Applied Soil Ecology最新文献

Plant growth-promoting microbes (PGPMs) are documented to stimulate nitrification rates and reduce N₂O emissions in acidic soils. These microbes play a role in the nitrogen (N) transformation process, although the specific functions and mechanisms by which they affect the gross N transformation are not well understood. In particular, the influence of PGPMs on the relative predominance of ammonia oxidizers in the nitrification process is still unclear. In this study, we conducted a ¹⁵N tracing experiment to reveal the impact of PGPM Bacillus velezensis SQR9 on gross N transformations in acidic soils, as well as the microbial pathways involved. SQR9 inoculation considerably enhanced the processes of soil gross mineralization and nitrification by 14.6 % and 29.5 %, respectively. This improvement was found to be associated with the soil's dissolved organic carbon (DOC) content and carbon-to‑nitrogen (C/N) ratio. SQR9 increased the abundance of ammonia-oxidizing bacteria (AOB), resulting in a substantial promotion of autotrophic nitrification, which occupied a dominant role (71.3–82.6 %) in the nitrification process. SQR9 significantly stimulated the proportion of AOB, indicating a transition from ammonia-oxidizing archaea (AOA) to AOB as the dominant ammonia oxidizers, hence promoting the gross nitrification rate. In conclusion, the heightened rates of N transformation are highly associated with the modification of the ammonia-oxidizer B. velezensis SQR9. Our findings offer an updated insight into how PGPMs cause N transformation and provide a theoretical basis for the sensible application of PGPMs in agricultural development.

Salt-tolerant rice (STR) cultivation is an effective way to remediate coastal saline land (CSL). However, soil bacterial community and ecological function groups, as well as their controlling factors under STR cultivation in CSL, are still unclear. Here, we evaluated the composition, diversity, and ecological function groups of soil bacteria under different STR cultivation years in a typical CSL in eastern China. Soil bacterial communities across soil samples were dominated primarily by the phyla Proteobacteria (14.3–26.2 %), Bacteroidetes (13.5–17.3 %), Chloroflexi (13.5–17.3 %), Patescibacteria (7.1–13.1 %) and Desulfobacterota (6.6–11.0 %). STR cultivation notably decreased the relative abundance of Proteobacteria and Planctomycetota phyla, while increasing the relative abundances of the Chloroflexi, Desulfobacterota, and Crenarchaeota phyla. The richness and diversity of soil bacterial communities were significantly increased after STR cultivation. Meanwhile, a significant difference in beta diversity of soil bacterial communities was found in STR fields and uncultivated CSL. Additionally, six functional categories were identified, among which metabolism and genetic information processing were the dominant functional groups. Compared with soil bacterial community composition, the bacterial community diversity has a greater impact on bacterial ecological functions. Moreover, the composition and diversity of soil bacterial communities are profoundly driven by soil water content, electrical conductivity, total nitrogen, and total phosphorus. In summary, STR cultivation altered the soil environment and bacterial community, and their ecological function groups, thus improving soil quality and being considered an effective measure for improving CSL.

Although nitrogen fertilizer is an important measure to increase grain yield, response of soil microbial community to nitrogen fertilizer is still unclear in alpine regions. Based on a long-term (>10 years) nitrogen fertilizer experiment (control, CF: chemical fertilizer, SM: sheep manure; CS: chemical fertilizer + sheep manure) in an alpine agroecosystem of the Lhasa, Xizang, responses of soil bacteria and fungi communities to nitrogen fertilizer was investigated. The CF treatment reduced fungi operational taxonomic unit (OTU) by 13.08 %, phylogenetic diversity by 11.13 % at 10–20 cm, but increased fungi guild number at 0–10 cm by 17.71 %. The SM treatment reduced fungi OTU at 10–20 cm by 11.82 %. Compared to CF and SM treatments, CS treatment had stronger positive effects on bacterial α-diversity, considering that CS treatment but not CF and SM treatments increased bacterial mean nearest taxon distance, species Shannon and Simpson at 10–20 cm. The CF, SM and CS treatments altered fungal community composition at 0–10 and 10–20 cm, bacterial community composition at 10–20 cm, and bacterial species composition at 0–10 cm. The CF and CS treatments altered bacterial phylogenetic composition at 0–10 cm, and the SM and CS treatments altered bacterial functional composition at 0–10 cm. The decreased magnitude of the relative abundance of symbiotroph fungi caused by CS treatment (90.44 %) was stronger than that (65.14 % and 53.62 %) caused by CF and SM treatments at 10–20 cm. Therefore, the SM and CS treatments had stronger effects on soil bacterial functional composition, but the CF treatment had stronger effects on fungal α-diversity. Compared with single application of organic or inorganic nitrogen fertilizer, mixed application of organic and inorganic nitrogen fertilizer was more beneficial to the maintenance and improvement of soil bacterial diversity, but caused more reduction of soil symbiotic fungi and in turn greater potential risk. These scientific findings observed by this study can provide guidance for fertilizer management and soil fertility improvement.

This comprehensive study investigated the distribution, dissipation, and environmental impact of diuron and its metabolites (DPMU, DPU, and DCA), as well as its effects on enzyme activities, bacterial abundance, and community composition in response to different soil treatments using two vermicomposts. One vermicompost was derived from vine shoot waste, and the other from wet olive cake (alperujo). The study was conducted under field conditions in a semi-arid region. The results indicated that diuron concentrations decreased with soil depth, with the highest levels in the upper 0–5 cm layer. The application of both vermicomposts reduced diuron leaching into the soil, facilitating its dissipation compared to the organically unamended soil. DPMU was the main metabolite detected in the soil, especially at the end of the experiment. Enzyme activities, including dehydrogenase, β-glucosidase, protease, and acid phosphatase, showed variations with treatment and time, indicating microbial adaptation. In general, both vermicomposts increased soil enzyme activities, even when diuron was co-applied. Bacterial communities were affected by diuron and vermicomposts, with Actinobacteria and Alphaproteobacteria showing significant shifts in relative abundance. Principal Component Analysis (PCA) confirmed structural changes in bacterial communities due to diuron and vermicomposts. Warmer temperatures and evapotranspiration may contribute to the distribution of diuron in the different layers of soil and affect microbial activity. Overall, vermicomposts from wet olive cake proved effective in mitigating diuron in the different soil layers, promoting enzyme activities, and influencing bacterial communities. These findings underscore the complexity of interactions between diuron, organic amendments, and soil microorganisms, highlighting the potential for enhanced herbicide dissipation and microbial resilience and adaptation.

The input of organic C strongly alters the magnitude and direction of the microbial mineralization of soil organic matter (SOM), a phenomenon known as the “priming effect” (PE). The C:N ratios of additives are expected to affect the intensity of PE as it balances the C and N requirements of microbial growth. Growing of green manure (GM) crops in agricultural system strongly regulates PE intensity as it enhances the level and stability of SOM. However, the driving factors of additive C:N ratios and long-term GM crops on PE remain unclear. We addressed this knowledge gap by performing a 92-day incubation of 10-year summer fallow-wheat and GM-wheat soils by adding mixtures of ¹³C-labelled glucose and ammonium sulfate differing in the C:N ratio (15 vs. 50). The PE was increased by 148–288 % due to the high C:N ratio of the added mixtures, indicating that the quality of input exerted effects on the PE across the two soils. The PE of green manured (GMd) soil was increased by 23 % (p < 0.05) compared with that of summer fallow soil, as microorganisms produce extracellular enzymes such as β-glucosidase and leucine aminopeptidase to co-metabolize SOM. Nevertheless, compared with the summer fallow soil, 26 % more glucose-C was sequestered in GMd soil to compensate for C loss. We propose a conceptual model of “N mining” and “co-metabolism” to explain the effect of additive C:N ratio on PE in the soils under different GM practices. The “N mining” is the main cause of PE when the additive C:N ratio is high, and the “co-metabolism” becomes the dominant factor in long-term GMd soil with high SOM content and stability. Our findings demonstrate the importance of long-term incorporation of GM-driven changes in organic C inputs and SOM content and stability in regulating PE and soil C dynamics. Understanding the C dynamics under long-term GM practices contributes to formulate optimized agricultural strategies for promoting C sequestration and accurately predict soil C dynamics in the future.

Besides uptake of nutrients by roots, plants can acquire nutrients through arbuscular mycorrhizal fungi (AMF). AMF play a crucial role in plant growth and competition. However, few studies have investigated the effects of AMF on root foraging and competition between invasive and native species in response to heterogeneous nutrients. Two pairs of invasive and native plants of the Asteraceae family were selected to create a common garden experiment involving three factors (heterogeneous vs. homogeneous phosphorus (P), with vs. without AMF, and monoculture vs. mixture). The results showed that AMF significantly reduced the foraging scale of the invasive species, Bidens pilosa, and decreased the precision of the invasive species, Praxelis clematidea, and the native species, Emilia sonchifolia. In monoculture, AMF significantly decreased the total biomass of the two invasive species under heterogeneous P rather than homogeneous P, which was confirmed by N and P uptake. In mixture, heterogeneity significantly decreased the tolerance competitive ability of B. pilosa but increased that of P. clematidea. In the homogeneous P, AMF significantly decreased the suppression ability of B. pilosa, while in the heterogeneous P, AMF decreased that of P. clematidea. Heterogeneous P with AMF increased the suppression ability of B. pilosa but decreased that of P. clematidea. The interactive effects of AMF and soil P distribution on root foraging and nutrient uptake and competition differ among the four species and show invasive-native pair differences. These findings provide valuable insights into the interactive effects and highlight the context dependency of these interactions.

Understanding belowground plant-microbial interactions is fundamental to predicting how plant species respond to climate change, particularly in global drylands. However, these interactions are poorly understood, especially for keystone grass species like the pan-palaeotropical Themeda triandra. Here, we used 16S rRNA amplicon sequencing to characterise microbiota in rhizospheres and bulk soils associated with T. triandra. We applied this method to eight native sites across a 3-fold aridity gradient (aridity index range = 0.318 to 0.903 = 87 % global aridity distribution) in southern Australia. By examining the relative contributions of climatic, edaphic, ecological, and host specific phenotypic traits, we identified the ecological drivers of core T. triandra-associated microbiota. We show that aridity had the strongest effect on shaping these core microbiotas, and report that a greater proportion of bacterial taxa that were from the core rhizosphere microbiomes were also differentially abundant in more arid T. triandra regions. These results suggest that T. triandra naturally growing in soils under more arid conditions have greater reliance on rhizosphere core taxa than plants growing under wetter conditions. Our study underscores the likely importance of targeted recruitment of bacteria into the rhizosphere by grassland keystone species, such as T. triandra, when growing in arid conditions. This bacterial soil recruitment is expected to become even more important under climate change.

Mungbean (Vigna radiata L. Wilczek) is an economically important legume crop grown across India. The growth and yield of the crop have been declining over the recent years due to climate change which leads to decrease in soil moisture. Applications of drought-tolerant plant growth-promoting (PGP) rhizobial strains have been found to enhance crop productivity under water deficiency. Therefore, the objective of this study was to screen the bacterial strains from the mungbean root nodule that may help in improving the plant growth under drought condition. Bacteria were isolated from mungbean root nodules and screened for in vitro drought-tolerance using different concentrations of PEG 6000 at 10, 20, 30 and 40 %, and temperature-tolerance at 30, 35, 40 and 45 °C. In primary screening, out of 98 root nodule bacterial isolates tested, only 25 % showed drought-tolerance at 40 % polyethylene glycol (PEG)-6000 while 22 % of bacteria survived at 45 °C. During secondary screening on combined stress-tolerance, only 8 % of isolates showed tolerance of 40 % PEG-6000 at 45 °C. The in vitro drought-tolerance of bacteria varied significantly according to their sampling region/district. Various PGP traits, i.e., nitrogen fixation, phosphate solubilization, and production of indole acetic acid, ammonia, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase, were analyzed in isolated stress-tolerant bacteria, which may contribute towards stress-tolerance and crop productivity in mungbean. The most promising drought-tolerant nodule bacterial isolates were identified as Rhizobium sp. and Pseudomonas indica, respectively by 16S rRNA sequencing. Moreover, bacterial isolates MuJs52b, MuJs53b, MuJs72a and MuBk32b, which exhibited drought-tolerance of 40 % PEG-6000 and different PGP activities, were used as bioinoculant on mungbean plants grown under moderate to severe drought at 50 and 25 % of field capacity (FC) in pot experiment. Bacteria inoculated plants showed maximum increase in nodule dry weight (56.5 %) and shoot dry weight (87.5 %) per plant even under severe drought at 25 % FC. The results indicated that application of four potential nodule bacterial isolates, which were able to tolerate drought stress of 40 % PEG-6000, and having multiple PGP traits, showed stimulation of the mungbean growth even up to 25 % FC. These plant growth-promoting nodule bacterial strains may be used for the enhancement of mungbean crop productivity under drought stress and could be used as biofertilizer.

Nitrogen (N) fertilizer input will likely increase to meet the food demands of a growing population under climate change conditions, characterized by increasing atmospheric CO₂ concentration and temperature. Nitrification inhibitors have the potential to reduce N₂O emissions from N fertilized croplands. However, it remains unclear whether future climate change scenarios could affect the effectiveness of nitrification inhibitors. In a two-year study, winter wheat (Triticum aestivum L.) was cultivated in climate-controlled growth chambers with an elevated CO₂ concentration (ambient +200 μmol mol⁻¹) and increased temperature (ambient +2 °C). Urea was applied with or without nitrapyrin (0.5 % of urea-N). In this study, we measured nitrous oxide (N₂O) fluxes, soil ammonium and nitrate levels, and the abundance of five nitrogen-cycling genes related to nitrification (amoA of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA)) and denitrification (nirS, nirK and nosZ). Key findings included the following: 1) without nitrapyrin, cumulative N₂O emissions were not significantly altered by increased temperature, but decreased 24.9 % by the combination of elevated CO₂ and temperature treatment and 17.5 % by the elevated CO₂ alone. NO₃⁻-N accumulation occurred in soils under increased CO₂ and temperature, both individual and in combination; 2) nitrapyrin effectively reduced AOB abundance, inhibiting NO₃⁻-N accumulation and N₂O emission, irrespective of CO₂ concentrations and temperature. However, under the combination of elevated CO₂ and temperature conditions, the efficiency of nitrapyrin in reducing N₂O emission was lower (−13 % to −49 %) than that in the control (−28 % to −65 %) and elevated CO₂ (−32 % to −71 %) conditions. This reduced effectiveness of the combined treatment can be attributed to the inability of nitrapyrin to inhibit the AOA, nirS and nirK genes. Thus, nitrapyrin is expected to reduce N₂O emissions under future climate change scenarios, but the efficacy may be lower than previously expected when CO₂ concentration and temperature increase simultaneously. The indirect effects of nitrapyrin on denitrifiers under climate change scenarios should be considered in future research.

Nutrient addition and grazing exclusion are effective methods to restore carbon and nitrogen pools in degraded grassland. However, how the combination of nutrient addition and grazing exclusion affect carbon and nitrogen pools through carbon and net nitrogen mineralization is unknown. A 56-day incubation study examined the effect of no additive (control — CK) and, the addition of sucrose (S), urea (U), sucrose + urea (SU), and yak dung (D) to the soil of grazed and fenced alpine grassland on carbon and net nitrogen mineralization. The ¹⁵N-tracer technique was used to determine nitrogen utilization by soil microorganisms. Nutrient addition with grazing exclusion increased soil organic carbon, microbial biomass carbon (MBC), inorganic nitrogen, and dissolved organic nitrogen (DON), and promoted carbon and net nitrogen mineralization in early incubation. The ¹⁵N recovery rate in soil was 4.5 to 21.7 % and decreased with time. Grazing exclusion altered the drivers of the carbon and net nitrogen mineralization rates, and increased carbon and net nitrogen mineralization rates by enhancing MBC and DON. The results indicated that nutrient addition: (1) decreased soil carbon and nitrogen stability by increasing nutrient availability and enhancing carbon and net nitrogen mineralization rates; and (2) in combination with grazing exclusion promoted carbon and net nitrogen mineralization. Consequently, soil carbon and net nitrogen mineralization depended on nutrient availability, and grazing stabilized soil carbon and nitrogen pools by reducing carbon and net nitrogen mineralization. The results could provide a theoretical basis for alpine grassland management.