References of "Gielen, B"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailContrasting response of European forest and grassland energy exchange to heatwaves
Teuling, A. J.; Seneviratne, S. I.; Stöckli, R. et al

in Nature Geoscience (2010), 3(10), 722-727

Detailed reference viewed: 82 (18 ULg)
Full Text
Peer Reviewed
See detailBiomass production in experimental grasslands of different species richness during three years of climate warming
De Boeck, H. J.; Lemmens, CMHM; Zavalloni, C. et al

in Biogeosciences (2008), 5

Here we report on the single and combined impacts of climate warming and species richness on the biomass production in experimental grassland communities. Projections of a future warmer climate have ... [more ▼]

Here we report on the single and combined impacts of climate warming and species richness on the biomass production in experimental grassland communities. Projections of a future warmer climate have stimulated studies on the response of terrestrial ecosystems to this global change. Experiments have likewise addressed the importance of species numbers for ecosystem functioning. There is, however, little knowledge on the interplay between warming and species richness. During three years, we grew experimental plant communities containing one, three or nine grassland species in 12 sunlit, climate-controlled chambers in Wilrijk, Belgium. Half of these chambers were exposed to ambient air temperatures (unheated), while the other half were warmed by 3 degrees C (heated). Equal amounts of water were added to heated and unheated communities, so that warming would imply drier soils if evapotranspiration was higher. Biomass production was decreased due to warming, both aboveground (-29%) and belowground (-25%), as negative impacts of increased heat and drought stress in summer prevailed. Complementarity effects, likely mostly through both increased aboveground spatial complementarity and facilitative effects of legumes, led to higher shoot and root biomass in multi-species communities, regardless of the induced warming. Surprisingly, warming suppressed productivity the most in 9-species communities, which may be attributed to negative impacts of intense interspecific competition for resources under conditions of high abiotic stress. Our results suggest that warming and the associated soil drying could reduce primary production in many temperate grasslands, and that this will not necessarily be mitigated by efforts to maintain or increase species richness. [less ▲]

Detailed reference viewed: 26 (6 ULg)
Full Text
Peer Reviewed
See detailChronic ozone exposure affects leaf senescence of adult beech trees: a chlorophyll fluorescence approach
Gielen, B.; Low, M.; Deckmyn, G. et al

in Journal of Experimental Botany (2007), 58(4), 785-795

Accelerated leaf senescence is one of the harmful effects of elevated tropospheric ozone concentrations ([O-3]) on plants. The number of studies dealing with mature forest trees is scarce however ... [more ▼]

Accelerated leaf senescence is one of the harmful effects of elevated tropospheric ozone concentrations ([O-3]) on plants. The number of studies dealing with mature forest trees is scarce however. Therefore, five 66-year-old beech trees (Fagus sylvatica L.) have been exposed to twice-ambient (2xambient) [O-3] levels by means of a free-air canopy O-3 exposure system. During the sixth year of exposure, the hypothesis of accelerated leaf senescence in 2xambient [O-3] compared with ambient [O-3] trees was tested for both sun and shade leaves. Chlorophyll (chl) fluorescence was used to assess the photosynthetic quantum yield, and chl fluorescence images were processed to compare functional leaf homogeneity and the proportion of O-3-injured leaf area (stipples) under ambient and 2xambient [O-3] regimes. Based on the analysis of chl fluorescence images, sun leaves of both ambient and 2xambient [O-3] trees had apparently developed typical necrotic O-3 stipples during high O-3 episodes in summer, while accelerated senescence was only observed with sun leaves of 2xambient [O-3] trees. This latter effect was indicated along with a faster decrease of photosynthetic quantum yield, but without evidence of changes in non-photochemical quenching. Overall, treatment effects were small and varied among trees. Therefore, compared with ambient [O-3], the consequence of the observed O-3-induced accelerated leaf senescence for the carbon budget is likely limited. [less ▲]

Detailed reference viewed: 26 (2 ULg)
Full Text
Peer Reviewed
See detailCombined effects of climate warming and plant diversity loss on above- and below-ground grassland productivity
De Boeck, H. J.; Lemmens, CMHM; Gielen, B. et al

in Environmental and Experimental Botany (2007), 60(1), 95-104

Projections of global change predict both increases of the surface temperature and decreases of biodiversity, but studies on the combined impact of both on terrestrial ecosystems are lacking. We assessed ... [more ▼]

Projections of global change predict both increases of the surface temperature and decreases of biodiversity, but studies on the combined impact of both on terrestrial ecosystems are lacking. We assessed the impact of these two global changes on above- and below-ground productivity of grassland communities. Experimental ecosystems containing one, three or nine grassland species were grown in 12 sunlit, climate-controlled chambers in Wilrijk, Belgium. Half of these chambers were exposed to ambient air temperatures, while the other half were warmed by 3 degrees C. Equal amounts of water were added to heated and unheated communities, so that any increases in evapotranspiration due to warmer conditions would result in a drier soil. Warming led to a decreased productivity of both above-ground plant parts (-18%) and roots (-23%), which coincided with a significantly lower soil water content. Complementarity in resource use and/or facilitation slightly enhanced above-ground productivity in multi-species communities, regardless of the induced warming. Interactive effects between temperature treatment and species richness level were found below-ground, however, where warming nullified the positive effect of richness on root productivity. Future warmer conditions could further increase losses of productivity associated with declining species numbers. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 54 (5 ULg)
Full Text
Peer Reviewed
See detailBiomass production in experimental grasslands of different species richness during three years of climate warming
de Boeck, H. J.; Lemmens, CMHM; Gielen, B. et al

in Biogeosciences Discussions (2007), 4

Here we report on the single and combined impacts of climate warming and species richness on the biomass production in experimental grassland communities. Projections of a future warmer climate have ... [more ▼]

Here we report on the single and combined impacts of climate warming and species richness on the biomass production in experimental grassland communities. Projections of a future warmer climate have stimulated studies on the response of terrestrial ecosystems to this global change. Experiments have likewise addressed the importance of species numbers for ecosystem functioning. There is, however, little knowledge on the interplay between warming and species richness. During three years, we grew experimental plant communities containing one, three or nine grassland species in 12 sunlit, climate-controlled chambers in Wilrijk, Belgium. Half of these chambers were exposed to ambient air temperatures (unheated), while the other half were warmed by 3 degrees C (heated). Equal amounts of water were added to heated and unheated communities, so that warming would imply drier soils if evapotranspiration was higher. Biomass production was decreased due to warming, both aboveground (-29%) and belowground (-25%), as negative impacts of increased heat and drought stress in summer prevailed. Complementarity effects, likely mostly through both increased aboveground spatial complementarity and facilitative effects of legumes, led to higher shoot and root biomass in multi-species communities, regardless of the induced warming. Surprisingly, warming suppressed productivity the most in 9-species communities, which may be attributed to negative impacts of intense interspecific competition for resources under conditions of high abiotic stress. Our results suggest that warming and the associated soil drying could reduce primary production in many temperate grasslands, and that this will not necessarily be mitigated by efforts to maintain or increase species richness. [less ▲]

Detailed reference viewed: 21 (7 ULg)
Full Text
Peer Reviewed
See detailCO2 balance of boreal, temperate, and tropical forests derived from a global database
Luyssaert, S.; Inglima, I.; Jung, M. et al

in Global Change Biology (2007), 13(12), 2509-2537

Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this ... [more ▼]

Terrestrial ecosystems sequester 2.1 Pg of atmospheric carbon annually. A large amount of the terrestrial sink is realized by forests. However, considerable uncertainties remain regarding the fate of this carbon over both short and long timescales. Relevant data to address these uncertainties are being collected at many sites around the world, but syntheses of these data are still sparse. To facilitate future synthesis activities, we have assembled a comprehensive global database for forest ecosystems, which includes carbon budget variables (fluxes and stocks), ecosystem traits (e.g. leaf area index, age), as well as ancillary site information such as management regime, climate, and soil characteristics. This publicly available database can be used to quantify global, regional or biome-specific carbon budgets; to re-examine established relationships; to test emerging hypotheses about ecosystem functioning [e.g. a constant net ecosystem production (NEP) to gross primary production (GPP) ratio]; and as benchmarks for model evaluations. In this paper, we present the first analysis of this database. We discuss the climatic influences on GPP, net primary production (NPP) and NEP and present the CO2 balances for boreal, temperate, and tropical forest biomes based on micrometeorological, ecophysiological, and biometric flux and inventory estimates. Globally, GPP of forests benefited from higher temperatures and precipitation whereas NPP saturated above either a threshold of 1500 mm precipitation or a mean annual temperature of 10 degrees C. The global pattern in NEP was insensitive to climate and is hypothesized to be mainly determined by nonclimatic conditions such as successional stage, management, site history, and site disturbance. In all biomes, closing the CO2 balance required the introduction of substantial biome-specific closure terms. Nonclosure was taken as an indication that respiratory processes, advection, and non-CO2 carbon fluxes are not presently being adequately accounted for. [less ▲]

Detailed reference viewed: 57 (5 ULg)
Full Text
Peer Reviewed
See detailEnd-of-season effects of elevated temperature on ecophysiological processes of grassland species at different species richness levels
Lemmens, CMHM; De Boeck, H. J.; Gielen, B. et al

in Environmental and Experimental Botany (2006), 56

The combined effect of declining diversity and elevated temperature is a less-studied aspect of global change. We investigated the influence of those two factors and their possible interactions oil leaf ... [more ▼]

The combined effect of declining diversity and elevated temperature is a less-studied aspect of global change. We investigated the influence of those two factors and their possible interactions oil leaf ecophysiological processes in artificial grassland communities. Changes at the leaf level are at the basis of changes at the community level (and vice versa) but have remained largely unexplored in biodiversity experiments. We focused on end-of-season responses to assess whether species richness and air temperature affect the duration of the growing season. Grassland model ecosystems were used in 12 sunlit, climate-controlled chambers. Half of these chambers were exposed to ambient air temperatures, while the other half were Nvarnied 3 degrees C. Each chamber contained 24 plant communities, created with nine grassland species: three grass species. three nitrogen (N) fixers and three non-N-fixing dicots. Each plant community consisted of either one, three or nine species in order to create different species richness levels. Various ecophysiological variables (processes and characteristics) and above ground biomass were influenced by temperature. In several variables, the effects of temperature and species richness varied with species. No single-factor species richness effect was found due to opposite responses of the species canceling out the effect. We expect that these interactions may increase with time. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 27 (2 ULg)
Full Text
Peer Reviewed
See detailThree years of free-air CO2 enrichment (POPFACE) only slightly affects profiles of light and leaf characteristics in closed canopies of Populus.
Gielen, B; Liberloo, M; Bogaert, Jan ULg et al

in Global Change Biology (2003), 9(7), 1022-1037

Detailed reference viewed: 2 (0 ULg)