bluuebunny/crossref_metadata_2025_split huggingface dataset:
Genetic variation and spatial structure in sugar maple (Acer saccharum Marsh.) and implications for predicted global‐scale environmental change
Authors: Gunter L.E.E. E. , Tuskan Gerald A. , Gunderson Carla A. , Norby R.I.chard J. 
Published: March 2003

SummaryCurrent ecosystem model predictions concerning the effects of global temperature increase on forest responses do not account for factors influencing long‐term evolutionary dynamics of natural populations. Population structure and genetic variability may represent important factors in a species' ability to adapt to global‐scale environmental change without experiencing major alterations in current range limits. Genetic variation and structure in sugar maple (Acer saccharum Marsh.) were examined across three regions, between two stands within regions, and among four to five open‐pollinated families within stands (total N = 547 genotypes) using 58 randomly amplified polymorphic DNA (RAPD) markers. Differences within open‐pollinated families account for the largest portion of the total variation (29%), while differences among regions represent less than 2% of the total variation. Genetic diversity, as indicated by estimates of percent polymorphic loci, expected heterozygosity, fixation coefficients, and genetic distance, is greatest in the southern region, which consists of populations with the maximum potential risk due to climate change effects. The high level of genetic similarity (greater than 90%) among some genotypes suggests that gene flow is occurring among regions, stands, and families. High levels of genetic variation among families indicate that vegetational models designed to predict species' response to global‐scale environmental change may need to consider the degree and hierarchical structure of genetic variation when making large‐scale inferences.
Phenology of British butterflies and climate change
Authors: Roy D. B. , Sparks T. H. 
Published: March 2003

SummaryData from a national butterfly monitoring scheme were analysed to test for relationships between temperature and three phenological measures, duration of flight period and timing of both first and peak appearance. First appearances of most British butterflies has advanced in the last two decades and is strongly related to earlier peak appearance and, for multibrooded species, longer flight period. Mean dates of first and peak appearance are examined in relation to Manley's central England temperatures, using regression techniques. We predict that, in the absence of confounding factors, such as interactions with other organisms and land‐use change, climate warming of the order of 1 °C could advance first and peak appearance of most butterflies by 2–10 days.
A global distribution of biodiversity inferred from climatic constraints: results from a process‐based modelling study
Authors: Kleidon Axel , Mooney Harold A. 
Published: March 2003

SummaryWe investigated the connection between plant species diversity and climate by using a process‐based, generic plant model. Different ‘species' were simulated by different values for certain growth‐related model parameters. Subsequently, a wide range of values were tested in the framework of a ‘Monte Carlo' simulation for success; that is, the capability of each plant with these parameter combinations to reproduce itself during its lifetime. The range of successful parameter combinations approximated species diversity. This method was applied to a global grid, using daily atmospheric forcing from a climate model simulation. The computed distribution of plant ‘species' diversity compares very well with the observed, global‐scale distribution of species diversity, reproducing the majority of ‘hot spot' areas of biodiversity. A sensitivity analysis revealed that the predicted pattern is very robust against changes of fixed model parameters. Analysis of the climatic forcing and of two additional sensitivity simulations demonstrated that the crucial factor leading to this distribution of diversity is the early stage of a plant's life when water availability is highly coupled to the variability in precipitation because in this stage root‐zone storage of water is small. We used cluster analysis in order to extract common sets of species parameters, mean plant properties and biogeographic regions (biomes) from the model output. The successful ‘species' cannot be grouped into typical parameter combinations, which define the plant's functioning. However, the mean simulated plant properties, such as lifetime and growth, can be grouped into a few characteristic plant ‘prototypes', ranging from short‐lived, fast growing plants, similar to grasses, to long‐lived, slow growing plants, similar to trees. The classification of regions with respect to similar combinations of successful ‘species' yields a distribution of biomes similar to the observed distribution. Each biome has typical levels of climatic constraints, expressed for instance by the number of ‘rainy days' and ‘warm days'. The less the number of days favourable for growth, the greater the level of constraints and the less the ‘species' diversity. These results suggest that climate as a fundamental constraint can explain much of the global scale, observed distribution of plant species diversity.
Modelling the recent historical impacts of atmospheric CO2 and climate change on Mediterranean vegetation
Authors: Osborne C. P. , Mitchell P. L. , Sheehy J. E. , Woodward F. I. 
Published: March 2003

SummaryDuring the past century, annual mean temperature has increased by 0.75°C and precipitation has shown marked variation throughout the Mediterranean basin. These historical climate changes may have had significant, but presently undefined, impacts on the productivity and structure of sclerophyllous shrubland, an important vegetation type in the region. We used a vegetation model for this functional type to examine climate change impacts, and their interaction with the concurrent historical rise in atmospheric CO2. Using only climate and soil texture as data inputs, model predictions showed good agreement with observations of seasonal and regional variation in leaf and canopy physiology, net primary productivity (NPP), leaf area index (LAI) and soil water. Model simulations for shrubland sites indicated that potential NPP has risen by 25% and LAI by 7% during the past century, although the absolute increase in LAI was small. Sensitivity analysis suggested that the increase in atmospheric CO2 since 1900 was the primary cause of these changes, and that simulated climate change alone had negative impacts on both NPP and LAI. Effects of rising CO2 were mediated by significant increases in the efficiency of water‐use in NPP throughout the region, as a consequence of the direct effect of CO2 on leaf gas exchange. This increase in efficiency compensated for limitation of NPP by drought, except in areas where drought was most severe. However, while water was used more efficiently, total canopy water loss rose slightly or remained unaffected in model simulations, because increases in LAI with CO2 counteracted the effects of reduced stomatal conductance on transpiration. Model simulations for the Mediterranean region indicate that the recent rise in atmospheric CO2 may already have had significant impacts on productivity, structure and water relations of sclerophyllous shrub vegetation, which tended to offset the detrimental effects of climate change in the region.
Effects of elevated CO2 and temperature‐grown red and sugar maple on gypsy moth performance
Authors: Williams Ray S. , Norby Richard J. , Lincoln David E. 
Published: March 2003

SummaryFew studies have investigated how tree species grown under elevated CO2 and elevated temperature alter the performance of leaf‐feeding insects. The indirect effects of an elevated CO2 concentration and temperature on leaf phytochemistry, along with potential direct effects on insect growth and consumption, may independently or interactively affect insects. To investigate this, we bagged larvae of the gypsy moth on leaves of red and sugar maple growing in open‐top chambers in four CO2/temperature treatment combinations: (i) ambient temperature, ambient CO2; (ii) ambient temperature, elevated CO2 (+ 300 μL L−1 CO2); (iii) elevated temperature (+ 3.5°C), ambient CO2; and (iv) elevated temperature, elevated CO2. For both tree species, leaves grown at elevated CO2 concentration were significantly reduced in leaf nitrogen concentration and increased in C: N ratio, while neither temperature nor its interaction with CO2 concentration had any effect. Depending on the tree species, leaf water content declined (red maple) and carbon‐based phenolics increased (sugar maple) on plants grown in an enriched CO2 atmosphere. The only observed effect of elevated temperature on leaf phytochemistry was a reduction in leaf water content of sugar maple leaves. Gypsy moth larval responses were dependent on tree species. Larvae feeding on elevated CO2‐grown red maple leaves had reduced growth, while temperature had no effect on the growth or consumption of larvae. No significant effects of either temperature or CO2 concentration were observed for larvae feeding on sugar maple leaves. Our data demonstrate strong effects of CO2 enrichment on leaf phytochemical constituents important to folivorous insects, while an elevated temperature largely has little effect. We conclude that alterations in leaf chemistry due to an elevated CO2 atmosphere are more important in this plant–folivorous insect system than either the direct short‐term effects of temperature on insect performance or its indirect effects on leaf chemistry.
Direct evidence that symbiotic N2 fixation in fertile grassland is an important trait for a strong response of plants to elevated atmospheric CO2
Authors: Lüscher Andreas , Hartwig Ueli A. , Suter Daniel , Nösberger Josef 
Published: March 2003

SummaryAlthough legumes showed a clearly superior yield response to elevated atmospheric pCO2 compared to nonlegumes in a variety of field experiments, the extent to which this is due to symbiotic N2 fixation per se has yet to be determined. Thus, effectively and ineffectively nodulating lucerne (Medicago sativa L.) plants with a very similar genetic background were grown in competition with each other on fertile soil in the Swiss FACE experiment in order to monitor their CO2 response. Under elevated atmospheric pCO2, effectively nodulating lucerne, thus capable of symbiotically fixing N2, strongly increased the harvestable biomass and the N yield, independent of N fertilization. In contrast, the harvestable biomass and N yield of ineffectively nodulating plants were affected negatively by elevated atmospheric pCO2 when N fertilization was low. Large amounts of N fertilizer enabled the plants to respond more favourably to elevated atmospheric pCO2, although not as strongly as effectively nodulating plants. The CO2‐induced increase in N yield of the effectively nodulating plants was attributed solely to an increase in symbiotic N2 fixation of 50–175%, depending on the N fertilization treatment. N yield derived from the uptake of mineral N from the soil was, however, not affected by elevated pCO2. This result demonstrates that, in fertile soil and under temperate climatic conditions, symbiotic N2 fixation per se is responsible for the considerably greater amount of above‐ground biomass and the higher N yield under elevated atmospheric pCO2. This supports the assumption that symbiotic N2 fixation plays a key role in maintaining the C/N balance in terrestrial ecosystems in a CO2‐rich world.
Leaf senescence of Quercus myrtifolia as affected by long‐term CO2 enrichment in its native environment
Authors: Li J. ‐H. , Dijkstra P. , Hymus G. J. , Wheeler R. M. , Piastuch W. C. , Hinkle C. R. , Drake B. G. 
Published: March 2003

SummaryThe long‐term effects of elevated (ambient plus 350 μmol mol−1) atmospheric CO2 concentration (Ca) on the leaf senescence of Quercus myrtifolia Willd was studied in a scrub‐oak community during the transition from autumn (December 1997) to spring (April 1998). Plants were grown in large open‐top chambers at the Smithsonian CO2 Research Site, Merritt Island Wildlife Refuge, Cape Canaveral, Florida. Chlorophyll (a + b) concentration, Rubisco activity and N concentration decreased by 75%, 82%, and 52%, respectively, from December (1997) to April (1998) in the leaves grown at ambient Ca. In contrast, the leaves of plants grown at elevated Ca showed no significant decrease in chlorophyll (a + b) concentration or Rubisco activity, and only a 25% reduction in nitrogen. These results indicate that leaf senescence was delayed during this period at elevated Ca. Delayed leaf senescence in elevated Ca had important consequences for leaf photosynthesis. In elevated Ca the net photosynthetic rate of leaves that flushed in Spring 1997 (last year's leaves) and were 13 months old was not different from fully‐expanded leaves that flushed in 1998, and were approximately 1 month old (current year's leaves). In ambient Ca the net photosynthetic rate of last year's leaves was 54% lower than for current year's leaves. When leaves were fully senesced, nitrogen concentration decreased to about 40% of the concentration in non‐senesced leaves, in both CO2 treatments. In April, net photosynthesis was 97% greater in leaves grown in elevated Ca than in those grown at ambient. During the period when elevated Ca delayed leaf senescence, more leaves operating at higher photosynthetic rate would allow the ecosystem dominated by Q. myrtifolia to gain more carbon at elevated Ca than at ambient Ca.
Optimum experimental design for Free‐Air Carbon dioxide Enrichment (FACE) studies
Authors: Filion Mathieu , Dutilleul Pierre , Potvin Catherine 
Published: March 2003

SummaryThis article presents the logical reasoning underlying the optimal design of an experiment. We used Free‐Air Carbon dioxide Enrichment (FACE) experiments to illustrate this trade‐off as such experiments are particularly costly. On a theoretical basis, two‐way nested designs and split‐plot designs have similar power in testing carbon dioxide (CO2) main effects. If researchers have the choice of adding two replicate rings or two control plots to their experiment, our results show that both options provide a substantial gain in statistical power, with a slightly greater gain in the former case and at reduced financial cost in the latter. The former option, however, provides an insurance against possible ring failure.On an empirical basis, we analysed a preliminary FACE photosynthesis dataset collected at Duke University. The experiment was designed as a split‐plot design to test the effects of growth environment (GROWTH) and measurement CO2 concentration (MEAS) on photosynthetic rates of loblolly pine. Although a significant effect of MEAS was observed, we failed to detect a significant main effect of GROWTH. Power analysis was used to understand why the GROWTH main effect was not significant. The minimum detectable difference between treatment means that we calculated for GROWTH in this experiment was 4.04 μmol CO2 m−2 s−1 for a statistical power of 0.90, whereas the observed difference was 0.16 μmol CO2 m−2 s−1.Our recommendations for the design of FACE experiments are: (i) consider a second treatment factor with many levels within each ring in order to obtain a split‐plot design that provides a powerful test of interaction between treatment factors; (ii) add control plots, unless financial constrictions disallow for necessary personnel; (3) pool the data of FACE experiments conducted in comparable ecosystems (e.g. forests or grasslands), with two rings per treatment level at each site.
Allocation responses to CO2 enrichment and defoliation by a native annual plant Heterotheca subaxillaris
Authors: Johnson Sandra L. , Lincoln David E. 
Published: March 2003

SummaryAmong plants grown under enriched atmospheric CO2, root:shoot balance (RSB) theory predicts a proportionately greater allocation of assimilate to roots than among ambient‐grown plants. Conversely, defoliation, which decreases the plant's capacity to assimilate carbon, is predicted to increase allocation to shoot. We tested these RSB predictions, and whether responses to CO2 enrichment were modified by defoliation, using Heterotheca subaxillaris, an annual plant native to south‐eastern USA. Plants were grown under near‐ambient (400 μmol mol−1) and enriched (700 μmol mol−1) levels of atmospheric CO2. Defoliation consisted of the weekly removal of 25% of each new fully expanded, but not previously defoliated, leaf from either rosette or bolted plants. In addition to dry mass measurements of leaves, stems, and roots, Kjeldahl N, protein, starch and soluble sugars were analysed in these plant components to test the hypothesis that changes in C:N uptake ratio drive shifts in root:shoot ratio. Young, rapidly growing CO2‐enriched plants conformed to the predictions of RSB, with higher root:shoot ratio than ambient‐grown plants (P < 0.02), whereas older, slower growing plants did not show a CO2 effect on root:shoot ratio. Defoliation resulted in smaller plants, among which both root and shoot biomass were reduced, irrespective of CO2 treatment (P < 0.03). However, H. subaxillaris plants were able to compensate for leaf area removal through flexible shoot allocation to more leaves vs. stem (P < 0.01). Increased carbon availability through CO2 enrichment did not enhance the response to defoliation, apparently because of complete growth compensation for defoliation, even under ambient conditions. CO2‐enriched plants had higher rates of photosynthesis (P < 0.0001), but this did not translate into increased final biomass accumulation. On the other hand, earlier and more abundant yield of flower biomass was an important consequence of growth under CO2 enrichment.
Consequences of CO2 and light interactions for leaf phenology, growth, and senescence in Quercus rubra
Authors: Cavender‐Bares J. , Potts M. , Zacharias E. , Bazzaz F. A. 
Published: March 2003

SummaryWe investigated how light and CO2 levels interact to influence growth, phenology, and the physiological processes involved in leaf senescence in red oak (Quercus rubra) seedlings. We grew plants in high and low light and in elevated and ambient CO2. At the end of three years of growth, shade plants showed greater biomass enhancement under elevated CO2 than sun plants. We attribute this difference to an increase in leaf area ratio (LAR) in shade plants relative to sun plants, as well as to an ontogenetic effect: as plants increased in size, the LAR declined concomitant with a decline in biomass enhancement under elevated CO2Elevated CO2 prolonged the carbon gain capacity of shade‐grown plants during autumnal senescence, thus increasing their functional leaf lifespan. The prolongation of carbon assimilation, however, did not account for the increased growth enhancement in shade plants under elevated CO2. Elevated CO2 did not significantly alter leaf phenology. Nitrogen concentrations in both green and senesced leaves were lower under elevated CO2 and declined more rapidly in sun leaves than in shade leaves. Similar to nitrogen concentration, the initial slope of A/Ci curves indicated that Rubisco activity declined more rapidly in sun plants than in shade plants, particularly under elevated CO2. Absolute levels of chlorophyll were affected by the interaction of CO2 and light, and chlorophyll content declined to a minimal level in sun plants sooner than in shade plants. These declines in N concentration, in the initial slope of A/Ci curves, and in chlorophyll content were consistent with declining photosynthesis, such that elevated CO2 accelerated senescence in sun plants and prolonged leaf function in shade plants. These results have implications for the carbon economy of seedlings and the regeneration of red oak under global change conditions.
Scaling phenology from the local to the regional level: advances from species‐specific phenological models
Authors: Chuine I. , Cambon G. , Comtois P. 
Published: March 2003

SummaryPlant phenology, the study of seasonal plant activity driven by environmental factors, has found a renewal in the context of global climate change. Phenological events, such as leaf unfolding, exert strong control over seasonal exchanges of matter and energy between the land surface and the atmosphere. Phenological models that simulate the start of the growing season should be efficient tools to predict vegetation responses to climatic changes and related changes in energy balance. Species‐specific phenological models developed in the eighties have not been used for global‐scale predictions because their predictions were inaccurate in external conditions. Recent advances in phenology modelling at the species level suggest that prediction at a large scale may now be possible. In the present study, we tested the performance of species‐specific phenological models in time and space, looking at their ability (i) to predict regional phenology when previously fitted at a local scale, and (ii) to predict phenological trends, linked to climate changes, observed over a long‐term. For that task we used an historical phenological dataset from Ohio from the late ninetieth century and an airborne pollen dataset from Ontario, Québec and Maryland from the late twentieth century. The results show that the species‐specific phenological models used in this study were able to predict regional phenology even though they were fitted locally. The reconstruction of a phenological time series over the twentieth century showed a significant advancement of 0.2 days per year in the date of flowering of Ulmus americana, but very weak trends for Fraxinus americana and Quercus velutina.
Impacts of extreme climatic events on competition during grassland invasions
Authors: White TodD. A. , Campbell Bruce D. , Kemp Peter D. , Hunt Chris L. 
Published: March 2003

SummaryPhytometers of five C3 and five C4 species were transplanted into three different grasslands to study the effects of extreme climatic events on community invasibility and competition. Single extreme heating (eight hours at 52.5 °C) and rainfall (the equivalent of 100 mm) events in factorial combinations were superimposed on the grassland communities. A novel technique involving portable computer‐controlled chambers was used to create the heating events. In order to generate predictions of response to the extreme climatic events, the 10 phytometer species were categorized on the basis of 12 key plant functional traits. Using principal component analysis, two functional types (FTs) were identified as most likely to be advantaged (FT1, fast‐growing C4 annuals) and disadvantaged (FT2, slower‐growing C3 perennials) by an extreme climatic event. Competition between the resident vegetation and FT1 plus other C4 phytometers was consistently more intense within the exclusively C3 community compared to the dry C3/C4 community or moist C3/C4 community. The single extreme heating event had the greatest impact on competition, lowering the intensity of competition between the phytometers and resident vegetation. Our results indicate that competition is highly important in limiting the invasion of C3 grasslands by C4 species. The FT1 and FT2 responses confirmed predictions based on plant functional traits, whether growing as phytometers or as part of the resident vegetation. Future increases in climatic variability and the incidence of extreme climatic events are expected to suppress C3 competitive dominance and promote invasion of C4 species, in particular, the FT1 species.