Günther Seufert

Europe-wide reduction in primary productivity caused by the heat and drought in 2003

Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate, their impact on terrestrial carbon cycling is unclear. Here we report measurements of ecosystem carbon dioxide fluxes, remotely sensed radiation absorbed by plants, and country-level crop yields taken during the European heatwave in 2003. We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003, and their consequences for the net carbon balance. We estimate a 30 per cent reduction in gross primary productivity over Europe, which resulted in a strong anomalous net source of carbon dioxide (0.5 Pg C yr-1) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration. Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat, respectively. We also find that ecosystem respiration decreased together with gross primary productivity, rather than accelerating with the temperature rise. Model results, corroborated by historical records of crop yields, suggest that such a reduction in Europes primary productivity is unprecedented during the last century. An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes.

Seasonal and diurnal patterns of monoterpene emissions from Pinus pinea (L.) under field conditions

Abstract Within the activity of the BEMA project (Biogenic Emission in the Mediterranean Area), the emission of volatile organic compounds from Pinus pinea L. was studied in a nature reservation close to Rome (Italy). Measurements were carried out during five campaigns from June 1993 to October 1994 using a dynamic branch enclosure technique. Investigations principally focused on studying diurnal and seasonal variability. P. pinea emitted mainly monoterpenes of which limonene, trans -β-ocimene, linalool, α-pinene, myrcene and 1,8-cineole were the most abundant. At a temperature of 30°C and PAR > 600 μmol photons m -2 s −1 the sum of emissions was about 2–3.5 μg g −1 leaf dry weight h −1 in spring and autumn, and about 7 to 15 μg g −1 h −1 in summer. Absolute daytime emission rates were very high in summer (35 μg g −1 h −1 ) leading to a carbon loss of up to 8% of the 24 h photosynthetic carbon gain. α-pinene and limonene emissions were found in all campaigns and were emitted during day and night. Other compounds like trans -β-ocimene, linalool and 1,8-cineole occurred seasonally and were not or hardly emitted in the night. The lack of emissions during night point to a strong influence of light as confirmed by an artificial darkening experiment. Diurnal emissions of limonene and trans -β-ocimene were simulated by the monoterpene model. of Tingey et al. (1980, Plant Physiology 65 , 797–801) and the isoprene model of Guenther et al . (1991, J. geophys. Res. , 96 , 10,799–10,808), using parameters suggested by Guenther et al. (1993, J. geophys. Res. , 96 ,10,799–10,808) and parameters adjusted to data by best-fit regression analysis. Model predictions were fairly good with the adjusted parameters ( R 2 = 0.71 and 0.77, n = 139 and 72). Trans -β-ocimene data clearly fitted better with the isoprene model while Tingeys monoterpene model was more appropriate for limonene data. The pronounced seasonality in amount and composition of the emissions demonstrate that the existing models describing the short-term response of emissions to temperature and light cannot always be used alone to estimate the annual monoterpene release from vegetation.

Diurnal and seasonal course of monoterpene emissions from Quercus ilex (L.) under natural conditions application of light and temperature algorithms

Abstract Quercus ilex is a common oak species in the Mediterranean vegetation and a strong emitter of monoterpenes. Since the short-term control of monoterpene emissions from this species involved both temperature and light, the usual exponential function of temperature may not be sufficient to model the diurnal and seasonal emission course. In the frame of the BEMA-project (Biogenic Emissions in the Mediterranean Area), we investigated the tree-to-tree, branch-to-branch, diurnal, and seasonal variability of monoterpene emissions from Q. ilex over one and a half years at Castelporziano (Rome, Italy). In addition, we checked the suitability of the model developed for isoprene by Guenther et al. (1991, 1993) to simulate the short- and long-term variations of monoterpene emissions from this particular species. We found that the tree-to-tree variability was rather small compared to the experimental error during air sampling acid analysis by diverse laboratories. The branch-to-branch variability was noticeable between sun- and shade-adapted branches only. 80% of total emissions were represented by α-pinene, β-pinene and sabinene, whose proportions were stable over the year and independent of light exposure. The emission factor (emission rate at 30°C and 1000 μmol photon m −2 s −1 ) estimated by the isoprene model or extrapolated from measurements was similar: it was about 22 μg g dw −1 h −1 for sun-exposed branches and 2.3 μg g dw −1 h −1 for shade-adapted branches. It was rather stable over the seasons except during leaf development. The diurnal and seasonal emission patterns from Q. ilex were simulated in a satisfying way by Guenthers algorithms especially if we excluded the laboratory variability. For shade-adapted branches, an emission factor 17 times lower had to be applied, but temperature and light responses were unchanged.

An overview of the Castelporziano experiments

This paper reviews the major outcomes of the measuring campaigns performed at the Castelporziano nature preserve near Rome, Italy, by 14 European laboratories as part of the BEMA (Biogenic Emissions in the Mediterranean Area)-project. Six campaigns of 1–4 weeks duration were carried out in different seasons of the years 1993–1994 at semi-continuously running test plots in the nature reserve, representing common Mediterranean vegetation types. The aim was to characterise, at the different test plots, the atmospheric chemical and meteorological situations, the plant biomass and physiology, the type, amount and controls of emissions from different plants by means of branch enclosures, and the BVOC emission fluxes from different ecosystems, by scaling up enclosure data from individual sources, and by measuring fluxes directly by use of micrometeorological methods. An important focus during the initial phase of the five year BEMA-project was the harmonisation and improvement of the analytical, physiological and micrometeorological methods used, and the development and testing of new methods for measuring BVOC fluxes.

Stomatal Constraints May Affect Emission of Oxygenated Monoterpenoids from the Foliage of Pinus pinea

Dependence of monoterpenoid emission and fractional composition on stomatal conductance (G V) was studied in Mediterranean conifer Pinus pinea, which primarily emits limonene and trans-β-ocimene but also large fractions of oxygenated monoterpenoids linalool and 1,8-cineole. Strong decreases in G V attributable to diurnal water stress were accompanied by a significant reduction in total monoterpenoid emission rate in midday. However, various monoterpenoids responded differently to the reduction in G V, with the emission rates of limonene and trans-β-ocimene being unaffected but those of linalool and 1,8-cineole closely following diurnal variability in G V. A dynamic emission model indicated that stomatal sensitivity of emissions was associated with monoterpenoid Henrys law constant (H, gas/liquid phase partition coefficient). Monoterpenoids with a large Hsuch as trans-β-ocimene sustain higher intercellular partial pressure for a certain liquid phase concentration, and stomatal closure is balanced by a nearly immediate increase in monoterpene diffusion gradient from intercellular air-space to ambient air. The partial pressure rises also in compounds with a low H, but more than 1,000-fold higher liquid phase concentrations of linalool and 1,8-cineole are necessary to increase intercellular partial pressure high enough to balance stomatal closure. The system response is accordingly slower, and the emission rates may be transiently suppressed by low G V. Simulations further suggested that linalool and 1,8-cineole synthesis rates also decreased with decreasing G V, possibly as the result of selective inhibition of various monoterpene synthases by stomata. We conclude that physicochemical characteristics of volatiles not only affect total emission but also alter the fractional composition of emitted monoterpenoids.

Climatic feedbacks and desertification: The Mediterranean model

Abstract Mesometeorological information obtained in several research projects in southern Europe has been used to analyze perceived changes in the western Mediterranean summer storm regime. A procedure was developed to disaggregate daily precipitation data into three main components: frontal precipitation, summer storms, and Mediterranean cyclogenesis. Working hypotheses were derived on the likely processes involved. The results indicate that the precipitation regime in this Mediterranean region is very sensitive to variations in surface airmass temperature and moisture. Land-use perturbations that accumulated over historical time and greatly accelerated in the last 30 yr may have induced changes from an open, monsoon-type regime with frequent summer storms over the mountains inland to one dominated by closed vertical recirculations where feedback mechanisms favor the loss of storms over the coastal mountains and additional heating of the sea surface temperature during summer. This, in turn, favors Medite...

Fluxes of biogenic VOC from Mediterranean vegetation by trap enrichment relaxed eddy accumulation

Abstract Results are presented for the application of a modified relaxed eddy accumulation system for the determination of VOC fluxes in the atmosphere (TREA). First, system design, performances and testing against eddy covariance carbon dioxide fluxes are presented. Subsequently, the capability of TREA to discriminate between biogenic and anthropogenic VOC fluxes is discussed with some examples. TREA fluxes are also compared with the major biogenic VOC fluxes calculated with the gradient method and the relative merits and problems of the two techniques are discussed. TREA fluxes for two consecutive days are presented for 18 biogenic compounds. Compounds mostly emitted from the canopy were α-pinene, β-pinene, limonene and trans -β ocimene. The parallel analysis of fluxes determined by TREA and bag enclosures is carried out and discrepancies are discussed in terms of the removal processes of VOC in the atmosphere.

Above-ground woody carbon sequestration measured from tree rings is coherent with net ecosystem productivity at five eddy-covariance sites

• Attempts to combine biometric and eddy-covariance (EC) quantifications of carbon allocation to different storage pools in forests have been inconsistent and variably successful in the past. • We assessed above-ground biomass changes at five long-term EC forest stations based on tree-ring width and wood density measurements, together with multiple allometric models. Measurements were validated with site-specific biomass estimates and compared with the sum of monthly CO₂ fluxes between 1997 and 2009. • Biometric measurements and seasonal net ecosystem productivity (NEP) proved largely compatible and suggested that carbon sequestered between January and July is mainly used for volume increase, whereas that taken up between August and September supports a combination of cell wall thickening and storage. The inter-annual variability in above-ground woody carbon uptake was significantly linked with wood production at the sites, ranging between 110 and 370 g C m(-2) yr(-1) , thereby accounting for 10-25% of gross primary productivity (GPP), 15-32% of terrestrial ecosystem respiration (TER) and 25-80% of NEP. • The observed seasonal partitioning of carbon used to support different wood formation processes refines our knowledge on the dynamics and magnitude of carbon allocation in forests across the major European climatic zones. It may thus contribute, for example, to improved vegetation model parameterization and provides an enhanced framework to link tree-ring parameters with EC measurements.

Integrating nitrogen fluxes at the European scale

Executive summary Nature of the problem • Environmental problems related to nitrogen concern all economic sectors and impact all media: atmosphere, pedosphere, hydrosphere and anthroposphere. • Therefore, the integration of fluxes allows an overall coverage of problems related to reactive nitrogen (Nr) in the environment, which is not accessible from sectoral approaches or by focusing on specific media. Approaches • This chapter presents a set of high resolution maps showing key elements of the N flux budget across Europe, including N2 and Nr fluxes. • Comparative nitrogen budgets are also presented for a range of European countries, highlighting the most efficient strategies for mitigating Nr problems at a national scale. A new European Nitrogen Budget (EU-27) is presented on the basis of state-of-the-art Europe-wide models and databases focusing on different segments of Europe’s society. Key findings • From c. 18 Tg Nr yr −1 input to agriculture in the EU-27, only about 7 Tg Nr yr− 1 find their way to the consumer or are further processed by industry. • Some 3.7 Tg Nr yr−1 is released by the burning of fossil fuels in the EU-27, whereby the contribution of the industry and energy sectors is equal to that of the transport sector. More than 8 Tg Nr yr−1 are disposed of to the hydrosphere, while the EU-27 is a net exporter of reactive nitrogen through atmospheric transport of c. 2.3 Tg Nr yr−1. • The largest single sink for Nr appears to be denitrifi cation to N2 in European coastal shelf regions (potentially as large as the input of mineral fertilizer, about 11 Tg N yr–1 for the EU-27); however, this sink is also the most uncertain, because of the uncertainty of Nr import from the open ocean. Major uncertainties • National nitrogen budgets are diffi cult to compile using a large range of data sources and are currently available only for a limited number of countries. • Modelling approaches have been used to fill in the data gaps in some of these budgets, but it became obvious during this study that further research is needed in order to collect necessary data and make national nitrogen budgets inter-comparable across Europe. • In some countries, due to inconsistent or contradictory information coming from different data sources, closure of the nitrogen budget was not possible. Recommendations • The large variety of problems associated with the excess of Nr in the European environment,including adverse impacts, requires an integrated nitrogen management approach that would allow for creation and closure of N budgets within European environments. • Development of nitrogen budgets nationwide, their assessment and management could become an effective tool to prioritize measures and prevent unwanted side effects.

Sampling and analysis of terpenes in air. An interlaboratory comparison

Abstract An interlaboratory comparison on the sampling and analysis of terpenes in air was held within the framework of the BEMA (Biogenic Emissions in the Mediterranean Area) project in May 1995. Samples were drawn and analysed by 10 European laboratories from a dynamic artificial air generator in which five terpenes were present at low ng l −1 levels and ozone varied between 8 and 125 ppbv. Significant improvements over previous inter-comparison exercises in the quality of results were observed. At the ozone mixing ratio of 8 ppbv a good agreement among laboratories was obtained for all test compounds with mean values close to the target concentration. At higher mixing ratios, ozone reduced terpene recoveries and decreased the precision of the measurements due to ozonolysis during sampling. For β-pinene this effect was negligible but for the more reactive compounds significant losses were observed in some laboratories ( cis -β-ocimene = trans -β-ocimene > linalool > d-limonene). The detrimental effect of ozone was significantly lower for the laboratories which removed ozone prior to sampling by scrubbers. Parallel sampling was carried out with a standardised sampler and each individual laboratorys own device. A good agreement between the two sets of results was obtained, clearly showing that the majority of laboratories used efficient sampling systems. Two different standard solutions were analysed by each laboratory. Only in a few cases did interference in the GC separation cause problems for the quantification of the terpenes (nonanal/linalool). However, making up of standards for the calibration of the analytical equipment (GC-MS or GC-FID) was pointed out as a source of error in some laboratories.