ALBERT

Notes: Carbon dioxide, energy flux measurements and methane chamber measurements were carried out in an arctic wet tussock grassland located on a flood plane of the Kolyma river in NE Siberia over a summer period of 155 days in 2002 and early 2003. Respiration was also measured in April 2004. The study region is characterized by late thaw of the top soil (mid of June) and periodic spring floods. A stagnant water table below the grass canopy is fed by thawing of the active layer of permafrost and by flood water. The climate is continental with average daily temperature in the warmest months of 13°C (maximum temperature at midday: 28°C by the end of July), dry air (maximum vapour pressure deficit at midday: 28 hPa) and low rainfall of 50 mm during summer (July–September). Summer evaporation (July–September: 103 mm) exceeded rainfall by a factor of 2. The daily average Bowen ratio (H/LE) was 0.62 during the growing season. Net ecosystem CO2 uptake reached 10 μmol m−2 s−1 and was related to photon flux density (PFD) and vapour pressure deficit (VPD). The cumulative annual net carbon flux from the atmosphere to the terrestrial surface was estimated to be about −38 g C m−2 yr−1 (negative flux depicts net carbon sink). Winter respiration was extrapolated using the Lloyd and Taylor function. The net carbon balance is composed of a high rate of assimilation in a short summer and a fairly large but uncertain respiration mainly during autumn and spring. Methane flux (about 12 g C m−2 measured over 60 days) was 25% of C uptake during the same period of time (end of July to end of September). Assuming that CH4 was emitted only in summer, and taking the greenhouse gas warming potential of CH4 vs. CO2 into account (factor 23), the study site was a greenhouse gas source (at least 200 g Cequivalent m−2 yr−1). Comparing different studies in wetlands and tundra ecosystems as related to latitude, we expect that global warming would rather increase than decrease the CO2-C sink.

Notes: Based on review and original data, this synthesis investigates carbon pools and fluxes of Siberian and European forests (600 and 300 million ha, respectively). We examine the productivity of ecosystems, expressed as positive rate when the amount of carbon in the ecosystem increases, while (following micrometeorological convention) downward fluxes from the atmosphere to the vegetation (NEE = Net Ecosystem Exchange) are expressed as negative numbers. Productivity parameters are Net Primary Productivity (NPP=whole plant growth), Net Ecosystem Productivity (NEP = CO2 assimilation minus ecosystem respiration), and Net Biome Productivity (NBP = NEP minus carbon losses through disturbances bypassing respiration, e.g. by fire and logging). Based on chronosequence studies and national forestry statistics we estimate a low average NPP for boreal forests in Siberia: 123 gC m–2 y–1. This contrasts with a similar calculation for Europe which suggests a much higher average NPP of 460 gC m–2 y–1 for the forests there. Despite a smaller area, European forests have a higher total NPP than Siberia (1.2–1.6 vs. 0.6–0.9 × 1015 gC region–1 y–1). This arises as a consequence of differences in growing season length, climate and nutrition. For a chronosequence of Pinus sylvestris stands studied in central Siberia during summer, NEE was most negative in a 67-y old stand regenerating after fire (– 192 mmol m–2 d–1) which is close to NEE in a cultivated forest of Germany (– 210 mmol m–2 d–1). Considerable net ecosystem CO2-uptake was also measured in Siberia in 200- and 215-y old stands (NEE:174 and – 63 mmol m–2 d–1) while NEP of 7- and 13-y old logging areas were close to the ecosystem compensation point. Two Siberian bogs and a bog in European Russia were also significant carbon sinks (– 102 to – 104 mmol m–2 d–1). Integrated over a growing season (June to September) we measured a total growing season NEE of – 14 mol m–2 summer–1 (– 168 gC m–2 summer–1) in a 200-y Siberian pine stand and – 5 mol m–2 summer–1 (– 60 gC m–2 summer–1) in Siberian and European Russian bogs. By contrast, over the same period, a spruce forest in European Russia was a carbon source to the atmosphere of (NEE: + 7 mol m–2 summer–1 = + 84 gC m–2 summer–1). Two years after a windthrow in European Russia, with all trees being uplifted and few successional species, lost 16 mol C m–2 to the atmosphere over a 3-month in summer, compared to the cumulative NEE over a growing season in a German forest of – 15.5 mol m–2 summer–1 (– 186 gC m–2 summer–1; European flux network annual averaged – 205 gC m–2 y–1). Differences in CO2-exchange rates coincided with differences in the Bowen ratio, with logging areas partitioning most incoming radiation into sensible heat whereas bogs partitioned most into evaporation (latent heat). Effects of these different surface energy exchanges on local climate (convective storms and fires) and comparisons with the Canadian BOREAS experiment are discussed. Following a classification of disturbances and their effects on ecosystem carbon balances, fire and logging are discussed as the main processes causing carbon losses that bypass heterotrophic respiration in Siberia. Following two approaches, NBP was estimated to be only about 13–16 mmol m–2 y–1 for Siberia. It may reach 67 mmol m–2 y–1 in North America, and about 140–400 mmol m–2 y–1 in Scandinavia. We conclude that fire speeds up the carbon cycle, but that it results also in long-term carbon sequestration by charcoal formation. For at least 14 years after logging, regrowth forests remain net sources of CO2 to the atmosphere. This has important implications regarding the effects of Siberian forest management on atmospheric concentrations. For many years after logging has taken place, regrowth forests remain weaker sinks for atmospheric CO2 than are nearby old-growth forests.

Notes: [Auszug] Soils are major players in the carbon cycle — globally, they store the equivalent of about 300 times the amount of carbon now released annually through the burning of fossil fuels. It is generally assumed that most of the carbon locked up in soils is inert, and stays there. But as Bellamy et ...

Notes: Summary The relationship of leaf biomass and leaf area to the conductive area of stems and branches was investigated in Picea abies. A total of 30 trees were harvested to determine if these relationships were different in different crown zones and in trees growing with and without competition for light. Two methods were compared. In the first, data were accumulated from crown zones situated at the top of trees to the bottom; in the second, data were used from individual crown zones. The results indicated that the latter method is much more sensitive in detecting differences in the relationship of leaf biomass or leaf area to conductive area. The analysis also indicated that ratios such as leaf area/sapwood area are frequently size-dependent. This size-dependency can in some cases result in the differences being abscured, but more often leads to the false impression that the relationship between the variables changes. The relationship between leaf biomass and leaf area and conductive area of stems or branches was different in different crown zones and under different growth conditions. The slopes of these regressions appear to increase with decreasing transpirational demand and decrease with increasing hydraulic conductivity. The intercepts are probably related to the amount of identified sapwood actually involved in water conductance.

Notes: Summary Individual 33-year-old forest trees of the deciduous conifer speciesLarix decidua, Larix leptolepis andLarix decidua x leptolepis were investigated with respect to the phenomenon of stem heterosis in hybrid larch; the first part of this study compares the gas exchange responses of leaves. CO2 assimilation per leaf area was similar in the three larch species, but on a dry weight basis the nitrogen content of the needles and maximum CO2 assimilation rate (Amax) were slightly higher in the hybrid. This increase was accompanied by a higher protein content than in the Japanese and a lower specific leaf weight than in the European larch. All three species were similar in terms of the photosynthetic “nitrogen use” and stomatal conductance atA max. The similar slopes of the area-related steady-state responses of gas exchange against irradiance, evaporative demand and internal CO2 concentration led to similar rates of CO2 uptake under ambient conditions. The natural combinations and variability of the environmental factors also reduced the small dry weight-related difference inA max between hybrid larch and the parent species, such that all trees achieved similar daily carbon gains. Thus, the ecological significance of small interspecific differences in the metabolism of leaves has very little effect under the natural habitat conditions of a temperate climate. The second part of the study will investigate the effect of growth characteristics on the heterosis of hybrid larch.

Notes: Summary Among 33-year-old forest trees ofLarix decidua, L. leptolepis andL. decidua x leptolepis, the hybrid possessed an above-ground biomass which was three times greater, although all larches displayed similar relative distributions of biomass. At a “relative growth rate” slightly lower than in the parent species, hybrid larch achieved twice the annual carbon gain, increment in stem length and above-ground production, and its foliage-related stem growth was higher than in European (L. decidua) but similar to Japanese (L. leptolepis) larch. A similar “relative growth efficiency” and foliage-related total above-ground production in all trees did reflect the similarity of photosynthetic capacity of the hybrid found at the leaf level. While the lengths of lateral twigs on hybrid branches were intermediate between the European larch with short, and the Japanese larch with large, twigs the hybrid possessed the longest branches with the highest needle biomass. This resulted in a crown structure of the hybrid crown similar to the Japanese larch together with a high needle density on branches as in the European larch. In total, the foliage biomass per crown length was about 30% higher in hybrid larch than in both of the parent species. Thus, the high carbon input for the stem heterosis was based on a “complementation principle” of advantageous parent features at the crown level. Similar slopes of foliage against sapwood area of stem and branches did not indicate a special need for a thick hybrid stem with respect to water transport.

Notes: Summary Uptake of water and magnesium chloride solution was investigated through the outer surface of twigs of Picea abies (L.) Karst. Water uptake was determined by using pressure/volume (P/V) curves of the twigs as a basis for calculation to avoid problems of superficial extraneous water. When water was sprayed on bark and needles of 3- to 7-year-old twigs at a xylem water potential of -1.00 MPa, they absorbed as much as 80 mm3 water in 200 min/g twig dry weight as the twig water potential recovered to -0.15 MPa. With fluorescent dyes, pathways for absorption of water and solutes through the twig bark were found, particularly through the radially orientated ray tissue. In addition to uptake by mass flow, magnesium could also diffuse along a concentration gradient from the twig surface into the xylem. In the field, the magnitude of these uptake processes would depend on the concentration of elements deposited by atmospheric precipitation, the concentration gradient between the plant surface and the xylem sap, the xylem water potential and the intensity and duration of each precipitation event.

Notes: Abstract  Until now, many extracellular matrix proteins, e.g. osteopontin and osteonectin, have been used to determine a cell’s osteogenic maturation. The disadvantage in evaluation of these proteins is their relative wide-ranging appearance throughout the osteogenic differentiation process. Thus, the aim of this study was to establish an immunohistochemical setup using E11, a marker that binds selectively to cells of the late osteogenic cell lineage. In addition, the histochemical expression of the bone matrix proteins osteonectin, osteopontin and fibronectin was compared to that of E11 using monoclonal antibodies. For light microscopical detection of osteogenic markers in cultured cells we developed a simple paraffin technique using a fibrin glue as embedding medium. This allows the handling of cultured cells such as a tissue sample and includes the use of stored biological specimens for further immunohistochemical experiments. We used newborn rat calvariae for whole tissue preparations and for isolation and cultivation of bone cells. In addition, we included the rat osteosarcoma cell line ROS 17/2.8 in this study. For the first time, we have localised E11 in osteocytes of rat calvaria preparations at the electron microscopical level. E11 was detected at plasma membranes of osteocytes and their processes, but not at those of osteoblasts. Accompanying experiments with cultured newborn rat calvaria cells and ROS 17/2.8 cells revealed E11 reactivity on a subset of cells. The results obtained confirm the suitability of the differentiation marker E11 as a sensitive instrument for the characterisation of bone cell culture systems.

Notes: Summary In a previous paper seasonal shifts of the temperature optimum (OP) and of the upper temperature compensation point (CP) of net photosynthesis were described for Hammada scoparia growing wild, and for Prunus armeniaca cultivated in the Negev Desert (Israel). In this paper the relationships between these shifts and the microclimatic conditions, plant-water relations, and plant development are studied. The energy budged of the thin, round photosynthesizing stems of H. scoparia growing in an open desert habitat differes from that of the broad leaves of P. armeniaca within the orchard. This explains the fact that daily maximum temperatures of the apricot increased until August and September, whereas maximum temperatures of H. scoparia reached a peak in May and June and decreased thereafter during the second half of the growing season. For H. scoparia a correspondence was found between the daily maximum tissue temperatures (and also the average temperatures of the warmest periods of the day) and the seasonal changes of the OP and CP values. This may indicate that the shifts in the temperature sensitivity of net photosynthesis of this plant are adaptations to the temperature conditions of the plant. This, however, cannot be the case for P. armeniaca, where during the second part of the growing season a period of rising leaf temperatures coincides with a period of decreasing OP and CP values. Therefore, the seasonal changes of the temperature dependence of net photosynthesis of P. armeniaca could not always be considered an adaptation to the prevailing temperature conditions of the plant. In this case, the changes in temperature sensitivity of photosynthesis could be due to developmental processes such as aging. In both lants the seasonal changes of the OP and CP values correspond to changes of the daily photoperiod and to changes of the daily average light intensity. It appears possible that this correlation indicates a causal relationship.

Notes: Summary The gas exchange of the apricot (Prunus armeniaca L.) growing in the runoff farm at Avdat (Negev, Israel) was measured during its growing period using temperature- and humidity-controlled chambers. Water potentials of the xylem were measured with a pressure bomb, and the mesophyll internal CO2 concentration was calculated from simultaneous measurements of net photosynthesis and transpiration. The daily changes in water potential Ψ had only little effect on the daily course of stomatal resistance. The early morning peak of CO2 uptake was reached when Ψ had already dropped to very low values. On dry days, Ψ and the relative water content of the leaf were improved at noon during the time of stomatal closure. On humid days, Ψ dropped to very low values (43.5 bar) at a high transpiration rate without causing stomatal closure, as much as on the dry days when stomata where more closed at less water stress. The observed changing sensitivity of the stomata to changes in air humidity during the season is related to the water status in the plant. This change is possibly caused by a long-term effect of stress in this habitat. The daily changes in stomatal diffusion resistance did not consistently correlate with changes of the CO2 concentration in the intercellular air spaces. In the morning a decreasing internal CO2 concentration was even inversely correlated to the stomatal response. In the afternoon the effect of an increasing internal CO2 concentration and the effect of external climate on stomatal response could be additive. However, at the time, when CO2 uptake reached a second peak in the afternoon the same value of diffusion resistance is reached at very different levels of internal CO2 concentration as compared to the morning. For the regulation of the diffusion resistance in apricot under the natural conditions, the effects of plant internal control mechanisms are overruled and/or modified by the external climatic factors of air humidity and temperature. The significance of the climate-controlled stomatal response for the existence and cultivation of this plant species in an arid habitat is discussed.