Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland; Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland.
Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland.
Sci Total Environ. 2018 Dec 10;644:60-67. doi: 10.1016/j.scitotenv.2018.06.323. Epub 2018 Jul 4.
Land-use intensification is the major threat for biodiversity in agricultural grasslands, and fertilization has been suggested as the most important driver. A common explanation for the decline of bryophyte diversity with higher land-use intensity is an indirect negative effect via the increase in vascular plant productivity, which reduces light levels for bryophytes. However, direct negative effects of land-use intensification may also be important. Here, we disentangle direct and vascular plant biomass mediated indirect effects of land use on bryophytes. We analyzed two complementary datasets from agricultural grasslands, an observational study across 144 differently managed grasslands in Germany and an experimental fertilization and irrigation study of eleven grasslands in the Swiss Alps. We found that bryophyte richness and cover strongly declined with land-use intensity and in particular with fertilization. However, structural equation modelling revealed that although both direct and indirect effects were important, the direct negative effect of fertilization was even stronger than the indirect effect mediated by increased plant biomass. Thus, our results challenge the widespread view that the negative effects of fertilization are mostly indirect and mediated via increased light competition with vascular plants. Our study shows that land use intensification reduces bryophyte diversity through several different mechanisms. Therefore, only low-intensity management with limited fertilizer inputs will allow the maintenance of bryophyte-rich grasslands.
土地利用集约化是农业草原生物多样性的主要威胁，施肥被认为是最重要的驱动因素。随着土地利用强度的增加，苔藓植物多样性下降的一个常见解释是通过增加维管束植物生产力的间接负效应，这减少了苔藓植物的光照水平。然而，土地利用集约化的直接负面效应也可能很重要。在这里，我们梳理了土地利用对苔藓植物的直接和维管束植物生物量介导的间接影响。我们分析了来自农业草原的两个互补数据集，一个是德国 144 个不同管理的草原的观测研究，另一个是瑞士阿尔卑斯山 11 个草原的施肥和灌溉实验研究。我们发现，苔藓植物的丰富度和盖度随着土地利用强度的增加而强烈下降，特别是随着施肥的增加。然而，结构方程模型显示，尽管直接和间接效应都很重要，但施肥的直接负效应甚至比通过增加植物生物量介导的间接效应更强。因此，我们的研究结果挑战了施肥的负面影响主要是间接的，并通过与维管束植物的光竞争加剧来介导的普遍观点。我们的研究表明，土地利用集约化通过多种不同的机制降低了苔藓植物的多样性。因此，只有低强度的管理和有限的肥料投入才能允许维持苔藓植物丰富的草原。
