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.

 

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

 

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.