Atmospheric deposition, CO2, and change in the land carbon sink
The reduction in acidic deposition of nitrogen and Sulphur should lead to a slow recovery of forests to a pre-acid deposition state. Photo by Pixabay

Human activities result in increasing atmospheric concentrations of CO2 that affects the terrestrial biosphere in multiple ways: warming the climate, increasing photosynthesis (CO2 fertilization), decreasing transpiration by stimulating stomatal closure and changing the stoichiometry of carbon, nitrogen and phosphorus (C:N:P) in ecosystem carbon pools. Concentrations of atmospheric carbon dioxide (CO2) have continued to increase whereas, due to air-quality policies, atmospheric deposition of sulphur and nitrogen has declined in Europe and the USA during recent decades.

Terrestrial ecosystems are key components of the global carbon cycle, as indicated by the fact that, since the 1960s, they have been sequestering an average of about 30% of the annual anthropogenic CO2 emitted into the atmosphere.

In a new study in the journal Scientific Reports authors used time series of flux observations from 23 forests distributed throughout Europe and the USA, and generalised mixed models to end up finding  that forest-level net ecosystem production and gross primary production have increased by 1% annually from 1995 to 2011.

In this study, authors test the hypothesis that gross primary production, ecosystem respiration and the net C-sink strength (net land-atmosphere CO2 flux) or net ecosystem production (NEP), have accelerated during the last two decades because of the increased atmospheric CO2 concentrations and temperature, and because of the recovery from high loads of S deposition in Europe and North America. “We expected these deposition reductions to have modulated the biogeochemical effects of rising CO2” added Dr. Marcos Fernández-Martínez from CREAF-CSIC Barcelona

Statistical models indicated that increasing atmospheric CO2 was the most important factor driving the increasing strength of carbon sinks in these forests. Authors also found that the reduction of sulphur deposition in Europe and the USA led to higher recovery in ecosystem respiration than in gross primary production, thus limiting the increase of carbon sequestration. By contrast, the study shows that trends in climate and nitrogen deposition did not significantly contribute to changing carbon fluxes during the studied period. “Our findings support the hypothesis of a general CO2-fertilization effect on vegetation growth and suggest that, so far unknown, sulphur deposition plays a significant role in the carbon balance of forests in industrialized regions”, said Prof. Josep Peñuelas from CREAF-CSIC Barcelona

“Our results show the need to include the effects of changing atmospheric composition, beyond CO2, to assess future dynamics of carbon-climate feedbacks not currently considered in earth system/climate modelling”, said Dr. Fernández-Martínez from CREAF-CSIC Barcelona

This study was funded by the European Research Council Synergy grant ERC-2013-SyG-610028, the Spanish Government project CGL2016-79835-P and the Catalan Government grant FI-2013

Journal Reference: Fernández-Martínez, M., Vicca, S., Janssens, I.A., Ciais, P., Obersteiner, M., Bartrons, M., Sardans, J., Verger, A., Canadell, J.G., Chevallier, F., Wang, X., Bernhofer, C., Curtis, P.S., Gianelle, D., Grünwald, T., Heinesch, B., Ibrom, A., Knohl, A., Laurila, T., Law, B.E., Limousin, J.M., Longdoz, B., Loustau, D., Mammarella, I., Matteucci, G., Monson, R.K., Montagnani, L., Moors, E.J., Munger, J.W., Papale, D., Piao, S.L., Peñuelas, J. 2017. Atmospheric deposition, CO2, and change in the land carbon sink. Scientific Reports 7, 9632.

Relative contribution of groundwater to plant transpiration estimated with stable isotopes
Water is generally taken up by roots (with important exceptions), so root structure and function should play a central role in research of plant-water relations. Photo by Pixabay

Water stored underground in the saturated and subsurface zones below the soil are important sources of water for plants in water-limited ecosystems. Arid and seasonally dry ecosystems contain the deepest root systems, and some species grow roots to depths of more than 4 m, even in temperate and tropical ecosystems. The presence of deep-rooted plants worldwide, however, suggests that the use of groundwater is not restricted to arid and seasonally dry ecosystems.

In a new study in the journal Scientific Reports authors compiled the available data (71 species) on the relative contribution of groundwater to plant water estimated using stable isotopes and mixing models, which provided information about relative groundwater use, and analysed their variation across different climates, seasons, plant types, edaphic conditions, and landscape positions.

Plant use of groundwater was more likely at sites with a pronounced dry season, and represented on average 49 per cent of transpired water in dry seasons and 28 per cent in wet seasons. The relative contribution of groundwater to plant-water uptake was higher on rocky substrates (saprolite, fractured bedrock), which had reduced groundwater uptake when this source was deep belowground.

Notably, authors found that the connectivity between groundwater pools and plant water is quantitatively larger and more widespread than reported by recent global estimations based on isotopic averaged values. Thus, “in order to improve the representation of groundwater-surface interactions in models, a quantification of the relative contribution of groundwater to transpiration and its variability across environmental gradients was required”, said Dr. Adrià Barbeta from CREAF-CSIC Barcelona, now in INRA Bourdeaux

Prof. Josep Peñuelas from CREAF-CSIC Barcelona claims also that “further research on plant-water sources in boreal, polar regions and tropical rainforests would help our understanding of the global patterns of groundwater uptake and may substantially improve the biosphere-atmosphere models by a realistic representation of this important component of the water cycle”.

This study was funded by the European Research Council Synergy grant ERC-2013-SyG-610028, the Spanish Government project CGL2016-79835-P and the Catalan Government grant FI-2013

Journal Reference: Barbeta, A., Peñuelas, J. 2017. Relative contribution of groundwater to plant transpiration estimated with stable isotopes. Scientific Reports

β-Ocimene, a Key Floral and Foliar Volatile Involved in Multiple Interactions between Plants and Other Organisms
Plants generally synthesize and emit species-specific floral volatile organic compounds (VOCs) mixtures to attract pollinators by mixing several of these common VOCs. Photo by Pexels

More than 1700 volatile organic compounds (VOCs) have been identified in the floral scents of flowering plants. These VOCs are not equally distributed across the phylogeny of flowering plants, so that the commonness and predominance of these compounds in floral scents varies widely among species. Common floral VOCs have a widespread phylogenetic distribution, which means that they are present in the floral scents of many species from different plant families. Instead, less common floral VOCs are only present in plants that are pollinated by specific pollinator groups with specific innate preferences for those VOCs.

β-Ocimene is a very common plant volatile released in important amounts from the leaves and flowers of many plant species. This acyclic monoterpene can play several biological functions in plants, by potentially affecting floral visitors and also by mediating defensive responses to herbivory.

In a new study in the journal Molecules authors indicated that the ubiquity and high relative abundance of β-ocimene in the floral scents of species from most plant families and from different pollination syndromes (ranging from generalism to specialism) strongly suggest that this terpenoid may play an important role in the attraction of pollinators to flowers.

In this study authors compiled abundant evidence from published studies that supports β-ocimene as a generalist attractant of a wide spectrum of pollinators. They found no studies testing behavioural responses of pollinators to β-ocimene, that could directly demonstrate or deny the function of β-ocimene in pollinator attraction; but “several case studies support that the emissions of β-ocimene in flowers of different species follow marked temporal and spatial patterns of emission, which are typical from floral volatile organic compound (VOC) emissions that are involved in pollinator attraction”, said Dr. Gerard Farré-Armengol from CREAF-CSIC Barcelona, now in the University of Salzburg.

Furthermore, important β-ocimene emissions are induced from vegetative plant tissues after herbivory in many species, which have relevant functions in the establishment of tritrophic interactions. Authors thus conclude that β-ocimene is a key plant volatile with multiple relevant functions in plants, depending on the organ and the time of emission.

Experimental behavioural studies on pure β-ocimene conducted with pollinating insects will be necessary to prove the assumptions made here. “In view of the presented indirect evidences, we strongly encourage the inclusion of β-ocimene alone or in combination with other floral volatiles in coupled gas chromatography electroantennographic detection (GC-EAD) analyses and behavioural tests when conducting future studies in order to provide a solid experimental proof for the assumptions made in the study”, said Prof. Josep Peñuelas from CREAF-CSIC Barcelona.

This study was funded by the European Research Council Synergy grant ERC-2013-SyG-610028, the Spanish Government project CGL2016-79835-P and the Catalan Government grant FI-2013

Journal Reference: Farré-Armengol, G., Filella, I., Llusià, J., Peñuelas, J. 2017. β-Ocimene, a Key Floral and Foliar Volatile Involved in Multiple Interactions between Plants and Other Organisms. Molecules 2017, 22, 1148; doi: 10.3390/molecules22071148.

Temperature increase reduces global yields of major crops in four independent estimates
kornfeld / cornfield
Understanding climate change is critical to ensure global food security. In this study authors combine four analytical methods to assess the impact of increasing temperatures on yields of wheat, rice, maize and soybean. Photo by Pexels

All agricultural production is vulnerable to climate change including wheat, rice, maize and soybean that provide two-thirds of human caloric intake. Assessing the impact of global temperature increase on production of these major crops is therefore critical to maintain global food supply.

In a new study in the journal Proceedings of the National Academy of Sciences authors investigated the impacts of temperature on yields of the four crops by compiling extensive published results from four analytical methods: global grid-based and local point-based models, statistical regressions and field-warming experiments.

“By combining four different methods, our comprehensive assessment of the impacts of increasing temperatures on major global crops shows substantial risks for agricultural production, already stagnating in some parts of the world”, said Prof. Josep Peñuelas from CREAF-CSIC Barcelona.

The study shows that results from the different methods consistently indicate negative temperature impacts on crop yield at the global scale, generally underpinned by similar impacts at country and site scales. Without CO2 fertilization, effective adaptation and genetic improvement, each degree Celsius increase in global mean temperature would on average reduce global yields of wheat by 6.0%, rice by 3.2%, maize by 7.4% and soybean by 3.1%. In any case, researchers point out that results are highly heterogeneous across crops and geographical areas with some positive impact estimates.

Multi-method analyses improved the confidence in assessments of future climate impacts on global major crops, and suggest crop- and region-specific adaptation strategies to ensure food security for an increasing world population.

Journal Reference: Zhao, C., Liu, B., Piao, S., Wang, X., Lobell, D., Huang, Y., Huang, M., Yao, Y., Bassu, S., Ciais, P., Durand, J-L., Elliott, L., Ewert, F., Janssens, I., Li, T., Lin, E., Liu, Q., Martre, P., Müller, C., Peng, S., Peñuelas, J., Ruane, A., Wallach, D., Wang, T., Wu, D., Liu, Z., Zhu, Y., Zhu, Z., Asseng, S. 2017. Temperature increase reduces global yields of major crops in four independent estimates. Proceedings of the National Academy of Sciences.

Final meeting of the 2016-2017 course

On the 28th of June, the four PIs of Imbalance-P gathered together for the final meeting of the 2016-2017 course. The discussed subjects were:

– The 2016-17 field campaigns

– Integration of Earth System Models and Integrated Assessment Models

– The need to work on the proof of concept of our hypothesis.

– The possibility of engaging into citizen science.

– Discussion on the economics of the P market

– Preparation of the 4rth annual Imbalance-P meeting in Antwerp

– Preparing our teams for the next financial report, at the end of September

– Preparation of the following campaigns from August to October in Guyana (Nourages, Paracou and Guyafor transect) and Iceland.

– The link between biodiversity and nutrients and how land use affects biodiversity

–  Possibilities of new complementary funding

More news soon!

The secret plant communication

The websites of disseminating scientific knowledge SINC (La Ciencia es Notica) and NCYT (Notícias de la Ciencia y la Tecnología) have published an article on The secret plant communication, that includes declarations of Prof Josep Penuelas about Volatile organic compounds and plants communication.

SINC read the full text in Spanish

NCYT read the full text Spanish

10 years of excellent research in Catalonia

Prof Penuelas will participate as speaker in the celebration that will take place next day May 29 in Barcelona.

10 anys de recerca d’excel·lència a Catalunya Barcelona, 29 maig de 2017
Next 10 years critical for achieving climate change goals

Carbon dioxide (CO2) and other greenhouse gases in the atmosphere can be reduce in two ways — by cutting our emissions, or by removing it from the atmosphere, for example through plants, the ocean, and soil.

In a new study, published in the journal Nature Communications, researchers from the International Institute for Applied Systems Analysis (IIASA) used a global model of the carbon system that accounts for carbon release and uptake through both natural and anthropogenic activities.

“The study shows that the combined energy and land-use system should deliver zero net anthropogenic emissions well before 2040 in order to assure the attainability of a 1.5°C target by 2100,” says IIASA Ecosystems Services and Management Program Director Michael Obersteiner, a study coauthor.

According to the study, fossil fuel consumption would likely need to be reduced to less than 25% of the global energy supply by 2100, compared to 95% today. At the same time, land use change, such as deforestation, must be decreased. This would lead to a 42% decrease in cumulative emissions by the end of the century compared to a business as usual scenario.

“This study gives a broad accounting of the carbon dioxide in our atmosphere, where it comes from and where it goes. We take into account not just emissions from fossil fuels, but also agriculture, land use, food production, bioenergy, and carbon uptake by natural ecosystems,” explains World Bank consultant Brian Walsh, who led the study while working as an IIASA researcher.

The compares four different scenarios for future energy development, with a range of mixtures of renewable and fossil energy. In a “high-renewable” scenario where wind, solar, and bioenergy increase by around 5% a year, net emissions could peak by 2022, the study shows. Yet without substantial negative emissions technologies, that pathway would still lead to a global average temperature rise of 2.5°C, missing the Paris Agreement target.

Walsh notes that the high-renewable energy scenario is ambitious, but not impossible — global production of renewable energy grew 2.6% between 2013 and 2014, according to the IEA. In contrast, the study finds that continued reliance on fossil fuels (with growth rates of renewables between 2% and 3% per year), would cause carbon emissions to peak only at the end of the century, causing an estimated 3.5°C global temperature rise by 2100.

The authors note that not only the mix of energy matters, but also the overall amount of energy consumed. The study also included ranges for high energy consumption and low energy consumption.

The study adds to a large body of IIASA research on climate mitigation policy and the chances of achieving targets.

“Earlier work on mitigation strategies by IIASA has shown the importance of demand-side measures, including efficiency, conservation, and behavioral change. Success in these areas may explain the difference between reaching 1.5C instead of 2C,” says IIASA Energy Program Director Keywan Riahi, who also contributed to the new work.

A new model

The study is one of the first published results from the newly developed FeliX model, a system dynamics model of social, economic, and environmental earth systems and their interdependencies. The model is freely available for download and use at

“Compared to other climate and integrated assessment models, the FeliX model is less detailed, but it provides a unique systemic view of the whole carbon cycle, which is vital to our understanding of future climate change and energy,” says IIASA Ecosystem Services and Management Program Director.

This study received support from the European Research Council Synergy grant ERC-2013-SyG-610028


Brian Walsh, Philippe Ciais, Ivan A. Janssens, Josep Peñuelas, Keywan Riahi, Felicjan Rydzak, Detlef P. van Vuuren, Michael Obersteiner. Pathways for balancing CO2 emissions and sinks. Nature Communications, 2017; 8: 14856 DOI: 10.1038/NCOMMS14856

Human population growth offsets climate-driven increase in woody vegetation in sub-Saharan Africa
Africa_woody vegetations_Pixabay2017
Woody cover has actually increased over the past 20 years in large parts of Africa, and in particular in drylands. Researchers attribute much of this increase to changes in rainfall and the growing concentration of CO2 in the atmosphere. Photo by Pixabay

The rapidly growing human population in sub-Saharan Africa generates increasing demand for agricultural land and forest products, which presumably leads to deforestation. Conversely, a greening of African drylands has been reported, but this has been difficult to associate with changes in woody vegetation. There is thus an incomplete understanding of how woody vegetation responds to socio-economic and environmental change.

Deforestation in Africa has been high on the environmental agenda for decades. In a new study published in Nature Ecology and Evolution, researchers used a passive microwave Earth observation data set to demonstrate that the realities are more complex.

Many earlier studies have overlooked that woody cover has actually increased over the past 20 years in large parts (~30%) of Africa, and in particular in drylands. This increase explains the observed ‘greening’ of drylands, both north and south the Equator. Authors further find that much of this increase may be explained by changes in rainfall and the growing concentration of CO2 in the atmosphere. In humid parts of Africa trends in woody cover are more diverse. Negative trends dominate where population density is high, and often in areas with dense forests with high ecological and economic value. The agreement between the map showing woody cover changes and the one with human population growth is so striking that statistics are almost needless to transport the message:


The findings thus contradict, on one hand, generally held views of loss of woody cover in drylands, e.g. in the Sahel-belt across Africa, yet on the other hand it supports the concerns for deforestation, due to agricultural expansion in more densely populated regions, and due to logging in the sparsely populated Congo basin.

The positive and negative impacts of observed trends are difficult to balance (increase in carbon stocks, lower albedo due to greater woody cover in drylands may have a positive effect on rainfall, the loss of forests in certain humid areas may imply serious losses of biodiversity and ecosystem services…).”At continental scale, it is thus impossible to draw final conclusions, and difficult to state if positive and negative effects are balanced. Local and regional scaled studies have to be evaluated and combined with these continental scale attempts”, said Dr. Martin Brandt from University of Copenhagen.

“Given that Africa’s population is expected to continue growing throughout much of this century, there is a clear need to sharpen natural resource management strategies to counter losses while taking advantage of increases in woody cover in drylands which are large enough to act as a carbon sink” said Dr. Aleixandre Verger from CREAF-CSIC.

“The great new thing is that we are now able to localize and quantify areas of change and we are working hard to quantify the amount of carbon which is affected by observed changes. This knowledge is critical in the fight against climate change”, said Prof. Josep Peñuelas from CSIC-CREAF.

Citation: Brandt, M., Rasmussen, K., Penuelas, J., Tian, F., Schurgers, G., Verger, A., Mertz, O., Palmer, J., Fensholt, R. 2017. Human population growth offsets climate driven woody vegetation increase in sub-Saharan Africa. Nature Ecology and Evolution, 1, 0081 (2017), doi: 10.1038/s41559-017-0081.

Celebrating 10 years of ERC

The European Research Council turns 10 in 2017 – Congratulations!

10-years ERC_LOGO_WHITE1-300x300The following video prepared by Consejo Superior de Investigaciones Científicas (CSIC) commemorates this anniversary

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