Global trends in carbon sinks and their relationships with CO2 and temperature

Fernández-Martínez M., Sardans J., Chevallier F., Ciais P., Obersteiner M., Vicca S., Canadell J.G., Bastos A., Friedlingstein P., Sitch S., Piao S.L., Janssens I.A., Peñuelas J. (2019) Global trends in carbon sinks and their relationships with CO2 and temperature. Nature Climate Change. 9: 73-79.
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Doi: 10.1038/s41558-018-0367-7

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Elevated CO2 concentrations increase photosynthesis and, potentially, net ecosystem production (NEP), meaning a greater CO2 uptake. Climate, nutrients and ecosystem structure, however, influence the effect of increasing CO2. Here we analysed global NEP from MACC-II and Jena CarboScope atmospheric inversions and ten dynamic global vegetation models (TRENDY), using statistical models to attribute the trends in NEP to its potential drivers: CO2, climatic variables and land-use change. We found that an increased CO2 was consistently associated with an increased NEP (1995–2014). Conversely, increased temperatures were negatively associated with NEP. Using the two atmospheric inversions and TRENDY, the estimated global sensitivities for CO2 were 6.0 ± 0.1, 8.1 ± 0.3 and 3.1 ± 0.1 PgC per 100 ppm (~1 °C increase), and −0.5 ± 0.2, −0.9 ± 0.4 and −1.1 ± 0.1 PgC °C−1 for temperature. These results indicate a positive CO2 effect on terrestrial C sinks that is constrained by climate warming. © 2018, The Author(s), under exclusive licence to Springer Nature Limited.

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Effects of nitrogen loading on emission of carbon gases from estuarine tidal marshes with varying salinity

Hu M., Peñuelas J., Sardans J., Huang J., Li D., Tong C. (2019) Effects of nitrogen loading on emission of carbon gases from estuarine tidal marshes with varying salinity. Science of the Total Environment. 667: 648-657.
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Doi: 10.1016/j.scitotenv.2019.02.429

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Estuarine tidal marshes sequester significant quantities of carbon and are suffering from anthropogenic nitrogen (N) enhancement. However, the effects of this N loading on carbon gas emissions from freshwater-oligohaline tidal marshes are unknown. In this paper, we report on our evaluation of the effects of a N gradient (0, 24, 48 and 96 g NH 4 NO 3 –N m −2 y −1 ) on the methane (CH 4 ) and carbon dioxide (CO 2 ) emissions from freshwater and oligohaline tidal marshes in the Min River estuary, southeast China. On an annual scale, the oligohaline marsh has significantly higher CO 2 emissions, while it has slightly lower CH 4 emissions relative to freshwater marsh. The addition of N increased CH 4 emission from the freshwater marsh and decreased CH 4 emission from the oligohaline marsh, although there was no statistically significant difference in CH 4 emission between either of the two marshes and the control. The addition of 96 g NH 4 NO 3 –N m −2 y −1 significantly increased CO 2 emission from the freshwater marsh, while it did not significantly influence CO 2 emission from the oligohaline marsh. CH 4 and CO 2 emission levels were positively correlated with soil temperature under all conditions. The CH 4 flux resulting from both the control and the addition of N was negatively correlated with porewater SO 4 2− and Cl − concentrations and soil EC in the oligohaline marsh. Overall, N addition significantly increased carbon gas emissions under freshwater conditions while slightly inhibiting carbon gas emissions from the oligohaline marsh. Our findings suggested that even under low salinity conditions, the effects of N loading on CH 4 and CO 2 emissions from freshwater and oligohaline tidal marshes can vary. We propose that the addition of N to estuarine tidal marshes has a significant effect on the carbon cycle and promotes soil carbon loss, phenomena which may be influenced by salinity. © 2019 Elsevier B.V.

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Winter warming is ecologically more relevant than summer warming in a cool-temperate grassland

Kreyling J., Grant K., Hammerl V., Arfin-Khan M.A.S., Malyshev A.V., Peñuelas J., Pritsch K., Sardans J., Schloter M., Schuerings J., Jentsch A., Beierkuhnlein C. (2019) Winter warming is ecologically more relevant than summer warming in a cool-temperate grassland. Scientific Reports. 9: 0-0.
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Doi: 10.1038/s41598-019-51221-w

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Climate change affects all seasons, but warming is more pronounced in winter than summer at mid- and high latitudes. Winter warming can have profound ecological effects, which are rarely compared to the effects of summer warming, and causal explanations are not well established. We compared mild aboveground infrared warming in winter to warming in summer in a semi-natural, cool-temperate grassland in Germany for four years. Aboveground plant biomass increased following winter warming (+18%) and was unaffected by summer warming. Winter warming affected the composition of the plant community more than summer warming, favoring productive species. Winter warming increased soil respiration more than summer warming. Prolonged growing seasons and changes in plant-community composition accounted for the increased aboveground biomass production. Winter warming stimulated ecological processes, despite causing frost damage to plant roots and microorganisms during an extremely cold period when warming reduced the thermal insulation provided by snow. Future warming beyond such intermittent frosts may therefore further increase the accelerating effects of winter warming on ecological processes. © 2019, The Author(s).

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The bioelements, the elementome, and the biogeochemical niche

Peñuelas J., Fernández-Martínez M., Ciais P., Jou D., Piao S., Obersteiner M., Vicca S., Janssens I.A., Sardans J. (2019) The bioelements, the elementome, and the biogeochemical niche. Ecology. 100: 0-0.
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Doi: 10.1002/ecy.2652

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Every living creature on Earth is made of atoms of the various bioelements that are harnessed in the construction of molecules, tissues, organisms, and communities, as we know them. Organisms need these bioelements in specific quantities and proportions to survive and grow. Distinct species have different functions and life strategies, and have therefore developed distinct structures and adopted a certain combination of metabolic and physiological processes. Each species is thus also expected to have different requirements for each bioelement. We therefore propose that a “biogeochemical niche” can be associated with the classical ecological niche of each species. We show from field data examples that a biogeochemical niche is characterized by a particular elementome defined as the content of all (or at least most) bioelements. The differences in elementome among species are a function of taxonomy and phylogenetic distance, sympatry (the bioelemental compositions should differ more among coexisting than among non-coexisting species to avoid competitive pressure), and homeostasis with a continuum between high homeostasis/low plasticity and low homeostasis/high plasticity. This proposed biogeochemical niche hypothesis has the advantage relative to other associated theoretical niche hypotheses that it can be easily characterized by actual quantification of a measurable trait: the elementome of a given organism or a community, being potentially applicable across taxa and habitats. The changes in bioelemental availability can determine genotypic selection and therefore have a feedback on ecosystem function and organization, and, at the end, become another driving factor of the evolution of life and the environment. © 2019 by the Ecological Society of America

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Atmo-ecometabolomics: a novel atmospheric particle chemical characterization methodology for ecological research

Rivas-Ubach A., Liu Y., Steiner A.L., Sardans J., Tfaily M.M., Kulkarni G., Kim Y.-M., Bourrianne E., Paša-Tolić L., Peñuelas J., Guenther A. (2019) Atmo-ecometabolomics: a novel atmospheric particle chemical characterization methodology for ecological research. Environmental Monitoring and Assessment. 191: 0-0.
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Doi: 10.1007/s10661-019-7205-x

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Aerosol particles play important roles in processes controlling the composition of the atmosphere and function of ecosystems. A better understanding of the composition of aerosol particles is beginning to be recognized as critical for ecological research to further comprehend the link between aerosols and ecosystems. While chemical characterization of aerosols has been practiced in the atmospheric science community, detailed methodology tailored to the needs of ecological research does not exist yet. In this study, we describe an efficient methodology (atmo-ecometabolomics), in step-by-step details, from the sampling to the data analyses, to characterize the chemical composition of aerosol particles, namely atmo-metabolome. This method employs mass spectrometry platforms such as liquid and gas chromatography mass spectrometries (MS) and Fourier transform ion cyclotron resonance MS (FT-ICR-MS). For methodology evaluation, we analyzed aerosol particles collected during two different seasons (spring and summer) in a low-biological-activity ecosystem. Additionally, to further validate our methodology, we analyzed aerosol particles collected in a more biologically active ecosystem during the pollination peaks of three different representative tree species. Our statistical results showed that our sampling and extraction methods are suitable for characterizing the atmo-ecometabolomes in these two distinct ecosystems with any of the analytical platforms. Datasets obtained from each mass spectrometry instrument showed overall significant differences of the atmo-ecometabolomes between spring and summer as well as between the three pollination peak periods. Furthermore, we have identified several metabolites that can be attributed to pollen and other plant-related aerosol particles. We additionally provide a basic guide of the potential use ecometabolomic techniques on different mass spectrometry platforms to accurately analyze the atmo-ecometabolomes for ecological studies. Our method represents an advanced novel approach for future studies in the impact of aerosol particle chemical compositions on ecosystem structure and function and biogeochemistry. © 2019, Springer Nature Switzerland AG.

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We are what we eat: A stoichiometric and ecometabolomic study of caterpillars feeding on two pine subspecies of Pinus sylvestris

Rivas-Ubach A., Peñuelas J., Hódar J.A., Oravec M., Paša-Tolić L., Urban O., Sardans J. (2019) We are what we eat: A stoichiometric and ecometabolomic study of caterpillars feeding on two pine subspecies of Pinus sylvestris. International Journal of Molecular Sciences. 20: 0-0.
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Doi: 10.3390/ijms20010059

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Many studies have addressed several plant-insect interaction topics at nutritional, molecular, physiological, and evolutionary levels. However, it is still unknown how flexible the metabolism and the nutritional content of specialist insect herbivores feeding on different closely related plants can be. We performed elemental, stoichiometric, and metabolomics analyses on leaves of two coexisting Pinus sylvestris subspecies and on their main insect herbivore; the caterpillar of the processionary moth (Thaumetopoea pityocampa). Caterpillars feeding on different pine subspecies had distinct overall metabolome structure, accounting for over 10% of the total variability. Although plants and insects have very divergent metabolomes, caterpillars showed certain resemblance to their plant-host metabolome. In addition, few plant-related secondary metabolites were found accumulated in caterpillar tissues which could potentially be used for self-defense. Caterpillars feeding on N and P richer needles had lower N and P tissue concentration and higher C:N and C:P ratios, suggesting that nutrient transfer is not necessarily linear through trophic levels and other plant-metabolic factors could be interfering. This exploratory study showed that little chemical differences between plant food sources can impact the overall metabolome of specialist insect herbivores. Significant nutritional shifts in herbivore tissues could lead to larger changes of the trophic web structure. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.

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Responses of forest ecosystems in Europe to decreasing nitrogen deposition

Schmitz A., Sanders T.G.M., Bolte A., Bussotti F., Dirnböck T., Johnson J., Peñuelas J., Pollastrini M., Prescher A.-K., Sardans J., Verstraeten A., de Vries W. (2019) Responses of forest ecosystems in Europe to decreasing nitrogen deposition. Environmental Pollution. : 980-994.
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Doi: 10.1016/j.envpol.2018.09.101

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Average nitrogen (N) deposition across Europe has declined since the 1990s. This resulted in decreased N inputs to forest ecosystems especially in Central and Western Europe where deposition levels are highest. While the impact of atmospheric N deposition on forests has been receiving much attention for decades, ecosystem responses to the decline in N inputs received less attention. Here, we review observational studies reporting on trends in a number of indicators: soil acidification and eutrophication, understory vegetation, tree nutrition (foliar element concentrations) as well as tree vitality and growth in response to decreasing N deposition across Europe. Ecosystem responses varied with limited decrease in soil solution nitrate concentrations and potentially also foliar N concentrations. There was no large-scale response in understory vegetation, tree growth, or vitality. Experimental studies support the observation of a more distinct reaction of soil solution and foliar element concentrations to changes in N supply compared to the three other parameters. According to the most likely scenarios, further decrease of N deposition will be limited. We hypothesize that this expected decline will not cause major responses of the parameters analysed in this study. Instead, future changes might be more strongly controlled by the development of N pools accumulated within forest soils, affected by climate change and forest management. We find limited indication for response of Europe's forests to declining N deposition. Reactions have been reported for soil solution NO3 − and potentially foliar N concentrations but not for other indicators. © 2018 Elsevier Ltd

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Responses of greenhouse-gas emissions to land-use change from rice to jasmine production in subtropical China

Wang C., Li X., Min Q., Wang W., Sardans J., Zeng C., Tong C., Peñuelas J. (2019) Responses of greenhouse-gas emissions to land-use change from rice to jasmine production in subtropical China. Atmospheric Environment. 201: 391-401.
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Doi: 10.1016/j.atmosenv.2018.12.032

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We studied the impacts of an increasingly common change in land use from paddy field to jasmine fields on the emission of greenhouse gases (GHGs), which have supposed the transformation of more than 1200 ha only in the last decade in the surroundings of Fuzhou city in response to economic changes. The possible increases that this can suppose constitutes and environmental concern in China. We studied areas dedicated to rice crop that have been partially converted to jasmine cultivation with some parts still kept as rice fields. Emissions of CO2, CH4 and N2O varied significantly among the seasons. CO2 and CH4 cumulative emissions and the global-warming potential (GWP) of these emissions were significantly lower in the jasmine than the paddy field. N2O emission, N2O cumulative emission, however, were higher in the jasmine than the paddy field, despite in some concrete studied periods the differences were not statistically significant. The total decrease in GHG emissions from the conversion from rice to jasmine production was strongly influenced by the indirect effects of various changes in soil conditions. The expected changes due to the great differences in water and fertilization use and management and organic matter input to soil between these two crops were in great part due to modified soil traits. According to structural equation models, the strong direct effects of the change from rice to Jasmine crop reducing the emissions of CO2 and N2O were partially decreased by the indirect effects of crop type change decreasing soil pH and soil [Fe2+] for CO2 emissions and by decreasing soil salinity and soil [Fe3+] for N2O emissions. The negative effects of the crop conversion on CH4 emissions were mostly due to the globally negative indirect effects on soil conditions, by decreases in soil salinity, water content and [Fe2+]. Soil salinity, water content, pH, [Fe2+], [Fe3+] and [total Fe] were significantly lower in the jasmine than the paddy field, but temperature had the opposite pattern. CO2 emissions were generally correlated positively with salinity, temperature, and water content and negatively with [Fe3+] and [total Fe] in both fields. CH4 emissions were positively correlated with salinity, temperature, water content and pH in both fields. N2O emissions were positively correlated with temperature and were negatively correlated with water content, pH, [Fe2+], [Fe3+] and [total Fe] in both fields. CO2 was the most important GHG for the GWPs, and the total GWP was significantly lower for the jasmine than for the rice cropland field. The change in the land use in this area of paddy fields will decreased the global GHG emission, and the effect on the GWPs was mostly due to changes in soil properties. © 2018 Elsevier Ltd

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Optimal coupling of straw and synthetic fertilizers incorporation on soil properties, active Fe dynamics, and green house gas emission in Jasminum sambac (L.) field in southeastern China

Wang C., Min Q., Abid A.A., Sardans J., Wu H., Lai D.Y.F., Peñuelas J., Wang W. (2019) Optimal coupling of straw and synthetic fertilizers incorporation on soil properties, active Fe dynamics, and green house gas emission in Jasminum sambac (L.) field in southeastern China. Sustainability (Switzerland). 11: 0-0.
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Doi: 10.3390/su11041092

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In agriculture, synthetic fertilizers have played a key role in enhancing food production and keeping the world's population adequately fed. China's participation is essential to global efforts in reducing greenhouse gas (GHG) emissions because it is the largest producer and consumer of synthetic fertilizers. A field experiment was conducted in a Jasminum sambac (L.) field to evaluate the impact different doses of fertilizers (half, standard, and double) and their combination with straw on ecosystem (including crop plants and soil) GHG emissions. The results showed that in comparison with the control or straw treatments, the straw + standard fertilizer treatment increased the soil water content. The fertilizer treatments decreased the soil pH, but the straw and combination treatments, especially the straw + standard fertilizer treatment, had higher soil pH in comparison with the fertilizer treatment. The active soil Fe (Fe 2+ and Fe 3+ ) concentration was slightly increased in the straw + standard fertilizer treatment in comparison with the control. Moreover, fertilizer increased the CO 2 emission, and we detected a positive interaction between the straw application and the double fertilization dose that increased CO 2 emission, but the straw + standard fertilizer treatment decreased it. Fertilizer decreased CH 4 and N 2 O emissions, but when straw and fertilizer treatments were applied together, this increased CH 4 and N 2 O emissions. Overall, considering the soil properties and GHG emissions, the straw + standard fertilizer treatment was the best method to enhance soil water retention capacity, improve soil acid, and mitigate greenhouse gas emissions for sustainable management of J. sambac dry croplands. © 2019 by the authors.

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The response of stocks of C, N, and P to plant invasion in the coastal wetlands of China

Wang W., Sardans J., Wang C., Zeng C., Tong C., Chen G., Huang J., Pan H., Peguero G., Vallicrosa H., Peñuelas J. (2019) The response of stocks of C, N, and P to plant invasion in the coastal wetlands of China. Global Change Biology. 25: 733-743.
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Doi: 10.1111/gcb.14491

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The increasing success of invasive plant species in wetland areas can threaten their capacity to store carbon, nitrogen, and phosphorus (C, N, and P). Here, we have investigated the relationships between the different stocks of soil organic carbon (SOC), and total C, N, and P pools in the plant–soil system from eight different wetland areas across the South-East coast of China, where the invasive tallgrass Spartina alterniflora has replaced the native tall grasses Phragmites australis and the mangrove communities, originally dominated by the native species Kandelia obovata and Avicennia marina. The invasive success of Spartina alterniflora replacing Phragmites australis did not greatly influence soil traits, biomass accumulation or plant–soil C and N storing capacity. However, the resulting higher ability to store P in both soil and standing plant biomass (approximately more than 70 and 15 kg P by ha, respectively) in the invasive than in the native tall grass communities suggesting the possibility of a decrease in the ecosystem N:P ratio with future consequences to below- and aboveground trophic chains. The results also showed that a future advance in the native mangrove replacement by Spartina alterniflora could constitute a serious environmental problem. This includes enrichment of sand in the soil, with the consequent loss of nutrient retention capacity, as well as a sharp decrease in the stocks of C (2.6 and 2.2 t C ha-1 in soil and stand biomass, respectively), N, and P in the plant–soil system. This should be associated with a worsening of the water quality by aggravating potential eutrophication processes. Moreover, the loss of carbon and nutrient decreases the potential overall fertility of the system, strongly hampering the reestablishment of woody mangrove communities in the future. © 2018 John Wiley & Sons Ltd

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