Kurzbeschreibung
(Englisch)
|
Atmospheric deposition of nitrogen (N) is a threat for the functioning of natural or near-natural ecosystems and for the quality of runoff or ground water they produce. We propose to use a paired-catchment experiment where N deposition is manipulated since 14 years to improve our knowledge on the N cycle and especially on nitrate leaching as related to both the long-term N deposition rates and a short-term disturbance. A combination of modelling and field-based analyses is planned to study this interaction. A bark beetle outbreak will be simulated by a tree-girdling experiment within the paired-catchment study. Its effects will be measured on nitrate leaching, soil respiration and denitrification. The results of this experiment will be used to validate an ecosystem model (TRACE) first calibrated on control data, including previous 15N labellings at the catchment scale. After validation, the model will be used to test hypotheses on future deposition, climate, disturbances and forest management options.
|
Partner und Internationale Organisationen
(Englisch)
|
AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GR, HR, IL, IS, IT, LT, NO, PL, PT, SE, SI, SK, TR, UK
|
Abstract
(Englisch)
|
Atmospheric deposition of nitrogen (N) is a threat for the functioning of natural or near-natural ecosystems and for the quality of runoff or ground water they produce. At our research site Alptal (SZ), we are running a paired-catchment experiment where N deposition to a subalpine coniferous forest is manipulated since 15 years. The fate and effects of deposited N are assessed on soil, soil biota, trees, other vegetation, gas exchanges and nitrate leaching. As a disturbance factor, a bark beetle outbreak is simulated since June 2009, as half of the large trees were girdled (removing a cylinder of bark around the stem) in the experimental catchments. In August 2010, these trees have been felled. The effects of this manipulation are measured mainly on nitrate leaching, soil respiration and denitrification. The results of this experiment have been used to validate an ecosystem model (TRACE) calibrated on control data, including previous N-15 labellings at the catchment scale. After validation, the model has been used to test hypotheses on future deposition, climate and disturbance scenarios, as well as forest management options. It predicts that the ecosystem will be able to retain most of the deposited N during decades. The impact of the long-term N addition on tree growth has also been assessed, showing that it progressively enhanced tree growth. C and O isotopes in wood did not point to a significant N-induced improvement of photosynthetic rates. This corresponds to the fac that the size rather the N concentration of the needles was increased by the N addition. The resulting effect on tree growth, however was quite small; expressed as C sequestration in wood, it amounted to only 4 kg C per kg N. N deposition is thus barely improving C sequestration by the trees.
|
