Abstract Tree species-mixing has been suggested as one option to counteract the adverse effects of global change on tree mineral nutrition, yet the effect of mixing on nutrient availability remains poorly documented. We therefore analyzed the current foliar nutrient (N, P, K, Ca, Mg) quantities and ilr balances (isometric log transformed ratios between elements or groups of elements) for 261 European beech and 248 Scots pine trees from 15 sites, each consisting of one beech-pine mixed stand and the respective monocultures, across a gradient of environmental conditions in Europe. We hypothesized an overall positive effect of mixing on tree foliar nutrient content, and that this mixing effect would be stronger on nutrient-poor sites. Using linear mixed models and multivariate linear regression models, we first tested for the effects of species (beech/pine) and composition (pure/mixed) across all sites; we then investigated whether the species-mixing effect was related to site fertility. The nutrient composition of beech leaves and pine needles differed significantly for all ilr balances. For both species, significant mixing effects were detected for some nutrients and ilr balances; those effects, however, could not be consistently related to contrasted nutrient composition between species. For most nutrients and ilr balances, the mixing effect was influenced by the site nutritional status, but the pattern differed from expectation: absence or minor differences between monocultures and mixtures at the lower end of the chemical fertility gradient, and maximum differences in rich soils. The contrasting foliar nutrient composition of pine and beech trees and the site nutrient status only partly explained the mixing effects on tree mineral nutrition. Our results claim for a better understanding of nutrient-related mechanisms associated with complementarity and points towards the need to further expand the existing frameworks to account for the multivariate nature of tree nutrition.

中文翻译：

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混合对欧洲山毛榉和苏格兰松树的叶面营养影响有限

摘要 树种混合已被建议作为抵消全球变化对树木矿物质营养的不利影响的一种选择，但混合对养分有效性的影响仍然鲜有记录。因此，我们分析了来自 15 个地点的 261 棵欧洲山毛榉和 248 棵苏格兰松树的当前叶面养分（N、P、K、Ca、Mg）数量和 ilr 平衡（元素或元素组之间的等距对数转换比），每个地点包括一个山毛榉 - 松混合林和各自的单一栽培，跨越欧洲的环境条件梯度。我们假设混合对树的叶面养分含量有总体的积极影响，而且这种混合作用在营养贫乏的地方会更强。使用线性混合模型和多元线性回归模型，我们首先测试了所有地点的物种（山毛榉/松树）和成分（纯/混合）的影响；然后我们调查了物种混合效应是否与场地肥力有关。山毛榉叶和松针的营养成分对于所有 ilr 平衡都有显着差异。对于这两个物种，在某些营养物质和 ilr 平衡方面都检测到了显着的混合效应；然而，这些影响与物种之间的营养成分对比并不一致。对于大多数养分和 ilr 平衡，混合效果受场地营养状况的影响，但模式与预期不同：在化学肥力梯度的下端，单一栽培和混合栽培之间没有或存在微小差异，而肥沃土壤的差异最大。松树和山毛榉树的叶面营养成分和立地营养状况的对比只是部分解释了混合对树木矿物质营养的影响。我们的结果声称可以更好地理解与互补性相关的营养相关机制，并指出需要进一步扩展现有框架以解释树木营养的多元性质。