the inheritance mode of tetraploid bermudagrass was complete or near complete disomic. It is evident that the two bermudagrass parents had an allotetraploid genome with two distinct subgenomes since 33 SSR primer pairs amplified 34 loci, each having two alleles. Severe transmission ratio distortions occurred in the Zebra population while less so in the A12359 population. The findings of disomic inheritance and segregation ratio distortion in common bermudagrass is significant in subsequent linkage map construction, quantitative trait locus mapping and marker-assisted selection in the species.     

Effects of rapidly imposed water deficit on photosynthetic parameters of three C<Subscript>4</Subscript> grasses

Water deficit, when rapidly imposed on three C₄ grasses of the different metabolic subtypes, Paspalum dilatatum Poiret (NADP-malic enzyme), Cynodon dactylon (L.) Pers (NAD-malic enzyme) and Zoysia japonica Steudel (phosphoenolpyruvate carboxykinase), caused decreases in photosynthetic rates, in the quantum yield of PS II and photochemical quenching, and in the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC). The results provide evidence for non-stomatal limitations of photosynthesis differing in nature between the three species.     

Physiological and biochemical adaptations of Cynodon dactylon (L.) Pers. from the Salt Range (Pakistan) to salinity stress

Naturally adapted salt tolerant populations provide a valuable material for exploring the adaptive components of salt tolerance. Under this aspect, two populations of Cynodon dactylon (L.) Pers. were subjected to salt stress in hydroponics. One was collected from a heavily salt-affected soil in the vicinity of a natural salt lake, Uchhali Lake, in the Salt Range of the Punjab province of Pakistan, and the other from a normal non-saline habitat from the Faisalabad region. The NaCl treatments in Hoagland's nutrient solution were: Control (no salt), 50, 100, 150 and 200 mM of NaCl. After 8 weeks of growth in hydroponics produced biomass, ion relations, and photosynthetic capacity were measured in the differently adapted ecotypes. In the ecotype of C. dactylon from the Salt Range, shoot dry weight was only slightly affected by varying levels of salt. However, in contrast, its root weight was markedly increased. On the other hand, the ecotype from Faisalabad (non-saline habitat) showed a marked decrease in shoot and root dry weights under saline regimes. The ecotype from the Salt Range accumulated relatively less amount of Na⁺ in the shoot than did that from Faisalabad, particularly at higher salt levels. Shoot or root K⁺ and Ca²⁺ contents varied inconsistently in both ecotypes under salt stress. All the photosynthetic parameters, leaf water potential and osmotic potential, and chlorophyll content in both ecotypes were adversely affected by salt stress, but all these physiological attributes except turgor potential and soluble sugars were less affected at high salinities in the salt tolerant ecotype from Salt Range. This ecotype accumulated significantly higher organic osmotica (total free amino acids, proline, total soluble proteins, and total soluble sugars) under saline conditions than its intolerant counterpart. Overall, the salt tolerant ecotype of C. dactylon from the Salt Range showed high salt tolerance due to its restricted uptake of Na⁺ accompanied by an increased uptake of K⁺ and Ca²⁺ in the roots as well as shoot due to its higher photosynthetic capacity and accumulation of organic osmotica such as free amino acids and proline under saline conditions.     

Competition between a Lawn-Forming Cynodon dactylon and a Tufted Grass Species Hyparrhenia hirta on a South-African Dystrophic Savanna

South African savanna grasslands are often characterised by indigestible tufted grass species whereas lawn grasses are far more desirable in terms of herbivore sustenance. We aimed to investigate the role of nutrients and/or the disturbance (grazing, trampling) by herbivores on the formation of grazing lawns. We conducted a series of common garden experiments to test the effect of nutrients on interspecific competition between a typical lawn-forming grass species (Cynodon dactylon) and a species that is frequently found outside grazing lawns (Hyparrhenia hirta), and tested for the effect of herbivore disturbance in the form of trampling and clipping. We also performed a vegetation and herbivore survey to apply experimentally derived insights to field observations. Our results showed that interspecific competition was not affected by soil nutrient concentrations. C. dactylon did show much more resilience to disturbance than H. hirta, presumably due to the regenerative capacity of its rhizomes. Results from the field survey were in line with these findings, describing a correlation between herbivore pressure and C. dactylon abundance. We conclude that herbivore disturbance, and not soil nutrients, provide C. dactylon with a competitive advantage over H. hirta, due to vegetative regeneration from its rhizomes. This provides evidence for the importance of concentrated, high herbivore densities for the creation and maintenance of grazing lawns.     

Root water potential in polycormon plants

Water potential of roots was measured by thermocouple psyohometers in a series of two or more plants ofCynodon dactylon (L.)Pers. interconnected by overground stolons and thus forming one s.c. polycormon. Root water potential was lowest (most negative) in the oldest “mother” plant and increased in younger individua to highest walues in the youngest “doughter” plants. This gradient of root water potential was found although the “mother” plants continued to be watered while watering all daughter plants had been stopped one week before the water potential was measured. Thus the whole polycormon consisting of a series of interconnected individua behaves as one hydrodynamic system where all individual root systems act as if being parts of one sole root system.     

Geographic patterns of genetic diversity in Poulsenia armata (Moraceae): implications for the theory of Pleistocene refugia and the importance of riparian forest

Abstract. Tropical forests are species-diverse communities, but we know very little about the geographical distribution of genetic diversity within a species. During the late Pleistocene, lower temperatures and rainfall reduced the distribution of tropical wet forests, and in Central America lowland species may have been limited to riparian habitats. Approximately 12,000 years bp , temperature and rainfall increased in Central America, the distribution of wet forest species expanded, and today the distribution of some species extends into southern Mexico. The distribution of genetic diversity, based on RAPD markers, among ten populations of Poulsenia armata (Miq.) Standl. (Moraceae) suggests that these populations did not originate from a single refugium or region in the late Pleistocene. The Central American populations had high genetic diversity and unique bands giving support to the hypothesis that populations of P. armata occurred in Central American during the late Pleistocene. The majority of genetic diversity was partitioned among populations and there was no geographical relationship among populations, suggesting that these populations were isolated for a long period and there has been little gene flow. Populations of P. armata may have persisted in riparian zones along the Caribbean coast during the late Pleistocene. Given that riparian forest can support high levels of biodiversity in ecological time, and they have played an important role during periods of climate change over geological time, their conservation is of utmost importance particularly with the threat of a rapid shift in climatic patterns.     

河滨湿地不同植物群落根系分布特征与土壤理化性状的关系——以黄河中游荥阳段为例

在黄河中游郑州荥阳段,选择了5种河滨湿地植物群落进行根系和土壤性状特征研究,以期阐明不同植物群落的根系分布规律与土壤性状的关系,为河滨湿地植物群落组成以及土壤质量恢复提供科学参考。结果表明(1)在0—40 cm土层,根生物量密度与根长密度的平均值均表现为：芦苇群落(Phragmites australis)和芦苇-狗牙根(Cynodon dactylon)群落均大于芦苇-拂子茅(Calamagrostis epigeios)-狗牙根群落、拂子茅-狗牙根群落、拂子茅-狗牙根-水莎草(Juncellus serotinus)群落。拂子茅-狗牙根、芦苇-拂子茅-狗牙根、拂子茅-水莎草-狗牙根三种植物群落类型下根生物量密度、根长密度在0—20 cm表层土壤较大,芦苇群落和芦苇-狗牙根群落的根生物量密度、根长密度在10—40 cm的土层较大。(2)黄河河滨湿地芦苇群落、芦苇-狗牙根群落的土壤以粉粒为主,拂子茅-狗牙根群落、芦苇-拂子茅-狗牙根群落、拂子茅-狗牙根-水莎草群落的土壤主要以砂粒为主。在0—40 cm土层,芦苇群落、芦苇-狗牙根群落的土壤含水率、土壤有机质、有效氮和有效磷含量均显著高于...     

Role of Ethylene in the Geotropic Response of Bermudagrass (Cynodon dactylon L. Pers.) Stolons

We studied the relationship between ethylene and gravity-induced upward bending of bermudagrass (Cynodon dactylon L. Pers.) stolons. Ethylene production begins within 3 hours of the onset of gravistimulation, and increases thereafter until the 15th hour, after which it declines. There is a close positive relationship between ethylene production and upward bending during the first 12 hours of gravistimulation. Incubation of stolons with AgNO₃ did not prevent ethylene evolution but delayed upward bending. In addition, ethylene production was 10-fold greater and peaked earlier in gravistimulated nodes incubated with 1-aminocyclopropane 1-carboxylic acid. The gravitational stimulation could be due to an increase in both 1-aminocyclopropane 1-carboxylic acid synthase and the ethylene forming enzyme. The results suggest that ethylene promotes the activity of indoleacetic acid.     

ULTRASTRUCTURAL CHANGES OF PLANTS EXPOSED TO LOW TEMPERATURES

Effects of low temperatures on cell ultrastructures of three grass species were studied. Secale cereale L., Cynodon dactylon (L.) Pers., and Paspalum notatum Flugge seedlings were given treatments of −5, 0, 10, or 25 C for 3 days and then evaluated for cellular response. Electron micrographs showed chloroplasts to be the most sensitive organelle in all three species, with the temperate Secale plastids responding differently than plastids from the subtropical and tropical species. Rough endoplasmic reticulum increased, but dictyosome numbers decreased in all species as treatment temperatures were lowered to 0 C. Mitochondria expanded slightly at reduced temperatures, but with little difference detected between species. The study indicated that the various cellular components of these species responded differently to reduced temperatures, with the species differing mainly in degree of response.     

Sulfate Ion Effect on Stability and Regulatory Properties of PEP Carboxylase from the C4Plant Cynodon dactylon

When Tris–SO₄was used as an extraction buffer for phosphoenolpyruvate carboxylase (PEPC) from leaves of the C₄plant Cynodon dactylon(L.) Pers., a higher extractable activity was obtained as compared to Tris–HCl, especially at low phosphoenolpyruvate concentrations and an assay pH of 7.2. The Tris–SO₄-extracted PEPC activity was stable under dilution and remained unchanged for at least 24 h at 22°C. This enzyme was less sensitive to both activation by glucose-6-phosphate and inhibition by L-malate. The effects of Tris–SO₄could be attributed to its preferential exclusion from the enzymic protein domain and, therefore, to a shifting of this oligomeric enzyme to a more aggregable form that is more stable and active.     

Amylolytic Activity in Taproots of Diploid and Tetraploid Medicago sativa L.

Our objective was to determine whether starch degradation intaproots of alfalfa (Medicago sativa L.) after defoliation wasassociated with activity and isoform complement of endo- andexo-amylases. Taproots of genetically comparable diploid (2x)and tetraploid (4x) populations and the tetraploid cultivarHi-Phy were recovered immediately after defoliation and at approx.4-d intervals thereafter. Taproot tissues were analysed forstarch concentrations and activities of endo- and exo-amylases.An electrophoretic blotting technique was used to examine amylaseisoforms. Starch degradation was most rapid in taproots of Hi-Phy,slowest in taproots of the 2x population, with the 4x populationbeing intermediate. The 4x population had a greater initialincrease in endo-amylase activity compared to the 2x population;however, Hi-Phy averaged eightfold greater endo-amylase activitythan either 2x or 4x populations. Although exo-amylase specificactivity was at least 500-fold greater than endo-amylase specificactivity in all populations, changes in endo-amylase activitywere more closely associated with trends in starch degradation.Multiple isoforms of endo- and exo-amylase were observed intaproots of all populations. Taproots of Hi-Phy contained anendo-amylase isoform that was not apparent in the 2x or 4x populationsthat may contribute to the high activity of this amylase intaproots of this cultivar. These results, although correlative,suggest an important role for endo-amylase in taproot starchhydrolysis after defoliation. Medicago sativa (L.), alfalfa, taproots, herbage, diploid, tetraploid, starch, endo-amylase, exo-amylase, isoforms, electrophoresis     

Drought stress increases the production of 5-hydroxynorvaline in two C4 grasses

Plants produce various compounds in response to water deficit. Here, the presence and identification of a drought-inducible non-protein amino acid in the leaves of two C₄ grasses is first reported. The soluble amino acids extracted from the leaves of three different species were measured by high-performance liquid chromatography of derivatives formed with o-phthaldialdehyde and β-mercaptoethanol. One amino acid that increased in amount with drought stress had a retention time not corresponding to any common amino acid. Its identity was determined by metabolite profiling, using ¹H NMR and GC-MS. This unusual amino acid was present in the dehydrated leaves of Cynodon dactylon (L.) Pers. and Zoysia japonica Steudel, but was absent from Paspalum dilatatum Poir. Its identity as 2-amino-5-hydroxypentanoic acid (5-hydroxynorvaline, 5-HNV) was confirmed by synthesis and co-chromatography of synthetic and naturally occurring compounds. The amount of 5-HNV in leaves of the more drought tolerant C₄ grasses, C. dactylon and Z. japonica, increased with increasing water deficit; therefore, any benefits from this unusual non-protein amino acid for drought resistance should be further explored.     

A Model for the Growth of Individuals in Plant Populations Cultivated at Different Concentrations of Fertilizer Solution

The growth of mean individual weight is the joint outcome ofthe growth of the individuals comprising a population. Fromthe growth data of individual weight in radish (Raphanus sativusL. var. radiculus Pers.) populations cultivated at differentconcentrations of ammonium sulphate solution, a deterministicmodel was proposed for integrating individual plant weight intomean weight per plant in a population. The model constructiondepended on the relation between mean individual weight andthe amount of fertilizer supplied to a population, and uponPearson's type VII distribution. The model related the weightof any individual to the amount of fertilizer. The fitness ofthe model to observed data was satisfactory, although the modelwas simple. Using the model, properties of the growth of componentindividuals of a population were examined in relation to thegrowth of mean individual weight. fertilizer, growth, individual, mean, Pearson's type VII distribution, plant weight, population, radish, Raphanus sativus L. var. radicula Pers     

Biotic Potential of a Short-Horned Grasshopper, <Emphasis Type="Italic">Oxya hyla hyla</Emphasis> Serville (Orthoptera: Acrididae) to Assess Its Biomass Producing Capacity

The growth of fishery and animal husbandry is being hindered by the scarcity of protein rich feed ingredients. Being rich in protein grasshoppers may be an alternative source of protein rich feed ingredients and hence rearing of these insects is essential for sustainable supply of insect biomass to the feed industry. The success of biomass production through insect rearing depends on the reproductive potentiality, rate of survival and growth of that particular insect. This study examines the biotic potential, fecundity, fertility, nymph mortality, life span and biomass production ability of a multivoltine grasshopper, Oxya hyla hyla (Serville, 1931) under semi-controlled condition. The grasshoppers are reared in 35 ± 2 °C temperature and 12L: 12D photoperiod and provided with food as fresh leaves of Cynodon dactylon (L.) Pers. to nymphs and Sorghum halepense (L.) Pers. to the adults. The result shows that a single pair of O. hyla hyla can lay on average 69.87 eggs in 4.96 ± 0.43 egg pods of which 7.37 ± 0.92 % eggs and 8.26 ± 0.99 % nymphs do not survive. The remaining survived nymphs metamorphose to 27.8 ± 3.35 male and 32.6 ± 3.21 female adults which produce a biomass of 18.48 ± 1.67 g wet weight. Thus a mass scale rearing of this insect may produce good amount of insect biomass which may be usable for fish and animal feed.