The effect of tree species diversity on foliar fungal pathogens

叶面真菌病原体通过树木对生长和生存的高度物种特异性影响森林的生态系统过程。因此，真菌病原体有助于维持树木的多样性。由于寄主专化的病原菌，如叶部真菌病原体，既是对森林中树木多样性的响应，也是对树木多样性的影响，两者都可以与北京森林论坛-中国的实验设计分开。在我的子项目中，我的目标是检验假设：(1)树种多样性降低了特定寄主物种上病原真菌的疾病风险和病原体负载，因为寄主物种密度和真菌栖息地的可用性随着树种多样性的增加而被稀释。(2)树种多样性增加了叶面真菌物种多样性。(3)寄主物种的系统发育相似性增加了不同树种上叶面真菌群落的系统发育相似性，这是病原菌与寄主共同进化的结果。(4)草食程度导致真菌病原菌载量增加。(5)病原菌负荷量的增加降低了树木个体和树种的生长和适合度。我将用北京东方经济论坛-中国项目的三个不同的实验设置来说明这些假设。WP1将在主要试验的所有地块中，以叶部真菌病原体感染所有树种的叶面积百分比来量化病原体负载。WP2将为总共16种选定的树种确定出现在特定树种叶片上的所有真菌物种，并构建树种特有的系统发育和营养生物网络。这一工作包将由中国合作伙伴济业燕项目对真菌的分子鉴定进行补充，该项目还将构建分子真菌系统发育图。WP3将在BEFmod方法中评估叶面真菌病原体对植物表现的影响，以及磷肥、草本层竞争和草食对病原体负载的影响(特别是SP1、2、8、9、11)。将这两个观测水平的信息与BEFmod的实验方法相结合，将使我能够解决功能生物多样性研究中的关键问题之一：病原体如何调节植物物种丰富度-生长关系，以应对草食和树木物种的丧失，重点是营养生物的相互作用。

Foliar fungal pathogens affect ecosystem processes in forests through highly speciesspecific effects of trees on growth and survival. Thus, fungal pathogens can contribute to maintain tree diversity. As host-specialized pathogenic organisms such as foliar fungal pathogens are both response to and effect of tree diversity in forests, both can be disentangled with the experimental design of BEF-China. In my subproject I aim to test the hypotheses: (1) Tree species diversity decreases disease risk and pathogen load of pathogenic fungi on a particular host species because host species density and thus, fungal habitat availability, is diluted with increasing tree species diversity. (2) Tree species diversity increases foliar fungal species diversity. (3) The phylogenetic similarity of host species increases the phylogenetic similarity of foliar fungal communities on different tree species, as a consequence of the co-evolution of the pathogens with their hosts. (4) The degree of herbivory leads to increased fungal pathogen load. (5) Increasing pathogen load decreases the growth and the fitness of tree individuals and species. I will address these hypotheses with three different experimental set ups of the BEF-China project. WP1 will quantify pathogen load as percentage of leaf area infected by foliar fungal pathogens across all tree species in all plots of the Main Experiment. WP2 will identify for a total of 16 selected tree species all fungus species that occur on leaves of a certain tree species and construct tree species-specific phylogenies and trophobiotic networks. This work package will be complemented by molecular identification of fungi by the Chinese partner project of Jiye Yan, who will also construct molecular fungal phylogenies. WP3 will assess the effect of foliar fungal pathogens on plant performance in the BEFmod approach as well as the effects of P fertilization, competition of the herb layer and herbivory on pathogen load (in particular with SP1, 2, 8, 9, 11). Combining information from the two observational levels and the experimental approach of BEFmod will allow me to address one of the key questions in functional biodiversity research: how pathogens mediate plant species richness-growth relationships in response to herbivory and tree species loss with a focus on trophobiotic interactions.