Landuyt Dries, Ampoorter Evy, Bastias Cristina C, Benavides Raquel, Müller Sandra, Scherer-Lorenzen Michael, Valladares Fernando, Wasof Safaa, Verheyen Kris
Forest & Nature Lab, Department of Environment, Ghent University, Ghent, Belgium.
LINCGlobal, Department of Biogeography and Global Change, National Museum of Natural Science-CSIC, Madrid, Spain.
For Ecosyst. 2020;7(1):45. doi: 10.1186/s40663-020-00256-x. Epub 2020 Jul 12.
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.
与森林林下植被对森林地上总植物生物量的贡献可忽略不计形成对比的是，其在年凋落物产生和养分循环中的份额可能更为重要。林下植被的这种功能作用在不同森林类型之间是否存在差异以及如何依赖于上层林冠特征仍有待研究。
我们对FunDivEUROPE探索平台的209个样地进行了采样，该平台是一个研究样地网络，涵盖了欧洲六种不同森林类型中树木多样性的局部梯度。为了估计林下植被对碳和养分循环的相对贡献，我们在所有样地中对非木质化地上林下生物量和上层林冠落叶进行了采样。分析林下样本的碳、氮和磷浓度，上层林冠落叶的碳和氮浓度。我们还量化了一组上层林冠属性，包括物种丰富度、常绿物种比例、光照可用性（代表树冠密度）和凋落物质量，并研究它们是否驱动林下植被对碳和养分循环的贡献。
所有森林类型中，上层林冠的凋落物产量和凋落物中的养分储量明显超过林下植被的贡献，且在气候梯度极端的森林中，林下植被的份额更高。在大多数被调查的森林类型中，主要是光照可用性决定了林下植被对年度碳和养分循环的贡献。在所调查的任何森林类型中，上层林冠物种丰富度均未影响林下植被对碳和养分循环的贡献。
