Vertical distribution patterns and drivers of soil bacterial communities across the continuous permafrost region of northeastern China

Background Soil microorganisms in the thawing permafrost play key roles in the maintenance of ecosystem function and regulation of biogeochemical cycles. However, our knowledge of patterns and drivers of permafrost microbial communities is limited in northeastern China. Therefore, we investigated the community structure of soil bacteria in the active, transition and permafrost layers based on 90 soil samples collected from 10 sites across the continuous permafrost region using high-throughput Illumina sequencing. Results Proteobacteria (31.59%), Acidobacteria (18.63%), Bacteroidetes (9.74%), Chloroflexi (7.01%) and Actinobacteria (6.92%) were the predominant phyla of the bacterial community in all soil layers; however, the relative abundances of the dominant bacterial taxa varied with soil depth. The bacterial community alpha-diversity based on the Shannon index and the phylogenetic diversity index both decreased significantly with depth across the transition from active layer to permafrost layer. Nonmetric multidimensional scaling analysis and permutation multivariate analysis of variance revealed that microbial community structures were significantly different among layers. Redundancy analysis and Spearman’s correlation analysis showed that soil properties differed between layers such as soil nutrient content, temperature and moisture mainly drove the differentiation of bacterial communities. Conclusions Our results revealed significant differences in bacterial composition and diversity among soil layers. Our findings suggest that the heterogeneous environmental conditions between the three soil horizons had strong influences on microbial niche differentiation and further explained the variability of soil bacterial community structures. This effort to profile the vertical distribution of bacterial communities may enable better evaluations of changes in microbial dynamics in response to permafrost thaw, which would be beneficial to ecological conservation of permafrost ecosystems.

Ancient Mitogenomes Suggest Stable Mitochondrial Clades of the Siberian Roe Deer

The roe deer (Capreolus spp.) has been present in China since the early Pleistocene. Despite abundant fossils available for detailed morphological analyses, little is known about the phylogenetic relationships of the fossil individuals to contemporary roe deer. We generated near-complete mitochondrial genomes for four roe deer remains from Northeastern China to explore the genetic connection of the ancient roe deer to the extant populations and to investigate the evolutionary history and population dynamics of this species. Phylogenetic analyses indicated the four ancient samples fall into three out of four different haplogroups of the Siberian roe deer. Haplogroup C, distributed throughout Eurasia, have existed in Northeastern China since at least the Late Pleistocene, while haplogroup A and D, found in the east of Lake Baikal, emerged in Northeastern China after the Mid Holocene. The Bayesian estimation suggested that the first split within the Siberian roe deer occurred approximately 0.34 million years ago (Ma). Moreover, Bayesian skyline plot analyses suggested that the Siberian roe deer had a population increase between 325 and 225 thousand years ago (Kya) and suffered a transient decline between 50 and 18 Kya. This study provides novel insights into the evolutionary history and population dynamics of the roe deer.

The Right-Skewed Distribution of Fine-Root Size in Three Temperate Forests in Northeastern China

Trees can build fine-root systems with high variation in root size (e.g., fine-root diameter) and root number (e.g., branching pattern) to optimize belowground resource acquisition in forest ecosystems. Compared with leaves, which are visible above ground, information about the distribution and inequality of fine-root size and about key associations between fine-root size and number is still limited. We collected 27,573 first-order fine-roots growing out of 3,848 second-order fine-roots, covering 51 tree species in three temperate forests (Changbai Mountain, CBS; Xianrendong, XRD; and Maoershan, MES) in Northeastern China. We investigated the distribution and inequality of fine-root length, diameter and area (fine-root size), and their trade-off with fine-root branching intensity and ratio (fine-root number). Our results showed a strong right-skewed distribution in first-order fine-root size across various tree species. Unimodal frequency distributions were observed in all three of the sampled forests for first-order fine-root length and area and in CBS and XRD for first-order fine-root diameter, whereas a marked bimodal frequency distribution of first-order fine-root diameter appeared in MES. Moreover, XRD had the highest and MES had the lowest inequality values (Gini coefficients) in first-order fine-root diameter. First-order fine-root size showed a consistently linear decline with increasing root number. Our findings suggest a common right-skewed distribution with unimodality or bimodality of fine-root size and a generalized trade-off between fine-root size and number across the temperate tree species. Our results will greatly improve our thorough understanding of the belowground resource acquisition strategies of temperate trees and forests.

Ritual, Legend, and Metaphor: Narratives of the Willow in Yuan Zaju

Narratives of willow trees in Yuan zaju 雜劇, or variety play, largely come in three types, namely, the ritual performance of shooting willows; the deliverance of willow spirits by Lü Dongbin, one of the Eight Immortals of Daoism; and the use of the word willow to refer to women. The willow shooting ritual depicted in Yuan zaju was highly reminiscent of the willow shooting ritual popular throughout the Song (960–1279), Liao (916–1125), Jin (1115–1234), and Yuan (1271–1368) dynasties, with its conceptual origins traceable to the ancient shamanic belief in the willow as a sacred tree prevalent among the Khitans and Jurchens who lived in what is now northeastern China. The legend of Lü Dongbin delivering a willow spirit to immortality is a recurring motif in Han Chinese folklore and Daoist hagiography, which also finds expression in the iconic image of Guanyin Pusa or Bodhisattva Avalokitesvara holding a willow branch with which they cure diseases for people and bring fulfillment to their wishes. The frequent use of “willow leaf-shaped eyebrows” (liumei 柳眉) and “willow-like waist” (liuyao 柳腰) in Yuan zaju as metaphorical references to women can be seen as a continuation of the great literary tradition of Shijing 詩經 (The Book of Songs) and also as a dramatic enactment of the fertility cult of the willow and women in Chinese folk religion. Evidence abounds that the narratives about the willow in Yuan zaju were not a new creation but an artistic manifestation of centuries-old folk belief and literary tradition.