Eutrophication due to increased nitrogen concentrations is known to alter species composition and threaten sensitive habitat types. The contribution of atmospheric nitrogen deposition to eutrophication is often difficult to determine. Various deposition models have been developed to estimate the amount of nitrogen deposited for both entire regions and different landscape surface types. The question arises whether the resulting deposition maps allow direct conclusions about the risk of eutrophication-related changes in the understory vegetation composition and diversity in nitrogen-sensitive forest ecosystems. We combined vegetation and soil data recorded across eutrophication gradients in ten oligo-mesotrophic forest types in southwest Germany with datasets from two different deposition models specifically fitted for forests in our study region. Altogether, 153 forest stands, with three sampling replicates each, were examined. Linear mixed-effect models and NMDS analyses revealed that other site factors, in particular the soil C/N ratio, soil pH and canopy cover, played a greater role in explaining vegetation gradients than nitrogen deposition. The latter only rarely had effects on species richness (positive), nitrophyte cover (positive or negative) and the cover of sensitive character species (negative). These effects varied depending on the deposition model used and the forest types examined. No effects of nitrogen deposition on average Ellenberg N values were found. The results reflect the complex situation in forests where nitrogen availability is not only influenced by deposition but also by nitrogen mineralization and retention which depend on soil type, pH and (micro)climate. This context dependency must be regarded when evaluating the effects of nitrogen deposition.

众所周知，由于氮浓度升高引起的富营养化会改变物种组成并威胁敏感的生境类型。大气氮沉积对富营养化的贡献通常很难确定。已经开发出各种沉积模型来估计整个区域和不同景观类型的氮沉积量。问题是，生成的沉积图是否能够直接得出氮敏感的森林生态系统中与富营养化有关的地下植被组成和多样性变化的风险。我们将德国西南部的十种中低营养森林类型的富营养化梯度上记录的植被和土壤数据与两个特别适合我们研究地区森林的沉积模型的数据集进行了组合。总共检查了153个林分，每个林分三个重复样本。线性混合效应模型和NMDS分析表明，其他地点因素，特别是土壤碳氮比，土壤pH和冠层覆盖度，在解释植被梯度方面比氮沉降起更大的作用。后者很少对物种丰富度（正），亚硝酸盐覆盖（正或负）和敏感特征物种的覆盖（负）产生影响。这些影响因所使用的沉积模型和所检查的森林类型而异。氮沉降对平均Ellenberg没有影响 在解释植被梯度方面比起氮沉积起更大的作用。后者很少对物种丰富度（正），亚硝酸盐覆盖（正或负）和敏感特征物种的覆盖（负）产生影响。这些影响因所使用的沉积模型和所检查的森林类型而异。氮沉降对平均Ellenberg没有影响 在解释植被梯度方面比起氮沉积起更大的作用。后者很少对物种丰富度（正），亚硝酸盐覆盖（正或负）和敏感特征物种的覆盖（负）产生影响。这些影响因所使用的沉积模型和所检查的森林类型而异。氮沉降对平均Ellenberg没有影响找到了N个值。结果反映了森林中的复杂情况，其中氮的有效性不仅受沉积的影响，而且还受取决于土壤类型，pH和（微）气候的氮矿化和保留的影响。在评估氮沉积的影响时，必须考虑这种环境依赖性。