Diversity

Pinus yunnanensis, an endemic tree species in southwest China, is regarded as a suitable candidate for afforestation. However, long-term disturbances have led to forest degradation and structural simplification. This study evaluated taxonomic and phylogenetic alpha (α) and beta (β) diversity across three P. yunnanensis vegetation types: evergreen coniferous forests (ECFs), evergreen coniferous and broad-leaved mixed forests (ECMFs), and deciduous and coniferous broad-leaved mixed forests (DCMFs), aiming to identify their optimal ecological configurations. A total of 120 vascular plant species from 33 families and 55 genera were recorded, with Ericaceae, Fagaceae, Pinaceae, and Adoxaceae as the co-dominant families. In the tree layer, species richness was significantly higher in DCMFs than in ECFs (p < 0.05), likely due to improved winter light availability resulting from seasonal canopy shedding. Both ECMFs and DCMFs supported significantly higher phylogenetic α diversity than ECFs, indicating a broader evolutionary history and potentially greater functional resilience. In contrast, taxonomic β diversity was lower in ECFs, suggesting a more homogeneous species composition dominated by closely related shrubs. Among the vegetation types, the P. yunnanensis–Pinus armandii community in ECFs showed the highest species richness and a stable microenvironment, making it particularly suitable for ecological restoration at high altitudes. Within ECMFs, the P. yunnanensis–Lyonia ovalifolia community appeared to be the most optimal, potentially reducing competition and promoting species coexistence through resource complementarity. In DCMFs, the P. yunnanensis–Alnus nepalensis community, with its strong nitrogen-fixing capacity, emerged as the preferred configuration for restoring degraded forests at lower elevations. These findings suggest that future vegetation restoration projects centered on P. yunnanensis should adopt tailored combinations of vegetation types based on specific environmental conditions.

The obligate symbiosis between aphids and their primary bacterial symbionts (Buchnera) is ecologically and evolutionarily significant, yet the genetic patterns underlying these associations require further clarification. This study investigated the coevolutionary relationships of two aphid species, Cinara formosana and Tuberolachnus salignus, with their Buchnera symbionts using COI (mitochondrial cytochrome c oxidase subunit I) and bacterial 16S rRNA (16S ribosomal RNA) markers revealed substantial genetic divergence between the two aphid species, with interspecific genetic distances ranging from 0.131 to 0.138. In contrast, populations of T. salignus from different regions showed minimal intraspecific variation (genetic distance 0.006). Phylogenetic analyses confirmed that populations of each aphid species formed distinct, monophyletic clusters. Crucially, the phylogenetic relationships inferred from the aphid COI gene were fully congruent with those derived from the Buchnera 16S rRNA gene sequences. This concordance further supports the application of the COI gene as a reliable marker for species identification within the studied Lachninae aphids. Our findings provide novel insights into the coupled genetic divergence and coevolution of aphids and their obligate symbionts, offering a molecular framework for the precise identification and population monitoring of these aphids, which can inform sustainable management strategies.

Haloxylon ammodendron plantations constitute a dominant vegetation component of the desert–oasis ecotone in the arid and semi-arid regions of northwest China, playing a critical role in maintaining oasis stability and ecological security. However, the effects of converting natural desert ecosystems into plantations on the soil food webs of arthropods remain poorly understood, particularly with respect to how these effects vary across plantation age. To address this knowledge gap, we conducted a field investigation in the desert–oasis ecotone of the middle reaches of the Hexi Corridor, Gansu Province. Using pitfall trapping, we sampled two key arthropod taxa (arachnids and soil mesofauna) from control areas (natural deserts) and H. ammodendron plantations representing different ages (young and old). The results indicated that both young and old plantations were associated with significantly higher abundance and richness of arachnids, soil mesofauna, mites, and springtails compared with natural deserts, with springtail richness exhibiting a further significant increase in old plantations. Arachnid responses to plantation conversion were strongly structured by body size. Medium arachnid abundance increased in both young and old plantations, whereas large arachnid abundance increased only in young plantations and declined in older ones. In contrast, small arachnid abundance exhibited significant increases exclusively in old plantations. In addition, relationships between arachnid, mite and springtail abundance varied with plantation age: the ratio of large arachnids to mites and springtails declined significantly in old plantations relative to young ones, while the corresponding ratio for small arachnids showed an opposite pattern. Variations in soil mesofauna community composition were primarily explained by shrub cover, herbaceous cover, coarse sand proportion, silt-clay content, and soil soluble salt, which together accounted for 48.9% of observed variation. For arachnids, soil mesofauna as a food resource significantly enhanced abundance and richness. Moreover, shrub cover and silt-clay content were also drivers of arachnid community variation, jointly explaining 6.7% of variance. Overall, the establishment of H. ammodendron plantations promoted the diversity of both arachnids and soil mesofauna, but their relationships shifted dynamically with plantation age, leading to a reorganization of detrital food web structure and functioning.