Applied Soil Ecology最新文献

Mining has led to dramatic ecosystem degradation, the destruction of vegetation and irreversible damage to soil structure and nutrient cycling; additionally, heavy metal (HM) contamination has affected soil nitrogen (N) cycle-associated microorganisms and disrupted soil aggregate structure. To explore the mechanism of soil N recovery in mining areas, we investigated the effects of two N fertilizers (urea (U) and ammonium chloride (AC)) and nine different fertilization patterns on the nitrification process and ammonia oxidizers in soil aggregates via incubation experiments. The results showed that different N treatments had different influences on the distribution of AOA and AOB amoA gene abundance and microbial community structure in soil aggregates. The AOB amoA gene abundance was significantly greater than the AOA amoA gene abundance in aggregates. The dominant species of AOA and AOB were Nitrososphaera and Nitrosospira, respectively, which were mainly found in microaggregates and accounted for 10.3 % to 25.0 % and 31.5 % to 60.1 %, respectively, of the microaggregates. Dissolved organic nitrogen (DON) can be used as an important variable to explain variations in AOA communities, and microbial nitrogen (MBN) content, tartaric acid content, cellulase activity and AOB amoA gene abundance can be used as important variables to explain variations in AOB communities. N fertilizer addition resulted in potential ammonia oxidation (PAO) values ranging from 0.079 to 0.236, 0.100 to 0.5953 and 0.146 to 0.905 μg⸱NO₂⁻-N d⁻¹ g⁻¹ in mega-, macro- and microaggregates, respectively, which suggested that PAO values increased with decreasing aggregate size. In addition, the total nitrification potential (TNP) in macroaggregates was greater than that in mega- and microaggregates, which was the main reason for the increase in the NO₃⁻ content in macroaggregates. AOB amoA gene abundance was significantly positively correlated with TNP, and AOB amoA gene abundance was more significantly positively correlated with PAO values than was AOA gene abundance, which suggests that AOB dominated ammonia oxidation and nitrification processes in aggregates. Our research contributes to an understanding of the mechanisms underlying the effects of different types of N fertilizers on nitrification processes and ammonia oxidizers in soil aggregates and provides insights into N management in contaminated soils in mining areas.

The newly discovered complete ammonia oxidizer (comammox Nitrospira) is able to single-step nitrification capability, and increased our understanding of soil nitrogen cycling. However, the response of comammox and ammonia-oxidizing bacteria (AOB) and archaea (AOA) to long-term fertilization and rhizosphere effects in paddy soils and their relative contribution to the nitrification-derived N₂O emissions is still unclear. Here, we collected rhizosphere and bulk soils with thirty years of different fertilization strategies, i.e., non-fertilization (CK), chemical N, P, and K application (NPK), and NPK plus pig manure application (NPKM), respectively, to test changes in nitrification potential rate (PNR), N₂O emission fluxes, abundance of ammonia oxidizers and their significant drivers. The result showed that NPKM significantly increased soil C and N levels, the proportion of soil middle-size particles (40.35–148.00 μm class), and soil PNR, but decreased soil N₂O emissions, especially in the drying time of paddy (P < 0.05), compared to NPK fertilization. NPKM had the highest values of AOA, AOB, and comammox clade A amoA gene copy numbers (P < 0.05), but clade B was increased by the NPK in the rhizosphere soil. Furthermore, fertilization showed greater effects on ammonia oxidizers (except for clade B) than the rhizosphere effect. Mantel test showed that SOM, TP, pH, NH₄⁺, and NO₃⁻ were main abiotic factors causing the niche separation among ammonia oxidizers. Linear regression analysis and structural equation model (SEM) showed that both PNR and N₂O emission fluxes were significantly associated with the abundance of AOB and comammox clade A (P < 0.05). Therefore, our results underline the importance of AOB together with comammox clade A in nitrification and N₂O production in long-term organic fertilized paddy fields, which could provide new ideas for the mitigation of N₂O emission by adopting organic fertilization scenarios in Chinese paddy fields.

The Lhasa River Basin currently faces severe land degradation. In recent years, several dams have been built on the main stream, whereas, their impact on land desertification remains less elucidated. Herein, we investigated variances of soil properties and microbial communities in biological soil crusts (BSCs) along the valley area of Lhasa River and the mountain slope (altitude gradient) in reservoir area after five years of dam construction. Soil nutrient and water contents, enzyme activities, and N-cycle related functional gene copies significantly increased in reservoir-affected areas and decreased with the increase of mountain slope altitude and the distance away from the reservoir, which were usually degraded soil patches; similarly, the relative abundance of bacteria, fungi and moss in BSCs significantly increased in reservoir-affected areas, whilst that of cyanobacteria was higher in degraded soil patches. The linear and structural equation models also showed that dam construction altered water distribution status of soil surface, which enhanced soil properties, N-cycle and increased the relative abundance of moss of BSCs, and successfully accelerated the development and succession of BSCs in degraded soil. This study firstly reported that dam construction could accelerate the succession process of degraded soil in the reservoir affected area and thus a reference for ecological restoration of desertification soil of the Lhasa River Basin in QTP.

Using a mesocosm experiment, we investigated the individual and interaction effects of two earthworm species with contrasting behaviour on soil structure and water transfers. The anecic species Amynthas zenkevichi (Thai, 1982) and the polyhumic endogeic species Pontoscolex corethrurus (Müller, 1857) were incubated in repacked soil columns alone or together for three months under laboratory conditions. The volume of belowground casts, empty burrows and lateral soil compaction were assessed using X-ray computed tomography. The production of surface casts and the amount of food ingested were also recorded. The soil moisture at 7 cm depth and water evaporation of the whole column were monitored regularly. Soil water infiltration was assessed using the Beerkan method at the end of the experiment. A. zenkevichi burrows were less numerous (25 vs. 85), more continuous (41 vs. 0 cm³), more connected from the surface to the bottom of the columns (17 vs. 0 cm³) and more compacted laterally (243 vs. 92 cm³) than those of P. corethrurus. Conversely, P. corethrurus burrows were more abundant in the top 5 cm of the columns and more backfilled by casts than those of A. zenkevichi (36 vs. 5 %). Both species ingested buffalo dung provided at the soil surface and produced surface casts at similar rates. Interactions resulted in an increase in surface activity of more than 40 % and a decrease in the depth and continuity of burrow systems. The water infiltration rate was increased by 3.5 times (compared to the control soil without earthworms) by A. zenkevichi burrows and was not modified by interactions. P. corethrurus increased the cumulative water evaporation by 10 % and decreased soil moisture by 3 % (compared to the control soil without earthworms), whereas A. zenkevichi had marginal effects on these parameters. Globally, interactions led to a slight positive synergistic effect on soil resistance to water loss by evaporation, which was likely related to the increase in surface casting activity. To conclude, this study stresses the importance of considering interactions between earthworms in soil and the need to confirm our findings under natural conditions.

The microbial communities associated with desert plants are influenced by many abiotic (such as soil factors, seasonal variations, etc.) and biotic factors, resulting in different microbial taxa. This study investigated the soil factors, microbial communities and microbial catabolism of Gymnocarpos przewalskii roots at different soil compartments (near-rhizosphere, far-rhizosphere, and blank soil) in three seasons (summer, autumn, and winter) from two sites in the hyperarid desert, northwest China. Microbial biomass and activity were relatively high in summer in the near-rhizosphere, whereas the fungal-bacterial ratio was dominant in autumn. Gram-negative bacterial biomass was the highest irrespective of season, and catabolic activity was dominated by carbohydrate, amino acid, and polymer metabolism for all three seasons and soil compartments. The influence of seasons and soil compartments on soil microbial composition mainly depended on their interactions with soil factors. Temperature, soil saccharase, alkaline phosphatase, and NO₃⁻-N content were the main factors determining microbial composition and carbon source metabolism. Moreover, environmentally induced changes in soil humidity increased glomalin content by affecting the arbuscular mycorrhizal fungal (AMF) PLFA biomass, which affected carbon sequestration, ultimately influencing AMF colonization. Understanding the feedback processes among organisms in desert soils was important for exploring the survival and protection strategies of desert relict plants.

Land use change alters the soil carbon (C) cycle, but it is unclear how change in land use modifies the function and composition of the microbial communities involved in soil C cycling. In this research, we examined the impact of land use change on soil C fractions, C-degrading enzymes, carbohydrate-active enzymes (CAZyme) and composition of microbial community in the southeastern Qinghai-Tibet Plateau of China. We collected surface soils (0–20 cm) from seven sites that simultaneously included four land uses: farmland (FL), natural forest (NF), shrubland (SL) and artificial forest (AF). We determined soil physicochemical properties and performed metagenomic analysis to determine the microbial community composition and CAZyme genes. The results showed that soil C fractions were significantly decreased by 19–55 % when NF was converted to AF, SL and FL due to a decline in litter inputs (p < 0.05). Similarly, C-degrading enzymes significantly declined after NF converted to other land uses (p < 0.05). Moreover, changes in land use significantly affected the soil microbial composition (p < 0.05). In NF, the relative abundances of Proteobacteria, Candidatus Rokuobacteria and Verrucomicrobia were higher compared to FL and SL. Conversely, FL and SL had a significantly higher abundance of Actinobacteria, Acidobacteria, Chloroflexi, and Gemmatimonadetes phyla than NF soil. Furthermore, CAZyme genes were mainly derived from three bacterial phyla: Actinobacteria, Acidobacteria and Proteobacteria. The abundance of CAZyme genes such as glycosyl transferases and carbohydrate esterase were significantly higher in NF, while glycoside hydrolases, carbohydrate-binding modules and polysaccharide lyases genes were significantly higher in FL (p < 0.05). Changes in relative abundances of microbial marker genes, genes coding C-degrading enzymes and CAZyme genes were mainly linked to changes in soil properties, such as soil C fractions, total nitrogen, moisture content, microbial biomass nitrogen, bulk density and pH. Overall, our study provides an in-depth insight into the responses of C-cycling microorganisms and functional genes to land use changes.

Cattle farming is a prominent economic activity in tropical ecosystems. However, this system can lead to biodiversity loss and decreased ecosystem functions. Due to land degradation or changes in farming practices, areas with different times after cattle grazing removal are new and common habitats in tropical landscapes. Therefore, understanding the impact of livestock grazing abandonment on the relationship between biodiversity and ecosystem function is crucial for tropical pastureland livestock production. We assessed the influence of livestock grazing abandonment (cattle removal time), local environmental conditions (herbaceous vegetation density, sand content, and soil compaction), and dung beetle community attributes (biomass and functional dispersion) on dung removal rates in pasturelands. We conducted this study at 24 natural grassland sites in the Brazilian Pantanal, a tropical landscape dominated by livestock. Our findings reveal that community attributes primarily explain the variation in dung removal rates, while the effects of local environment and cattle removal time were insignificant. The relationships between dung beetle functional diversity and ecosystem functioning may show substantial context-dependent variation. Biomass was particularly important in explaining shifts in dung removal. These results underscore the direct link between the decline of biomass of larger-bodied dung beetles and the loss of ecosystem services associated with dung removal, such as parasitic control and soil fertilization. Therefore, conserving dung beetle biomass of larger-bodied dung beetles through effective management plans is vital to sustain ecological functions in tropical livestock-dominated landscapes.

Earthworms, due to the important roles they play in the soil, are considered a cornerstone in agroecology. Despite this, the effects of different management practices (organic versus conventional) on their abundance, biomass, and diversity are not yet fully understood, especially in perennial crops. We took apple orchards in Southeastern France, with up to 30 pesticides applied annually, as a case study. We conducted a comparative analysis of earthworm communities, soil properties, and pesticide use among a total of 68 selected orchards. This dataset comprises 31 under Integrated Pest Management (IPM), 27 organic and 10 abandoned orchards. The soil properties were rather similar, and no significant difference was observed between organic and IPM orchards. Earthworm community composition differed between abandoned and commercial orchards mainly due to the presence of Prosellodrilus fragilis. Interestingly, total earthworm biomass and abundance were similar in all orchards, commercial or abandoned, with an average of 197 individuals m⁻². However, the diversity and the equitability of these communities were significantly lower in IPM orchards compared to both other types of orchards. The most striking difference was the almost 3-fold increase in the mean abundance of Lumbricus terrestris in the organic orchards compared to IPM ones and, in turn, the 2-fold increase in the anecic character of the communities. As the anecic ecological category is associated with typical behavioral facets (creation of deep vertical burrows and intense forging at the soil surface), it is assumed that organic and IPM orchards will have different soil functioning. When evaluating the risks associated with pesticide use, based on their potential effect on earthworms in standardized toxicity tests, IPM orchards are characterized by a much higher (+ 280 %) risk mainly related to insecticide use (including broad-spectrum compounds). However, pesticides are not the only possible explanation for the modification of the earthworm communities since we did not observe a clear link between mean risk per orchard and L. terrestris abundance. Other practices such as the use of organic fertilizers as in the case of organic farming could also play a role. Our study suggests that an accurate characterization of the different practices and farming systems is required to better understand which practices should be applied by farmers to reinforce the services provided by earthworms in their soil.

Continuous input of chemical fertilizers causes soil acidification, land degradation, and water eutrophication, but its impact on soil microbial communities and co-occurrence patterns of microboes is unclear. In this study, we evaluated the impact of chemical fertilizer on bacterial community diversity and ecological network at 75 citrus sites in a watershed where chemical fertilizer is continuously applied. In addition, 25 natural forest sites adjacent to citrus sites were used as references to compare the potential effects of land conversion from natural forests to citrus orchards on soil bacterial diversity and microbial network. The results showed that the cultivation of citrus results in soil phosphorus (P) accumulation, with significantly higher available and mineral-bound phosphate contents than those found in soils of natural forests. Citrus soil average soil available P was 73.2 mg/kg, which was 20 times higher than that in forest soils. As the P content accumulates, soil bacterial Shannon index linearly decreases from 7.06 to 5.93 and is significantly lower than that of adjacent natural forest soils (7.13). Low P fertility soils have higher microbial network complexity and stability, containing more microbial communities and tighter relationships between microbes compared to higher P fertility soils. Soil P content and soil pH regulates soil microbial network complexity and stability. In addition, soil bacterial community structure in soils of natural forests is significantly different from that in citrus soils, and the bacterial community structure in high P soils is different from that in medium and low P soils. Soil P fertility reduces the relative abundance of dominant communities including Proteobacteria, Bacteroidetes, and Gemmatimonadetes, and also changes the relative abundance of some functional microbial communities, such as some phosphorus cycling microorganisms, including Acetobacteraceae and Beijerinckiaceae. In conclusion, soil phosphate accumulation severely alters soil bacterial community diversity, complexity, stability, and functionality. This could have negative impacts on soil functional stability and the sustainability of citrus orchards.

Analyzing the root-associated microbial communities in desert plants during different seasons may provide a valuable understanding of how desert plants adapt to climate change in harsh environments. Hence, we selected root-associated microbial communities (bacteria and fungi) of Tamarix ramosissima from three regions (Cele, CL; Turpan, TLF; Mosuowan, MSW), focusing on three compartments: root endosphere (RE), rhizosphere soil (RS), and bulk soil (BS). Results indicated that the relative abundance of Actinobacteriota, Proteobacteria, and Ascomycota of root bacteria and fungi taxa was higher the in three compartments (RE, RS, and BS). In the CL region, there was a decline in the relative abundance of Proteobacteria within the RE followed by RS and BS during the autumn. During both summer and autumn, the relative abundance of Ascomycota declined with increasing sampling distance (from the TLF to the MSW to the CL) in the BS. Furthermore, in spring, the bacterial (BS) and fungal (BS) Chao1 and ACE index decreased in TLF compared to the MSW region. However, MSW had a higher bacterial Chao1 and Shannon index of the RE (in summer) and RS (in autumn) than the CL area. Overall, in spring, summer, and autumn, root-associated bacterial and fungal communities across various regions (CL, TLF, and MSW) were more responsive to climate and soil factors than plant nutrients. This research provides compelling theoretical evidence advocating for the restoration of degraded vegetation within arid environments, underscoring the critical significance of judicious plant management practices in these regions.