P. Levy - Academia.edu (original) (raw)
Papers by P. Levy
Global Change Biology, 2010
Agriculture, Ecosystems & Environment, 2007
Soil/atmosphere exchange fluxes of nitrous oxide were monitored for a 3-year period at 10 grassla... more Soil/atmosphere exchange fluxes of nitrous oxide were monitored for a 3-year period at 10 grassland sites in eight European countries (Denmark, France, Hungary, Ireland, Italy, The Netherlands, Switzerland and United Kingdom), spanning a wide range of climatic, environmental and soil conditions. Most study sites investigated the influence of one or several management practices on N 2 O exchange, such as nitrogen fertilization and grazing intensity. Fluxes were measured using non-steady state chambers at most sites, and alternative measurement techniques such as eddy covariance and fast-box using tunable diode laser spectroscopy were implemented at some sites. The overall uncertainty in annual flux estimates derived from chamber measurements may be as high as 50% due to the temporal and spatial variability in fluxes, which warrants the future use of continuous measurements, if possible at the field scale. Annual emission rates were higher from intensive than from extensive grasslands, by a factor 4 if grazed (1.77 versus 0.48 kg N 2 O-N ha À1 year À1 ) and by a factor 3 if ungrazed (0.95 versus 0.32 kg N 2 O-N ha À1 year À1 ). Annual emission factors for fertilized systems were highly variable, ranging from 0.01% to 3.56%, but the mean emission factor across all sites (0.75%) was substantially lower than the IPCC default value of 1.25%. Emission factors for individual fertilization events increased with soil temperature and were generally higher for water-filled pore space values in the range 60-90%, though precipitation onto dry soils was also shown to lead to high losses of N 2 O-N from applied fertilizer. An empirical, multiple www.elsevier.com/locate/agee Agriculture, Ecosystems and Environment 121 135-152 regression model to predict N 2 O emission factors on the basis of soil temperature, moisture and rainfall is developed, explaining half of the variability in observed emission factors. #
![Research paper thumbnail of Testing a process-based model of tree seedling growth by manipulating [CO2] and nutrient uptake](https://attachments.academia-assets.com/42145275/thumbnails/1.jpg)
](Tree Physiology, 2000
A model was developed that simulated photosynthesis, growth and allocation in tree seedlings. The... more A model was developed that simulated photosynthesis, growth and allocation in tree seedlings. The model was parameterized with data from experiments on seedlings of sycamore (Acer pseudoplatanus L.), Sitka spruce (Picea sitchensis (Bong) Carr.) and young birch trees (Betula pendula Roth.). In these experiments, CO 2 concentration ([CO 2 ]) and nutrient addition rate were varied. Parameters quantifying nutrient uptake, translocation and starch synthesis were fitted, based on data from control treatments. Elevated [CO 2 ] and low-nutrient treatments were then used to test the predicted response of growth and allocation against observations. The model accurately predicted total seedling growth in the elevated [CO 2 ] treatments. A response of growth to elevated [CO 2 ] was seen in the birch and sycamore experiments, but not in the Sitka spruce, because of photosynthetic down-regulation. Predictions of allocation were reasonably accurate in the birch and Sitka spruce experiments, but were notably poorer in the sycamore experiments, possibly because of differences in sink strength between root and shoot. In the birch and sycamore experiments, little change in allocation with elevated [CO 2 ] was observed or predicted. This was ascribed to the relative values of K Tc and K Tn , the translocation coefficients that determine the sensitivity of allocation to carbon and nitrogen uptake rates, respectively. Growth and allocation in the lownutrient treatments were poorly predicted by the model. In Sitka spruce, it was suspected that the photosynthetic parameters measured in August 1994 had been higher earlier in the season, before nutrients became depleted. In sycamore, the discrepancies were thought to relate to differences in sink strength between root and shoot that could not be described by the model.
Global Change Biology, 2010
Agriculture, Ecosystems & Environment, 2007
Soil/atmosphere exchange fluxes of nitrous oxide were monitored for a 3-year period at 10 grassla... more Soil/atmosphere exchange fluxes of nitrous oxide were monitored for a 3-year period at 10 grassland sites in eight European countries (Denmark, France, Hungary, Ireland, Italy, The Netherlands, Switzerland and United Kingdom), spanning a wide range of climatic, environmental and soil conditions. Most study sites investigated the influence of one or several management practices on N 2 O exchange, such as nitrogen fertilization and grazing intensity. Fluxes were measured using non-steady state chambers at most sites, and alternative measurement techniques such as eddy covariance and fast-box using tunable diode laser spectroscopy were implemented at some sites. The overall uncertainty in annual flux estimates derived from chamber measurements may be as high as 50% due to the temporal and spatial variability in fluxes, which warrants the future use of continuous measurements, if possible at the field scale. Annual emission rates were higher from intensive than from extensive grasslands, by a factor 4 if grazed (1.77 versus 0.48 kg N 2 O-N ha À1 year À1 ) and by a factor 3 if ungrazed (0.95 versus 0.32 kg N 2 O-N ha À1 year À1 ). Annual emission factors for fertilized systems were highly variable, ranging from 0.01% to 3.56%, but the mean emission factor across all sites (0.75%) was substantially lower than the IPCC default value of 1.25%. Emission factors for individual fertilization events increased with soil temperature and were generally higher for water-filled pore space values in the range 60-90%, though precipitation onto dry soils was also shown to lead to high losses of N 2 O-N from applied fertilizer. An empirical, multiple www.elsevier.com/locate/agee Agriculture, Ecosystems and Environment 121 135-152 regression model to predict N 2 O emission factors on the basis of soil temperature, moisture and rainfall is developed, explaining half of the variability in observed emission factors. #
Tree Physiology, 2000
A model was developed that simulated photosynthesis, growth and allocation in tree seedlings. The... more A model was developed that simulated photosynthesis, growth and allocation in tree seedlings. The model was parameterized with data from experiments on seedlings of sycamore (Acer pseudoplatanus L.), Sitka spruce (Picea sitchensis (Bong) Carr.) and young birch trees (Betula pendula Roth.). In these experiments, CO 2 concentration ([CO 2 ]) and nutrient addition rate were varied. Parameters quantifying nutrient uptake, translocation and starch synthesis were fitted, based on data from control treatments. Elevated [CO 2 ] and low-nutrient treatments were then used to test the predicted response of growth and allocation against observations. The model accurately predicted total seedling growth in the elevated [CO 2 ] treatments. A response of growth to elevated [CO 2 ] was seen in the birch and sycamore experiments, but not in the Sitka spruce, because of photosynthetic down-regulation. Predictions of allocation were reasonably accurate in the birch and Sitka spruce experiments, but were notably poorer in the sycamore experiments, possibly because of differences in sink strength between root and shoot. In the birch and sycamore experiments, little change in allocation with elevated [CO 2 ] was observed or predicted. This was ascribed to the relative values of K Tc and K Tn , the translocation coefficients that determine the sensitivity of allocation to carbon and nitrogen uptake rates, respectively. Growth and allocation in the lownutrient treatments were poorly predicted by the model. In Sitka spruce, it was suspected that the photosynthetic parameters measured in August 1994 had been higher earlier in the season, before nutrients became depleted. In sycamore, the discrepancies were thought to relate to differences in sink strength between root and shoot that could not be described by the model.