Effects of fire on CO2 , CH4 , and N2 O exchange in a well-drained Arctic heath ecosystem.

Wildfire frequency and expanse in the Arctic have increased in recent years and are projected to increase further with changes in climatic conditions due to warmer and drier summers. Yet, there is a lack of knowledge about the impacts such events may have on the net greenhouse gas (GHG) balances in Arctic ecosystems. We investigated in situ effects of an experimental fire in 2017 on carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2 O) surface fluxes in the most abundant tundra ecosystem in West Greenland in ambient and warmer conditions. Measurements from the growing seasons 2017 to 2019 showed that burnt areas became significant net CO2 sources for the entire study period, driven by increased ecosystem respiration (ER) immediately after the fire and decreased gross ecosystem production (GEP). Warming by open-top chambers significantly increased both ER and GEP in control, but not in burnt plots. In contrast to CO2 , measurements suggest that the overall sink capacity of atmospheric CH4 , as well as net N2 O emissions, were not affected by fire in the short term, but only immediately after the fire. The minor effects on CH4 and N2 O, which was surprising given the significantly higher nitrate availability observed in burnt plots. However, the minor effects are aligned with the lack of significant effects of fire on soil moisture and soil temperature. Net uptake and emissions of all three GHG from burnt soils were less temperature-sensitive than in the undisturbed control plots. Overall, this study highlights that wildfires in a typical tundra ecosystem in Greenland may not lead to markedly increased net GHG emissions other than CO2 . Additional investigations are needed to assess the consequences of more severe fires.

Challenges in measuring nitrogen isotope signatures in inorganic nitrogen forms: An interlaboratory comparison of three common measurement approaches.

RATIONALE: Stable isotope approaches are increasingly applied to better understand the cycling of inorganic nitrogen (Ni ) forms, key limiting nutrients in terrestrial and aquatic ecosystems. A systematic comparison of the accuracy and precision of the most commonly used methods to analyze δ15 N in NO3 - and NH4 + and interlaboratory comparison tests to evaluate the comparability of isotope results between laboratories are, however, still lacking. METHODS: Here, we conducted an interlaboratory comparison involving 10 European laboratories to compare different methods and laboratory performance to measure δ15 N in NO3 - and NH4 + . The approaches tested were (a) microdiffusion (MD), (b) chemical conversion (CM), which transforms Ni to either N2 O (CM-N2 O) or N2 (CM-N2 ), and (c) the denitrifier (DN) methods. RESULTS: The study showed that standards in their single forms were reasonably replicated by the different methods and laboratories, with laboratories applying CM-N2 O performing superior for both NO3 - and NH4 + , followed by DN. Laboratories using MD significantly underestimated the "true" values due to incomplete recovery and also those using CM-N2 showed issues with isotope fractionation. Most methods and laboratories underestimated the at%15 N of Ni of labeled standards in their single forms, but relative errors were within maximal 6% deviation from the real value and therefore acceptable. The results showed further that MD is strongly biased by nonspecificity. The results of the environmental samples were generally highly variable, with standard deviations (SD) of up to ± 8.4‰ for NO3 - and ± 32.9‰ for NH4 + ; SDs within laboratories were found to be considerably lower (on average 3.1‰). The variability could not be connected to any single factor but next to errors due to blank contamination, isotope normalization, and fractionation, and also matrix effects and analytical errors have to be considered. CONCLUSIONS: The inconsistency among all methods and laboratories raises concern about reported δ15 N values particularly from environmental samples.

Accumulation of soil carbon under elevated CO2 unaffected by warming and drought.

Elevated atmospheric CO2 concentration and climate change may substantially alter soil carbon (C) dynamics, which in turn may impact future climate through feedback cycles. However, only very few field experiments worldwide have combined elevated CO2 (eCO2 ) with both warming and changes in precipitation in order to study the potential combined effects of changes in these fundamental drivers of C cycling in ecosystems. We exposed a temperate heath/grassland to eCO2 , warming, and drought, in all combinations for 8 years. At the end of the study, soil C stocks were on average 0.927 kg C/m2 higher across all treatment combinations with eCO2 compared to ambient CO2 treatments (equal to an increase of 0.120 ± 0.043 kg C m-2  year-1 ), and showed no sign of slowed accumulation over time. However, if observed pretreatment differences in soil C are taken into account, the annual rate of increase caused by eCO2 may be as high as 0.177 ± 0.070 kg C m-2  year-1 . Furthermore, the response to eCO2 was not affected by simultaneous exposure to warming and drought. The robust increase in soil C under eCO2 observed here, even when combined with other climate change factors, suggests that there is continued and strong potential for enhanced soil carbon sequestration in some ecosystems to mitigate increasing atmospheric CO2 concentrations under future climate conditions. The feedback between land C and climate remains one of the largest sources of uncertainty in future climate projections, yet experimental data under simulated future climate, and especially including combined changes, are still scarce. Globally coordinated and distributed experiments with long-term measurements of changes in soil C in response to the three major climate change-related global changes, eCO2 , warming, and changes in precipitation patterns, are, therefore, urgently needed.

Biochar application as a tool to decrease soil nitrogen losses (NH3 volatilization, N2 O emissions, and N leaching) from croplands: Options and mitigation strength in a global perspective.

Biochar application to croplands has been proposed as a potential strategy to decrease losses of soil-reactive nitrogen (N) to the air and water. However, the extent and spatial variability of biochar function at the global level are still unclear. Using Random Forest regression modelling of machine learning based on data compiled from the literature, we mapped the impacts of different biochar types (derived from wood, straw, or manure), and their interactions with biochar application rates, soil properties, and environmental factors, on soil N losses (NH3 volatilization, N2 O emissions, and N leaching) and crop productivity. The results show that a suitable distribution of biochar across global croplands (i.e., one application of <40 t ha-1 wood biochar for poorly buffered soils, such as those characterized by soil pH<5, organic carbon<1%, or clay>30%; and one application of <80 t ha-1 wood biochar, <40 t ha-1 straw biochar, or <10 t ha-1 manure biochar for other soils) could achieve an increase in global crop yields by 222-766 Tg yr-1 (4%-16% increase), a mitigation of cropland N2 O emissions by 0.19-0.88 Tg N yr-1 (6%-30% decrease), a decline of cropland N leaching by 3.9-9.2 Tg N yr-1 (12%-29% decrease), but also a fluctuation of cropland NH3 volatilization by -1.9-4.7 Tg N yr-1 (-12%-31% change). The decreased sum of the three major reactive N losses amount to 1.7-9.4 Tg N yr-1 , which corresponds to 3%-14% of the global cropland total N loss. Biochar generally has a larger potential for decreasing soil N losses but with less benefits to crop production in temperate regions than in tropical regions.

Postfire nitrogen balance of Mediterranean shrublands: Direct combustion losses versus gaseous and leaching losses from the postfire soil mineral nitrogen flush.

Fire is a major factor controlling global carbon (C) and nitrogen (N) cycling. While direct C and N losses caused by combustion have been comparably well established, important knowledge gaps remain on postfire N losses. Here, we quantified both direct C and N combustion losses as well as postfire gaseous losses (N2 O, NO and N2 ) and N leaching after a high-intensity experimental fire in an old shrubland in central Spain. Combustion losses of C and N were 9.4 Mg C/ha and 129 kg N/ha, respectively, representing 66% and 58% of initial aboveground vegetation and litter stocks. Moreover, fire strongly increased soil mineral N concentrations by several magnitudes to a maximum of 44 kg N/ha 2 months after the fire, with N largely originating from dead soil microbes. Postfire soil emissions increased from 5.4 to 10.1 kg N ha-1  year-1 for N2 , from 1.1 to 1.9 kg N ha-1  year-1 for NO and from 0.05 to 0.2 kg N ha-1  year-1 for N2 O. Maximal leaching losses occurred 2 months after peak soil mineral N concentrations, but remained with 0.1 kg N ha-1  year-1 of minor importance for the postfire N mass balance. 15 N stable isotope labelling revealed that 33% of the mineral N produced by fire was incorporated in stable soil N pools, while the remainder was lost. Overall, our work reveals significant postfire N losses dominated by emissions of N2 that need to be considered when assessing fire effects on ecosystem N cycling and mass balance. We propose indirect N gas emissions factors for the first postfire year, equalling to 7.7% (N2 -N), 2.7% (NO-N) and 5.0% (N2 O-N) of the direct fire combustion losses of the respective N gas species.

Paddy soil drainage influences residue carbon contribution to methane emissions.

Water drainage is an important mitigation option for reducing CH4 (methane) emissions from residue-amended paddy soils. Several studies have indicated a long-term reduction in CH4 emissions, even after re-flooding, suggesting that the mechanism goes beyond creating temporary oxidized conditions in the soil. In this pot trial, the effects of different drainage patterns on straw-derived CH4 and CO2 (carbon dioxide) emissions were compared to identify the balance between straw-carbon CH4 and CO2 emissions influenced by soil aeration over different periods, including effects of drainage on emissions during re-flooding. The water treatments included were: continuous flooding [C] as the control and five drainage patterns (pre-planting drainage [P], early-season drainage [E], midseason drainage [M], pre-planting plus midseason drainage [PM], early-season-plus-midseason drainage [EM]). An equal amount of 13C-enriched rice straw was applied to all treatments to identify straw-derived 13C-gas emissions from soil carbon derived emissions. The highest fluxes of CH4 and δ13C-CH4 were recorded from the control treatment in the first week after straw application. The CH4 flux and δ13C-CH4 were reduced the most (0.1-0.8 µg CH4 g-1 soil day-1 and -13 to -34‰) in the pre-planting and pre-planting plus midseason drainage treatments at day one after transplanting. Total and straw-derived CH4 emissions were reduced by 69% and 78% in pre-planting drainage and 77% and 87% in pre-planting plus midseason drainage respectively, compared to control. The early-season, midseason, pre-planting plus midseason and early-season-plus-midseason drainage treatments resulted in higher total and straw-derived CO2 emissions compared to the control and pre-planting drainage treatments. The pre-planting and pre-planting plus midseason drainage treatments lowered the global warming potential by 47-53%, and early-season and early-season-plus-midseason drainage treatments reduced it by 24-31% compared to control. By using labelled crop residues, this experiment demonstrates a direct link between early drainage and reduced CH4 emissions from incorporated crop residues, eventually leading to a reduction in total global warming potential. It is suggested that accelerated decomposition of the residues during early season drainage prolonged the reduction in CH4 emissions. Therefore, it is important to introduce the early drainage as an effective measure to mitigate CH4 emissions from crop residues.

Activity of Type I Methanotrophs Dominates under High Methane Concentration: Methanotrophic Activity in Slurry Surface Crusts as Influenced by Methane, Oxygen, and Inorganic Nitrogen.

Livestock slurry is a major source of atmospheric methane (CH), but surface crusts harboring methane-oxidizing bacteria (MOB) could mediate against CH emissions. This study examined conditions for CH oxidation by in situ measurements of oxygen (O) and nitrous oxide (NO), as a proxy for inorganic N transformations, in intact crusts using microsensors. This was combined with laboratory incubations of crust material to investigate the effects of O, CH, and inorganic N on CH oxidation, using CH to trace C incorporation into lipids of MOB. Oxygen penetration into the crust was 2 to 14 mm, confining the potential for aerobic CH oxidation to a shallow layer. Nitrous oxide accumulated within or below the zone of O depletion. With 10 ppmv CH there was no O limitation on CH oxidation at O concentrations as low as 2%, whereas CH oxidation at 10 ppmv CH was reduced at ≤5% O. As hypothesized, CH oxidation was in general inhibited by inorganic N, especially NO, and there was an interaction between N inhibition and O limitation at 10 ppmv CH, as indicated by consistently stronger inhibition of CH oxidation by NH and NO at 3% compared with 20% O. Recovery of C in phospholipid fatty acids suggested that both Type I and Type II MOB were active, with Type I dominating high-concentration CH oxidation. Given the structural heterogeneity of crusts, CH oxidation activity likely varies spatially as constrained by the combined effects of CH, O, and inorganic N availability in microsites.

Common arbuscular mycorrhizal networks amplify competition for phosphorus between seedlings and established plants.

Common mycorrhizal networks (CMNs) influence competition between plants, but reports regarding their precise effect are conflicting. We studied CMN effects on phosphorus (P) uptake and growth of seedlings as influenced by various disruptions of network components. Tomato (Solanum lycopersicon) seedlings grew into established networks of Rhizophagus irregularis and cucumber (Cucumis sativus) in two experiments. One experiment studied seedling uptake of (32)P in the network in response to cutting of cucumber shoots; the other analysed seedling uptake of P and nitrogen (N) in the presence of intact or severed arbuscular mycorrhizal fungus networks and at two soil P concentrations. Pre-established and intact networks suppressed growth of tomato seedlings. Cutting of cucumber shoots mitigated P deficiency symptoms of seedlings, which obtained access to P in the extraradical mycelium and thereby showed improved growth. Solitary seedlings growing in a network patch that had been severed from the CMN also grew much better than seedlings of the corresponding CMN. Interspecific and size-asymmetric competition between plants may be amplified rather than relaxed by CMNs that transfer P to large plants providing most carbon and render small plants P deficient. It is likely that grazing or senescence of the large plants will alleviate the network-induced suppression of seedling growth.

In situ 13CO2 pulse-labeling in a temperate heathland--development of a mobile multi-plot field setup.

RATIONALE: Pulse-labeling with (13)CO2 and the subsequent analysis of (13)C-carbon via isotope ratio mass spectrometry (IRMS) have been shown to be an excellent method to investigate the terrestrial carbon cycle. Improving (13)CO2 manipulation experiments will facilitate our understanding of carbon cycling processes. METHODS: A mobile field setup for in situ (13)CO2 pulse-labeling was developed for low vegetation field experiments. Two pulse-labeling experiments were conducted in a Danish heathland in September 2010 (Exp1) and May 2011 (Exp2). A flow-through system was developed where labeling chambers were supplied with (13)CO2-enriched air from a gas reservoir. Reservoir and chamber air was sampled over the course of the experiments and analyzed for CO2 concentration and isotopic composition on a GasBench II interfaced with an isotope ratio mass spectrometer. The soil CO2 efflux and the atom% excess in soil respiration were assessed after the (13)CO2-pulse to verify the setup performance. RESULTS: The carbon dioxide concentrations and (13)CO2 enrichments were stable during the experiments. The CO2 concentrations conformed to the aimed values, whereas the (13)CO2 enrichments were lower than expected. The sources of error for the deviation in observed atom% (13)CO2 values are discussed, and a measurement procedure is suggested for samples highly enriched in (13)C by using adjusted resistor settings of the mass spectrometer. However, more work has to be done. Enrichment patterns in soil respiration agree with published observations indicating satisfactory performance of the developed system. CONCLUSIONS: A mobile flow-through system suitable for continuous in situ (13)CO2 pulse-labeling was successfully developed that is easily applicable in remote natural ecosystems.

Terrestrial plant methane production and emission.

In this minireview, we evaluate all experimental work published on the phenomenon of aerobic methane (CH(4) ) generation in terrestrial plants and plant. Clearly, despite much uncertainty and skepticism, we conclude that the phenomenon is true. Four stimulating factors have been observed to induce aerobic plant CH(4) production, i.e. cutting injuries, increasing temperature, ultraviolet radiation and reactive oxygen species. Further, we analyze rates of measured emission of aerobically produced CH(4) in pectin and in plant tissues from different studies and argue that pectin is very far from the sole contributing precursor. In consequence, scaling up of aerobic CH(4) emission needs to take into consideration other potential sources than pectin. Due to the large uncertainties related to effects of stimulating factors, genotypic responses and type of precursors, we conclude that current attempts for upscaling aerobic CH(4) into a global budget is inadequate. Thus it is too early to draw the line under the aerobic methane emission in plants. Future work is needed for establishing the relative contribution of several proven potential CH(4) precursors in plant material.

Fire increases soil nitrogen retention and alters nitrogen uptake patterns among dominant shrub species in an Arctic dry heath tundra.

Climate change increases the frequency and severity of fire in the Arctic tundra regions. We assessed effects of fire in combination with summer warming on soil biogeochemical N- and P cycles with a focus on mineral N over two years following an experimental fire in a dry heath tundra, West Greenland. We applied stable isotopes (15NH4+-N and 15NO3--N) to trace the post-fire mineral N pools. The partitioning of 15N in the bulk soils, soil dissolved organic N (TDN), microbes and plants (roots and leaves) was established. The fire tended to increase microbial P pools by four-fold at both one and two years after the fire. Two years after the fire, the bulk soil 15N recovery has decreased to 10.4% in unburned plots while relatively high recovery was maintained (30%) in burned plots, suggesting an increase in soil N retention after the fire. The contribution of microbial 15N recovery to bulk soil 15N recovery increased from 11.2% at 21 days to 31.5% two years after the fire, suggesting that higher post-fire N retention was due largely to the increased incorporation of N into microbial biomass. Fire also increased 15N recovery in bulk roots after one and two years, but only under summer warming. This suggests that higher retention of post-fire N can strongly increase the potential for N uptake of recovering plants under a future warmer climate. There was significantly lower 15N enrichment of Betula nana leaves while higher 15N enrichment of Vaccinium uliginosum leaves (after three years) in burned than control plots. This shows that fire can alter the N uptake differently among dominant shrub species in this tundra ecosystem, and implies that wildfires may change plant species composition in the longer term.

Organic matter flow in the food web at a temperate heath under multifactorial climate change.

The rising atmospheric CO(2) concentration, increasing temperature and changed patterns of precipitation currently expose terrestrial ecosystems to altered environmental conditions. This may affect belowground nutrient cycling through its intimate relationship with the belowground decomposers. Three climate change factors (elevated CO(2), increased temperature and drought) were investigated in a full factorial field experiment at a temperate heathland location. The combined effect of biotic and abiotic factors on nitrogen and carbon flows was traced in plant root → litter → microbe → detritivore/omnivore → predator food-web for one year after amendment with (15)N(13)C(2)-glycine. Isotope ratio mass spectrometry (IRMS) measurement of (15)N/(14)N and (13)C/(12)C in soil extracts and functional ecosystem compartments revealed that the recovery of (15)N sometimes decreased through the chain of consumption, with the largest amount of bioactive (15)N label pool accumulated in the microbial biomass. The elevated CO(2) concentration at the site for 2 years increased the biomass, the (15)N enrichment and the (15)N recovery in detritivores. This suggests that detritivore consumption was controlled by both the availability of the microbial biomass, a likely major food source, and the climatic factors. Furthermore, the natural abundance δ(13)C of enchytraeids was significantly altered in CO(2)-fumigated plots, showing that even small changes in δ(13)C-CO(2) can be used to detect transfer of carbon from primary producers to detritivores. We conclude that, in the short term, the climate change treatments affected soil organism activity, possibly with labile carbohydrate production controlling the microbial and detritivore biomass, with potential consequences for the decomposition of detritus and nutrient cycling. Hence, there appears to be a strong coupling of responses in carbon and nitrogen cycling at this temperate heath.

Effects of experimental fire in combination with climate warming on greenhouse gas fluxes in Arctic tundra soils.

The frequency and severity of fire is increasing in Arctic tundra regions with climate change. Here we investigated effects of experimental low-intensity fire and shrub cutting, in combination with warming, on soil biogeochemical cycles and post-fire greenhouse gas (GHG) emissions in a dry heath tundra, West Greenland. We performed in vitro incubation experiments based on soil samples collected for up to two years after the fire. We observed tendency for increased soil nitrate (14-fold) and significant increases in soil ammonium and phosphate (four-fold and five-fold, respectively) two years after the fire, but no effects of shrub cutting on these compounds. Thus, changes appear to be largely due to fire effects rather than indirect effects by vegetation destruction. Two years after fire, nitrous oxide (N2O) and carbon dioxide (CO2) production was significantly increased (three-fold and 32% higher, respectively), in burned than unburned soils, while methane (CH4) uptake remained unchanged. This stimulated N2O and CO2 production by the fire, however, was only apparent under conditions when soil was at maximum water holding capacity, suggesting that fire effects can be masked under dry conditions in this tundra ecosystem. There were positive effects by modest 2.5 °C warming on CO2 production in control but not in burned soils, suggesting that fire may decrease the temperature response in soil respiration. Methane uptake was neither altered by the modest warming in shrub-cut nor in burned soils after two years, suggesting that the removal of vegetation may play a key role in controlling future temperature response of CH4 oxidation. Altogether, our results show that post-fire tundra soils have the potential to enhance soil GHG emissions (e.g. N2O and CO2) especially during episodes with wet soil conditions. On the other hand, the lack of warming responses in post-fire soil respiration may weaken this positive feedback to climate change.

Analysis of narwhal tusks reveals lifelong feeding ecology and mercury exposure.

The ability of animals to respond to changes in their environment is critical to their persistence. In the Arctic, climate change and mercury exposure are two of the most important environmental threats for top predators.1-3 Rapid warming is causing precipitous sea-ice loss, with consequences on the distribution, composition, and dietary ecology of species4-7 and, thus, exposure to food-borne mercury.8 Current understanding of global change and pollution impacts on Arctic wildlife relies on single-time-point individual data representing a snapshot in time. These data often lack comprehensive temporal resolution and overlook the cumulative lifelong nature of stressors as well as individual variation. To overcome these challenges, we explore the unique capacity of narwhal tusks to characterize chronological lifetime biogeochemical profiles, allowing for investigations of climate-induced dietary changes and contaminant trends. Using temporal patterns of stable isotopes (δ13C and δ15N) and mercury concentrations in annually deposited dentine growth layer groups in 10 tusks from Northwest Greenland (1962-2010), we show surprising plasticity in narwhal feeding ecology likely resulting from climate-induced changes in sea-ice cover, biological communities, and narwhal migration. Dietary changes consequently impacted mercury exposure primarily through trophic magnification effects. Mercury increased log-linearly over the study period, albeit with an unexpected rise in recent years, likely caused by increased emissions and/or greater bioavailability in a warmer, ice-free Arctic. Our findings are consistent with an emerging pattern in the Arctic of reduced sea-ice leading to changes in the migration, habitat use, food web, and contaminant exposure in Arctic top predators.

Combined effects of glacial retreat and penguin activity on soil greenhouse gas fluxes on South Georgia, sub-Antarctica.

The effects of soil succession after glacial retreat and fertilisation by marine animals are known to have major impacts on soil greenhouse gas (GHG) fluxes in polar terrestrial ecosystems. While in many polar coastal areas retreating glaciers open up new ground for marine animals to colonise, little is known about the combination of both factors on the local GHG budget. We studied the magnitude of GHG fluxes (CO2, CH4 and N2O) on the combined effect of glacial retreat and penguin-induced fertilisation along a transect protruding into the world's largest King Penguin (Aptenodytes patagonicus) colony at Saint Andrews Bay on sub-Antarctic South Georgia. GHG production and consumption rates were assessed based on laboratory incubations of intact soil cores and nutrients and water additional experimental incubations. The oldest soils along the transect show significant higher contents of soil carbon, nutrients and moisture and were strongly influenced by penguin activity. We found a net CH4 consumption along the entire transect with a marked decrease within the penguin colony. CO2 production strongly increased along the transect, while N2O production rates were low near the glacier front and increased markedly within the penguin colony. Controlled applications of guano resulted in a significant increase in CO2 and N2O production, and decrease in CH4 consumption, except for sites already strongly influenced by penguin activity. The results show that soil microbial activity promptly catalyses a turnover of soil C and atmospheric methane oxidation in de-glaciated forelands. The methane oxidizers, however, may increase relatively slowly in their capacity to oxidise atmospheric CH4. Results show also that the increase of nutrients by penguins reduces CH4 oxidation whereas N2O production is greatly increased. A future expansion of penguins into newly available ice-free polar coastal areas may therefore markedly increase the local GHG budget.

Individual variation of persistent organic pollutants in relation to stable isotope ratios, sex, reproductive phase and oxidative status in Scopoli's shearwaters (Calonectris diomedea) from the Southern Mediterranean.

Little is known about the accumulation of persistent organic pollutants (POPs) and its consequences for seabirds in the Mediterranean basin. We characterised the plasma contaminant profile (polychlorinated biphenyls ΣPCBs; organochlorine pesticides ΣOCPs; polybrominated diphenyl ethers ΣPBDEs) of a population of the seabird Scopoli's shearwater (Calonectris diomedea) that breeds in the southern Mediterranean (Linosa Island) and investigated (i) whether sex, stable isotope ratios (related to diet), reproductive phase (early incubation vs. late breeding season) and body mass explained variation in contaminant burden and (ii) whether they predict health-related variables. The predominant category of POPs was ΣPCBs contributing between 53.0 and 92.4% of the total POPs in each shearwater. The percentage contribution of ΣOCPs to total POPs ranged between 7.6 and 47.0%, while that of ΣPBDEs ranged between <1% and 22.1%. Near the end of the breeding season, concentrations of ΣPCBs, ΣOCPs and ΣPOPs were significantly higher than at the beginning of the incubation period. ΣPBDEs were higher in males than females near the end of the breeding season, while they were higher in females than males at the beginning of the egg incubation period. Carbon- and nitrogen isotope ratios and individual body mass were not significantly associated with any contaminant class. Mates differed in the concentration of POPs, but they had similar stable isotope values. There was little evidence for a connection between contaminants and blood-based markers of oxidative balance. None of the contaminants predicted the probability of a bird being resighted as a breeder the following year. Thus, although POPs were present at high concentrations in some individuals, our study suggests little concern regarding POP exposure for this shearwater population.

The first exposure assessment of legacy and unrestricted brominated flame retardants in predatory birds of Pakistan.

The exposure to legacy polybrominated diphenyl ethers (PBDEs), hexabromocyclododecanes (HBCDDs) and unrestricted 1,2-bis (2,4,6-tribromophenoxy) ethane (BTBPE), bis (2-ethylhexyl)-2,3,4,5-tetrabromophthalate (BEH-TEBP) and 2-ethylhexyl-2,3,4,5-tetrabromo-benzoate (EH-TBB) was examined in tail feathers of 76 birds belonging to ten predatory species inhabiting Pakistan. In addition, different feather types of six individuals of Black kite (Milvus migrans) were compared for their brominated flame retardant (BFR) levels. Black kite was found to be the most contaminated species with a median (minimum-maximum) tail feather concentration of 2.4 (0.70-7.5) ng g-1 dw for ∑PBDEs, 1.5 (0.5-8.1) ng g-1 dw for ∑HBCDDs and 0.10 ( 0.05 for both). Similarly, no significant concentration differences were observed among different feather types (all P > 0.05) suggesting their similar exposure. While variables such as species, trophic guild and δ15N values were evaluated as major predictors for BFR accumulation in the studied species, we predict that combined effects of just mentioned factors may govern the intra- and interspecific differences in BFR contamination profiles. We urge for further investigation of BFR exposure and potential toxicological effects in predatory birds from Asia with a more extensive sample size per species and location.

Long-term and realistic global change manipulations had low impact on diversity of soil biota in temperate heathland.

In a dry heathland ecosystem we manipulated temperature (warming), precipitation (drought) and atmospheric concentration of CO2 in a full-factorial experiment in order to investigate changes in below-ground biodiversity as a result of future climate change. We investigated the responses in community diversity of nematodes, enchytraeids, collembolans and oribatid mites at two and eight years of manipulations. We used a structural equation modelling (SEM) approach analyzing the three manipulations, soil moisture and temperature, and seven soil biological and chemical variables. The analysis revealed a persistent and positive effect of elevated CO2 on litter C:N ratio. After two years of treatment, the fungi to bacteria ratio was increased by warming, and the diversities within oribatid mites, collembolans and nematode groups were all affected by elevated CO2 mediated through increased litter C:N ratio. After eight years of treatment, however, the CO2-increased litter C:N ratio did not influence the diversity in any of the four fauna groups. The number of significant correlations between treatments, food source quality, and soil biota diversities was reduced from six to three after two and eight years, respectively. These results suggest a remarkable resilience within the soil biota against global climate change treatments in the long term.

Productivity and carbon footprint of perennial grass-forage legume intercropping strategies with high or low nitrogen fertilizer input.

A three-season field experiment was established and repeated twice with spring barley used as cover crop for different perennial grass-legume intercrops followed by a full year pasture cropping and winter wheat after sward incorporation. Two fertilization regimes were applied with plots fertilized with either a high or a low rate of mineral nitrogen (N) fertilizer. Life cycle assessment (LCA) was used to evaluate the carbon footprint (global warming potential) of the grassland management including measured nitrous oxide (N2O) emissions after sward incorporation. Without applying any mineral N fertilizer, the forage legume pure stand, especially red clover, was able to produce about 15 t above ground dry matter ha(-1) year(-1) saving around 325 kg mineral Nfertilizer ha(-1) compared to the cocksfoot and tall fescue grass treatments. The pure stand ryegrass yielded around 3t DM more than red clover in the high fertilizer treatment. Nitrous oxide emissions were highest in the treatments containing legumes. The LCA showed that the low input N systems had markedly lower carbon footprint values than crops from the high N input system with the pure stand legumes without N fertilization having the lowest carbon footprint. Thus, a reduction in N fertilizer application rates in the low input systems offsets increased N2O emissions after forage legume treatments compared to grass plots due to the N fertilizer production-related emissions. When including the subsequent wheat yield in the total aboveground production across the three-season rotation, the pure stand red clover without N application and pure stand ryegrass treatments with the highest N input equalled. The present study illustrate how leguminous biological nitrogen fixation (BNF) represents an important low impact renewable N source without reducing crop yields and thereby farmers earnings.

Use of feathers to assess polychlorinated biphenyl and organochlorine pesticide exposure in top predatory bird species of Pakistan.

Little is known about the levels of organochlorines (OCs) in predatory bird species from Asia or the factors governing their concentrations. This study is the first report on concentrations of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in predatory birds of Pakistan. The concentrations of PCBs and OCPs were investigated using tail feathers of ten different species of predatory birds. In addition, concentration differences among body, tail, primary and secondary feathers were investigated for six individuals of black kite (Milvus migrans). Ranges of concentrations were highest for dichlorodiphenyldichloroethylene (p,p'-DDE: 0.11-2163ngg(-1) dry wt.) followed by dichlorodiphenyltrichloroethane (p,p'-DDT: 0.36-345ngg(-1) dry wt.), hexachlorobenzene (HCB: 0.02-34ngg(-1) dry wt.), ∑PCBs (0.03-16ngg(-1) dry wt.) and trans-nonachlor (TN; 0.01-0.13ngg(-1) dry wt.). CB 118, 153, 138, and 180 along with p,p'-DDE were found as the most prevalent compounds. ∑PCBs and ∑DDTs were significantly different among species (both p<0.01) and omnivorous, scavengers, carnivorous and piscivorous trophic guilds (all p<0.03). Only ∑PCBs were significantly differentamong different families of birds (p<0.01). Values of stable isotopes (δ(13)C and δ(15)N) differed significantly (all p<0.01) among species, families, trophic guilds as well as terrestrial and aquatic habitat but not between nocturnal and diurnal predators (p=0.22 for δ(13)C; p=0.50 for δ(15)N). Concentrations of ∑PCBs, ∑DDTs and trans-nonachlor, but not HCB (p=0.86), were significantly different among different feather types (all p<0.01). Trophic and taxonomic affiliation as well as dietary carbon sources (δ(13)C) for species were identified as the variables best explaining the observed variation in exposure to the studied compounds. The significance of contributing factors responsible for OC contamination differences in predatory birds should be further elucidated in future studies.