TerraData environmetrics, Via L. Bardelloni 19, Monterotondo Marittimo, I-58025, Italy; Dipartimento di Biotecnologie Agrarie, Sezione di Botanica Ambientale ed Applicata, Università di Firenze, Piazzale Cascine 28, Firenze, I-50144, Italy.
Glob Chang Biol. 2014 Nov;20(11):3423-38. doi: 10.1111/gcb.12552. Epub 2014 Apr 12.
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.
我们研究了 2000-2009 年间在意大利永久样地收集的森林监测数据，以确定氮（N）沉积对土壤化学、树木营养和生长的可能影响。平均氮穿透（N-NO3+N-NH4）在 4 至 29kg ha-1yr-1之间，几个地点的养分 N 临界负荷（CL）超过了临界负荷。有证据一致表明，N 沉积对土壤和树木营养有影响：表土可交换的基础阳离子（BCE）和 pH 值随着 N 沉积的增加而降低，叶片养分 N 比（特别是 N：P 和 N：K）增加。与大样开放地和穿透数据的比较表明，树冠可能吸收了 N，当总沉积量>4-6kg ha-1yr-1时，水平达到平衡。偏最小二乘（PLS）回归表明，尽管林分和气象变量解释了相对基面积增量（2000-2009 年 BAIrel）的最大部分变异，但与 N 相关的预测因子（表土 BCE、C：N、pH 值；叶片 N 比；N 沉积）几乎总是能提高 BAIrel 模型的解释变异（从 78.2%到 93.5%）和误差（从 2.98 到 1.50%）。即使考虑到林分、管理和大气相关变量（气象和对流层臭氧），N 沉积仍然是最强的预测因子。BAIrel 的最大年响应估计为每增加 1kgN 增加 0.074-0.085%。这相当于每增加 1kgN，地上木质生物量中碳的年最大相对增加 0.13-0.14%，即每公顷每年每增加 1kgN 可固定 159kgC，范围为 50-504kgC per kgN，具体取决于地点）。在可能存在、或许是最近的 N 饱和信号的地点也观察到了积极的生长反应。这可能表明 N 不利影响存在时间滞后，但也表明，在持续的高 N 输入下，报告的积极生长反应在长期内可能是不可持续的。
