Effects of climate on interactions between wood-decomposing microbes and insects at a global scale

枯枝落叶分解是全球森林碳循环的重要过程。木材分解的主要生物媒介是微生物和昆虫，但昆虫在热带加速木材分解，但在温带和寒带则有中性甚至负面影响。昆虫与木材分解微生物之间存在着密切的相互作用，包括共生、促进和竞争。然而，目前还不清楚昆虫对微生物群落的影响如何沿着全球气候梯度而变化。虽然当地的实地研究和实验室实验表明，昆虫-微生物的相互作用可以加速或减缓木材分解，但尚未分析这种机制是否可以解释为什么昆虫对分解的影响从热带森林到北方森林变化如此强烈。在拟议的项目中，我们将通过使用全球实验中的木材样本进行第一次全球性的昆虫-真菌相互作用研究，该实验包括允许昆虫进入或排除昆虫的处理（Seibold等人，2021，Nature）。木材样本已经收集，我们只需要通过下一代测序来识别真菌和细菌群落，并比较两种处理之间记录的微生物群落。这种方法可以研究全球气候梯度如何调节昆虫对木材分解真菌和细菌的影响，并将更好地了解昆虫如何影响微生物生物多样性以及这些影响如何转化为生态系统功能，即木材分解。我们将测试五个假设，在受昆虫影响的微生物组装过程沿着全球气候梯度。因此，我们认为不同的多样性措施，在阿尔法和贝塔水平，以及专业化指标的基础上，网络分析和系统发育多样性。考虑到全球气候变化和包括森林昆虫在内的生物多样性的持续丧失，需要更好地了解气候对栖息在木材上的昆虫和微生物之间复杂关系的影响，以预测全球森林碳汇的未来。我们相信，拟议的项目将是缩小这一知识差距的重要一步，因此不仅对科学而且对环境和碳政策都具有重大意义。

Deadwood decomposition represents an important process in the global forest carbon cycle. The main biotic agents of wood decomposition are microbes and insects, but while insects accelerate wood decomposition in the tropics, they have neutral or even negative effects in the temperate and boreal zone. Insects interact closely with wood-decomposing microbes, including symbiotic associations, facilitation and competition. However, it remains unclear how effects of insects on microbial communities change along global climate gradients. While local field studies and lab experiments showed that insect-microbe interactions can either accelerate or decelerate wood decomposition, it has not been analyzed whether this mechanism explains why effects of insects on decomposition change so strongly from tropical to boreal forests. In the proposed project, we will conduct the first global study of insect-fungal interactions in deadwood by using wood samples from a global experiment which included treatments that either gave access to insects or excluded insects (Seibold et al. 2021, Nature). Wood samples have already been collected and we will only need to identify fungal and bacterial communities by next-generation sequencing and compare the recorded microbial communities between both treatments. This approach allows studying how global climate gradients moderate effects of insects on wood-decomposing fungi and bacteria and will provide a better understanding of how insects affect microbial biodiversity and how these effects translate into ecosystem functioning, i.e. wood decomposition. We will test five hypotheses in relation to the microbial assembly processes affected by insects along the global climate gradients. We thereby consider different diversity measures at alpha and beta level as well as specialization metrics based on network analyses and phylogenetic diversity. Considering global climate change and the ongoing loss of biodiversity, including forest insects, a better understanding of climate effects on the complex relationships between wood-inhabiting insects and microbes is needed to predict the future of the global forest carbon sink. We are confident that the proposed project will be an important step to close this knowledge gap and thus be of major importance not only for science but also for environmental and carbon policies.