With over 3 trillion trees, forest ecosystems comprise nearly one-third of the terrestrial surface of the Earth. Very little attention has been given to the exploration of the above-ground plant microbiome of trees, its complex trophic interactions, and variations among tree species. To address this knowledge gap, we applied a primer-independent shotgun metatranscriptomic approach to assess the entire living canopy bark microbiome comprising prokaryotic and eukaryotic primary producers, decomposers, and various groups of consumers. With almost 1500 genera, we found a high microbial diversity on three tree species with distinct bark textures: oak (Quercus robur), linden (Tilia cordata), both with rough bark, and maple (Acer pseudoplatanus) with smooth bark. Core co-occurrence network analysis revealed a rich food web dominated by algal primary producers, and bacterial and fungal decomposers, sustaining a diverse community of consumers, including protists, microscopic metazoans and predatory bacteria. Whereas maple accommodated a depauperate microbiome, oak and linden accommodated a richer microbiome mainly differing in their relative community composition: Bacteria exhibited an increased dominance on linden, whereas co-occurring algae and fungi dominated on oak, highlighting the importance of algal-fungal lichen symbioses even at the microscopic scale. Further, due to bacteria-fungi co-exclusion, bacteria on bark are not the main beneficiaries of algae-derived carbon compounds as it is known from aquatic systems.

中文翻译：

---

藻类-真菌共生和细菌-真菌共排斥驱动树冠树皮微生物组的树种特异性差异


森林生态系统拥有超过 3 万亿棵树木，占地球陆地表面的近三分之一。对树木地上植物微生物组、其复杂的营养相互作用以及树种间差异的探索很少受到关注。为了解决这一知识差距，我们应用了一种不依赖引物的鸟枪法元转录组学方法来评估整个活的树冠树皮微生物组，包括原核和真核生物初级生产者、分解者和各种消费者群体。在近 1500 个属中，我们发现三种树种具有高度的微生物多样性，具有不同的树皮质地：橡树 （Quercus robur）、椴树 （Tilia cordata），两者都具有粗糙的树皮，以及树皮光滑的枫树 （Acer pseudoplatanus）。核心共生网络分析揭示了一个丰富的食物网，以藻类初级生产者以及细菌和真菌分解者为主，维持着多样化的消费者群落，包括原生生物、微观后生动物和捕食性细菌。枫树容纳了贫乏的微生物组，而橡树和菩提树容纳了更丰富的微生物组，主要区别在于它们的相对群落组成：细菌在菩提树上表现出增加的优势，而同时存在的藻类和真菌在橡树上占主导地位，突出了藻类-真菌地衣共生的重要性，即使在微观尺度上也是如此。此外，由于细菌-真菌的共同排斥，树皮上的细菌并不是水生系统中已知的藻类衍生碳化合物的主要受益者。