Nutritional exploitation of dead trunks: another function of cypress knees (Taxodium distichum)?

Summary In one cypress dome in the Everglades National Park, cypress knees seem to develop from vertical root loops that grow along and ramify into dead cypress stumps. Nearly all young root loops emerge close to a decaying stump. The proportion of these associations decreases as the diameter and presumed age of the loops increase. Loop density correlates with the density of dead but not of live trunks. These preliminary findings suggest that the root loops emerge primarily near dead stumps and exploit their nutrients until the stumps rot away and the loops develop into mature knees.     

Diel methane emissions in stands of Spartina alterniflora and Suaeda salsa from a coastal salt marsh

In this study, we aimed to understand the influence of plant type on the monthly variations of diel CH₄ fluxes from Spartina alterniflora and Suaeda salsa of coastal salt marshes at three growth stages (July, August and September). Dissolved CH₄ concentrations in porewater and sediment redox potentials were monitored, as were aboveground plant biomass and stem densities. CH₄ fluxes exhibited clear monthly variations and peaked in September in the S. alterniflora and S. salsa mesocosms. However, no discernible diel variation was observed in the CH₄ flux in the S. salsa mesocosm, probably due to its weak gas transport capacity. By contrast, notable diel variations of CH₄ flux with the peak of 1.42 and 3.67 mg CH₄ m⁻² h⁻¹ at 12:00 and the lowest of 0.75 and 2.11 mg CH₄ m⁻² h⁻¹ at 3:00 or 6:00 were observed in the S. alterniflora mesocosm on 11 August and 11 September, respectively, but not in July mainly due to low plant biomass masking diel variations in the porewater CH₄ concentration. The ratios of the maximum flux to minimum flux over the course of the day in the S. alterniflora mesocosm on 10 July, 11 August and 11 September were 1.28, 1.89 and 1.76, respectively, and corresponding values for porewater CH₄ concentration were 1.31, 1.39 and 1.17, respectively. CH₄ flux significantly correlated with CH₄ concentration in porewater, and both were significantly related to air temperature. These findings indicate that CH₄ production and CH₄ flux at the middle growth stage (August) exhibited greater responses to changes in air temperature, which in turn induced the higher diel variation. The higher diel cycle for CH₄ flux in August than in September was likely due to the higher proportion of CH₄ oxidized during diffusion within the aerenchyma system. Our results suggest that the extent of diel variations in CH₄ flux may have depended on the gas transport capacity of plants, and the highest diel variation occurred at the middle growth stage.     

Methane emissions from fen,bog and swamp peatlands in Quebec

A static chamber technique was used weekly from spring thaw to winter freezing to measure methane emissions from 10 sites representing subarctic fens and temperate swamps and bogs. Rates of < 200 mg CH₄ m^–2 d^–1 were recorded in subarctic fens: within-site emissions were primarily controlled by the evolution of the peat thermal regime, though significant releases during spring thaw were recorded at some sites. Between subarctic fens, topography and water table elevation were important controls on methane emissions, with the general sequence: pool = horizontal fen> string. Emission rates from the 2 swamp sites were lower (< 20 mg CH₄ m^–2 d^–1 ), except during the spring thaw and when the sites were saturated. The low water table ( < 80 cm depth) in abnormally dry years reduced emission rates; rates were also low from a swamp site which had been drained and cleared of vegetation for horticulture. Methane emission rates were also low (< 5 mg CH₄ m^–2 d^–1) from 2 ombrotrophic bog sites. Laboratory measurements of rates of methane production under anaerobic conditions and methane consumption under aerobic conditions revealed that production rates were generally highest in the surface layers (0 to 2.5 cm depth); production was high in the fens and very low in the bogs. The swamp samples were able to produce methane under anaerobic conditions, but were also able to consume methane under aerobic conditions. Annual methane emission rates are estimated to be 1 to 10 g CH₄ m^–2 from the fens, 1 to 4 g CH4 m^–2 from the swamps and <0.2 g CH₄ m^–2 from the bogs and drained swamp.     

Methane emissions from an Amazon floodplain lake: Enhanced release during episodic mixing and during falling water

Soil respiration rates vary significantly among major plant biomes, suggesting that vegetation type influences the rate of soil respiration. However, correlations among climatic factors, vegetation distributions, and soil respiration rates make cause-effect arguments difficult. Vegetation may affect soil respiration by influencing soil microclimate and structure, the quantity of detritus supplied to the soil, the quality of that detritus, and the overall rate of root respiration. At the global scale, soil respiration rates correlate positively with litterfall rates in forests, as previously reported, and with aboveground net primary productivity in grasslands, providing evidence of the importance of detritus supply. To determine the direction and magnitude of the effect of vegetation type on soil respiration, we collated data from published studies where soil respiration rates were measured simultaneously in two or more plant communities. We found no predictable differences in soil respiration between cropped and vegetation-free soils, between forested and cropped soils, or between grassland and cropped soils, possibly due to the diversity of crops and cropping systems included. Factors such as temperature, moisture availability, and substrate properties that simultaneously influence the production and consumption of organic matter are more important in controlling the overall rate of soil respiration than is vegetation type in most cases. However, coniferous forests had 10% lower rates of soil respiration than did adjacent broad-leaved forests growing on the same soil type, and grasslands had, on average, 20% higher soil respiration rates than did comparable forest stands, demonstrating that vegetation type does in some cases significantly affect rates of soil respiration.     

Seasonal variation of methane emissions from a temperate swamp

Methane flux measurements were made at four sites in a freshwater temperate swamp over the 13 month period of April 1985 through May 1986. Emissions were highly variable both between sites and over time at any one site. Ebullition from sediments was an important component of methane release. Although release of methane through bubbling occurred in only 19% of the measurements made between April and June 1985, when instrumentation allowed us to separate diffusive and bubble fluxes, ebullition accounted for 34% of the total flux during this period. Methane release rates showed a strong seasonal variation, with highest emission rates observed in early spring and again in late summer, which was associated with changes in plant growth and physiology. Emission rates were partially correlated with sediment temperature, but the relationship was not straightforward, and resembled a step function. Emissions responded strongly to temperature change through the range of 10–16°C. At winter sediment temperatures between 4–9°C, CH₄ flux continued at low rates (0–28 mg CH₄ m^–2d^–1; average = 7.9 mg CH₄m^–2d^–1) and appeared insensitive to changes in sediment temperature. Annual methane emission from three constantly flooded sites (mean water depth = 35 cm) was 43.7 +/- 7.8 gm^–2 (standard error); annual flux from a bank site was 41.4 +/- 20.5 gm^–2. A comparison of flux measurements from fresh and saline wetlands in the immediate area of Newport News Swamp emphasizes the importance of edaphic factors in controlling flux.     

Floating vegetation mats on a floodplain billabong in the Northern Territory of Australia

The floristics and physical structure of a floating mat of vegetation in the Finniss River area of the Northern Territory are described. During the dry season floating mats contain green productive vegetation when the adjacent flood plains are dry and many of the plants are withered. At this time insects are more abundant on the mats than on the adjacent flood plain. Some flood plain vertebrates appear to concentrate their activity on floating mats during the dry season. During the period 1963 to 1978 the area of floating mat in the Finniss River study area was greatly reduced, probably as a result of high densities of feral water buffalo (Bubalis bubalus).(Present address: c/o 38 Hardy Terrace, East Ivanhoe, Victoria 3079).(Present address: c/o 38 Hardy Terrace, East Ivanhoe, Victoria 3079).     

Methane emissions from a full-scale A/A/O wastewater treatment plant

Methane (CH₄) emissions from a full-scale anaerobic/anoxic/oxic (A/A/O) wastewater treatment plant (WWTP) (Jinan, China) were investigated during spring and summer of 2010. Results showed that the major emission sources of CH₄ performed the following descending order: anaerobic tanks, oxic tanks, aerated grit chambers and sludge concentration tanks. The total annual fluxes of CH₄ emissions from the Jinan WWTP were 1.69 × 10⁴ kg yr⁻¹, with the emission factors of per capita emissions of 11.3 g CH₄ person⁻¹ yr⁻¹ and flow-based emissions of 1.55 × 10⁻⁴ g CH₄ (L of wastewater)⁻¹. The estimated source strength of methane for all WWTPs in China was 6.2 Gg yr⁻¹ (1 Gg = 10⁹ g). The most significant factors influencing methane emissions were dissolved oxygen concentration in aerated grit chamber and oxic tank and water temperature in high density settler tanks.     

Nutrient release from swamp water,Cyperus papyrus L. organs and swamp sediments

Nitrogen and phosphorus releases from swamp water,Cyperus papyrus plant organs and papyrus swamp sediments were investigated over five weeks. The release of nutrients by dissolution of decomposing organic matter was very important for the swamp water under the prevailing anaerobic conditions. Large amounts of nutrients were found in the incubation water with plant organs and sediments within the first 48 hours. Leaching of the nutrients from the plant organs and sediment caused high initial values. Subsequently decomposition of the organic material caused slight changes in the nutrient levels in the water. Probably denitrification played a role in the nitrogen dynamics, while phosphorus was mineralized.     

Ectomycorrhizal fungal community structure across a bog-forest ecotone in southeastern Alaska

We examined the ectomycorrhizal (ECM) fungal community across a bog-forest ecotone in southeastern Alaska. The bog and edge were both characterized by poorly drained Histosols and a continuous layer of Sphagnum species, ericaceous shrubs, Carex species, and shore pine [Pinus contorta Dougl. ex Loud. var. contorta]. The forest had better-drained Inceptisols and Spodosols, a tree community comprised of western hemlock [Tsuga heterophylla (Raf.) Sarg.], yellow cedar (Thuja plicata Donn ex D. Don.), Sitka spruce [Picea sitchensis (Bong.) Carr.] and shore pine, and an understorey of ericaceous shrubs and herbs. ECM root tip density (tips cm^–3 soil) was significantly greater in the forest than the edge or bog and ECM colonization was significantly different in all three plant communities. The below ground ECM fungal taxa were analyzed using molecular techniques (PCR-RFLP and DNA sequencing). Three ECM fungal taxa, Suillus tomentosus (Kauffman) Singer, Cenococcum geophilum Fr.:Fr, and a Russula species, differed in relative frequency, yet were among the four most frequent in all three plant communities. Although differences in ECM fungal richness were observed across plant communities, unequal sampling of ECM roots due to root density and colonization differences confounded richness comparisons. Using resampling procedures for creating taxon-accumulation curves as a function of sampled ECM roots revealed similarities in cumulative ECM fungal taxa richness across the ecotone.     

The photosynthetic characteristics of papyrus in a tropical swamp

Summary Photosynthesis and transpiration was measured in the large emergent C₄ sedge Cyperus papyrus (papyrus) which occupies wide areas of wetland on the African continent. The maximum observed value of net assimilation was 35 mol CO₂ m^-2 s^-1 at full sunlight but light saturation of photosynthesis did not occur. The quantum yield of photosynthesis obtained from the initial slope of the light response curves (0.06 mol mol^-1 incident light) was relatively high and close to previously recorded values for some C₄ grasses. Measurements made over two days showed that stomatal conductance was sensitive to the ambient air vapour pressure deficit (VPD) and was consistently lower on the day when VPD's were higher. There was, however, no marked midday closure of the stomata. Photosynthesis was also reduced on the day when VPD's were higher. The relationship between net photosynthesis and stomatal conductance was close to linear over the range of measurement conditions, with the result that intercellular CO₂ concentrations (C _i ) did not vary markedly. There was some evidence that C _i decreased at high VPD's. The regulation of stomatal movement in papyrus appears to minimise excessive water loss while not severely limiting photosynthesis. The significance of this strategy for a wetland species with plentiful supplies of water is discussed.     

Methane emission from tidal freshwater marshes

In two tidal freshwater marshes, methane emission,production and accumulation in the pore-water have beenstudied. The two sites differ in their dominantvegetation, i.e., reed and bulrush, and in theirheights above sea level. The reed site was elevated inrelation to the bulrush site and had higher rates ofmethane emission and production. It is argued thatthis difference in methane emission between sites wasprimarily due to a different effect of reed andbulrush plants on methane dynamics rather than methaneoxidation related to tidal elevation. Methane emissionshowed strong seasonality related primarily to plantphysiology and only secondarily to temperature. Twocontrol sites at which vegetation was removedsystematically had lower emission rates indicating anoverall stimulating effect of plants on methaneemission from tidal marshes. Flooding reduced methaneemission, probably by blocking the primary sites ofmethane release in the lower part of the plantstems.     

Factors limiting the distribution of the annual legumeKummerowia striata in a river floodplain

The annual legumeKummerowia striata often predominates in river floodplains forming a large population, but it is rare in gravelly areas adjacent to it. In order to clarify the factors limiting the distribution ofK. striata, its distribution pattern, germination and survival of seeds sown artificially were studied in the floodplain of the Ohta River. There was a positive correlation between the cover value ofK. striata and the percentage of fine particles (<0.2 mm) in the soil. In the winter season, there was a number of seeds (up to 47 seeds 20 cm⁻²) on the ground where aK. striata population had existed in the previous year, but they were very sparse in areas apart from the population. Only a small proportion of seeds sown in the gravelly area germinated. Many of the germinated individuals died before the first leaf unfolded, but the rest survived to maturity despite repeated floodings. Plants germinated in the gravelly area and those inoculated with soil from the gravelly area bore nodules, showing the presence ofRhizobium in the gravelly area. It was concluded that the colonization ofK. striata in the gravelly area was limited by slow dispersal, and by a low percentage of germination and high mortality in the early stage of establishment.     

Passive irrigation and functional morphology of crustacean burrows in a tropical mangrove swamp

Flushing measurements and a resin cast of a burrow inhabited by Sesarma messa and Alpheus cf macklay were taken from a Rhizophoraspp. forest. The burrow had 9 openings and occupied a swamp surface area of 0.64 m². Passive irrigation of the burrow was investigated by recording change in conductivity of burrow water in a chamber 45 cm below the swamp surface during tidal inundation of the swamp. The chamber was completely flushed within approximately one hour, i.e. by a single tidal event. Burrow morphology was determined by means of resin casting. The investigated burrow was of discrete structure, with an overall depth of 1.2 m and a total volume of 68 l, i.e. ca. 9% of the volume of swamp soil. The below ground surface area of chambers and tunnels was 3.8 m². The mean and maximum chamber/tunnel diameter was 7 cm and 11 cm respectively. The soil in the close vicinity of the burrow was extensively penetrated by roots, and any two parts of the burrow were located no further than 20 cm away from each other. By reducing diffusion distances within the soil and by being well flushed, the burrows provide an efficient mechanism for removal of excess salt accumulated in the soil around mangrove roots due to exclusion.     

Zapoteca quichoi (Leguminosae, Mimosoideae), a new species from southeastern Mexico

Zapoteca quichoi, a new species endemic to southern Tabasco, Mexico, is described and illustrated. This species exhibits morphological characteristics that place it within subgenus Amazonica, together with Z. amazonica and Z. microcephala, from Peru and Colombia, respectively.

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Resumen  Se describe e ilustra Zapoteca quichoi (Leguminosae, Mimosoideae), una nueva especie de Tabasco, México. Esta especie exhibe características morfológicas que la ubican dentro del subgénero Amazonica, junto con Z. amazonica y Z. microcephala, especies nativas de Perú y Colombia respectivamente.

     

Two new species of Serjania (Sapindaceae) from southeastern Brazil

One new species ofSerjania (S. erythrocaulis) belonging to theS. paradoxa group ofSerjania sect.Eurycoccus is described and illustrated bringing the total number of species in this group to eight. A second new species,Serjania divaricocca, belonging to sect.Serjania is also described and illustrated.

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Resumen  Una especie neuva deSerjania (S. erythrocaulis) perteneciente al grupoS. paradoxa de la secciónEurycoccus es descrita e ilustrada. Con esta especie, el numero total de especies conocidas para este grupo aumenta a ocho. Una segunda nueva especie,Serjania divaricocca, perteneciente a la secciónSerjania es también descrita e ilustrada.

     

Three new species of melastomataceae from the southeastern Atlantic Forest of Brazil

Three species are described here that occur in montane and high-montane forests in Southeastern Brazil.Miconia shepherdii belongs to sectionGlossocentrum and occurs on the Serra da Mantiqueira, on the border between the states of São Paulo, Minas Gerais, and Rio de Janeiro.Miconia kollmannii belongs to sectionHypoxanthus (formerChaenanthera) and occurs in the state of Espírito Santo.Ossaea suprabasalis was also collected in the state of Espírito Santo.     

Just add water: sources of chironomid drift in a large river floodplain

Although seasonal floodplains represent one of the most dynamic and productive of aquatic ecosystems, the sources of this productivity are poorly understood. We examined composition and sources of chironomid drift in the Yolo Bypass, the primary floodplain of the Sacramento River. We found that invertebrate drift during winter floodplain inundation is dominated by a single species, the newly identified chironomid Hydrobaenus saetheri (Diptera: Chironomidae). In order to determine sources of chironomids in the Yolo Bypass, invertebrates were sampled from several potential sources prior to and during initial floodplain inundation. Rehydration of dried floodplain sediments from several locations showed that H. saetheri dominated insect emergence from this colonization pathway. By contrast, H. saetheri was not a substantial component of inundated floodplain ponds or of tributary inputs to the floodplain. We conclude that the initial pulse of invertebrate abundance in Yolo Bypass floodwaters is dominated by chironomid emergence from sediments in multiple regions of the floodplain. Handling editor: S. Declerck     

High-quality seed dispersal by fruit-eating fishes in Amazonian floodplain habitats

Seed dispersal is a critical stage in the life history of plants. It determines the initial pattern of juvenile distribution, and can influence community dynamics and the evolutionary trajectories of individual species. Vertebrate frugivores are the primary vector of seed dispersal in tropical forests; however, most studies of seed dispersal focus on birds, bats and monkeys. Nevertheless, South America harbors at least 200 species of frugivorous fishes, which move into temporarily flooded habitats during lengthy flood seasons and consume fruits that fall into the water; and yet, we know remarkably little about the quality of seed dispersal they effect. We investigated the seed dispersal activities of two species of large-bodied, commercially important fishes (Colossoma macropomum and Piaractus brachypomus, Characidae) over 3 years in Pacaya-Samiria National Reserve (Peru). We assessed the diet of these fishes during the flood season, conducted germination trials with seeds collected from digestive tracts, and quantified fruit availability. In the laboratory, we fed fruits to captive Colossoma, quantified the proportion of seeds defecated by adult and juvenile fish, and used these seeds in additional germination experiments. Our results indicate that Colossoma and Piaractus disperse large quantities of seeds from up to 35% of the trees and lianas that fruit during the flood season. Additionally, these seeds can germinate after floodwaters recede. Overexploitation has reduced the abundance of our focal fish species, as well as changed the age structure of populations. Moreover, older fish are more effective seed dispersers than smaller, juvenile fish. Overfishing, therefore, likely selects for the poorest seed dispersers, thus disrupting an ancient interaction between seeds and their dispersal agents. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Waterfowl of a subtropical African floodplain

Many water bodies in arid southern Africa are seasonal and waterfowl habitats become restricted during the dry winters. Nevertheless, some tropical species, such as the white-faced duck, are expanding their ranges into more temperate regions where summer habitats are available, thus increasing pressure on overwintering habitats. The subtropical Pongolo River floodplain is an important overwintering area for a diverse water-fowl community that includes 13 of the 16 species that breed in South Africa and one of the few regular migrants. Historical evidence suggests that numbers of white-faced duck, which represent over 70% of the floodplain community, have increased 10-fold over the last two decades. An abundant, nutritious food (Potamogeton crispus turions) attracts waterfowl to the Pongolo floodplain during winter and an increase in bird fat reserves suggests that they leave for summer breeding grounds in good condition. Unseasonal flood releases from an upstream reservoir may cause low food supplies in late spring before the onset of the summer rainy season when breeding habitats become available. This study emphasizes the need for a better understanding of the role of winter habitats in maintaining waterfowl populations.     

Elevated CO2 and water depth regulation of methane emissions: Comparison of woody and non-woody wetland plant species

Elevated CO₂ has been shown to increase methane emissions in herbaceous wetlands, but it is not clear that this will occur in wetlands dominated by woody plants or in wetlands that are not inundated. We determined the effects of elevated CO₂ and water table position on methane emission and oxidation rates from plant-soil microcosms planted with a woody tree, Taxodium distichum, or an emergent aquatic macrophyte, Orontium aquaticum. Experiments were conducted in replicate glasshouses (n = 2) at CO₂ concentrations of either 350 or 700 ppmv. Plants were grown from seed and subjected to two water level depths, flooded (+5 cm above the soil surface) and non-flooded (–10 cm for T. distichum and –6 cm for O. aquaticum). Elevated CO₂ increased whole-plant photosynthetic rates in both water table treatments. Methane emission rates increased by 62 to 69% in the T. distichum treatment and 27 to 29% in the O. aquaticum treatment. Whole-plant photosynthesis and biomass were strongly correlated with methane emissions (r² 0.75, P 0.01). This relationship provides evidence of a tight coupling between plant and microbial activity and suggests that similar relationships from other wetland studies measured at ambient CO₂ can be extrapolated into the future. In the O. aquaticum, non-flooded treatment, methanotrophy consumed 14 and 22% (replicate glasshouses) of the methane produced in the ambient treatment compared to 29 and 36% in the elevated CO₂ treatment. However, there was no significant methane oxidation detected in the flooded treatment. We concluded that woody and non-woody wetland ecosystems growing in a future CO₂-enriched atmosphere will emit more methane regardless of water table position, but the degree of stimulation will be sensitive to changes in water table position, particularly in forested wetlands.