Showing papers by "Ernst Detlef Schulze published in 2006"

Reconciling carbon-cycle concepts, terminology, and methods

Abstract: Recent projectionsofclimatic change havefocused a great deal of scientific and public attention on patterns of carbon (C) cycling as well as its controls, particularly the factors that determine whether an ecosystem is a net source or sink of atmospheric carbon dioxide (CO2). Net ecosystem production (NEP), a central concept in C-cycling research, has been used by scientists to represent two different concepts. We propose that NEP be restricted to just one of its two original definitions—the imbalance between gross primary production (GPP) and ecosystem respiration (ER). We further propose that a new term—net ecosystem carbon balance (NECB)—be applied to the net rate of C accumulation in (or loss from [negative sign]) ecosystems. Net ecosystem carbon balance differs from NEP when C fluxesotherthanCfixationandrespiration occur,or when inorganic C enters or leaves in dissolved form. These fluxes include the leaching loss or lateral transfer of C from the ecosystem; the emission of volatile organic C, methane, and carbon monoxide; and the release of soot and CO2 from fire. Carbon fluxes in addition to NEP are particularly important determinants of NECB over long time scales. However, even over short time scales, they are important in ecosystems such as streams, estuaries, wetlands, and cities. Recent technological advances have led to a diversity of approaches to the measurement of C fluxes at different temporal and spatial scales. These approaches frequently capture different components of NEP or NECB and can therefore be compared across scales only by carefully specifying the

Atlas of Woody Plant Stems: Evolution, Structure, and Environmental Modifications

Abstract: Introduction1 1 The Evolution of Plant Stems in the Earth's History The Landscape in the Paleozoic Plant Body of Vascular Plants The Evolution of a Stabilizaton System The Contemporary Fossil Psilotum Nudum? Diversification of Plants Containing Tracheids The Lycopods The Horsetails The Fossil and Living Ferns Contemporary Ferns Trees Grow Taller and Bigger Successful Seed Plants with Naked Seeds Ginkgos and Cycads Gnetophytes (Ephedra, Gnetum and Welwitschia) The Most Successful Seed Plants with Naked Seeds: Conifers Successful Plants with Seeds Enclosed in a Carpel: Angiospermae 2 The Structure of the Plant Body Life Forms in Different Vegetation Zones Principal Growth Forms Principal Construction of Roots and Shoots Principal Construction of the Xylem and Phloem Cell Types, Cell Walls and Cell Contents 3 Secondary Growth: Advantages and Risks Primary and Secondary Growth Principle Structure of Plants with Secondary Growth Physiological and Ontogenetic Ageing The Risks of Water Transport: Stabilized and Permeable Cell Walls The Risks of Stem Thickening: Dilatation and Phellem Formation The Risks of Over-Production: Programmed Cell Death The Risks of Instability: Eccentricity Reaction Wood Formation of Lignin and Thick Cell Walls Internal Optimization The Risk of Decomposition: Natural Boundaries and Protection Systems Defence Barriers around Wounds The Risk of Shedding Plant Parts: Abscission 4 Modification of the Stem Structure The Primary Stage of Growth: The Construction of Vascular Bundles TheArrangement of Vascular Bundles in Mosses, Lycopods and Ferns The Arrangement of Vascular Bundles in Conifer and Dicotyledonous Plant Shoots The Secondary Stage of Growth: Conifer Xylem The Xylem of Dicotyledonous Angiosperms The Primary and Secondary Stages of Growth of Monocotyledons: Macroscopic View Microscopic View The Secondary Stage of Growth: Conifer Phloem The Phloem of Dicotyledonous Angiosperms Cambial Growth Variants and Successive Cambia The Third Stage of Growth: The Periderm 5 Modification of the Xylem within a Plant Modification of the Xylem within a Plant Conifer: Root, Twig and Stem Deciduous Tree: Root, Twig and Stem From Root to Stem Structure Modification by Aging: Changing Growth Forms Changing Growth and Leaf Forms Changing Wood Anatomical Structures Change of Phloem and Periderm Structures 6 Modification of the Xylem and Phloem by Ecological Factors Intra-Annual Density Fluctuations, Phenolic and Crystal Deposits Intra-Annual Cell Collapse, Callous Tissue and Ducts Interannual Variation of Latewood Zones Long Term Variations: Sudden Growth Changes Inter- and Intra-Annual Variations of the Phloem 7 Modification of Organs Modification of Shoots: Long and Short Shoots Shedding Needles, Male and Female Flowers Thorns and Spines Vertical, Horizontal and Drooping Twigs Latent and Adventitious Shoots The Lateral Modification of Stems 8 Anatomical Plasticity Wood Structural Variability In Different Families In Different Growth Forms Under Different Site Conditions Modification Caused by Different Shoot and Root Function

Carbon dynamics in successional and afforested spruce stands in Thuringia and the Alps

Abstract: Changes in the carbon stocks of stem biomass, organic layers and the upper 50 cm of the mineral soil during succession and afforestation of spruce (Picea abies) on former grassland were examined along six chronosequences in Thuringia and the Alps. Three chronosequences were established on calcareous and three on acidic bedrocks. Stand elevation and mean annual precipitation of the chronosequences were different. Maximum stand age was 93 years on acid and 112 years on calcareous bedrocks. Stem biomass increased with stand age and reached values of 250–400 t C ha � 1 in the oldest successional stands. On acidic bedrocks, the organic layers accumulated linearly during forest succession at a rate of 0.34 t C ha � 1 yr � 1 . On calcareous bedrocks, a maximum carbon stock in the humus layers was reached at an age of 60 years. Total carbon stocks in stem biomass, organic layers and the mineral soil increased during forest development from 75 t C ha � 1 in the meadows to 350 t C ha � 1 in the oldest successional forest stands (2.75 t C ha � 1 yr � 1 ). Carbon sequestration occurred in stem biomass and in the organic layers (0.34 t C ha � 1 yr � 1 on acid bedrock), while mineral soil carbon stocks declined. Mineral soil carbon stocks were larger in areas with higher precipitation. During forest succession, mineral soil carbon stocks of the upper 50 cm decreased until they reached approximately 80% of the meadow level and increased slightly thereafter. Carbon dynamics in soil layers were examined by a process model. Results showed that sustained input of meadow fine roots is the factor, which most likely reduces carbon losses in the upper 10 cm. Carbon losses in 10–20 cm depth were lower on acidic than on calcareous bedrocks. In this depth, continuous dissolved organic carbon inputs and low soil respiration rates could promote carbon sequestration following initial carbon loss. At least 80 years are necessary to regain former stock levels in the mineral soil. Despite the comparatively larger amount of carbon stored in the regrowing vegetation, afforestation projects under the Kyoto protocol should also aim at the preservation or increase of carbon in the mineral soil regarding its greater stability of compared with stocks in biomass and humus layers. If grassland afforestation is planned, suitable management options and a sufficient rotation length should be chosen to achieve these objectives. Maintenance of grass cover reduces the initial loss.

Inter-annual and seasonal variability of radial growth, wood density and carbon isotope ratios in tree rings of beech (Fagus sylvatica) growing in Germany and Italy

Abstract: We investigated the variability of tree-ring width, wood density and 13C/12C in beech tree rings (Fagus sylvatica L.), and analyzed the influence of climatic variables and carbohydrate storage on these parameters. Wood cores were taken from dominant beech trees in three stands in Germany and Italy. We used densitometry to obtain density profiles of tree rings and laser-ablation-combustion-GC-IRMS to estimate carbon isotope composition (δ 13C) of wood. The sensitivity of ring width, wood density and δ 13C to climatic variables differed; with tree-ring width responding to environmental conditions (temperature or precipitation) during the first half of a growing season and maximum density correlated with temperatures in the second part of a growing season (July–September). δ 13C variations indicate re-allocation and storage processes and effects of drought during the main growing season. About 20% of inter-annual variation of tree-ring width was explained by the tree-ring width of the previous year. This was confirmed by δ 13C of wood which showed a contribution of stored carbohydrates to growth in spring and a storage effect that competes with growth in autumn. Only mid-season δ 13C of wood was related to concurrent assimilation and climate. The comparison of seasonal changes in tree-ring maximum wood density and isotope composition revealed that an increasing seasonal water deficit changes the relationship between density and 13C composition from a negative relation in years with optimal moisture to a positive relationship in years with strong water deficit. The climate signal, however, is over-ridden by effects of stand density and crown structure (e.g., by forest management). There was an unexpected high variability in mid season δ 13C values of wood between individual trees (−31 to −24‰) which was attributed to competition between dominant trees as indicated by crown area, and microclimatological variations within the canopy. Maximum wood density showed less variation (930–990 g cm−3). The relationship between seasonal changes in tree-ring structure and 13C composition can be used to study carbon storage and re-allocation, which is important for improving models of tree-ring growth and carbon isotope fractionation. About 20–30% of the tree-ring is affected by storage processes. The effects of storage on tree-ring width and the effects of forest structure put an additional uncertainty on using tree rings of broad leaved trees for climate reconstruction.

Leaf and wood carbon isotope ratios, specific leaf areas and wood growth of Eucalyptus species across a rainfall gradient in Australia.

Abstract: Leaves and samples of recent wood of Eucalyptus species were collected along a rainfall gradient parallel to the coast of Western Australia between Perth in the north and Walpole in the south and along a southwest to northeast transect from Walpole in southwestern Australia, to near Mount Olga in central Australia. The collection included 65 species of Eucalyptus sampled at 73 sites and many of the species were collected at several sites along the rainfall gradient. Specific leaf area (SLA) and isotopic ratio of 13C to 12C (delta 13C) of leaves that grew in 2002, and tree ring growth and delta 13C of individual cell layers of the wood were measured. Rainfall data were obtained from the Australian Bureau of Meteorology for 29 locations that represented one or a few closely located collection sites. Site-averaged data and species-specific values of delta 13C decreased with decreasing annual rainfall between 1200 and 300 mm at a rate of 1.63 per thousand per 1000 mm decrease in rainfall. Responses became variable in the low rainfall region ( 300 mm of annual rainfall. Specific leaf area varied between 2 and 6 m2 kg(-1) and tended to increase with decreasing annual rainfall in some species, but not all, whereas delta 13C decreased with SLA. The relationship between delta 13C and SLA was highly species and soil-type specific. Leaf-area-based nitrogen (N) content varied between 2 and almost 6 g m(-2) and decreased with rainfall. Thus, thicker leaves were associated with higher N content and this compensated for the effect of drought on delta 13C. Nitrogen content was also related to soil type and species identity. Based on a linear mixed model, statistical analysis of the whole data set showed that 27% of the variation in delta 13C was associated with changes in SLA, 16% with soil type and only 1% with rainfall. Additionally, 21% was associated with species identity. For a subset of sites with > 300 mm rainfall, 43% of the variation was explained by SLA, 13% by soil type and only 3% by rainfall. The species effect decreased to 9% because there were fewer species in the subset of sites. The small effect of rainfall on delta 13C was further supported by a path analysis that yielded a standardized path coefficient of 0.38 for the effect of rainfall on SLA and -0.50 for the effect of SLA on delta 13C, but an insignificantly low standardized path coefficient of -0.05 for the direct effect of rainfall on delta 13C. Thus, in contrast to our hypothesis that delta 13C decreases with rainfall independent of soil type and species, we detected no statistically significant relationship between rainfall and delta 13C in leaves of trees growing at sites receiving < 300 mm of rainfall annually. Rainfall affected delta 13C indirectly through soil type (a surrogate for water-holding capacity) across the rainfall gradient. Annual tree rings are not clearly visible in evergreen Eucalyptus species, even in the seasonally cool climate of SW Australia. Generally, visible density transitions in the wood are related not to a strict annual cycle but to periods of growth associated mainly with rainfall. The relationship between delta 13C of leaves and the width of these stem increments was not statistically significant. Analysis of stem growth periods showed that delta 13C in wood responded to rainfall events, but carbohydrate storage and reallocation also affected the isotopic signature. Although delta 13C in wood of any one species varied over a range of 2 to 4 per thousand, there was a general relationship between delta 13C of the leaves and the annual range of delta 13C in wood. We conclude that species-specific traits are important in understanding the response of Eucalyptus to rainfall and that the diversity of the genus may reflect its response to the large climatic gradient in Australia and to the large annual and interannual variations in rainfall at any one location.

Species differences in carbon isotope ratios, specific leaf area and nitrogen concentrations in leaves of Eucalyptus growing in a common garden compared with along an aridity gradient

Abstract: Leaves produced in 2004 of 422 species of Eucalyptus whose natural habitat is southern Australia were sampled at the Currency Creek Arboretum in South Australia where the annual (mainly winter) rainfall is about 400 mm. Tree height, leaf area, leaf dry weight, leaf nitrogen (N) concentration and leaf carbon isotope ratio (δ 13 C) were measured and the specific leaf area (SLA) calculated. Among the 422 species, the SLA varied from 1.5 to 8.8 m 2 kg -1 and N concentration varied from 0.6 to 2.1%, much greater than in 64 species collected along an aridity transect from southwestern Western Australia to central Australia in 2003. Also, the range of leaf δ 13 C values was similar in the common garden to that across the aridity transect. For the 45 species present in both studies, the SLA and leaf N concentration in the common garden were similar to those measured in leaves along the aridity transect, indicating that these characteristics are inherent in the species and vary little with environment. The variation in leaf δ 13 C in the common garden was just as great as along the transect, but the values measured in the one location were poorly correlated with those along the transect. This was not expected, as the variation in δ 13 C at one common site in South Australia was anticipated to be less than along the aridity gradient where annual rainfall varied from 250 to 1200 mm. Path analysis on the 45 species common to both studies indicated that rainfall did not have a direct effect on δ 13 C, but the differences in δ 13 C resulted from indirect effects of rainfall on SLA and N concentration. δ 13 C was negatively correlated with SLA but positively correlated with N. Thus, both effects may compensate for each other so that no significant relationship between δ 13 C and rainfall was observable. However, there is a large degree of variation of δ 13 C at any level of rainfall. The origin and ecological implications of this observation are discussed.

Productivity of mosses and organic matter accumulation in the litter of sphagnum larch forest in the permafrost zone

Abstract: Productivity of the moss cover and necromass accumulation in the litter of a sphagnum larch forest have been estimated on the basis of tree age. It has been shown that the total carbon stock in the litter of a 100-year-old stand, including organic matter not destroyed by fire, exceeds the corresponding value for the tree stand itself by more than an order of magnitude. The accumulation of organic matter on the soil surface inhibits the growth of larch. In particular, this factor impairs hydrothermal conditions in the soil and causes a rise of the permafrost table; as a consequence, lower layers of the root system die off.