On the tracks of Nitrogen deposition effects on temperate forests at their southern European range – an observational study from Italy |
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Authors: | Marco Ferretti Aldo Marchetto Silvia Arisci Filippo Bussotti Marco Calderisi Stefano Carnicelli Guia Cecchini Gianfranco Fabbio Giada Bertini Giorgio Matteucci Bruno de Cinti Luca Salvati Enrico Pompei |
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Institution: | 1. TerraData environmetrics, , Monterotondo Marittimo, I‐58025 Italy;2. Dipartimento di Biotecnologie Agrarie, Sezione di Botanica Ambientale ed Applicata, Università di Firenze, , Firenze, I‐50144 Italy;3. CNR‐Istituto per lo Studio degli Ecosistemi, , Verbania Pallanza, 28922 Italy;4. Dipartimento di Scienze della Terra, , Firenze, 50121 Italy;5. CRA‐ Centro di ricerca per la selvicoltura, , Arezzo, I‐52100 Italy;6. CNR‐ Istituto di Biologia Agroambientale e Forestale, , Monterotondo, I‐00015 Italy;7. CNR‐ Istituto per i Sistemi Agricoli e Forestali del Mediterraneo, , Cosenza, I‐87036 Italy;8. CRA‐Centro di ricerca per lo studio delle relazioni fra pianta e suolo, , Roma, 2/4‐00184 Italy;9. CFS ‐ Divisione 6^, , Roma, 5 – 00187 Italy |
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Abstract: | We studied forest monitoring data collected at permanent plots in Italy over the period 2000–2009 to identify the possible impact of nitrogen (N) deposition on soil chemistry, tree nutrition and growth. Average N throughfall (N‐NO3+N‐NH4) ranged between 4 and 29 kg ha?1 yr?1, with Critical Loads (CLs) for nutrient N exceeded at several sites. Evidence is consistent in pointing out effects of N deposition on soil and tree nutrition: topsoil exchangeable base cations (BCE) and pH decreased with increasing N deposition, and foliar nutrient N ratios (especially N : P and N : K) increased. Comparison between bulk openfield and throughfall data suggested possible canopy uptake of N, levelling out for bulk deposition >4–6 kg ha?1 yr?1. Partial Least Square (PLS) regression revealed that ‐ although stand and meteorological variables explained the largest portion of variance in relative basal area increment (BAIrel 2000–2009) ‐ N‐related predictors (topsoil BCE, C : N, pH; foliar N‐ratios; N deposition) nearly always improved the BAIrel model in terms of variance explained (from 78.2 to 93.5%) and error (from 2.98 to 1.50%). N deposition was the strongest predictor even when stand, management and atmosphere‐related variables (meteorology and tropospheric ozone) were accounted for. The maximal annual response of BAIrel was estimated at 0.074–0.085% for every additional kgN. This corresponds to an annual maximal relative increase of 0.13–0.14% of carbon sequestered in the above‐ground woody biomass for every additional kgN, i.e. a median value of 159 kgC per kgN ha?1 yr?1 (range: 50–504 kgC per kgN, depending on the site). Positive growth response occurred also at sites where signals of possible, perhaps recent N saturation were detected. This may suggest a time lag for detrimental N effects, but also that, under continuous high N input, the reported positive growth response may be not sustainable in the long‐term. |
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Keywords: | CONECOFOR forest monitoring growth and carbon sequestration N critical loads PLS regression soil and foliar nutrients |
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