Neglect of mowing and manuring leads to slower nitrogen cycling in subalpine grasslands
2007
Matthew Robson, T. | Lavorel, Sandra | Clement, Jean-Christophe | Le Roux, Xavier | Laboratoire d'Ecologie Alpine (LECA) ; Université Joseph Fourier - Grenoble 1 (UJF)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS) | Station alpine Joseph Fourier - UMS 3370 (SAJF) ; Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS) | Laboratoire d'Ecologie Microbienne - UMR 5557 (LEM) ; Institut National de la Recherche Agronomique (INRA)-Université Claude Bernard Lyon 1 (UCBL) ; Université de Lyon-Université de Lyon-Ecole Nationale Vétérinaire de Lyon (ENVL)-VetAgro Sup - Institut national d'enseignement supérieur et de recherche en alimentation, santé animale, sciences agronomiques et de l'environnement (VAS)-Centre National de la Recherche Scientifique (CNRS)
Nitrogen (N) availability in grasslands varies with agricultural land use. Traditional management regimes of mowing for hay and manuring in subalpine meadows maintain plant communities with exploitative functional strategies suited to fertile soils with fast turnover of nutrients. We investigated whether the neglect of traditional practices has led to a reduction in N availability in two parallel ecosystems (terraced and unterraced fields). Soil nitrate and ammonium contents were assessed using soil cores and ion exchange resins over a 1-year period, and assays of microbial nitrifying and denitrifying enzyme activities, made early in the growing season. A large difference in pH between the two ecosystems, caused by historical ploughing, facilitated greater N availability in terraced than unterraced fields. Abandonment of manuring and mowing caused a reduction in N availability and N transformation processes, which correlated with a shift in the plant community towards more-conservative functional strategies and greater dominance by grasses. We propose that positive feedback between the grassland management regime and dominant plant functional strategy maintained high N availability in these managed subalpine grasslands. When traditional practices of mowing and manuring are neglected, direct management effects combined with the spread of grass species with conservative strategies force down N availability in the soil, reduce microbial activity, change the pH, and lead to a long-term loss of characteristic herbaceous subalpine-meadow species.
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