Effects of vegetation restoration on soil quality in fragile karst ecosystems of southwest China

Conversion of farmland to forest or grassland improves soil carbon, nitrogen, and ecosystem multi-functionality in a subtropical karst region of southwest China

The conversion of farmland to forest in China has been recognized for its positive impact on above-ground vegetation and carbon sequestration. However, the impact on soil quality during land conversion, particularly in vulnerable karst areas, has received less attention. In this study conducted in a karst area of southwest China, eight different farmland conversion strategies were investigated to assess improvements in surface soil carbon, nitrogen, and ecosystem multi-functionality (EMF). Our results showed that farmland converted to afforestation areas or farmland that was abandoned contained higher amounts of carbon (total, organic, active) and ammonium nitrogen (NH4+-N) in the soil compared to farmland converted to grassland or maize crop. Soluble organic carbon levels were higher in afforestation and grassland areas compared to maize crop controls. By contrast, soil from grassland and abandoned land exhibited higher levels of nitrate nitrogen (NO3--N) compared to afforestation land or maize crop controls. There were no differences in NH4+-N content between any condition, except for afforestation land that specifically contained the Zenia insignis plant species. Afforestation land consistently exhibited higher EMF values than grassland. Pearson correlation analysis revealed positive relationships between soil indices and EMF scores, except for NO3--N.Random forest analysis explained 95% of the variation in soil EMF and identified specific soil factors: total carbon, organic carbon, active labile organic carbon, total nitrogen, and ammonium nitrogen, as the main drivers of soil multi-functionality. Our studies show how various reforestation strategies can enhance soil nutrient sequestration and improve soil multi-functionality of farmland in the karst areas.These findings provide insight into sustainable soil management practices for converting farmland into natural areas.

Rocky desertification succession alters soil microbial communities and survival strategies in the karst context

Rocky desertification is one of the most ecological problems in the karst context. Although extensive research has been conducted to explore how to restore and protect, the responses of soil fungi and archaea to rocky desertification succession remain limited. Here, four grades of rocky desertification in a karst ecosystem were selected, amplicon sequencing analysis was conducted to investigate fungal and archaeal community adaptation in response to rocky desertification succession. Our findings revealed that the diversity and community structure of fungi and archaea in soils declined with the aggravation of rocky desertification. As the rocky desertification succession intensified, microbial interactions shifted from cooperation to competition. Microbial survival strategies were K-strategist and r-strategist dominated in the early and late stages of succession, respectively. Additionally, the driving factors affecting microorganisms have shifted from vegetation diversity to soil properties as the intensification of rocky desertification. Collectively, our study highlighted that plant diversity and soil properties play important roles on soil microbiomes in fragile karst ecosystems and that environmental factors induced by human activities might still be the dominant factor exacerbating rocky desertification, which could significantly enrich our understanding of microbial ecology within karst ecosystems.

Identification and predictability of soil quality indicators from conventional soil and vegetation classifications

The physical, chemical and biological attributes of a soil combined with abiotic factors (e.g. climate and topography) drive pedogenesis and some of these attributes have been used as proxies to soil quality. Thus, we investigated: (1) whether appropriate soil quality indicators (SQIs) could be identified in soils of Great Britain, (2) whether conventional soil classification or aggregate vegetation classes (AVCs) could predict SQIs and (3) to what extent do soil types and/ or AVCs act as major regulators of SQIs. Factor analysis was used to group 20 soil attributes into six SQI which were named as; soil organic matter (SOM), dissolved organic matter (DOM), soluble N, reduced N, microbial biomass, DOM humification (DOMH). SOM was identified as the most important SQI in the discrimination of both soil types and AVCs. Soil attributes constituting highly to the SOM factor were, microbial quotient and bulk density. The SOM indicator discriminated three soil type groupings and four aggregate vegetation class groupings. Among the soil types, only the peat soils were discriminated from other groups while among the AVCs only the heath and bog classes were isolated from others. However, the peat soil and heath and bog AVC were the only groups that were distinctly discriminated from other groups. All other groups heavily overlapped with one another, making it practically impossible to define reference values for each soil type or AVC. The two-way ANOVA showed that the AVCs were a better regulator of the SQIs than the soil types. We conclude that conventionally classified soil types cannot predict the SQIs defined from large areas with differing climatic and edaphic factors. Localised areas with similar climatic and topoedaphic factors may hold promise for the definition of SQI that may predict the soil types or AVCs.

Tree cover mediate indices related to the content of organic matter and the size of microbial population in semi-arid ecosystems

The type of vegetation cover affects the contents of organic matter and other soil features that can lead to variability of soil microbial processes, which play a key role in the nutrient cycle. This issue is especially important in mountainous semi-arid ecosystems, which have been introduced as fragile and vulnerable habitats. In the present study, labile contents of soil organic matter (SOM), microbial and enzymatic indices under the influence of forest and rangeland cover [i.e. natural forest with dominant species of Zelkova carpinifolia (Pall.) K. Koch. And three rangeland covers, converted form forest site almost 30 years ago, with dominant species of Festuca ovina L. Dactylis glomerata L. and Stachys byzantina K. Koch.] in Northern Iran have been considered including seasonal changes. The study aimed to investigate i) the effect of forest conversion to rangelands on SOM fractions, (ii) temporal dynamics of soil microbial processes and enzyme functions in different vegetation types, and (iii) determining the relationship between indices related to the content of organic matter and the size of microbial population in mountain ecosystems. Results showed that Zelkova tree type enhanced the levels of SOM contents, carbon and nutrient (nitrogen, phosphorous, potassium, calcium and magnesium) pools, and also with higher values in the summer season, the size of microbial population and processes. Additionally, the SOM turnover and microbial efficiency were almost suppressed in order to Zelkova > Festuca > Dactylis > Stachys vegetation types, respectively. Based on the obtained results, it can be concluded that the presence of tree cover in mountain ecosystems can strengthen soil function and create fertile islands. Therefore, the protection of natural forests is emphasized for the proper management and sustainability of habitats in semi-arid regions.