Complexing of glycofuranosides with calcium ion,and its effect on their acid-catalysed solvolysis

Stability constants for the calcium-ion complexes of several methyl aldo-furanosides have been determined in aqueous solution by using a potentiostatic technique with an electrode that is selective for calcium ions. The results obtained have been verified by examining the chromatographic behaviour of the compounds on a strong cation-exchange resin in the Ca²⁺ form. The rate constants for the acid-catalyzed hydrolysis and methanolysis of a few 4-chlorophenyl aldofuranosides having different complexing abilities have been determined at various concentrations of calcium chloride. The dependences of the observed salt effects on the complexing ability of the substrate are discussed.     

Continuous VOC flux measurements on boreal forest floor

Background and Aims

Volatile organic compound (VOC) emissions from biogenic sources are important contributors to chemical reactions in the air. Soil/forest floor VOCs contribute significantly to the ecosystem scale emissions, however, these emissions and their temporal and spatial variations are poorly characterised. The below-canopy VOC emissions have been measured mainly in campaigns; continuous measurements over the whole growing season are rare.

Methods

VOCs were measured from boreal forest floor over the snow-free season 2010 in southern Finland with automated flow-through chambers connected to proton transfer reaction-mass spectrometer (PTR-MS). We measured 10 masses in total, of which five quantitatively (M33, M45, M59, M69, M137).

Results

All of the fluxes showed clear diurnal and seasonal variation, being at their highest in early summer. Spatial variation in the fluxes was great and the lowest rates were found in chambers with dense vegetation cover. Also, VOCs deposition was observed regularly. Monoterpene (M137) emissions were one magnitude higher (up to 264 ng?m^?2?s^?1) than other emissions. The VOC fluxes correlated positively with temperature and light, while relative humidity correlated negatively.

Conclusions

Results indicated that forest floor plays a substantial role in the boreal forest total VOC emissions. Understanding the processes controlling VOC emissions requires more detailed analysis and long-time measurements with sufficient time resolution and analytical accuracy.     

Edin Expression in the Fat Body Is Required in the Defense Against Parasitic Wasps in Drosophila melanogaster

The cellular immune response against parasitoid wasps in Drosophila involves the activation, mobilization, proliferation and differentiation of different blood cell types. Here, we have assessed the role of Edin (elevated during infection) in the immune response against the parasitoid wasp Leptopilina boulardi in Drosophila melanogaster larvae. The expression of edin was induced within hours after a wasp infection in larval fat bodies. Using tissue-specific RNAi, we show that Edin is an important determinant of the encapsulation response. Although edin expression in the fat body was required for the larvae to mount a normal encapsulation response, it was dispensable in hemocytes. Edin expression in the fat body was not required for lamellocyte differentiation, but it was needed for the increase in plasmatocyte numbers and for the release of sessile hemocytes into the hemolymph. We conclude that edin expression in the fat body affects the outcome of a wasp infection by regulating the increase of plasmatocyte numbers and the mobilization of sessile hemocytes in Drosophila larvae.     

Pan-European δ13C values of air and organic matter from forest ecosystems

We present carbon stable isotope, δ¹³C, results from air and organic matter samples collected during 98 individual field campaigns across a network of Carboeuroflux forest sites in 2001 (14 sites) and 2002 (16 sites). Using these data, we tested the hypothesis that δ¹³C values derived from large‐scale atmospheric measurements and models, which are routinely used to partition carbon fluxes between land and ocean, and potentially between respiration and photosynthesis on land, are consistent with directly measured ecosystem‐scale δ¹³C values. In this framework, we also tested the potential of δ¹³C in canopy air and plant organic matter to record regional‐scale ecophysiological patterns. Our network estimates for the mean δ¹³C of ecosystem respired CO₂ and the related ‘discrimination’ of ecosystem respiration, δ_er and Δ_er, respectively, were ?25.6±1.9‰ and 17.8 ±2.0‰ in 2001 and ?26.6±1.5‰ and 19.0±1.6‰ in 2002. The results were in close agreement with δ¹³C values derived from regional‐scale atmospheric measurement programs for 2001, but less so in 2002, which had an unusual precipitation pattern. This suggests that regional‐scale atmospheric sampling programs generally capture ecosystem δ¹³C signals over Europe, but may be limited in capturing some of the interannual variations. In 2001, but less so in 2002, there were discernable longitudinal and seasonal trends in δ_er. From west to east, across the network, there was a general enrichment in ¹³C (～3‰ and ～1‰ for the 2 years, respectively) consistent with increasing Gorczynski continentality index for warmer and drier conditions. In 2001 only, seasonal ¹³C enrichment between July and September, followed by depletion in November (from about ?26.0‰ to ?24.5‰ to ?30.0‰), was also observed. In 2001, July and August δ_er values across the network were significantly related to average daytime vapor pressure deficit (VPD), relative humidity (RH), and, to a lesser degree, air temperature (T_a), but not significantly with monthly average precipitation (P_m). In contrast, in 2002 (a much wetter peak season), δ_er was significantly related with T_a, but not significantly with VPD and RH. The important role of plant physiological processes on δ_er in 2001 was emphasized by a relatively rapid turnover (between 1 and 6 days) of assimilated carbon inferred from time‐lag analyses of δ_er vs. meteorological parameters. However, this was not evident in 2002. These analyses also noted corresponding diurnal cycles of δ_er and meteorological parameters in 2001, indicating a rapid transmission of daytime meteorology, via physiological responses, to the δ_er signal during this season. Organic matter δ¹³C results showed progressive ¹³C enrichment from leaves, through stems and roots to soil organic matter, which may be explained by ¹³C fractionation during respiration. This enrichment was species dependent and was prominent in angiosperms but not in gymnosperms. δ¹³C values of organic matter of any of the plant components did not well represent short‐term δ_er values during the seasonal cycle, and could not be used to partition ecosystem respiration into autotrophic and heterotrophic components.     

Evaluating the utility of stable isotope analyses of archived freshwater sample materials

We evaluated the potential utility of stable isotope analysis of tissues commonly archived by aquatic biologists. Previous studies with chemically preserved samples have shown contradictory results, which present an obstacle for the use of archived sample materials. We tested the effects of ethanol and formalin preservation on zooplankton and of ethanol on benthic macroinvertebrate δ¹³C and δ¹⁵N values. We found that neither formalin nor ethanol had a significant effect on δ¹³C and δ¹⁵N values of preserved zooplankton. Nor did ethanol significantly affect δ¹³C or δ¹⁵N values of macroinvertebrates. However, ethanol preservation slightly, but significantly decreased C:N ratios of both zooplankton and macroinvertebrates, probably reflecting some extraction of lipids. Overall, the effects of preservatives on δ¹³C and δ¹⁵N values that we observed were minor. We also compared δ¹³C and δ¹⁵N values analysed from roach scales and perch operculum bones with those analysed from muscle tissue. Decalcification of scales and operculum bones only slightly improved our comparison to muscle tissue δ¹³C and δ¹⁵N values. Decalcified scales had slightly higher δ¹³C and lower δ¹⁵N values. Similarly, decalcified operculum bones showed slightly increased δ¹³C and decreased δ¹⁵N values to those for fish muscle. Our results confirm that scales and operculum bones can provide a suitable proxy for fish muscle in isotope studies with minor correction. We conclude that various archived sample materials can indeed be used with confidence for historical reconstructions of freshwater food webs by stable isotope analysis. Handling editor: K. Martens     

Whole-Lake Sugar Addition Demonstrates Trophic Transfer of Dissolved Organic Carbon to Top Consumers

Terrestrial dissolved organic carbon (DOC) provides an external carbon source to lake ecosystems. However, there is ongoing debate about whether external DOC that enters a lake can pass up the food web to support top consumers. We show, from experimental manipulation of a whole lake, that externally loaded DOC can contribute appreciably to fish biomass. Monthly additions of cane sugar with a distinct carbon stable isotope value during 2 years rapidly enriched the ¹³C content of zooplankton and macroinvertebrates, with a more gradual ¹³C enrichment of fish. After sugar addition stopped, the ¹³C content of consumers reverted towards original values. A simple isotope mixing model indicated that by the end of the sugar addition almost 20% of fish carbon in the lake was derived from the added sugar. Our results provide the first direct experimental demonstration at relevant ecological spatial and temporal scales that externally loaded DOC to lakes can indeed transfer to top consumers.     

On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm

This paper discusses the advantages and disadvantages of the different methods that separate net ecosystem exchange (NEE) into its major components, gross ecosystem carbon uptake (GEP) and ecosystem respiration (R_eco). In particular, we analyse the effect of the extrapolation of night‐time values of ecosystem respiration into the daytime; this is usually done with a temperature response function that is derived from long‐term data sets. For this analysis, we used 16 one‐year‐long data sets of carbon dioxide exchange measurements from European and US‐American eddy covariance networks. These sites span from the boreal to Mediterranean climates, and include deciduous and evergreen forest, scrubland and crop ecosystems. We show that the temperature sensitivity of R_eco, derived from long‐term (annual) data sets, does not reflect the short‐term temperature sensitivity that is effective when extrapolating from night‐ to daytime. Specifically, in summer active ecosystems the long‐term temperature sensitivity exceeds the short‐term sensitivity. Thus, in those ecosystems, the application of a long‐term temperature sensitivity to the extrapolation of respiration from night to day leads to a systematic overestimation of ecosystem respiration from half‐hourly to annual time‐scales, which can reach >25% for an annual budget and which consequently affects estimates of GEP. Conversely, in summer passive (Mediterranean) ecosystems, the long‐term temperature sensitivity is lower than the short‐term temperature sensitivity resulting in underestimation of annual sums of respiration. We introduce a new generic algorithm that derives a short‐term temperature sensitivity of R_eco from eddy covariance data that applies this to the extrapolation from night‐ to daytime, and that further performs a filling of data gaps that exploits both, the covariance between fluxes and meteorological drivers and the temporal structure of the fluxes. While this algorithm should give less biased estimates of GEP and R_eco, we discuss the remaining biases and recommend that eddy covariance measurements are still backed by ancillary flux measurements that can reduce the uncertainties inherent in the eddy covariance data.     

Evaluation of six process‐based forest growth models using eddy‐covariance measurements of CO2 and H2O fluxes at six forest sites in Europe

Reliable models are required to assess the impacts of climate change on forest ecosystems. Precise and independent data are essential to assess this accuracy. The flux measurements collected by the EUROFLUX project over a wide range of forest types and climatic regions in Europe allow a critical testing of the process‐based models which were developed in the LTEEF project. The ECOCRAFT project complements this with a wealth of independent plant physiological measurements. Thus, it was aimed in this study to test six process‐based forest growth models against the flux measurements of six European forest types, taking advantage of a large database with plant physiological parameters. The reliability of both the flux data and parameter values itself was not under discussion in this study. The data provided by the researchers of the EUROFLUX sites, possibly with local corrections, were used with a minor gap‐filling procedure to avoid the loss of many days with observations. The model performance is discussed based on their accuracy, generality and realism. Accuracy was evaluated based on the goodness‐of‐fit with observed values of daily net ecosystem exchange, gross primary production and ecosystem respiration (gC m^?2 d^?1), and transpiration (kg H₂O m^?2 d^?1). Moreover, accuracy was also evaluated based on systematic and unsystematic errors. Generality was characterized by the applicability of the models to different European forest ecosystems. Reality was evaluated by comparing the modelled and observed responses of gross primary production, ecosystem respiration to radiation and temperature. The results indicated that: Accuracy. All models showed similar high correlation with the measured carbon flux data, and also low systematic and unsystematic prediction errors at one or more sites of flux measurements. The results were similar in the case of several models when the water fluxes were considered. Most models fulfilled the criteria of sufficient accuracy for the ability to predict the carbon and water exchange between forests and the atmosphere. Generality. Three models of six could be applied for both deciduous and coniferous forests. Furthermore, four models were applied both for boreal and temperate conditions. However, no severe water‐limited conditions were encountered, and no year‐to‐year variability could be tested. Realism. Most models fulfil the criterion of realism that the relationships between the modelled phenomena (carbon and water exchange) and environment are described causally. Again several of the models were able to reproduce the responses of measurable variables such as gross primary production (GPP), ecosystem respiration and transpiration to environmental driving factors such as radiation and temperature. Stomatal conductance appears to be the most critical process causing differences in predicted fluxes of carbon and water between those models that accurately describe the annual totals of GPP, ecosystem respiration and transpiration. As a conclusion, several process‐based models are available that produce accurate estimates of carbon and water fluxes at several forest sites of Europe. This considerable accuracy fulfils one requirement of models to be able to predict the impacts of climate change on the carbon balance of European forests. However, the generality of the models should be further evaluated by expanding the range of testing over both time and space. In addition, differences in behaviour between models at the process level indicate requirement of further model testing, with special emphasis on modelling stomatal conductance realistically.     

The community of needle endophytes reflects the current physiological state of Norway spruce

This study investigated fungal endophytes in the needles of Norway spruce (Picea abies) cuttings in relation to host tree growth. We also determined the prevalence of endophytes in needles incubated for six months. The cuttings originated from clonal origins showing slow- and fast-growth in long-term field trials but the heritable differences in growth rate were not yet detected among the studied cutting. Endophytes were isolated from surface-sterilized needles with culture-free DNA techniques. No significant differences were observed between endophyte communities of slow- and fast-growing clonal origins. However, the endophyte community correlated with the current growth rate of cuttings suggesting that endophytes reflect short- rather than long-term performance of a host. The concentration of condensed tannins was similar in slow- and fast-growing clonal origins but it showed a negative relationship with endophyte species richness, implying that these secondary compounds may play an important role in spruce tolerance against fungal infections. More than a third of endophyte species were detected in both fresh and decomposing needles, indicating that many needle endophytes are facultative saprotrophs. Several potentially pathogenic fungal species were also found within the community of saprotrophic endophytes.