In contrast with the negligible contribution of the forest understorey to the total aboveground phytobiomass of a forest, its share in annual litter production and nutrient cycling may be more important. Whether and how this functional role of the understorey differs across forest types and depends upon overstorey characteristics remains to be investigated. We sampled 209 plots of the FunDivEUROPE Exploratory Platform, a network of study plots covering local gradients of tree diversity spread over six contrasting forest types in Europe. To estimate the relative contribution of the understorey to carbon and nutrient cycling, we sampled non-lignified aboveground understorey biomass and overstorey leaf litterfall in all plots. Understorey samples were analysed for C, N and P concentrations, overstorey leaf litterfall for C and N concentrations. We additionally quantified a set of overstorey attributes, including species richness, proportion of evergreen species, light availability (representing crown density) and litter quality, and investigated whether they drive the understorey’s contribution to carbon and nutrient cycling. Overstorey litter production and nutrient stocks in litterfall clearly exceeded the contribution of the understorey for all forest types, and the share of the understorey was higher in forests at the extremes of the climatic gradient. In most of the investigated forest types, it was mainly light availability that determined the contribution of the understorey to yearly carbon and nutrient cycling. Overstorey species richness did not affect the contribution of the understorey to carbon and nutrient cycling in any of the investigated forest types.

中文翻译：

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上层属性对于欧洲森林下层凋落物生产和养分循环的重要性。

与森林下层植物对森林地上植物总生物量的贡献可以忽略不计相比，它在年凋落物生产和养分循环中的份额可能更为重要。林下层的这种功能作用是否以及如何因森林类型的不同而不同，并且取决于林上层的特征，还有待研究。我们对 FunDivEUROPE 探索平台的 209 个地块进行了采样，该平台是一个研究地块网络，涵盖欧洲六种对比森林类型中树木多样性的局部梯度。为了估计林下层对碳和养分循环的相对贡献，我们对所有地块中的非木质化地上林下生物量和地上落叶落叶进行了采样。分析了林下样品的 C、N 和 P 浓度，分析了上层落叶物的 C 和 N 浓度。我们还量化了一系列上层属性，包括物种丰富度、常绿物种比例、光利用率（代表树冠密度）和凋落物质量，并调查了它们是否推动了下层植物对碳和养分循环的贡献。所有森林类型的林下凋落物产量和养分储量明显超过林下层的贡献，并且在气候梯度极端的森林中林下层所占的​​比例更高。在大多数调查的森林类型中，主要是光的可用性决定了林下层对年度碳和养分循环的贡献。在任何被调查的森林类型中，上层物种丰富度并不影响下层对碳和养分循环的贡献。