Scirpus Species Research Articles

Morphological and reproductive responses of coastal pioneer sedge vegetation to inundation intensity

Coastal plants have unique adaptability to cope with strong hydrological stresses in tidal wetlands. A fundamental understanding of the establishment and maintenance of coastal plants is needed for conservation and restoration. In the Yangtze Estuary, the plasticity of the morphological and reproductive traits of a pioneer Scirpus species (sedge), in terms of phenotypic growth, biomass allocation, and sexual and asexual reproductive traits, was investigated with increasing flooding intensity (elevation gradient) in a tidal flat. The varying response extents (thresholds) of plant zonation and morphological and reproductive traits to multiscale environmental heterogeneity were also assessed. Our results showed that plant colonization and performance at coastal frontiers are sensitive to the microtopography of elevation and reflect the ecological adaptability at both the landscape and individual scales. Sedge species typically exhibit morphological and reproductive flexibility across the inundation intensity. The plants allocated more biomass to belowground tissues in response to decreasing elevation. The elevation thresholds for the yield of reproductive organs were higher (2.38–2.50 m based on the local Wusong datum) than those for morphology (2.05–2.14 m). The thresholds for the yield of asexual reproductive organs shifted to a lower elevation by approximately 0.15 m relative to that of the sexual reproductive organs. The increasing corm: spike ratios of plants with longer inundation durations also indicated this reproductive plasticity. This study revealed that the combination of morphological and reproductive responses of pioneer sedges contributed to survival and colonization at the foremost coastal flat. Our results are useful for developing restoration strategies for the native Scirpus species on China's coast.

The importance of the propagule-sediment-tide "power balance" for revegetation at the coastal frontier.

Revegetation of pioneer plants is a critical phase in community establishment for mudflats in seriously degraded coastal wetlands. We tested a hypothesis of the importance of a "power balance" among propagule resilience and sedimentary and tidal disturbances for vegetation reestablishment. Our experiment used three types of propagules (seeds, seedlings, and corms) of native Scirpus species in the fringing flats with similar tidal flows and varying sedimentary intensities in the Yangtze Estuary. Regardless of the initial planting densities, the seed germination rate was extremely low in the field situation. Although the incubated seedlings were planted directly on the bare flat, the wave movement easily flushed the seedlings, even at the site with moderate sedimentary accretion. Failure of the revegetation practice using the seed and seedling materials indicated that the combined "growing and anchoring power" of young seedlings and "stabilizing power" of the sediment were insufficient to withstand the "dislodging power" of the tidal energy. In contrast, the planting approach with underground propagules (corms) proved to be feasible for vegetation establishment at the sites with moderate and low-level sedimentary intensities. The successful practice improved the tipping point of plant survival and tussock formation could be surpassed when the combined growing and anchoring power of seedlings that developed from corms with the stabilizing power of the sediment was greater than the dislodging power of the wave energy. However, at the site with high-level sedimentary intensity, the excessive sediment converted to the burying stress power as seedlings developed from the corms, revealing a burial threshold for seedling survival. The risk of seedling establishment was high when the burying stress power of the sediment far outweighed the combination of the growing power of the seedlings and the sediment removal power of the tidal current and surpassed the tipping point of vegetation die-off. Additionally, we checked the practice cost of the different approaches to ensure a highly cost-effective revegetation planning based on site suitability. This study highlights that understanding of the propagule-sediment-tide power balance offers a tool for improvement of the revegetation and management of site-specific sedimentary and hydrological environments for many degraded coastal ecosystems.

Do short-term increases in river and sediment discharge determine the dynamics of coastal mudflat and vegetation in the Yangtze Estuary?

Sediment loads by large rivers play a crucial role in determining the fate of estuarine and coastal ecosystems. From 2013 to 2017, this study investigated the dynamics of mudflats and marsh pioneering vegetation (Scirpus species) in the coastal wetland at downstream end of the Yangtze Estuary. The results showed that, even with the historically lowest scale of upstream sediment load, the mudflat accretion (increase in elevation) and vegetation expansion in the marsh frontier still occurred. In the different monitoring sites, the net increases in the mudflat elevation were 24.34–57.51 cm, and the area of the pioneering vegetation increased by 2.18–4.74 times over 5 years. During the 2016–2017 period, with higher water discharges, the rates of mudflat accretion and vegetation colonization were much higher than those in former years. It was declared that a single-year high water discharge could trigger an intensive increase in sediment transport to the coastal region. Relative to water discharge, the year-to-year sediment load recorded upstream (Datong hydrographical gauging station) might not be a suitable indicator to interpret the mudflat and vegetation dynamics in the Yangtze Delta due to the high uncertainty of sediment loading processes along the transportation path. The recent monitoring indicated that positive interaction between vegetation establishment and sedimentary processes probably contribute to a continuous mudflat accretion and vegetation expansion in the mudflat frontier. We also suggest that a short-term substantial impulse in river and sediment discharge highly stimulated the accretion of coastal mudflat and the consequent expansion of marsh vegetation in the Yangtze Estuary.

Phytoremediation-A Miracle Technique for Waste Water Treatment

Waste water treatment is a vital component in any community, without which water borne disease pathogens can spread resulting in diseases. Moreover, water cannot be recycled to fulfil the requirement of growing population. Thus, this treatment is necessary to protect the human beings as well as aquatic living organisms from harmful diseases such as cholera, typhoid, etc. Different techniques have been applied for waste water treatment mainly activated sludge, induced gas flotation, ultraviolet disinfection and supercritical water oxidation (SCWO). These techniques are cumbersome, time consuming and expensive. Thus, phytoremediation can be potent alternative of these techniques. Phytotremediation is a solar energy assisted clean up technique. Moreover, this technique has more ecologically advantageous as compared to other techniques. The present paper describes the morphology, mechanism, phytochemistry of certain plants that are mainly used for waste water treatment such as Scirpus species, Vetiver zizanioides, Eleocharis ochrostachys, Typha species, Pistia stratiotes, Lemma gibba, Phragmites communis, Hydrilla verticullata, Gracillaria gracilis, Ipomoea aquatic and Azolla pinnata. These plants readily facilitate absorption of nutrients that are in excess in addition to toxic elements such as lead, iron, copper, cadmium and mercury. The objective of the review is to sum up the literature of existing plants which was not used earlier for phytoremediation of waste water and to provide a baseline for new research alongside their usage in environmental clean up especially near pharmaceutical industries.

Rhodoscirpus (Cyperaceae: Scirpeae), a new South American sedge genus supported by molecular, morphological, anatomical and embryological data

AbstractIn its broadest sense, Scirpus consists of a heterogeneous assemblage of up to 250 species, but modern circumscriptions suggest that only 40–50 species are part of the genus. Despite a narrower definition of the genus, atypical species continue to be segregated from Scirpus with a common pattern being the removal of Southern Hemisphere taxa to other genera and tribes. In South America, the morphology of remaining Scirpus species also suggests that they are not closely related to Scirpus s.str., but most of these taxa are only known from their types, making a detailed analysis of their generic affinities difficult. One notable exception is Scirpus asper, a species that is relatively common in the mountains and adjacent lowlands of Peru south to Argentina. Although this species possesses features used in the circumscription of Scirpus, such as cauline leaves, flat leaf blades and anthelate inflorescences, it is known to differ from Scirpus s.str. by its Schoenus‐type embryo, and most of its presumed allies are now placed in different genera (e.g., Scirpus analecti ≡ Cypringlea analecta; Scirpus giganteus ≡ Androtrichum giganteum). In this study, we use DNA sequence data from the plastid (matK, ndhF) and nuclear (ETS‐1f) genomes to demonstrate that Scirpus asper is not closely related to Scirpus s.str., but sister to Phylloscirpus within the predominantly South American Zameioscirpus clade (Amphiscirpus, Phylloscirpus, Zameioscirpus). When combined with morphological, anatomical and embryological data, results indicate that S. asper is best treated as the sole species of a new monotypic genus, Rhodoscirpus. The implications of these results on the taxonomy of tribe Scirpeae are discussed.

Seminavis recta comb. nov. et stat. nov.: morphology and distribution in salt marshes from southern Brazil.

Cymbella (Encyonema) grossestriata var. recta was studied based on analysis of the type material from Argentina and newly collected material from southern Brazil. In light microscopy the taxon presents dorsiventral valves, asymmetric and expanded central area, striae slightly radiate at the ends, becoming strongly radiate, and sigmoid in the center of valve. In scanning electron microscopy it is possible to observe features that are similar to the Navicula genus, such as slit-like areolae, accessory rib in the primary side, which is wider (expanded) at the center and valves with a marked virgae. Beyond these features the presence of two chloroplasts per cell definitively excludes the taxon from the Cymbellales group and allows us to transfer it to the genus Seminavis. Seminavis recta comb. et stat. nov. was found associated to Spartina and Scirpus species and living in the sediment of salt marshes in oligo to mesohaline zones, in a wide range of temperature and pH. This species is rare, and has been reported only to South America until now.

Interspecific hybridization between Scirpus mariqueter Ts. Tang & F.T. Wang and S. planiculmis F. Schmidt and their selfing

Self-pollination and bidirectional interspecific crosses were carried out in Scirpus mariqueter Ts. Tang & F.T. Wang and S. planiculmis F. Schmidt. Self-pollination experiments suggest that S. mariqueter is a completely self-compatible species despite that its flowers are protogynous, whereas S. planiculmis is a predominantly outcrossing species, possessing a low level of self-compatibility. For the interspecific crossing experiments, hybrid seeds were obtained from bidirectional pollination. However, only 4% of the hybrid seeds from the cross of S. mariqueter ♀×S. planiculmis ♂ germinated successfully, with hybrid offsprings exhibiting similar morphological characters to the maternal parent S. mariqueter, while hybrid seeds from the cross of S. planiculmis ♀×S. mariqueter ♂ were unviable. These results suggest asymmetrical gene flow from S. planiculmis to S. mariqueter and the existence of some post-pollination reproductive barriers between these two Scirpus species.

Taxonomic Study of Korean Scirpus L. s.l. (Cyperaceae) II: Pattern of Phenotypic Evolution Inferred from Molecular Phylogeny

Scirpus L. s.l. is well known as one of the polyphyletic groups in Cyperaceae. Recent molecular phylogenetic studies clearly suggested that Scirpus s.l. should be separated into several independent genera. In this study, we intend to present the morphological variations and patterns of phenotypic evolution based on molecular phylogeny of Korean Scirpus s.l. Five genera, including 21 taxa from Korean Scirpus s.l., were examined: three species of Bolboschoenus, three species of Schoenoplectus, eight species of Schoenoplectiella including one hybrid, five species of Scirpus, and two species of Trichophorum. For morphological analyses, 23 and 48 characters were selected from vegetative and reproductive organs, respectively. Molecular phylogeny was inferred from a nuclear ribosomal internal transcribed spacer, the chloroplast rbcL gene, and the chloroplast trnL-F region. Distinct characteristics and quantitative variation was presented for identification of the five genera and their species. A pronounced pattern of morphological character change was reduction, although many other character states seem to be homoplastic. We suggest that the reduction of phenotypic characteristics has been expressed in terms of condensation of internodes, reduction of leaf blade, and simplification of inflorescence among five genera of Korean Scirpus s.l.

Internal dispersal of seeds by waterfowl: effect of seed size on gut passage time and germination patterns

Long distance dispersal may have important consequences for gene flow and community structure. The dispersal of many plants depends on transport by vertebrate seed dispersers. The shapes of seed shadows produced by vertebrates depend both on movement patterns of the dispersers and on the dynamics and effects of passage through the disperser's gut (i.e. the retention time, survival and germination of ingested seeds). A combination of experiments with captive waterbirds and aquatic plant seeds was used to analyse the following: (a) the effects of inter- and intra-specific variation in seed size and duck species on seed retention time in the gut and (b) the relationship between retention time and the percent germination and germination rates of seeds. Among the three Scirpus species used, those with smaller seeds showed higher survival after ingestion by birds and longer retention times inside their guts than those with larger seeds. For Potamogeton pectinatus, only seeds from the smaller size class (<8 mg) survived ingestion. Retention time affected the percent germination and germination rate of Scirpus seeds but in a manner that varied for the different plant and bird species studied. We recorded both linear and non-linear effects of retention time on percent germination. In addition, germination rate was positively correlated with retention time in Scirpus litoralis but negatively correlated in Scirpus lacustris. Small seed size can favour dispersal over larger distances. However, the effects of retention time on percent germination can modify the seed shadows produced by birds due to higher percent germination of seeds retained for short or intermediate periods. The changes in dispersal quality associated with dispersal distance (which is expected to be positively related to retention time) will affect the probability of seedling establishment over longer distances and, thus, the spatial characteristics of the effective seed shadow.

Contribution à l'étude de la dynamique de l'occupation des sols de la plaine de la Macta (Algérie) à l'aide de la télédétection et des systèmes d'information géographique

The plains of Macta, where the Macta marshes are located, form a wetland with particular ecological characteristics in the Maghreb and are subject to distinct land use dynamics. The plant formations are exposed to multiple forms of degradation, primarily due to climate (period of dryness) and to increasing anthropogenic activities in the area. The new methods of breeding and cultivation contribute to ongoing degradation in this natural ecosystem, with a deterioration of the wetland's biological potentialities. With the aim of safeguarding Macta's marshes, a better knowledge of vegetation distribution patterns and dynamics, together with the interpretation of the remote sensing data and GIS, makes it possible to consider programmes of natural environment restoration and sustainable management. The results of land-use dynamics analysis show a decline in agricultural land use from 33,000 ha in 1958 to 21,000 ha in 2005. Halophytic vegetation currently occupies 47,000 ha, while in 1958 it occupied only 27,000 ha. Tamarix, Inula, Joncus and Scirpus species are experiencing a decrease in surface cover, while Salicornia, Suaeda, and Atriplex are extending their area. To cite this article: T. Sitayeb, K. Benabdeli, C. R. Biologies 331 (2008).

The use of random amplified polymorphic DNA (RAPD) for hybrid detection in Scirpus from the river Schelde (Belgium)

Along the unique freshwater tidal zone of the river Schelde (Belgium), plants of Scirpus species occur primarily in small and fragmented populations. The majority of these are native Scirpus lacustris, S. pungens, S. triqueter, S. tabernaemontani and intermediate morphological forms. The distribution area of S. triqueter is even restricted to this tidal habitat. However, several cultivated S. tabernaemontani strains have recently been introduced. The latter species is often used to stabilize riverbanks. To determine the existing genetic diversity among these species, stems from plants from 44 different locations were subjected to random amplified polymorphic DNA (RAPD) analysis, using 22 decanucleotide primers. Data analysis of the amplified DNA fragments enabled us to unambiguously differentiate among these Scirpus taxa. Hybridization between S. triqueter and S. tabernaemontani was documented, and the studied hybrids were always genetically more similar to S. triqueter than to S. tabernaemontani. Among the introduced clones, at least two different origins could be distinguished. Several of the introduced S. tabernaemontani clones were clearly different from individuals of the same species that were native to this region. As there were different hybrid genotypes owing to different hybrid events or to introgression, this complex should be safeguarded from genetic pollution. New S. tabernaemontani genotypes with markers not previously observed in that hybrid complex of the unique tidal freshwater habitat should be avoided in replantation projects.

Endophytic fungi from plants living on gypsum soils as a source of secondary metabolites with antimicrobial activity

Endophytic fungi were isolated from nine plant species growing on gypsum and saline soils in central Spain. The plants sampled were Arundo donax, Afriplex halimus, Diplotaxis erucoides, Ephedra nebrodensis, Phragmites australis, Rosmarinus officinalis, Scirpus holoschoenus, S maritimus and Stipa tenacissima. A total of 152 fungal species were recovered from 2880 samples of leaves, stems or twigs, taken from 45 individual plants. Ephedra and Rosmarinus showed the highest diversity of endophytes, whereas both species of Scirpus showed the lowest. The most frequently isolated fungi were Allernaria alternata, Sporormiella intermedia, Rhizoctonia sp., Epicoccum purpurascens, Pleospora herbarum, Cladosporium herbarum, Sporormiella australis and a sterile fungus. A total of 187 strains belonging to 136 species were tested for the production of antimicrobial activities, using a panel of bacteria and yeasts, some of them of clinical relevance. Production of antimicrobial compounds was detected in 45 strains, belonging to 37 species. Large differences were observed among isolates from the same species, with respect to their ability to produce metabolites with antimicrobial activity.

Water-depth tolerances of the dominant emergent macrophytes of the Delta Marsh, Manitoba

The growth (shoot height, cumulative shoot length, shoot density, above- and below-ground biomass) of seven emergent species growing at five different water depths was measured for 2 years. These species belonged to three different ecological classes: (i) upper marsh species (Carex atherodes, Scolochloa festucacea, and Phragmites australis) that occupy sections of the water-depth gradient that are only seasonally flooded in the Delta Marsh; (ii) lower marsh species (Typha glauca and Scirpus lacutris spp. glaucus) that occupy permanently flooded areas; and (iii) drawdown species (Scirpus lacustris spp. validus and Scirpus maritimus) that become established temporarily during drawdowns. Upper marsh species could not adjust their shoot length if they were growing in water deeper than 20 cm. Lower marsh species were able to do this in water up to 70 cm deep. All three types survived for 1 or 2 years in water too deep for long-term persistence. Scirpus species survived as tubers in areas with water too deep for them to grow. The distributions of the seven species in the experiments overlapped considerably, and all species cooccurred at water depths to 70 cm after 2 years of flooding. The predicted distribution in the four dominant species along a water-depth gradient were consistent with their actual distributions in the Delta Marsh, but their predicted distributions overlapped much more than is the case in the field. Key words: emergent vegetation, experiment, water-depth tolerance, plant growth, distributions.

Cytological Observations on Scirpus Linn. from North India.

Population studies on five species of Scirpus namely, S. kyllingioides, S. litoralis, S. mucronatus, S. roylei and S. triqueter show fixed chromosome numbers in S. mucronatus (n=22) and S. triqueter (n=21) while S. kyllingioides and S. litoralis show high incidence of aneuploidy. Both diploid (n=11) and octaploid (n=44) cytotypes are recorded for S. roylei. On the basis of recorded base numbers (X=5, 7, 8) in Scirpus, it is very difficult to guess correctly the ploidy level for S. kyllingioides and S. litoralis cytotypes.Sedges show a high incidence of euploid and aneuploid numbers which is due to vegetative propagation so common in the group because this mechanism of race perpetuation helps in conservation of all the evolved cytotypes which is normally not the case with other groups of flowering plants not exhibiting vegetative propagation.

Achene Microstructure in Eriophorum (Cyperaceae): Taxonomic Implications and Paleobotanical Applications

TucKER, G. C. AND N. G. MILLER (Biological Survey, New York State Museum, The State Education Department, Albany, NY 12230). Achene microstructure in Eriophorum (Cypera­ ceae): Taxonomic implications and paleobotanical applications. Bull. Torrey Bot. Club 117: 266-283. 1990.-Silica bodies in the outer cells of the achene epidermis in 17 species of Eriophorum-and nine species of Scirpus, some of which have been placed in Eriophorum, were revealed by sonication and/or acetolysis and examined by scanning electron microscopy. A silica body consists of a basal platform, one or more large elevated protuberances, and sometimes smaller satellite protuberances. Individual species differ in the number of protuberances, the presence/absence of satellites, the texture of the platform, and the occurrence of nodules on the larger protuberances. These features, combined with achene shape and characteristics of the anticlinal walls of the epidermal cells (undulate vs. straight, thick vs. thin, buttressed or not), are expressed in a unique combination for each species. Scirpus hudsonianus was examined for geographic and developmental variation in the microstructure of its silica bodies. All samples had similar bodies, characterized by conspicuous nodules on the protuberances and a smooth platform. Nodules were much less evident in immature achenes. Achene epidermal microstruc­ ture supports the placement of S. hudsonianus in Scirpus sect. Baeothryon and S. maximowiczii in Scirpus sect. Trichophorum. Achenes of S. hudsonianus and Scirpus cespitosus share similar silica bodies and other achene features. Achene microstructure of a late-Pleistocene fossil proved to be the same as that in Scirpus hudsonianus. Our studies establish the feasibility of identifYing all species of Eriophorum by utilizing microstructural characteristics of isolated achenes.

Epidermal patterns of leaf blades in Korean sedge taxa characterized by SEM and LM ( 2 . Cyperus )

The epidermal patterns of four taxa (3 species and 1 subspecies) of Korean Scirpus were investigated by using SEM and LM. Epidermal patterns of the leaf blades are characteristics and useful in identification and classification of Scirpus species. As the result of this study, the shape of epidermal elements such as subsidiary cells, wavy of intercostal cell walls, shape of interstomatal cells, cuticle, papillae, prickles, silica body and the arrangement of each element are considered to significant taxonomic characters in the sedge taxa.

Algunos aspectos ecológicos y fitogeográficos de las especies de Cyperaceae en el Valle de México. I. Afinidades ecológicas

Las ciperáceas se encuentran ampliamente distribuidas en el Valle de México, en prácticamente todos los tipos de vegetación , pero principalmente en lugares de suelo húmedo o inundado dentro de bosques de encino, pastizales, bosques de pino, matorrales xerófilos y bosques de Abies, entre los 2 230 y 4 100 m de altitud. Hay varias especies francamente acuáticas, por ejemplo todas las del género Scirpus, algunas de Eleocharis y unas pocas de Cyperus y Carex, pero también hay otras adaptadas a condiciones de poca humedad. El grueso de las especies ajusta la fenología de su reproducción a la época lluviosa; sólo algunas de las manifiestamente hidrófitas pueden encontrarse en flor durante la mayor parte del año.

Pyrolysis mass spectrometry of some Scirpus species and their decomposition products1

Four species of bulrushes (Scirpus acutus, Scirpus subterminalis, Scirpus validus, and Scirpus americanus) and the particulate decomposition products of S. acutus and S. subterminalis were analyzed by Curie‐point pyrolysis low‐voltage ionization mass spectrometry. The mass pyrograms of the emergent foliage of the fresh plants showed similarity in distribution of the pyrolysis products from polysaccharides, lignin, and protein. Mass peak m/z 120 differed markedly in relative abundance in these plants and was identified by pyrolysis gas‐chromatography MS as parahydroxystyrene, a pyrolysis product of paracoumaric esters. Decomposition was carried out in the laboratory under aerobic and anaerobic conditions at 10° and 25°C for 180 days. The mass spectra of the senescent S. acutus differed only slightly from the decomposition stages after 180 days at 25°C, but the mass spectra of decomposed senescent submersed foliage of S. subterminalis showed a reduction in pyrolysis products of neutral polysaccharides and an increase in products from proteins and bacterial amino sugar polymers especially after anaerobic decomposition. Large amounts of paracoumaric esters and lignin derivatives were found in all species. These compounds were resistant to degradation, suggesting that paracoumaric esters can influence the slow decay of emergent plants in the littoral zone of lakes.

Decomposition of aquatic angiosperms. II. Particulate components

The decomposition of particulate organic matter (POM) from five species of freshwater vascular macrophytes was analyzed over a 180-day period under controlled conditions of temperature and oxygen (10 and 25°C; aerobic and anaerobic). In addition, a series of seasonal decomposition experiments were conducted in situ under different lake conditions. Plant species studied included the emergent Scirpus acutus Bigelow, the floating-leaved lily Nuphar variegatum Engelm., and the submersed Myriophyllum heterophyllum Michx., Najas flexilis (Willd.) Rostk. & Schmidt, and the submersed bulrush Scirpus subterminalis Torrey. At 2, 4, 10, 24, 48, 90, and 180-day intervals, organic weight, ash, carbon, nitrogen, total non-structural carbohydrates (TNC), and fiber components (lignin, cellulose, and hemicellulose) were determined under each of the experimental conditions. A model was developed that fit the observed weight-loss data, which demonstrated that decay-rate coefficients decreased exponentially with time in response to increasing resistance to decomposition of residual organic constituents. The fastest decomposing species, Nuphar, exhibited losses from 60 (cold, anaerobic) to 90% (warm, aerobic) over a 180-day period; the slowest, Scirpus acutus, lost only 20 and 40% under comparable conditions. TNC content decreased more rapidly under warm aerobic than under cold anaerobic conditions. Reduction of TNC was greatest in Nuphar, less in Myriophyllum and Najas, and lowest in the two Scirpus species. Structural carbohydrates decreased slowly among all species with the lignin fraction being the most resistant to degradation. However, decay rates of the macrophytes were negatively correlated to total fiber content rather than to individual fiber components (hemicellulose, cellulose, and lignin). Floating-leaved plants contained the least amount of structural tissue and decayed most rapidly, followed by submersed and then emergent species. Scirpus subterminalis, although submersed, retains the structural characteristics of the emergent species of this genus and decayed in much the same way as S. acutus. The C:N ratios of tissue of Scirpus acutus were higher than for other species and continuously declined during decomposition under warm, aerobic conditions. In this species, the C:N ratios decreased very slowly under cold, anaerobic conditions. The C:N ratios of the other species were constant after initial rapid declines. Among all species, the proportion of nitrogen in the dissolved organic and inorganic matter of the media decreased rapidly to low levels during decomposition at both low and high temperatures under anaerobic conditions; reductions were less when oxygen was available and decreased least in cultures of the two Scirpus species. Thus, resistance of particulate tissue to microbial decomposition was strongly influenced by the composition of the plant species. The floating-leaved plant decomposed faster than the submersed plants, which decomposed more rapidly than the emergent species. Decay rates were related to initial nitrogen and fiber contents, with high-nitrogen, low-fiber plants decomposing most rapidly. Unlike the leached dissolved organic matter (DOM) of the plants whose rate of decomposition was found to be mostly influenced by oxygen availability, the rate of conversion of particulate matter to carbon dioxide and/or DOM was regulated primarily by temperature, tissue nitrogen, and fiber content. All species showed similar trends in decomposition under both laboratory and in situ conditions, but the species-specific rates differed under the various laboratory conditions of temperature and oxygen.

Cytological Studies in Indian Cyperaceae

Cytotaxonomical studies have been carried out on 30 species and varieties under 4 genera belonging to the tribe Scirpeae, as part of a programme of investigation of Indian representatives of the family Cyperaceae with the aid of suitable schedules. Detailed karyotype analysis shows a general resemblance of the chromosome morphology, testifying to the homogeneity of the group as a whole. The genus Fimbristylis has been found to represent a very primitive level of evolution as compared to the genus Eleocharis. On the basis of evidences, it has been pointed out that possibly the evolution from diffuse to localised centromere has been achieved in a short step, since both types of centromere have been recorded in the species of Scirpus and Eleocharis.