Regulation of nitrous oxide emission associated with benthic invertebrates

1. A number of freshwater invertebrate species emit N₂O, a greenhouse gas that is produced in their gut by denitrifying bacteria (direct N₂O emission). Additionally, benthic invertebrate species may contribute to N₂O emission from sediments by stimulating denitrification because of their bioirrigation behaviour (indirect N₂O emission). 2. Two benthic invertebrate species were studied to determine (i) the dependence of direct N₂O emission on the preferred diet of the animals, (ii) the regulation of direct N₂O emission by seasonally changing factors, such as body size, temperature and availability and (iii) the quantitative relationship between direct and indirect N₂O emission. 3. Larvae of the mayfly Ephemera danica, which prefer a bacteria‐rich detritus diet, emitted N₂O at rates of up to 90 pmol Ind.^?1 h^?1 under in situ conditions and 550 pmol Ind.^?1 h^?1 under laboratory conditions. In contrast, larvae of the alderfly Sialis lutaria, which prefer a bacteria‐poor carnivorous diet, emitted N₂O at invariably low rates of 0–20 pmol Ind.^?1 h^?1. The N₂O emission rate of E. danica larvae was positively correlated with seasonally changing factors (body size, temperature and availability). Direct N₂O emission by E. danica larvae was limited by low temperature in winter, larval development in spring and low availability in summer. 4. Both E. danica and the non‐emitting S. lutaria increased the total N₂O and N₂ emission from sediment in a density‐dependent manner. While N₂O directly emitted by benthic invertebrates can be partially consumed in the sediment (E. danica), non‐emitting species can still indirectly contribute to total N₂O emission from sediment (S. lutaria).     

Over‐expression of bacterial γ‐glutamylcysteine synthetase (GSH1) in plastids affects photosynthesis,growth and sulphur metabolism in poplar (Populus tremula × Populus alba) dependent on the resulting γ‐glutamylcysteine and glutathione levels

We compared three transgenic poplar lines over‐expressing the bacterial γ‐glutamylcysteine synthetase (GSH1) targeted to plastids. Lines Lggs6 and Lggs12 have two copies, while line Lggs20 has three copies of the transgene. The three lines differ in their expression levels of the transgene and in the accumulation of γ‐glutamylcysteine (γ‐EC) and glutathione (GSH) in leaves, roots and phloem exudates. The lowest transgene expression level was observed in line Lggs6 which showed an increased growth, an enhanced rate of photosynthesis and a decreased excitation pressure (1‐qP). The latter typically represents a lower reduction state of the plastoquinone pool, and thereby facilitates electron flow along the electron transport chain. Line Lggs12 showed the highest transgene expression level, highest γ‐EC accumulation in leaves and highest GSH enrichment in phloem exudates and roots. This line also exhibited a reduced growth, and after a prolonged growth of 4.5 months, symptoms of leaf injury. Decreased maximum quantum yield (F_v/F_m) indicated down‐regulation of photosystem II reaction centre (PSII RC), which correlates with decreased PSII RC protein D1 (PsbA) and diminished light‐harvesting complex (Lhcb1). Potential effects of changes in chloroplastic and cytosolic GSH contents on photosynthesis, growth and the whole‐plant sulphur nutrition are discussed for each line.     

Patterns and gradients of diversity in South Patagonian ombrotrophic peat bogs

Many north‐hemispherical mires seemingly untouched by drainage and cultivation are influenced by a diffuse sum of man‐made environmental changes, such as atmospherical nitrogen deposition that mask general patterns in species richness and functional group responses along resource gradients. To obtain insights into natural diversity‐environment relationships, we studied the vegetation and the peat chemistry of pristine bog ecosystems in southern Patagonia along a west–east transect across the Andes. The studied bog ecosystems covered a floristic gradient from hyperoceanic blanket bogs dominated by cushion building vascular plants via a transitional mixed type to Sphagnum‐dominated raised bogs east of the mountain range. To test the influence of resource availability on diversity patterns, species richness and functional groups were related to environmental variables by calculating general regression models and generalized additive models. Species richness showed strong linear correlations to peat chemical features and the general regression model resulted in three major environmental variables (water level, total nitrogen, NH₄Cl soluble calcium), altogether explaining 76% of variance. Functional group response illustrated a clear separation along environmental gradients. Mosses dominated at the low end of a nitrogen gradient, whereas cushion plants had their optimum at intermediate levels, and graminoids dominated at high nitrogen contents. Further shifts were related to NH₄Cl soluble calcium and water level. The models documented partly non‐linear relationships between functional group response and trophical peat properties. Within the three bog types, the calculated models differed remarkably illustrating the scale‐dependency of the explanatory factors. Our findings confirmed several general patterns of species richness and functional shifts along resource gradients in a surprisingly clear way and underpin the significance of undisturbed peatlands as reference systems for testing of ecological theory and for conservation and ecological restoration in landscapes with strong human impact.     

Meristem temperature substantially deviates from air temperature even in moderate environments: is the magnitude of this deviation species‐specific?

Meristem temperature (T_meristem) drives plant development but is hardly ever quantified. Instead, air temperature (T_air) is usually used as its approximation. Meristems are enclosed within apical buds. Bud structure and function may differ across species. Therefore, T_meristem may deviate from T_air in a species‐specific way. Environmental variables (air temperature, vapour pressure deficit, radiation, and wind speed) were systematically varied to quantify the response of T_meristem. This response was related to observations of bud structure and transpiration. Tomato and cucumber plants were used as model plants as they are morphologically distinct and usually growing in similar environments. T_meristem substantially deviated from T_air in a species‐specific manner under moderate environments. This deviation ranged between ?2.6 and 3.8 °C in tomato and between ?4.1 and 3.0 °C in cucumber. The lower T_meristem observed in cucumber was linked with the higher transpiration of the bud foliage sheltering the meristem when compared with tomato plants. We here indicate that for properly linking growth and development of plants to temperature in future applications, for instance in climate change scenarios studies, T_meristem should be used instead of T_air, as a species‐specific trait highly reliant on various environmental factors.     

Sixteen years of winter stress: an assessment of cold hardiness,growth performance and survival of hybrid poplar clones at a boreal planting site

In recent years, thousands of hectares of hybrid poplar plantations have been established in Canada for the purpose of carbon sequestration and wood production. However, boreal planting environments pose special challenges that may compromise the long‐term survival and productivity of such plantations. In this study, we evaluated the effect of winter stress, that is, frequent freeze‐thaw and extreme cold events, on growth and survival of 47 hybrid poplar clones in a long‐term field experiment. We further assessed physiological and structural traits that are potentially important for cold tolerance for a selected set of seven clones. We found that trees with narrow xylem vessels showed reduced freezing‐induced embolism and showed superior productivity after 16 growing seasons. With respect to cold hardiness of living tissues, we only observed small differences among clones in early autumn, which were nonetheless significantly correlated to growth. Maximum winter cold hardiness and the timing of leaf senescence and budbreak were not related to growth or survival. In conclusion, our data suggest that reduction of freezing‐induced embolism due to small vessel diameters is an essential adaptive trait to ensure long‐term productivity of hybrid poplar plantations in boreal planting environments.     

The Quilon Limestone,Kerala Basin,India: an archive for Miocene Indo‐Pacific seagrass beds

Reuter, M., Piller, W.E., Harzhauser, M., Kroh, A., Rögl, F. & ?ori?, S. 2010: The Quilon Limestone, Kerala Basin, India: an archive for Miocene Indo‐Pacific seagrass beds. Lethaia, Vol. 44, pp. 76–86. The facies of the fossiliferous Quilon Limestone in SW India is described for the first time in detail at the Padappakkara‐type locality. Facies (fossiliferous, micrite‐rich, bioturbated sediment with intercalated sand pockets) and faunal composition (epiphytic foraminifers, seagrass feeding Smaragdia gastropods, bioimmuration of celleporiform bryozoan colonies) indicate a seagrass environment. The large discoidal archaiasin foraminifer Pseudotaberina malabarica, in particular, is considered as a proxy for seagrass communities. Recent seagrasses have their centre of generic richness in the Indo‐Pacific where they cover wide areas in the tidal and shallow sub‐tidal zones. However, their geological record is only fragmentary and their palaeobiogeographic distribution has a big stratigraphical gap in the Miocene Western Indo‐Pacific region. The described nannoplankton flora and planktonic foraminifers from the Quilon Formation demonstrate that the deposition of the studied seagrass bed occurred in nannoplankton biozone NN3. This timing suggests formation during the closure of the Tethyan Seaway. The Quilon Limestone is thus an early Western Indo‐Pacific seagrass bed and an important step in reconstructing the history of seagrass communities. □Quilon Formation, Pseudotaberina malabarica, seagrass facies, Burdigalian, Indo‐Pacific.     

Genetic and phenotypic variation across a hybrid zone between ecologically divergent tree squirrels (Tamiasciurus)

A hybrid zone along an environmental gradient should contain a clinal pattern of genetic and phenotypic variation. This occurs because divergent selection in the two parental habitats is typically strong enough to overcome the homogenizing effects of gene flow across the environmental transition. We studied hybridization between two parapatric tree squirrels (Tamiasciurus spp.) across a forest gradient over which the two species vary in coloration, cranial morphology and body size. We sampled 397 individuals at 29 locations across a 600‐km transect to seek genetic evidence for hybridization; upon confirming hybridization, we examined levels of genetic admixture in relation to maintenance of phenotypic divergence despite potentially homogenizing gene flow. Applying population assignment analyses to microsatellite data, we found that Tamiasciurus douglasii and T. hudsonicus form two distinct genetic clusters but also hybridize, mostly within transitional forest habitat. Overall, based on this nuclear analysis, 48% of the specimens were characterized as T. douglasii, 9% as hybrids and 43% as T. hudsonicus. Hybrids appeared to be reproductively viable, as evidenced by the presence of later‐generation hybrid genotypes. Observed clines in ecologically important phenotypic traits—fur coloration and cranial morphology—were sharper than the cline of putatively neutral mtDNA, which suggests that divergent selection may maintain phenotypic distinctiveness. The relatively recent divergence of these two species (probably late Pleistocene), apparent lack of prezygotic isolating mechanisms and geographic coincidence of cline centres for both genetic and phenotypic variation suggest that environmental factors play a large role in maintaining the distinctiveness of these two species across the hybrid zone.     

Embryogenesis of Dinocras cephalotes, Perla grandis and P. marginata (Plecoptera: Perlidae) in different temperature regimes

1. Temperature dependence of embryogenesis of the three perlid stoneflies Dinocras cephalots , Perla grandis and P. marginata was investigated by means of incubation experiments. Special emphasis was laid on the effect of fluctuating temperatures and on intraspecific differences between populations from two different field sites in the Swiss prealps (i.e. River Necker and River Thur).
2. Dinocras cephalotes embryos develop between 6.3 and 26.6 °C. The lower threshold temperature is lower than has been reported for more northern populations (i.e. from England and Norway), indicating the existence of a latitudinal gradient. Perla grandis eggs only developed between 9.9 and 18.4 °C. In P. marginata , successful embryogenesis was observed between 9.9 and 18.4 °C, but not enough eggs were available to explore the threshold temperatures.
3. Embryogenesis of D. cephalotes and P. grandis was significantly faster at a 12/16 °C daily fluctuating temperature regime than at a constant 14 °C. However, no significant difference was found between the development under simulated field temperature regimes (with less distinct daily amplitudes) and constant temperatures.
4. D. cephalotes , hatching of eggs from the Necker population was much less synchronous than that in the Thur population. Since the Necker discharge regime is harsher than the Thur regime, it is possible that this asynchrony spreads the risk of destruction during bed-moving floods.     

AN ALMOST COMPLETE JUVENILE SPECIMEN OF THE CHELONIID TURTLE CTENOCHELYS STENOPORUS (HAY, 1905) FROM THE UPPER CRETACEOUS NIOBRARA FORMATION OF KANSAS,USA

Abstract: A new, unusually well‐preserved juvenile specimen of Ctenochelys stenoporus from the Niobrara Formation is described. The skull has come apart at its sutures and all bones of the braincase and ear region are preserved three‐dimensionally. This allows a detailed reconstruction of the important brain structures of a basal juvenile cheloniid turtle. It is compared with adult Ctenochelys specimens, and the major ontogenetic changes in the skull and postcranial skeleton are described. Furthermore, the specimen is compared with other fossil and extant cheloniids with well‐known braincases and the differences between basal and advanced cheloniids turtles are specified.