Biomedical subjects

Reinhart Ceulemans

Publications and source records attributed to Reinhart Ceulemans.

15 recordsLinked to original sources

PubMed2006

Chronic ozone exposure affects leaf senescence of adult beech trees: a chlorophyll fluorescence approach.

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.

Acclimatization↗

PubMed2006

Plasticity of growth and sylleptic branchiness in two poplar families grown at three sites across Europe.

Two hybrid poplar maternal half-sib families, resulting from controlled crosses of the female parent Populus deltoides 'S9-2' with P. nigra 'Ghoy' and P. trichocarpa 'V24', were grown at three sites: northern Italy, central France and southern England. Juvenile stem growth traits (height, circumference and volume) and sylleptic branchiness (number of branches, density of branches per unit of stem height, percentage of the stem carrying branches and distance of the highest sylleptic branch to the top of the stem) were measured on 1-year-old shoots. Our general objectives were to determine the degree to which the expression of stem growth and syllepsis and the relationships between them are affected by environmental conditions and to evaluate the efficiency of indirect selection for stem growth using branching traits as secondary criteria. The performance of both families differed significantly within and between sites. Pronounced heterosis was observed and highly significant genotype x environment interactions were found for all traits across the sites. Syllepsis showed more marked genetic variation and plasticity than stem growth traits. Relationships between sylleptic branchiness and stem growth depended on environmental conditions. Heritability values at the individual level ranged between 0.09 and 0.59, but genetic gain in stem volume was not significantly improved when selection was based on sylleptic branch characteristics. However, despite strong phenotypic plasticity among sites, genotypic ranking among the sites was relatively stable.

Adaptation, Physiological↗

PubMed2005

Forest response to elevated CO2 is conserved across a broad range of productivity.

Climate change predictions derived from coupled carbon-climate models are highly dependent on assumptions about feedbacks between the biosphere and atmosphere. One critical feedback occurs if C uptake by the biosphere increases in response to the fossil-fuel driven increase in atmospheric [CO(2)] ("CO(2) fertilization"), thereby slowing the rate of increase in atmospheric [CO(2)]. Carbon exchanges between the terrestrial biosphere and atmosphere are often first represented in models as net primary productivity (NPP). However, the contribution of CO(2) fertilization to the future global C cycle has been uncertain, especially in forest ecosystems that dominate global NPP, and models that include a feedback between terrestrial biosphere metabolism and atmospheric [CO(2)] are poorly constrained by experimental evidence. We analyzed the response of NPP to elevated CO(2) ( approximately 550 ppm) in four free-air CO(2) enrichment experiments in forest stands. We show that the response of forest NPP to elevated [CO(2)] is highly conserved across a broad range of productivity, with a stimulation at the median of 23 +/- 2%. At low leaf area indices, a large portion of the response was attributable to increased light absorption, but as leaf area indices increased, the response to elevated [CO(2)] was wholly caused by increased light-use efficiency. The surprising consistency of response across diverse sites provides a benchmark to evaluate predictions of ecosystem and global models and allows us now to focus on unresolved questions about carbon partitioning and retention, and spatial variation in NPP response caused by availability of other growth limiting resources.

Atmosphere↗

PubMed2005

Elevated CO2 concentration, fertilization and their interaction: growth stimulation in a short-rotation poplar coppice (EUROFACE).

We investigated the individual and combined effects of elevated CO2 concentration and fertilization on aboveground growth of three poplar species (Populus alba L. Clone 2AS-11, P. nigra L. Clone Jean Pourtet and P. x euramericana Clone I-214) growing in a short-rotation coppice culture for two growing seasons after coppicing. Free-air carbon dioxide enrichment (FACE) stimulated the number of shoots per stool, leaf area index measured with a fish-eye-type plant canopy analyzer (LAIoptical), and annual leaf production, but did not affect dominant shoot height or canopy productivity index. Comparison of LAIoptical with LAI estimates from litter collections and from allometric relationships showed considerable differences. The increase in biomass in response to FACE was caused by an initial stimulation of absolute and relative growth rates, which disappeared after the first growing season following coppicing. An ontogenetic decline in growth in the FACE treatment, together with strong competition inside the dense plantation, may have caused this decrease. Fertilization did not influence aboveground growth, although some FACE responses were more pronounced in fertilized trees. A species effect was observed for most parameters.

Biomass↗

PubMed2005

Carbon budget of Pinus sylvestris saplings after four years of exposure to elevated atmospheric carbon dioxide concentration.

To study the responses of Scots pine (Pinus sylvestris L.), a commercially important tree species in Europe, to future increases in atmospheric CO2 concentration ([CO2]), we grew saplings for 4 years in the ground in open-top chambers in ambient or ambient + 400 micromol mol(-1) CO2, without supplemental addition of nutrients and water. Carbon (C) budgets were developed for trees in both CO2 treatments based on productivity and biomass data obtained from destructive harvests at the end of the third and fourth years of treatment, and simulations of annual gross photosynthesis (P(tot)) and maintenance respiration by the model MAESTRA. Simulated P(tot) was enhanced by elevated [CO2], despite significant down-regulation of photosynthetic capacity. The subsequent increase in C uptake was allocated primarily to tissues with limited longevity (needles and fine roots), which explains why the measured annual increment in woody biomass did not differ between CO2 treatments. Thus, our results suggest that accelerated stem growth only occurs in the first 2 years in the presence of elevated [CO2] and that forest rotations will not be shortened significantly in response to increasing [CO2]. In elevated [CO2], a higher proportion of available C was allocated below ground, resulting in altered biomass distribution patterns. In trees of equal size, measured ratios of fine root/needle biomass and belowground/aboveground biomass were almost twice as large in the elevated [CO2] treatment. Although there are uncertainties in scaling from saplings to mature canopies, the data indicate that, in nutrient-limited Scots pine forests, elevated [CO2] is unlikely to accelerate tree growth significantly, but is likely to increase C inputs to soil.

Biomass↗

PubMed2004

Decision tree algorithm for detection of spatial processes in landscape transformation.

The conversion of landscapes by human activities results in widespread changes in landscape spatial structure. Regardless of the type of land conversion, there appears to be a limited number of common spatial configurations that result from such land transformation processes. Some of these configurations are considered optimal or more desirable than others. Based on pattern geometry, we define ten processes responsible for pattern change: aggregation, attrition, creation, deformation, dissection, enlargement, fragmentation, perforation, shift, and shrinkage. A novelty in this contribution is the inclusion of transformation processes causing expansion of the land cover of interest. Consequently, we propose a decision tree algorithm that enables detection of these processes, based on three parameters that have to be determined before and after the transformation of the landscape: area, perimeter length, and number of patches of the focal landscape class. As an example, the decision tree algorithm is applied to determine the transformation processes of three divergent land cover change scenarios: deciduous woodland degradation in Cadiz Township (Wisconsin, USA) 1831-1950, canopy gap formation in a terra firme rain forest at the Tiputini Biodiversity Station (Amazonian Ecuador) 1997-1998, and forest regrowth in Petersham Township (Massachusetts, USA) 1830-1985. The examples signal the importance of the temporal resolution of the data, since long-term pattern conversions can be subdivided in stadia in which particular pattern components are altered by specific transformation processes.

Algorithms↗

PubMed2004

Petiole length and biomass investment in support modify light interception efficiency in dense poplar plantations.

Leaf architecture, stand leaf area index and canopy light interception were studied in 13 poplar clones growing in a second rotation of a coppice plantation, to determine the role of leaf architectural attributes on canopy light-harvesting efficiency and to assess biomass investment in leaf support tissue. Stand leaf area index (L) varied from 2.89 to 6.99, but L was only weakly associated with canopy transmittance (TC). The weak relationship between TC and L was a result of a higher degree of foliage aggregation at larger values of L, leading to lower light-interception efficiency in stands with greater total leaf area. We observed a strong increase in leaf aggregation and a decrease in light-harvesting efficiency with decreasing mean leaf petiole length (PL) but not with leaf size, possibly because, in cordate or deltoid poplar leaves, most of the leaf area is located close to the petiole attachment to the lamina. Although PL was the key leaf characteristic of light-harvesting efficiency, clones with longer petioles had larger biomass investments in petioles, and there was a negative relationship between PL and L, demonstrating that enhanced light harvesting may lead to an overall decline in photosynthesizing leaf surface. Upper-canopy leaves were generally larger and had greater dry mass (MA) and nitrogen per unit area (NA) than lower-canopy leaves. Canopy plasticity in MA and NA was higher in clones with higher foliar biomass investment in midrib, and lower in clones with relatively longer petioles. These relationships suggest that there is a trade-off between photosynthetic plasticity and biomass investment in support, and also that high light-harvesting efficiency may be associated with lower photosynthetic plasticity. Our results demonstrate important clonal differences in leaf aggregation that are linked to leaf structure and biomass allocation patterns within the leaf.

Biomass↗

PubMed2003

Europe's terrestrial biosphere absorbs 7 to 12% of European anthropogenic CO2 emissions.

Most inverse atmospheric models report considerable uptake of carbon dioxide in Europe's terrestrial biosphere. In contrast, carbon stocks in terrestrial ecosystems increase at a much smaller rate, with carbon gains in forests and grassland soils almost being offset by carbon losses from cropland and peat soils. Accounting for non-carbon dioxide carbon transfers that are not detected by the atmospheric models and for carbon dioxide fluxes bypassing the ecosystem carbon stocks considerably reduces the gap between the small carbon-stock changes and the larger carbon dioxide uptake estimated by atmospheric models. The remaining difference could be because of missing components in the stock-change approach, as well as the large uncertainty in both methods. With the use of the corrected atmosphere- and land-based estimates as a dual constraint, we estimate a net carbon sink between 135 and 205 teragrams per year in Europe's terrestrial biosphere, the equivalent of 7 to 12% of the 1995 anthropogenic carbon emissions.

Agriculture↗

PubMed2003

Stem respiration of Populus species in the third year of free-air CO2 enrichment.

Carbon cycling in ecosystems, and especially in forests, is intensively studied to predict the effects of global climate change, and the role which forests may play in 'changing climate change'. One of the questions is whether the carbon balance of forests will be affected by increasing atmospheric CO2 concentrations. Regarding this question, effects of elevated [CO2] on woody-tissue respiration have frequently been neglected. Stem respiration of three Populus species (P. alba L. (Clone 2AS-11), P. nigra L. (Clone Jean Pourtet), and P. x euramericana (Clone I-214)) was measured in a managed, high-density forest plantation exposed to free-air CO2 enrichment (POPFACE). During the period of measurements, in May of the third year, stem respiration rates were not affected by the FACE treatment. Moreover, FACE did not influence the relationships between respiration rate and both stem temperature and relative growth rate. The results were supported by the reported absence of a FACE-effect on growth and stem wood density.

Journal Article↗

PubMed2002

The Euler number as an index of spatial integrity of landscapes: evaluation and proposed improvement.

The spatial integrity of a habitat or landscape is determined by the occurrence of habitat fragments and of perforations inside them. A landscape is said to have less spatial integrity with increasing numbers of fragments and perforations. The Euler number (epsilon) is a numerical measure of spatial integrity, based upon the difference (nf-np) between the number of fragments (nf) and the number of perforations (np). In this contribution, epsilon is evaluated, and an improvement is presented as a new index epsilon*, which is a combination of two metrics (epsilon j, epsilon d) based on nf and np. The term epsilon j quantifies the intensity of perforation and/or fragmentation. The term epsilon d measures the extent to which fragmentation predominates perforation, and vice versa. The intensity and dominance measures are combined into an Euclidean distance measure, generating the new ensemble value epsilon*, calculated as epsilon* = (nf + np)-1 square root of [1 + nf2]. Use, sensitivity, and application of epsilon*, epsilon j, and epsilon d are illustrated using percolation maps. Application of the new metrics by environmental scientists is encouraged because (1) no negative values can be generated with epsilon*, epsilon j, and epsilon d; (2) the range of epsilon*, epsilon j, and epsilon d is fixed; (3) process dominance and intensity are both assessed; (4) epsilon*, epsilon j, and epsilon d are easy to calculate and to interpret; and (5) epsilon* is not only based upon (nf - np), as epsilon is. Guidelines for practical use by means of a biplot of epsilon j and epsilon d are given.

Conservation of Natural Resources↗

PubMed2002

Radial patterns of sap flow in woody stems of dominant and understory species: scaling errors associated with positioning of sensors.

We studied sap flow in dominant coniferous (Pinus sylvestris L.) and broadleaf (Populus canescens L.) species and in understory species (Prunus serotina Ehrh. and Rhododendron ponticum L.) by the heat field deformation (HFD) method. We attempted to identify possible errors arising during flow integration and scaling from single-point measurements to whole trees. Large systematic errors of -90 to 300% were found when it was assumed that sap flow was uniform over the sapwood depth. Therefore, we recommend that the radial sap flow pattern should be determined first using sensors with multiple measuring points along a stem radius followed by single-point measurements with sensors placed at a predetermined depth. Other significant errors occurred in the scaling procedure even when the sap flow radial pattern was known. These included errors associated with uncertainties in the positioning of sensors beneath the cambium (up to 15% per 1 mm error in estimated xylem depth), and differences in environmental conditions when the radial profile applied for integration was determined over the short term (up to 47% error). High temporal variation in the point-to-area correction factor along the xylem radius used for flow integration is also problematic. Compared with midday measurements, measurements of radial variation of sap flow in the morning and evening of sunny days minimized the influence of temporal variations on the point-to-area correction factor, which was especially pronounced in trees with a highly asymmetric sap flow radial pattern because of differences in functioning of the sapwood xylem layers. Positioning a single-point sensor at a depth with maximum sap flow is advantageous because of the high sensitivity of maximum sap flow to water stress conditions and changes in micro-climate, and because of the lower random errors associated with the positioning of a single-point sensor along the xylem radius.

Pinus↗

PubMed2000

Assessing forest soil CO(2) efflux: an in situ comparison of four techniques.

A dynamic, closed-chamber infrared gas analysis (IRGA) system (DC-1: CIRAS-1, PP-Systems, Hitchin, U.K.) was compared with three other systems for measuring soil CO(2) efflux: the soda lime technique (SL), the eddy correlation technique (EC), and another dynamic, closed-chamber IRGA system (DC-2: LI-6250, Li-Cor, Inc., Lincoln, NE). Among the four systems, the DC-1 systematically gave the highest flux rates. Relative to DC-1, SL, EC and DC-2 underestimated fluxes by 10, 36 and 46%, respectively. These large and systematic differences highlight uncertainties in comparing fluxes from different sites obtained with different techniques. Although the three chamber methods gave different results, the results were well correlated. The SL technique underestimated soil CO(2) fluxes compared with the DC-1 system, but both methods agreed well when the SL data were corrected for the underestimation at higher fluxes, indicating that inter-site comparisons are possible if techniques are properly crosscalibrated. The EC was the only system that was not well correlated with DC-1. Under low light conditions, EC values were similar to DC-1 estimates, but under high light conditions the EC system seriously underestimated soil fluxes. This was probably because of interference by the photosynthetic activity of a moss layer. Although below-canopy EC fluxes are not necessarily well suited for measuring soil CO(2) efflux in natural forest ecosystems, they provide valuable information about understory gas exchange when used in tandem with soil chambers.

Journal Article↗

PubMed1999

Seasonal variations in leaf area index, leaf chlorophyll, and water content; scaling-up to estimate fAPAR and carbon balance in a multilayer, multispecies temperate forest.

Seasonal differences in phenology between coniferous and deciduous tree species need to be considered when developing models to estimate CO(2) exchange in temperate forest ecosystems. Because seasonal variations in CO(2) flux in temperate forests are closely correlated with plant phenology, we quantified the phenology of forest species in a multilayered forest with patches of Scots pine (Pinus sylvestris L.) and oak (Quercus robur L.) in Brasschaat, Belgium. A scaling-up modeling approach was developed to simulate reflectance at the leaf and canopy scales over a one-year cycle. Chlorophyll concentration, water content, specific leaf area and leaf area index of the forest species were measured throughout an entire year (1997). Scaling-up from the leaf to canopy was achieved by linking the PROSPECT and SAIL models. The result is the annual progression of the fraction of absorbed photosynthetically active radiation (fAPAR) in a 1 km(2) forest area, which can be directly related to high-resolution, remotely sensed data.

Journal Article↗

PubMed1999

Effects of elevated atmospheric CO(2) on phenology, growth and crown structure of Scots pine (Pinus sylvestris) seedlings after two years of exposure in the field.

Three-year-old Scots pine (Pinus sylvestris L.) seedlings were grown for two years in the ground in open-top chambers supplied with either an ambient or elevated (ambient + 400 &mgr;mol mol(-1)) CO(2) concentration. Phenological observations and measurements of height and stem diameter growth, absolute and relative growth rates, starch and soluble carbohydrate concentrations of the needles, and crown structure and needle properties were made at frequent intervals throughout the two growing seasons. Elevated CO(2) significantly advanced the date of bud burst in both years. The increase in total needle area in response to elevated CO(2) was accounted for by longer shoots and an increase in individual needle area in the first year, and by an increase in the number and length of shoots in the second year. Stem diameter and tree height were enhanced more by the elevated CO(2) treatment in the first year than in the second, indicating a decreased effect of CO(2) on growth over time. This was confirmed by a study of absolute and relative growth rates of leader shoots. During the first growing season of CO(2) enrichment, mean weekly relative growth rates over the growing season (RGR(m)) were significantly enhanced. During the second year, RGR(m) in ambient CO(2) closely matched that in elevated CO(2).

Journal Article↗

PubMed1990

Crown architecture of Populus clones as determined by branch orientation and branch characteristics.

Crown architecture, including branching pattern, branch characteristics and orientation of proleptic and sylleptic branches was studied in five poplar clones (Populus deltoides, P. trichocarpa and P. trichocarpa x P. deltoides hybrids), grown under intensive culture in the Pacific Northwest, USA. Branch characteristics measured were number, length, diameter, biomass and the angles of origin and termination. The results suggest that genotype has a major influence on crown architecture in Populus. Clonal differences in branch characteristics and branching patterns were found that resulted in striking differences in crown form and architecture. Branch angle and curvature differed significantly among clones, and among height growth increments within clones. Branch length and diameter were significantly correlated in all clones. Sylleptic branches and the considerable leaf area they carry have important implications for whole tree light interception, and thus, play a critical role in the superior growth and productivity of certain hybrid poplar clones. The considerable variation in branch characteristics implies a strong justification for including them in selection and breeding programs for Populus.

Journal Article↗