No impact of tropospheric ozone on the gross primary productivity of a Belgian pine forest

Imbalance-P paper. Contact with Lore Verryckt: [email protected] stomatal ozone (O3) uptake has been shown to negatively affect crop yields and the growth of tree seedlings. However, little is known about the effect of O3 on the carbon uptake by mature forest trees. This study investigated the effect of high O3 events on gross primary productivity (GPP) for a Scots pine stand near Antwerp, Belgium over the period 1998-2013. Stomatal O3 fluxes were modelled using in situ O3 mixing ratio measurements and a multiplicative stomatal model, which was parameterised and validated for this Scots pine stand. Ozone-induced GPP reduction is most likely to occur during or shortly after days with high stomatal O3 uptake. Therefore, a GPP model within an artificial neural network was parameterised for days with low stomatal O3 uptake rates and used to simulate GPP during periods of high stomatal O3 uptake. Possible negative effects of high stomatal O3 uptake on GPP would then result in an overestimation of GPP by the model during or after high stomatal O3 uptake events. The O3 effects on GPP were linked to AOT40 and POD1. Although the critical levels for both indices were exceeded in every single year, no significant negative effects of O3 on GPP were found, and no correlations between GPP residuals and AOT40 and POD1 were found. Overall, we conclude that no O3 effects were detected on the carbon uptake by this Scots pine stand

Vertical variation in photosynthetic parameters in two different tropical forest ecosystems

Màster project submitted to obtain the degree of Master in Biology, specialisation Biodiversity: conservation and restoration. Universiteit Antwerpen. Faculty of Science. Department of Biology. Academic year 2015-2016Forests contribute to the carbon balance as the largest vegetative sink for atmospheric carbon (CO2). Anthropogenic emissions are counteracted by carbon sequestration in trees, but nutrients could be limiting photosynthesis and the effect could possibly be not as large as believed. In tropical forests, phosphorus (P) is only available from weathered bedrock and is thereby in an imbalance with the rising levels of carbon and nitrogen in the atmosphere. If P is limiting carbon uptake in tropical forests, global carbon cycle models are likely overestimating uptake by forests. Another overestimation might be to only conduct photosynthesis measurements on sunlit leaves of the canopy and take this as an overall canopy average, whilst a vertical profile in photosynthesis is very likely. Our study was conducted on two sites of the Amazonian rain forest in French Guiana. Photosynthesis and dark respiration (Rd) was measured of 120 trees in 12 plots per site. The plots were situated along a geographical gradient (at top, slope and bottom) to cover a large variety in soil P concentration. We derived the photosynthetic parameters Vcmax and Jmax from the photosynthesis measurements using the Farquhar model (Farquhar et al., 1980). The measurements were performed at two different height levels in the canopy to investigate the vertical profile. In this study we aimed to relate the spatial and vertical variability to parameters such as leaf P concentration, leaf height, light availability, the specific leaf area and the chlorophyll content (SPAD). Soil P concentrations were correlated with the leaf P concentrations, which indicates P uptake from the soil is limited. There were significant vertical differences in the leaves in Vcmax, Jmax, Rd and leaf P concentrations. We conclude that P limits the photosynthetic capacity in our study areas and vertical profiles of photosynthesis should be taken into account when estimating carbon uptake by a tropical forest ecosystem

Different "metabolomic niches" of the highly diverse tree species of the French Guiana rainforests

Tropical rainforests harbor a particularly high plant diversity. We hypothesize that potential causes underlying this high diversity should be linked to distinct overall functionality (defense and growth allocation, anti-stress mechanisms, reproduction) among the different sympatric taxa. In this study we tested the hypothesis of the existence of a metabolomic niche related to a species-specific differential use and allocation of metabolites. We tested this hypothesis by comparing leaf metabolomic profiles of 54 species in two rainforests of French Guiana. Species identity explained most of the variation in the metabolome, with a species-specific metabolomic profile across dry and wet seasons. In addition to this "homeostatic" species-specific metabolomic profile significantly linked to phylogenetic distances, also part of the variance (flexibility) of the metabolomic profile was explained by season within a single species. Our results support the hypothesis of the high diversity in tropical forest being related to a species-specific metabolomic niche and highlight ecometabolomics as a tool to identify this species functional diversity related and consistent with the ecological niche theory

31P-NMR metabolomics revealed species-specific use of phosphorous in trees of a French Guiana rainforest

Productivity of tropical lowland moist forests is often limited by availability and functional allocation of phosphorus (P) that drives competition among tree species and becomes a key factor in determining forestall community diversity. We used non-target³¹P-NMR metabolic profiling to study the foliar P-metabolism of trees of a French Guiana rainforest. The objective was to test the hypotheses that P-use is species-specific, and that species diversity relates to species P-use and concentrations of P-containing compounds, including inorganic phosphates, orthophosphate monoesters and diesters, phosphonates and organic polyphosphates. We found that tree species explained the 59% of variance in ³¹P-NMR metabolite profiling of leaves. A principal component analysis showed that tree species were separated along PC 1 and PC 2 of detected P-containing compounds, which represented a continuum going from high concentrations of metabolites related to non-active P and P-storage, low total P concentrations and high N:P ratios, to high concentrations of P-containing metabolites related to energy and anabolic metabolism, high total P concentrations and low N:P ratios. These results highlight the species-specific use of P and the existence of species-specific P-use niches that are driven by the distinct species-specific position in a continuum in the P-allocation from P-storage compounds to P-containing molecules related to energy and anabolic metabolism

Decay of similarity across tropical forest communities : integrating spatial distance with soil nutrients

Altres ajuts: Acord transformatiu CRUE-CSICUnderstanding the mechanisms that drive the change of biotic assemblages over space and time is the main quest of community ecology. Assessing the relative importance of dispersal and environmental species selection in a range of organismic sizes and motilities has been a fruitful strategy. A consensus for whether spatial and environmental distances operate similarly across spatial scales and taxa, however, has yet to emerge. We used censuses of four major groups of organisms (soil bacteria, fungi, ground insects, and trees) at two observation scales (1-m sampling point vs. 2,500-m plots) in a topographically standardized sampling design replicated in two tropical rainforests with contrasting relationships between spatial distance and nutrient availability. We modeled the decay of assemblage similarity for each taxon set and site to assess the relative contributions of spatial distance and nutrient availability distance. Then, we evaluated the potentially structuring effect of tree composition over all other taxa. The similarity of nutrient content in the litter and topsoil had a stronger and more consistent selective effect than did dispersal limitation, particularly for bacteria, fungi, and trees at the plot level. Ground insects, the only group assessed with the capacity of active dispersal, had the highest species turnover and the flattest nonsignificant distance−decay relationship, suggesting that neither dispersal limitation nor nutrient availability were fundamental drivers of their community assembly at this scale of analysis. Only the fungal communities at one of our study sites were clearly coordinated with tree composition. The spatial distance at the smallest scale was more important than nutrient selection for the bacteria, fungi, and insects. The lower initial similarity and the moderate variation in composition identified by these distance-decay models, however, suggested that the effects of stochastic sampling were important at this smaller spatial scale. Our results highlight the importance of nutrients as one of the main environmental drivers of rainforest communities irrespective of organismic or propagule size and how the overriding effect of the analytical scale influences the interpretation, leading to the perception of greater importance of dispersal limitation and ecological drift over selection associated with environmental niches at decreasing observation scales

Rapid post-fertilisation plant phosphorus uptake indicates phosphorus limitation in French Guiana

International audienc

Vertical variation in photosynthetic parameters in two different tropical forest ecosystems

Màster project submitted to obtain the degree of Master in Biology, specialisation Biodiversity: conservation and restoration. Universiteit Antwerpen. Faculty of Science. Department of Biology. Academic year 2015-2016Forests contribute to the carbon balance as the largest vegetative sink for atmospheric carbon (CO2). Anthropogenic emissions are counteracted by carbon sequestration in trees, but nutrients could be limiting photosynthesis and the effect could possibly be not as large as believed. In tropical forests, phosphorus (P) is only available from weathered bedrock and is thereby in an imbalance with the rising levels of carbon and nitrogen in the atmosphere. If P is limiting carbon uptake in tropical forests, global carbon cycle models are likely overestimating uptake by forests. Another overestimation might be to only conduct photosynthesis measurements on sunlit leaves of the canopy and take this as an overall canopy average, whilst a vertical profile in photosynthesis is very likely. Our study was conducted on two sites of the Amazonian rain forest in French Guiana. Photosynthesis and dark respiration (Rd) was measured of 120 trees in 12 plots per site. The plots were situated along a geographical gradient (at top, slope and bottom) to cover a large variety in soil P concentration. We derived the photosynthetic parameters Vcmax and Jmax from the photosynthesis measurements using the Farquhar model (Farquhar et al., 1980). The measurements were performed at two different height levels in the canopy to investigate the vertical profile. In this study we aimed to relate the spatial and vertical variability to parameters such as leaf P concentration, leaf height, light availability, the specific leaf area and the chlorophyll content (SPAD). Soil P concentrations were correlated with the leaf P concentrations, which indicates P uptake from the soil is limited. There were significant vertical differences in the leaves in Vcmax, Jmax, Rd and leaf P concentrations. We conclude that P limits the photosynthetic capacity in our study areas and vertical profiles of photosynthesis should be taken into account when estimating carbon uptake by a tropical forest ecosystem