● Biocrusts are one of the most important components of the land cover in frozen ground regions on the Qinghai–Tibet Plateau, which increased the silt particle content, enhanced field moisture capacity, and reduced soil bulk density.

Biocrusts (BSCs) are widely distributed in frozen ground regions on the Qinghai-Tibet Plateau, and they are considered an important component of cold ecosystems. However, the specific impacts of BSCs on frozen soil remains relatively unclear. The aim of our study was to clarify the influence of BSCs (light BSCs and dark BSCs in two different succession stages) on the physical properties and ecological stoichiometry characteristics of frozen soil. Our results showed that BSCs increased the silt particle content in 20–40 cm soil layer, leading to a decrease in soil bulk density. And the field water capacity increased about 10%–40% compared to bare land. Additionally, BSCs significantly increased the contents of soil organic carbon (SOC, 22.6–30.8 g kg⁻¹) and total nitrogen (TN, 2.1–2.8 g kg⁻¹) in the upper 40 cm soil layer, both of them were approximately 1.3–2.0 and 1.3–4.0 times higher than those observed in bare land. However, BSCs did not have significant influence on soil total phosphorus (TP). BSCs had a significant impact on the stoichiometric ratios within 40 cm. The C/N ratios of the two types of BSCs ranged from 8.8 to 13.5, the C/P ratios ranged from 6.6 to 13.8, and the N/P ratios ranged from 0.6 to 1.2, which were all higher than those of the bare land. There were no significant differences among the C/N, C/P, and N/P ratios between two types of BSCs. However, the increment of C/P and N/P ratios of dark BSCs were significantly higher than those of light BSCs within 0–30 cm, which indicated that a reduction in the availability of phosphorus during the later stages of BSCs succession. These findings provided a theoretical basis for further research on the ecological functions of BSCs in frozen ground regions.

● Soil abundant taxa diversity positively related to multifunctionality under Hg stress.

It is known that soil microbial communities are intricately linked to multiple ecosystem functions and can maintain the relationship between soil biodiversity and multifunctionality (SBF) under environmental stresses. However, the relative contributions and driving forces of abundant and rare taxa within the communities in maintaining soil biodiversity-multifunctionality relationship under pollution stresses are still unclear. Here, we conducted microcosm experiments to estimate the importance of soil abundant and rare taxa in predicting these relationships under heavy metal mercury (Hg) stress in paired paddy and upland fields. The results revealed that the diversity of abundant taxa, rather than rare taxa, was positively related to multifunctionality, with the abundant subcommunity tending to maintain a larger proportion of soil functions including chitin degradation, protein degradation, and phosphorus mineralization. Soil multitrophic network complexity consisting of abundant species showed positive correlations with biodiversity and multifunctionality, and supported the strength of SBF within a network complexity range. Stochastic assembly processes of the abundant subcommunity were positively correlated with the strength of SBF, although stochastic processes decreased the biodiversity and the multifunctionality, respectively. After simultaneously accounting for multiple factors on the strength of SBF, we found that the stochastic community assembly ratio of abundant taxa was the most important predictor for SBF strength under Hg stress. Our results highlight the importance of abundant taxa in supporting soil multifunctionality, and elucidate the linkages between community assembly, network complexity and SBF relationship under environmental stresses.

● Past human activities result in the formation of Anthrosols and the accumulation of nutrients.

The fertility of human-altered soils, Anthrosols, developed from past settlement activities for crop production is scarcely studied. The study evaluated the fertility of Anthrosols developed from the 15th to mid-20th century AD settlement in Old Buipe, Savanna region, Ghana, to determine whether abandoned localities are suitable for arable fields. Human activities enhanced the physical attributes of the Anthrosols: brown to dark brown intergrain fine soil, 15%−35% organic matter, 15%−30% potsherd, and 5%−15% charred materials. The Anthrosols were slightly acidic to neutral reactions (\text{textcolor}[RGB]32,147,147{\mathrm{p}\mathrm{H}}_{[{\mathrm{H}}_2\mathrm{O}]} 5.67−6.83, \text{textcolor}[RGB]32,147,147{\mathrm{p}\mathrm{H}}_{[\mathrm{C}\mathrm{a}\mathrm{C}{\mathrm{l}}_2]} 5.83−6.95), high cation exchange capacity (CEC; 18.77−45.31me/100 g), electric conductivity (EC = 0.28−0.36 dS m⁻¹), accumulation, and distribution of organic C, total N, P, Mn, Cu, Zn, K, and Fe, and available P, K, Ca, Mg, S, Mn, Fe, Cu, and Zn. Plant-available nutrients were comparatively higher than concentrations in non-anthropogenic soils. The level of releasability (bioavailable fractions of total concentrations) of P, K, Ca, Mn, Fe, Cu, and Zn partly compensates for low plant-available portions. Enrichment of chemical and physical properties of Anthrosols make them fertile for arable fields. The signatures of settlement activities are strong and can remain in soils for a long time, even under harsh environmental conditions.