Comparative study of periphyton colonisation on common reed (Phragmites australis) and artificial substrate in a shallow lake,Manyas, Turkey

Hydrobiologia - Colonisation of epiphytic algae on the common reed (Phragmites australis) and on glass slides were studied during a twenty-four week exposure period in a shallow, turbid lake,...     

Mass loss and nutrient dynamics during litter decomposition under three mixing treatments in a typical steppe in Inner Mongolia

Background and aims

Mixing effects during litter decomposition could occur between two or more different litter species because of the potential nutrient transfer. However, evidence of mixing effects is variable and the underlying mechanisms remain unclear. Using a three-year decomposition experiment, we aim to examine for the effects of litter mixing and position on decomposition rates and nitrogen (N) and phosphorus (P) dynamics.

Methods

We studied litter decomposition of Stipa krylovii (Sk) and Astragalus galactites (Ag), two dominant species with contrasting litter quality, in a typical steppe of northern China in both single decomposition and three mixing treatments. The three mixing treatments included thorough mixing (Sk-Ag), Ag over Sk (Ag/Sk), and Sk over Ag (Sk/Ag).

Results

Both the Sk-Ag and the Sk/Ag mixture had negative mixing effects on the mass loss of the litter mixture, while the Ag/Sk mixture had a neutral mixing effect. The percent mass loss was higher when the litter species was placed at the top (25.0 and 51.9 % of mass remaining for Ag and Sk, respectively) than at the bottom (38.3 and 61.8 % of mass remaining for Ag and Sk, respectively). The Sk/Ag mixture had negative effects on the release of N while all three mixing treatments had positive effects on the release of P.

Conclusions

Our results indicate that: (1) mixing treatments can induce different mixing effects; (2) environmental factors likely play an important role in controlling the mixing effect; and (3) litter-mixtures have different non-additive effects on N and P, which may further increase the heterogeneity of N and P availability as the two litter species may fall differentially in terms of space and time.     

Initial colonization, nutrient supply, and fungal activity on leaves decaying in streams

Aquatic hyphomycetes dominate leaf decomposition in streams, and their biomass is an important component in the diet of leaf-eating invertebrates. After 2 weeks of exposure in a first-order stream, maple leaf disks had low levels of fungal biomass and species diversity. Spore production by aquatic hyphomycetes also was low. Subsets of these disks were left in the stream for another 3 weeks or incubated in defined mineral solutions with one of three levels of nitrate and phosphate. Stream disks lost mass, increased ergosterol levels and spore production, and were colonized by additional fungal species. External N and P significantly stimulated mass loss, ergosterol accumulation, and spore production of laboratory disks. On disks incubated without added N and P, ergosterol levels declined while conidium production continued, suggesting conversion of existing hyphal biomass to propagules. In all other treatments, approximately equal amounts of newly synthesized biomass were invested in hyphae and conidia. Net yield (fungal biomass per leaf mass lost) varied between 1% (in the laboratory, without added N or P) and 31% (decay in stream). In most treatments, the three aquatic hyphomycete species that dominated spore production during the first 2 weeks in the stream also produced the largest numbers of conidia in the following 3 weeks. Principal-component analysis suggested two divergent trends from the initial fungal community established after 2 weeks in the stream. One culminated in the community of the second phase of stream exposure, and the other culminated in the laboratory treatment with the highest levels of N and P. The results suggest that fungal production in streams, and, by extension, production of invertebrates and higher tropic levels, is stimulated by inorganic N and P.     

Effects of oil on internal gas transport, radial oxygen loss, gas films and bud growth in Phragmites australis

Background and Aims

Oil pollution of wetlands is a world-wide problem but, to date, research has concentrated on its influences on salt marsh rather than freshwater plant communities. The effects of water-borne light oils (liquid paraffin and diesel) were investigated on the fresh/brackish wetland species Phragmites australis in terms of routes of oil infiltration, internal gas transport, radial O₂ loss (ROL), underwater gas films and bud growth.

Methods

Pressure flow resistances of pith cavities of nodes and aerenchyma of leaf sheaths, with or without previous exposure to oil, were recorded from flow rates under applied pressure. Convective flows were measured from living excised culms with oiled and non-oiled nodes and leaf sheaths. The effect of oil around culm basal nodes on ROL from rhizome and root apices was measured polarographically. Surface gas films on submerged shoots with and without oil treatment were recorded photographically. Growth and emergence of buds through water with and without an oil film were measured.

Key Results

Internodes are virtually impermeable, but nodes of senesced and living culms are permeable to oils which can block pith cavity diaphragms, preventing flows at applied pressures of 1 kPa, natural convective transport to the rhizome, and greatly decreasing ROL to phyllospheres and rhizospheres. Oil infiltrating or covering living leaf sheaths prevents humidity-induced convection. Oil displaces surface gas films from laminae and leaf sheaths. Buds emerge only a few centimetres through oil and die.

Conclusions

Oil infiltrates the gas space system via nodal and leaf sheath stomata, reducing O₂ diffusion and convective flows into the rhizome system and decreasing oxygenation of phyllospheres and rhizospheres; underwater gas exchange via gas films will be impeded. Plants can be weakened by oil-induced failure of emerging buds. Plants will be most at risk during the growing season.Key words: Phragmites australis, oil pollution, convective flow, pressure flow resistance, phyllosphere oxygenation, rhizosphere oxygenation, underwater gas films, bud emergence, stomata, pith cavity diaphragms, leaf sheath aerenchyma, rhizome aeration     

The endophytic fungal communities associated with the leaves and roots of the common reed (Phragmites australis) in Lake Trasimeno (Perugia,Italy) in declining and healthy stands

We surveyed the fungal endophytes in the leaves and roots of Phragmites australis plants along a gradient of reed decline at Lake Trasimeno (central Italy) in Oct. 2010. An integrated approach consisting of cultivation and molecular identification was used. Endophytes were recovered from 61.59 % of the samples, with a total of 1 541 isolates. On the basis of a molecular analysis of the rDNA Internal Transcribed Spacer (ITS) region, 25 operational taxonomic units (OTUs) were identified. Fusarium sp. (OTU 21) and Gibberella moniliformis (OTU 1) were the most frequently isolated fungi. Comparisons of the leaf and root samples demonstrated spatial heterogeneity in the endophyte assemblages among the plant parts and sites. In this study, we have shown that reed plants in different states of decline harbour different endophytic communities. This finding may help to understand the very complex scenario of reed die-back.     

Effect of broken dead culms of Phragmites australis on radial oxygen loss in relation to radiation and temperature

The amount of oxygen released from the roots of Phragmites australis was quantified to examine the effects of airflow through dead culms, radiation, and temperature on radial oxygen loss (ROL). To investigate the effect of dead culms on ROL quantitatively, the ROL of individual plants with open dead culms was compared to that of plants with sealed dead culms as a function of light intensity and temperature. The relationship between ROL and plant morphology (aboveground biomass, shoot diameter, shoot height) was investigated. When exposed to 300, 600, and 900 μmol m⁻² s⁻¹ light, the ROL was 15.6, 22.5, and 30.9 μmol O₂ g⁻¹ dry root day⁻¹, respectively, from plants with open dead culms and 11.0, 16.4, and 23.3 μmol O₂ g⁻¹ dry root day⁻¹, respectively, from plants with sealed dead culms. The ROL from plants with open dead culms was obviously higher than that from plants with sealed dead culms in every condition. The ROL from plants with open culms was 37% and 30% higher than that from plants with sealed culms at 20°C and 30°C, respectively. The effects of plant-specific parameters such as leaf area and shoot diameter on radial oxygen loss were evident. From the point of view of rhizosphere oxidation during the growing season, the existence of open dead culms should be taken into consideration for optimal plant management in constructed wetlands. This study provides a theoretical understanding of the effects of open dead culms, light conditions, and temperature on radial oxygen loss. Handling editor: S. M. Thomaz     

Effects of seasonal temperature on shoot growth dynamics and shoot morphology of common reed (Phragmites australis)

The shoot growth during the vegetation period andshoot morphology at the end of the season wereinvestigated in four monoclonal aquatic reed stands(Phragmites australis) with differentproductivity in Berlin and Brandenburg. Investigationswere conducted over a period of six years (1991–96) toascertain the effects of differences in temperatures.All clones showed significant year-to-year variationin shoot morphology. The mean final shoot length ofthe two clones with highest variation ranged from252 cm (1991) to 388 cm (1993; Templiner See), andfrom 170 cm (1993) to 229 cm (1994; Parsteiner See).In spite of this considerable variation, morphologicalparameters measured at the end of the growing seasonshowed only a slight relation to the average airtemperature either during the main growth phase (Aprilto June) or during the period of bud formation (Augustto October of the previous year). Contrary to meanshoot length at the end of the growing season, shootelongation during the main growth phase (from April toJune) was clearly related to the sum of daily averagetemperatures. Thus, taking into account temperaturemay enhance the accuracy of studies on reed growthwhenever these studies are carried out at localitiesdiffering in temperature or in different years.     

Genetics,novel weapons and rhizospheric microcosmal signaling in the invasion of Phragmites australis

Chemical communication and perception strategies between plants are highly sophisticated but are only partly understood. Among the different interactions, the suppressive interaction of a class of chemicals released by one plant through root exudates against the neighbouring plants (allelopathy) have been implicated in the invasiveness of many exotic weedy species. Phragmites australis (common reed) is one of the dominant colonizers of the North American wetland marshes and exhibits invasive behavior by virtually replacing the entire native vegetation in its niche. Recently, by adopting a systematic bioassay driven approach we elucidated the role of root derived allelopathy as one of the important mechanisms by which P. australis exerts its invasive behavior. Additionally, our recent preliminary data indicates the involvement of rhizobacterial signaling in the invasive success of P. australis. A better understanding of biochemical weaponry used by P. australis will aid scientists and technologists in addressing the impact of root secretions in invasiveness of weedy species and thus promote a more informed environmental stewardship.Key words: Phragmites australis, roots, phytotoxicity, reactive oxygen species, microtubules, microcosm     

Aspects of programmed cell death during early senescence of barley leaves: possible role of nitric oxide

Summary. Leaf senescence is a highly coordinated process which involves programmed cell death (PCD). Early stages of leaf senescence occurring during normal leaf ontogenesis, but not triggered by stress factors, are less well known. In this study, we correlated condensation of chromatin and nuclear DNA (nDNA) fragmentation, two main features of PCD during early senescence in barley leaves, with the appearance of nitric oxide (NO) within leaf tissue. With the help of the alkaline version of the comet assay, together with measurements of nDNA fluorescence intensity, we performed a detailed analysis of the degree of nDNA fragmentation. We localised NO in vivo and in situ within the leaf and photometrically measured its concentration with the NO-specific fluorochrome 4-amino-5-methylamino-2′,7′-difluorofluorescein. We found that both nDNA fragmentation and chromatin condensation occurred quite early during barley leaf senescence and always in the same order: first nDNA fragmentation, in leaves of 6-day-old seedlings, and later chromatin condensation, in the apical part of leaves from 10-day-old seedlings. PCD did not start simultaneously even in neighbouring cells and probably did not proceed at the same rate. NO was localised in vivo and in situ within the cytoplasm, mainly in mitochondria, in leaves at the same stage as those in which chromatin condensation was observed. Localisation of NO in vascular tissue and in a large number of mesophyll cells during the senescence process might imply its transport to other parts of the leaf and its involvement in signalling between cells. The fact that the highest concentration of NO was found in the cytoplasm of mesophyll cells in the earliest stage of senescence and lower concentrations were found during later stages might suggest that NO plays an inductive role in PCD. Correspondence: A. Mostowska, Department of Plant Anatomy and Cytology, Institute of Experimental Biology of Plants, University of Warsaw, Miecznikowa 1, 02-096 Warsaw, Poland.     

Interaction of cadmium with glutathione and photosynthesis in developing leaves and chloroplasts of Phragmites australis (Cav.) Trin. ex Steudel

We investigated how the presence of cadmium (Cd) at the emergence of Phragmites australis Trin. (Cav.) ex Steudel plants from rhizomes interacted with leaf and chloroplast physiological and biochemical processes. About 8.5 nmol Cd mg-1 chlorophyll was found in leaves, and 0.83 nmol Cd mg-1 chlorophyll was found in chloroplasts of plants treated with 50 microm Cd. As a result, a 30% loss of chlorophyll was measured concomitantly with a comparable percentage reduction in light-saturated photosynthesis. Rubisco content and activity were lowered by 10% and 60%, respectively. Antioxidant activity was stimulated by Cd treatment and was associated with an increase in the glutathione and pyridine pools, and with a larger pool of reduced glutathione. It is suggested that the glutathione pool and its predominance in the reduced state protected the activity of many key photosynthetic enzymes against the thiophilic binding of Cd. Chloroplast ultrastructure was not significantly altered with 50 microm treatment and the efficiency of photosystem II, measured as the fluorescence ratio Fv/Fm, remained high because F0 and Fm were proportionally decreased. In plants treated with 100 microm Cd, all effects were exacerbated, but Fv/Fm remained close to that of control leaves and the glutathione and pyridine nucleotides pools were lowered. The results suggest that glutathione exerted a direct important protective role on photosynthesis in the presence of Cd.     

Mass loss and macroinvertebrate colonisation of fish carcasses in riffles and pools of a NW Italian stream

In this study, we analysed the decomposition of trout carcasses in a low-order Apennine stream, with the aim to investigate the mass loss rate in a Mediterranean lotic system, and to examine the influence of microhabitats on the invertebrates colonising fish carcasses. In May 2003, we put 56 dead rainbow trout (Oncorhynchus mykiss) in the stream, placing seven sets (four trout each) in both riffle and pool habitats. At four dates, we removed one trout per set to measure its dry mass and determine the associated macroinvertebrate assemblage. Fifty-eight macroinvertebrate taxa colonised the carcasses, with significant differences between the erosive and depositional microhabitats. Riffle trouts hosted richer and denser colonist communities than pool trouts. Chironomidae, Serratella ignita, Habrophlebia sp., Dugesia sp. and Protonemura sp. were the five most abundant taxa. Decomposition was initially very rapid in both environments and then tapered off over time. The mass loss rate was higher (k= –0.057 day^–1) than that found in other studies. Higher Mediterranean temperatures probably increase the process. Although we found no significant difference between riffles and pools, mass loss was more regular in erosive habitats, underlining the importance of local, small-scale conditions. In small, low-order, heterotrophic streams, fish carcasses represent an important resource and shelter for rich and diversified invertebrate assemblages.     

Effects of fertilization levels in two farming systems on senescence and nutrient contents in potato leaves

The influence of fertilization on senescence and nutrient remobilization in potato leaves was investigated in two farming systems on a soil with a poor potassium availability. The Conventional farming system followed good local practices including industrial products, while in the Bio-Dynamic farming system industrial fertilizers and synthetic pesticides were avoided. Potassium concentrations in the dry matter of mature leaves varied over a wide range. Nitrogen compounds (protein, chlorophyll) were less affected, and phosphorus concentrations in the dry matter were similar. Magnesium and potassium concentrations in the leaves were negatively correlated. In both farming systems senescence was advanced in plants with a low nutrient supply. Alkaline pyrophosphatase and aminopeptidase activities (in general highest in expanding and mature leaves) were lower and endopeptidase activities peaked earlier on plots with low fertilizer levels. A high percentage of potassium was remobilized from senescing leaves on unfertilized plots, but the phosphorus concentration remained high at the end of the season. The results suggest that the differential net remobilization of nitrogen, phosphorus and potassium depended on actual source/sink relations in the plants.     

芦苇和香蒲地上部N和P积累动态及适宜收获时期分析

通过野外采样和室内分析相结合的方法,对5月至11月芦苇〔Phragmites australis(Cav.)Trin.ex Steud.〕和香蒲(Typha orientalis Presl)地上部生物量以及N和P的含量和积累量的动态变化进行了分析,并对生物量、N和P含量及N和P积累量间的相关性进行了研究;在此基础上,确定芦苇和香蒲的适宜收获时期。结果表明:在整个生长过程中,芦苇和香蒲地上部生物量随生长时间延长呈典型的单峰型曲线,最高值分别出现在9月份和10月份,且芦苇地上部生物量极显著高于香蒲(P<0.01)。芦苇和香蒲地上部N含量呈先升高后降低的趋势、P含量呈逐渐降低的趋势,香蒲地上部N和P含量均极显著高于芦苇地上部。芦苇地上部N和P积累量在8月份达到最高,香蒲地上部N和P积累量在9月份达到最高。芦苇和香蒲地上部C/N、C/P和N/P比在不同月份差异较大,C/N和N/P比呈波动趋势,C/P比则总体呈逐渐升高的趋势。总体来看,芦苇和香蒲的生长在生长初期和中期受N限制、在生长末期受P限制。相关性分析结果表明:芦苇和香蒲地上部的N含量与P含量、N积累量与P积累量间均呈极显著正相关;N和P积累量与其生物量呈显著正相关(P<0.05),但与N和P含量的相关性不显著(P>0.05)。综合分析结果表明:芦苇和香蒲的适宜收获时期分别为8月份和9月份。     

Subsurface hydrology and degree of burial affect mass loss and invertebrate colonisation of leaves in a woodland stream

SUMMARY 1. In deciduous forest streams, fallen leaves form a large component of the total organic matter budget, and many leaves become buried within stream sediments. We examined the processing of buried leaves as compared with those at the surface, and the influence of subsurface hydrology on processing rates.
2. Leaf packs were secured on the streambed surface or buried 10 cm deep in upwelling and downwelling reaches of a second-order stream in Michigan, U.S.A. Mass loss and invertebrate colonisation were measured from October to February.
3. Leaves buried in upwelling reaches lost mass more slowly (exponential decay coefficient, k =−0.0097) than did leaves from the other treatments (buried downwelling: −0.017; surface upwelling: −0.022; surface downwelling: −0.021).
4. Initially, more invertebrates colonised surface leaf packs than buried packs. During the remainder of the study, however, hydrology had a greater effect on invertebrate abundance than did burial, as more invertebrates were found in packs in downwelling reaches than in upwelling reaches.
5. Local subsurface hydrology and degree of burial, factors rarely considered in studies of detritus processing, can significantly influence mass loss and invertebrate colonisation of fallen leaves in streams. Furthermore, because of slower processing, subsurface zones may function as organic matter reservoirs that gradually 'spiral' carbon to downstream subsurface and surface habitats.     

Changes of chloroplasts density and heterogeneity during the senescence of barley leaves

The equilibrium density of chloroplasts from barley (Hordeum vulgare L. cv. Hassan) was analyzed by sucrose gradient centrifugation. Natural and detachment-induced leaf senescence were associated with a decrease in density and an increase in heterogeneity of the chloroplast population. Treatments (with growth regulators and light) which retarded or accelerated senescence, respectively, retarded or accelerated chloroplast density decrease. Accelerators as well as retardants of senescence decreased the heterogeneity of the chloroplast population.     

The production and behaviour of phytoferritin particles during senescence of Phaseolus leaves

Summary Phytoferritin-like particles were found within chloroplasts of senescing Phaseolus leaves. Large quantities of the particles were laid down at an early stage of senescence, and no further deposition occurred. All but a few groups of particles had been removed by the time the leaves turned yellow, this removal taking place at a late stage of senescence which coincided with the release of the vacuolar contents.     

The effects of grazing on local colonisation and extinction during early succession

Estimates of colonisation of plant species were made at three spatial scales in an old-field on limestone subject to five experimental sheep grazing regimes. Local extinctions within grazing treatments were estimated in 1-m² permanent quadrats. These data were used to assess the effects of grazing treatment and spatial scale on the process of species change over a period of six years. Colonisation of the lOha field was virtually a random draw of plant species from adj acent vegetation, irrespective of plant life-history traits including dispersal strategy. The effects of grazing on colonisation increased at smaller spatial scales. Colonisation rates changed little during the study on the 10 ha scale, but declined steeply with time at smaller scales. Colonisation rates of short-lived species declined more than those of perennials, and short-lived species were subject to erratic episodes of extinction which did not affect perennials. Short periods of grazing enhanced colonisation rates of all species, but extinction rates were the same as in ungrazed controls. Grazing for longer periods further enhanced colonisation rates, but also increased extinction rates. This produced diversity patterns consistent with a ‘hump-backed model’, except that no grazing treatment was heavy enough to decrease diversity. Ungrazed controls had low species diversity, but areas grazed for longer periods were no more diverse after six years than those grazed for short periods.