Publikasjoner
NIBIOs ansatte publiserer flere hundre vitenskapelige artikler og forskningsrapporter hvert år. Her finner du referanser og lenker til publikasjoner og andre forsknings- og formidlingsaktiviteter. Samlingen oppdateres løpende med både nytt og historisk materiale. For mer informasjon om NIBIOs publikasjoner, besøk NIBIOs bibliotek.
2011
Sammendrag
A changing climate will likely influence the selection of tree species in the future, and this may in turn affect the size of the pools and fluxes of carbon. Tree species differ in growth rate, fine-root turnover and quality of litter and tend to produce different types of understory vegetation. In Sweden three tree species (Norway spruce [Picea abies] 43%, Scots pine [Pinus sylvestris] 39% and birch [Betula spp.] 11%) dominate. In the present study we used field experiments in southern Sweden to test if these tree species differed in root distribution and turnover.
Sammendrag
The main task of the C1-Dep-22(SI) action was to compare national throughfall collectors with a harmonized collector which was designed according to the requirements of the WMO. The action spread onthe took place in very different climate zones and vegetation, and included a very different types of national collectors with different sampling procedures. The number of harmonized throughfall collectors was 30 for all participants. The spatial arrangement in the plot, sampling times, sampling and cleaning procedures, bulking of the subsamples and chemical analysis procedures were in all cases the national procedures. The time when the precipitation was in the form of snow was excluded from the sampling periods. The associated beneficiaries reported the amounts of the precipitation per collector and the results from chemical analysis per pooled sample. The measured quantities were compared for different types of forest or main tree species. The deviations between collectors were lower in the plots with the broadleaf trees than in the plots with conifers as the main tree species. The median deviations for conifers and for broadleaves trees is not significantly different from zero. Except in a few cases, a good agreement in the amount of precipitation was found between the national and harmonized collectors for both throughfall and bulk precipitation. In a few incidents this was not the case but we assume that where this was not the case, this was due to happened in extreme weather conditions e. g. heavy storms. Also good agreement was also found within for the chemical composition of the solutions, gathered with different types of collectors. Again, there were some deviations limited to on single occasions. It was found that the harmonized collectors were attractive to birds and thus a bird ring is a must in this (white) -coloured version of the collector. Chemical analysis (chemical composition) together with the collected amount of the solution depends on give the total deposition values. It was made a close up to the deposition values of ammonium-nitrogen, nitrate-nitrogen and sulphate-sulphur were compared in detail. For ammonium-nitrogen no bigger difference was found for the one-year deposition values except in one case what which turned out to be almost certainly a consequence of birds activity. Differences in all other cases were no more than 0.3 g m-2 yr-1. For nitrate-nitrogen smaller deviations were found but in none of the case was the difference was in total annual deposition higher than 0.3 g m-2 yr-1. For sulphate-sulphur good agreement was found for all associated beneficiaries except two. One of the Possible reasons could be in the difference of in the ability in collecting dry deposition and/or the total area which contributes to the capturing area for dry deposition. Despite their heterogeneity and some unlack of adaptation for representative sampling at the plot scale, the national devices for throughfall collection gave comparable results infor throughfall deposition to the harmonized, optimal collectors. In conclusion national throughfall collection devices can be maintained to ensure the continuity of the time series in deposition monitoring. And to improve the harmonized collector even more, problems with the possible blockages of the tube at the bottom of the funnel because of debris should be solved.
Sammendrag
We used two datasets of 14C analyses of archived soil samples to study carbon turnover in O horizons from spruce dominated old-growth stands on well-drained podsols in Scandinavia. The main data set was obtained from archived samples from the National Forest Soil Inventory in Sweden and represents a climatic gradient in temperature. Composite samples from 1966, 1972, 1983 and 2000 from four different regions in a latitude gradient ranging from 57 to 67oN were analysed for 14C content. Along this gradient the C stock in the O horizon ranges from 2.1 kg m-2 in the north to 3.7 kg m-2 in the southwest. The other data set contains 14C analyses from 1986, 1987, 1991, 1996 and 2004 from the O horizons in Birkenes, Norway. Mean residence times (MRT) were calculated using a two compartment model, with a litter decomposition compartment using mass loss data from the literature for the three first years of decomposition and a humus decomposition compartment with a fitted constant turnover rate. We hypothesized that the climatic gradient would result in different C turnover in different parts of the country between northern and southern Sweden. The use of archived soil samples was very valuable for constraining the MRT calculations, which showed that there were differences between the regions. Longest MRT was found in the northernmost region (41 years), with decreasing residence times through the middle (36 years) and central Sweden (28 years), then again increasing in the southwestern region (40 years). The size of the soil organic carbon (SOC) pool in the O horizon was mainly related to differences in litter input and to a lesser degree to MRT. Because N deposition leads both to larger litter input and to longer MRT, we suggest that N deposition contributes significantly to the latitudinal SOC gradient in Scandinavia, with approximately twice as much SOC in the O horizon in the south compared to the north. The data from Birkenes was in good agreement with the Swedish dataset with MRT estimated to 34 years.
Sammendrag
There is a great demand for involving rapid, non destructive and less time consuming methods for quick control and prediction of soil quality, environmental monitoring, and other precision measurements in agriculture. Near infrared reflectance spectroscopy (NIRS) is considered as an appropriate alternative method to conventional analytical methods for large scale measurements. The objective of this study was to investigate the possibilities of NIRS for prediction of some chemical properties of soil samples. A total of 97 samples from Stara Zagora, Kazanlak and Gurkovo region taken from the 0-40 cm layer were collected. Soil types were Luvisols, Vertisols, Fluvisols and Rankers. The samples were analyzed for total phosphorus by spectrometric determination of phosphorus soluble in sodium hydrogen carbonate solution, total nitrogen by Kjeldahl method, pH (H O)-potentiometrically and electrical conductivity (EC). 2 The spectral data of all air dried samples were measured using an Perkin Elmer Spectrum One NTS, FT-NIR Spectrometer, within the range from 700 to 2500 nm. Partial Least Squares (PLS) regression was used to built models to determine soil chemical parameters from the NIR spectra. Two-third of the samples were used as a calibration set and the remaining samples as independent validation test set. The best model was obtained for total nitrogen with a coefficient of determination r=0,91, standard error of calibration SEP=336 mg/kg, and the ratio of the standard variation of the reference data to the SEP, indicating the performance of the calibration, of RPD=2,3. The accuracy of prediction was poor for electrical conductivity. The results obtained clearly indicated that NIRS had the potential to predict some soil components rapidly and without sample preparation.
Forfattere
Markus Reichstein Miguel D. Mahecha Nuño Carvalhais Gitta Lasslop Sonia I. Seneviratne Holger Lange Alessandro Cescatti Mirco MigliavaccaSammendrag
The release of carbon dioxide (CO2) from the land surface via different respiratory processes is a major flux in the global carbon cycle, antipodal to CO2 uptake via photosynthesis. Understanding the sensitivity of respiratory processes to temperature is central for quantifying the climate–carbon cycle feedback. In a recent study we approximated the sensitivity of terrestrial ecosystem respiration to air temperature (Q10) across 60 FLUXNET sites. For this objective, we developed a novel methodology that circumvents seasonally confounding effects. Contrary to previous findings, our results suggest that Q10 is independent of mean annual temperature, does not differ among biomes, and is confined to values around 1.4 ± 0.1. However, the shape of the strong relation between photosynthesis and respiration is highly variable among sites. The results may partly explain a less pronounced climate–carbon cycle feedback than suggested by current carbon cycle climate models. In the talk we put our findings into context with other recent results and critically discuss their potential for evaluating temperature sensitivity of respiration in terrestrial biosphere models and parameterizing future land surface schemes.
Forfattere
Miguel D. Mahecha Markus Reichstein Nuño Carvalhais Gitta Lasslop Holger Lange Sonia I. Seneviratne Rodrigo Vargas Christof Ammann M. Altaf Arain Alessandro Cescatti Ivan A. Janssens Mirco Migliavacca Leonardo Montagnani Andrew D. RichardsonSammendrag
We estimated the sensitivity of terrestrial ecosystem respiration to air temperature across 60 FLUXNET sites by minimizing the effect of seasonally confounding factors. Graf et al. now offer a theoretical perspective for an extension of our methodology. However, their critique does not change our main findings and, given the currently available observational techniques, may even impede a comparison across ecosystems.
Sammendrag
Long-term monitoring of headwater semi-natural catchments is used to document persistence and changes in ecosystems. At three headwater catchments in the Bramke basin in Northern Germany, physical and chemical variables in rainfall, soil solution from various depths (20–300 cm) and streamwater have been monitored. The Lange Bramke catchment is largely covered by a Norway spruce (Picea abies, Karst.) stand planted in the 1950ies. Over 29 years, 4310 water samples from streamwater and 5475 soil water samples were analysed for major constituents. Both linear methods (principal component analysis (PCA) and cross correlation (CC)) as well as non-linear methods (isometric feature mapping (ISOMAP) and maximum variance unfolding (MVU)) were used to analyze the spatiotemporal patterns of dissolved major ion concentrations in soil solution and streamwater. This approach provides a multiscale characterisation of links between soil water and streamwater at the catchment scale. Pattern identification augments the interpretation of processes in terms of transport and storage. The long time scales were dominated by trends in ions implicated in soil acidification. This reflects the decreasing input of acid deposition. At the annual scale, where hydrological effects dominate, each of the three adjacent catchments showed different patterns. Various empirical and process-based models have been applied in the past to the Bramke catchments. Results of the data-oriented approach can be used to indicate the potential and limits of process-oriented models for this data set.
Sammendrag
For tracer studies at the catchment scale, travel times are often assumed to be stationary. We question the validity of this assumption. We analyzed a series of tracer experiments conducted under exceptionally controlled conditions at Gårdsjön, Sweden. The Gårdsjön G1 catchment was covered by a roof underneath which natural throughfall has been replaced by artificial irrigation with a pre-defined chemical composition. This unique setup was used to perform replicated catchment scale Br tracer experiments under steady state storm flow conditions in five different years. A log-normal distribution function was fitted to all Br breakthrough curves. Fitted parameter values differed significantly for some of the experiments. These differences were not only related to the slightly different hydrologic boundary and initial conditions for the experiments, but also to seasonal changes in catchment properties that may explain the different flow paths during the experiments. We conclude that the travel time distribution is not only linked to discharge but also explicitly related to other water fluxes such as evapotranspiration, and that it is not stationary even under steady-state flow conditions. Since the attenuation of soluble pollutants is fundamentally linked to the travel times of water through the subsurface of a catchment, it is of crucial importance to understand the latter in detail. However, it is still unclear which are the dominant processes controlling their distribution.
Sammendrag
Remote sensing of the activity of vegetation in relation to environmental conditions provides an invaluable basis for investigating the spatiotemporal dynamics and patterns of variability for ecosystem processes. We investigate the fraction of Absorbed Photosynthetically Active Radiation (fAPAR) using SeaWiFS satellite observations from 1998 to 2005 and ancillary meteorological variables from the CRU-PIK dataset with a global coverage at a spatial resolution of 0.5o x 0.5o. A pixel-by-pixel spectral decomposition using Singular System Analysis leads to a global “classification” of the terrestrial biosphere according to prevalent time-scale dependent dynamics of fAPAR and its relation to meteorology. A complexity analysis and a combined subsignal extraction and dimensionality reduction reveals a series of dominant geographical gradients, separately for different time scales. At the annual scale, which explains around 50% of the fAPAR variability as a global average, patterns largely resemble the biomes of the world as mapped by biogeographical methods, and are driven by temperature and by pronounced rain seasons in the tropics. On shorter time scales, fAPAR fluctuations are exclusively driven by water supply, inducing, e.g., semiannual cycles in the equatorial belt of Africa or the Indo-Gangetic Plain. For some regions however, in particular South America, altitude, mean temperature, drought probability and fire occurrences are parameters that seem to shape the spatial patterns of fAPAR across time scales. Overall, we provide a first global multiscale characterization of fAPAR and highlight different mechanisms in land-surface-climate couplings.
Forfattere
Jihong Liu Clarke Carl Jonas Jorge Spetz Sissel Haugslien Merete Dees Roar Moe Dag-Ragnar BlystadSammendrag
Det er ikke registrert sammendrag