Tree canopies are colonized by billions of highly specialized microorganisms that are well adapted to the highly variable microclimatic conditions, caused by diurnal fluctuations and seasonal changes. In this study, we investigated seasonality patterns of protists in the tree canopies of a temperate floodplain forest via high-throughput sequencing with group-specific primers for the phyla Cercozoa and Endomyxa. We observed consistent seasonality, and identified divergent spring and autumn taxa. Tree crowns were characterized by a dominance of bacterivores and omnivores, while eukaryvores gained a distinctly larger share in litter and soil communities on the ground. In the canopy seasonality was largest among communities detected on the foliar surface: In spring, higher variance within alpha diversity of foliar samples indicated greater heterogeneity during initial colonization. However, communities underwent compositional changes during the aging of leaves in autumn, highly reflecting recurring phenological changes during protistan colonization. Surprisingly, endomyxan root pathogens appeared to be exceptionally abundant across tree canopies during autumn, demonstrating a potential role of the canopy surface as a physical filter for air-dispersed propagules. Overall, about 80% of detected OTUs could not be assigned to known species—representing dozens of microeukaryotic taxa whose canopy inhabitants are waiting to be discovered.

中文翻译：

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关于原生生物的物候学：反复出现的模式揭示了树冠中原生生物（根菌：尾虫和内粘虫）群落的季节性变化

树冠上栖息着数十亿种高度专业化的微生物，这些微生物很好地适应了由昼夜波动和季节变化引起的高度变化的小气候条件。在这项研究中，我们通过使用尾虫门和内粘虫门的组特异性引物进行高通量测序，研究了温带洪泛区森林树冠中原生生物的季节性模式。我们观察到一致的季节性，并确定了不同的春季和秋季类群。树冠的特点是食菌动物和杂食动物占主导地位，而真核动物在地面的凋落物和土壤群落中所占的份额明显更大。在冠层中，在叶表面检测到的群落中，季节性是最大的：在春季，叶样本的α多样性内较高的方差表明初始定植期间的异质性较大。然而，在秋季叶子老化过程中，群落经历了组成变化，高度反映了原生生物定植期间反复出现的物候变化。令人惊讶的是，秋季树冠内的内粘菌根病原体似乎异常丰富，这表明树冠表面作为空气传播繁殖体的物理过滤器的潜在作用。总体而言，约 80% 的检测到的 OTU 无法归属于已知物种——代表了数十种微真核类群，其树冠居民正等待被发现。