Modelling the climatic response of soil nitrogen cycle in three Mediterranean forests.

Anna Lupon1, Stefan Gerber2, Francesc Sabater1, Susana Bernal3
1 Departament d'Ecologia, Universitat de Barcelona
2 Soil and Water Science Department, Universiy of Florida
3 Department of Continental Ecology, Center for Advanced Studies of Blanes (CEAB-CSIC)

P 2.40 in Environmental controls on fluxes and processes in ecosystems

Poster Session 2 on Tuesday, 16:30-18:00

Soil nitrogen (N) transformations regulate N losses from terrestrial to stream ecosystems, which in turn affects headwater stream N loads and downstream water quality. In this study, we investigated the response of net N mineralization (NNM) and net nitrification (NN) to climate variability in three Mediterranean forests (oak, beech and riparian) that held different temperature and water availability. We analyzed data by optimizing a mechanistic yet simple model to evaluate the response of key nitrogen variables to climatic variability (temperature, moisture, and precipitation). The model described sources and sinks of the inorganic N pool at the upper soil layer (0-10 cm depth), including NNM, NN, atmospheric deposition, plant uptake and hydrological losses (leaching and infiltration). For the three forest types, model optimization values matched with the temporal pattern of available empirical data (one year of fortnightly soil data) for both, NNM (R2=63-67%) and NN (R2=59-73%). The modeled annual fluxes were higher at the riparian than at the oak and beech forests for both, NNM (384, 135, and 128 kg N ha-1 yr-1) and NN (317, 30, and 15 kg N ha-1 yr-1). Soil N processes exhibit different climatic response among forest types. Increments in soil moisture were important drivers for NNM and NN at the hillslopes, but did not affect soil N dynamics at the riparian forest. Concordantly, soil microbial processes were more responsive to precipitation pulses in the hillslopes than in the riparian forest. Increases in temperature promoted higher NNM and NN at the riparian forest than at both hillslope forests. On average, the simulated soil inorganic N pool and soil N hydrological losses were 2- and 10-fold higher at the riparian than at the oak and beech forests, respectively. In this talk, we will further explore the effects of future climatic conditions (based on A2B scenarios) on soil N transformations in order to better understand how increased temperature and reduced precipitation would change soil N cycling in these Mediterranean forests. We predict that changes in precipitation would strongly affect soil N dynamics at hillslope forests, whereas changes in temperature may be more relevant for soil N dynamics at the riparian forest.

last modified 2014-03-29