Functional Prokaryotic-Like Deoxycytidine Triphosphate Deaminases and Thymidylate Synthase in Eukaryotic Social Amoebae: Vertical, Endosymbiotic, or Horizontal Gene Transfer?

The de novo synthesis of deoxythymidine triphosphate uses several pathways: gram-negative bacteria use deoxycytidine triphosphate deaminase to convert deoxycytidine triphosphate into deoxyuridine triphosphate, whereas eukaryotes and gram-positive bacteria instead use deoxycytidine monophosphate deaminase to transform deoxycytidine monophosphate to deoxyuridine monophosphate. It is then unusual that in addition to deoxycytidine monophosphate deaminases, the eukaryote Dictyostelium discoideum has 2 deoxycytidine triphosphate deaminases (Dcd1Dicty and Dcd2Dicty). Expression of either DcdDicty can fully rescue the slow growth of an Escherichia coli dcd knockout. Both DcdDicty mitigate the hydroxyurea sensitivity of a Schizosaccharomyces pombe deoxycytidine monophosphate deaminase knockout. Phylogenies show that Dcd1Dicty homologs may have entered the common ancestor of the eukaryotic groups of Amoebozoa, Obazoa, Metamonada, and Discoba through an ancient horizontal gene transfer from a prokaryote or an ancient endosymbiotic gene transfer from a mitochondrion, followed by horizontal gene transfer from Amoebozoa to several other unrelated groups of eukaryotes. In contrast, the Dcd2Dicty homologs were a separate horizontal gene transfer from a prokaryote or a virus into either Amoebozoa or Rhizaria, followed by a horizontal gene transfer between them. ThyXDicty, the D. discoideum thymidylate synthase, another enzyme of the deoxythymidine triphosphate biosynthesis pathway, was suggested previously to be acquired from the ancestral mitochondria or by horizontal gene transfer from alpha-proteobacteria. ThyXDicty can fully rescue the E. coli thymidylate synthase knockout, and we establish that it was obtained by the common ancestor of social amoebae not from mitochondria but from a bacterium. We propose horizontal gene transfer and endosymbiotic gene transfer contributed to the enzyme diversity of the deoxythymidine triphosphate synthesis pathway in most social amoebae, many Amoebozoa, and other eukaryotes.

Synthetic consortia of four strains promote Schisandra chinensis growth by regulating soil microbial community and improving soil fertility.

MAIN CONCLUSION: Synthetic consortia performed better in promoting Schisandra chinensis growth than individual strains, and this result provides valuable information for the development of synthetic microbial fertilizers. Schisandra chinensis is an herbal medicine that can treat numerous diseases. However, the excessive reliance on chemical fertilizers during the plantation of S. chinensis has severely restricted the development of the S. chinensis planting industry. Plant growth-promoting rhizobacteria (PGPR) can promote the growth of a wide range of crops, and synthetic consortia of them are frequently superior to those of a single strain. In this study, we compared the effects of four PGPR and their synthetic consortia on S. chinensis growth. The pot experiment showed that compared with the control, synthetic consortia significantly increased the plant height, biomass, and total chlorophyll contents of S. chinensis, and their combined effects were better than those of individual strains. In addition, they improved the rhizosphere soil fertility (e.g., TC and TN contents) and enzyme activities (e.g., soil urease activity) and affected the composition and structure of soil microbial community significantly, including promoting the enrichment of beneficial microorganisms (e.g., Actinobacteria and Verrucomicrobiota) and increasing the relative abundance of Proteobacteria, a dominant bacterial phylum. They also enhanced the synergistic effect between the soil microorganisms. The correlation analysis between soil physicochemical properties and microbiome revealed that soil microorganisms participated in regulating soil fertility and promoting S. chinensis growth. This study may provide a theoretical basis for the development of synthetic microbial fertilizers for S. chinensis.

Rhizosphere microbial community construction during the latitudinal spread of the invader Chromolaena odorata.

The colonization of alien plants in new habitats is typically facilitated by microorganisms present in the soil environment. However, the diversity and structure of the archaeal, bacterial, and fungal communities in the latitudinal spread of alien plants remain unclear. In this study, the rhizosphere and bulk soil of Chromolaena odorata were collected from five latitudes in Pu' er city, Yunnan Province, followed by amplicon sequencing of the soil archaeal, bacterial, and fungal communities. Alpha and beta diversity results revealed that the richness indices and the structures of the archaeal, bacterial, and fungal communities significantly differed along the latitudinal gradient. Additionally, significant differences were observed in the bacterial Shannon index, as well as in the structures of the bacterial and fungal communities between the rhizosphere and bulk soils. Due to the small spatial scale, trends of latitudinal variation in the archaeal, bacterial, and fungal communities were not pronounced. Total potassium, total phosphorus, available nitrogen, available potassium and total nitrogen were the important driving factors affecting the soil microbial community structure. Compared with those in bulk soil, co-occurrence networks in rhizosphere microbial networks presented lower complexity but greater modularity and positive connections. Among the main functional fungi, arbuscular mycorrhizae and soil saprotrophs were more abundant in the bulk soil. The significant differences in the soil microbes between rhizosphere and bulk soils further underscore the impact of C. odorata invasion on soil environments. The significant differences in the soil microbiota along latitudinal gradients, along with specific driving factors, demonstrate distinct nutrient preferences among archaea, bacteria, and fungi and indicate complex microbial responses to soil nutrient elements following the invasion of C. odorata.

Microplastic pollution promotes soil respiration: A global-scale meta-analysis.

Microplastic (MP) pollution likely affects global soil carbon (C) dynamics, yet it remains uncertain how and to what extent MP influences soil respiration. Here, we report on a global meta-analysis to determine the effects of MP pollution on the soil microbiome and CO2 emission. We found that MP pollution significantly increased the contents of soil organic C (SOC) (21%) and dissolved organic C (DOC) (12%), the activity of fluorescein diacetate hydrolase (FDAse) (10%), and microbial biomass (17%), but led to a decrease in microbial diversity (3%). In particular, increases in soil C components and microbial biomass further promote CO2 emission (25%) from soil, but with a much higher effect of MPs on these emissions than on soil C components and microbial biomass. The effect could be attributed to the opposite effects of MPs on microbial biomass vs. diversity, as soil MP accumulation recruited some functionally important bacteria and provided additional C substrates for specific heterotrophic microorganisms, while inhibiting the growth of autotrophic taxa (e.g., Chloroflexi, Cyanobacteria). This study reveals that MP pollution can increase soil CO2 emission by causing shifts in the soil microbiome. These results underscore the potential importance of plastic pollution for terrestrial C fluxes, and thus climate feedbacks.

Metagenomic analysis reveals gene taxonomic and functional diversity response to microplastics and cadmium in an agricultural soil.

Both microplastics (MPs) and heavy metals are common soil pollutants and can interact to generate combined toxicity to soil ecosystems, but their impact on soil microbial communities (e.g., archaea and viruses) remains poorly studied. Here, metagenomic analysis was used to explore the response of soil microbiome in an agricultural soil exposed to MPs [i.e., polyethylene (PE), polystyrene (PS), and polylactic acid (PLA)] and/or Cd. Results showed that MPs had more profound effects on microbial community composition, diversity, and gene abundances when compared to Cd or their combination. Metagenomic analysis indicated that the gene taxonomic diversity and functional diversity of microbial communities varied with MPs type and dose. MPs affected the relative abundance of major microbial phyla and genera, while their coexistence with Cd influenced dominant fungi and viruses. Nitrogen-transforming and pathogenic genera, which were more sensitive to MPs variations, could serve as the indicative taxa for MPs contamination. High-dose PLA treatments (10%, w/w) not only elevated nitrogen metabolism and pathogenic genes, but also enriched copiotrophic microbes from the Proteobacteria phylum. Overall, MPs and Cd showed minimal interactions on soil microbial communities. This study highlights the microbial shifts due to co-occurring MPs and Cd, providing evidence for understanding their environmental risks.

The effect of AMF combined with biochar on plant growth and soil quality under saline-alkali stress: Insights from microbial community analysis.

Arbuscular mycorrhizal fungi (AMF) and biochar application individually can enhance plant tolerance to saline-alkali stress and promote plant growth efficiency. However, little is known about the potential synergistic effects of their combination on improving plant growth and soil quality under saline-alkali stress. This experiment adopted the potted method to explore the effects of four treatments on switchgrass growth and soil quality: biochar (BC), Rhizophagus irregularis (Ri), biochar + Ri (BR) and a control without biochar or Ri (CK). Compared to the CK treatment, the switchgrass biomass increased by 92.4 %, 148.6 %, and 177.3 % in the BC, Ri, and BR treatment groups, respectively. Similarly, the rhizosphere soil quality index increased by 29.33 %, 22.7 %, and 49.1 % in the respective treatment groups. The BR treatment significantly altered the rhizosphere soil microbial composition and diversity. Notably, compared to the other treatments, the archaeal α-diversity in the BR group showed a significant decrease. BR treatment significantly increased the relative abundance of bacteria, fungi and archaea at the genus level (e.g., Bacillus, Trichome and candidatus_methanopenens). Network analysis showed that the complexity and closeness of interactions between different microbial taxa were stronger in the BC, Ri and BR treatments than in the CK treatment, with BR being the more prominent. In summary, biochar combined with Ri has a better effect on promoting the growth of switchgrass under saline-alkali stress, improving the quality of saline-alkali soil, and increasing soil microbial diversity. This study provides a new approach for the efficient development and utilization of saline-alkali land.

Ecological characteristics of sugar beet plant and rhizosphere soil in response to high boron stress: A study of the remediation potential.

High boron (B) stress degrades the soil environment and reduces plant productivity. Sugar beet has a high B demand and potential for remediation of B-toxic soils. However, the mechanism regarding the response of sugar beet plants and rhizosphere soil microbiome to high B stress is not clear. In the potted soil experiment, we set different soil effective B environments (0.5, 5, 10, 30, 50, and 100 mg kg-1) to study the growth status of sugar beets under different B concentrations, as well as the characteristics of soil enzyme activity and microbial community changes. The results showed that sugar beet growth was optimal at 5 mg kg-1 of B. Exceeding this concentration the tolerance index decreased. The injury threshold EC20 was reached at an available B concentration of 35.8 mg kg-1. Under the treatment of 100 mg kg-1, the B accumulation of sugar beet reached 0.22 mg plant-1, and the tolerance index was still higher than 60%, which had not yet reached the lethal concentration of sugar beet. The abundance of Acidobacteriota, Chloroflexi and Patescibacteria increased, which was beneficial to the resistance of sugar beet to high B stress. In summary, under high B stress sugar beet had strong tolerance, enhanced capacity for B uptake and enrichment, and changes in soil microbial community structure. This study provides a theoretical basis for clarifying the mechanism of sugar beet resistance to high B stress and soil remediation.

Floristic changes and environmental drivers of soil fungi and archaea in different salt-tolerant plant communities in the intertidal habitat of coastal wetlands.

Microorganisms are crucial elements of terrestrial ecosystems, which play significant roles in improving soil physicochemical properties, providing plant growth nutrients, degrading toxic and harmful chemicals, and biogeochemical cycling. Variations in the types and quantities of root exudates among different plants greatly alter soil physicochemical properties and result in variations in the diversity, structure, and function of soil microorganisms. Not much is understood about the differences of soil fungi and archaea communities for different plant communities in coastal wetlands, and their response mechanisms to environmental changes. In this study, fungal and archaea communities in soils of Suaeda salsa, Phragmites australis, and Spartina alterniflora in the intertidal habitat of coastal wetlands were selected for research. Soil fungi and archaea were analyzed for diversity, community structure, and function using high throughput ITS and 16S rRNA gene sequencing. The study revealed significant differences in fungi and archaea's diversity and community structure in the rhizosphere soil of three plant communities. At the same time, there is no significant difference in the functional groups. SOM, TP, AP, MC, EC and SOM, TN, TP, AP, MC, EC are the primary environmental determinants affecting changes in soil fungal and archaeal communities, respectively. Variations in the diversity, community structure, and ecological functions of fungi and archaea can be used as indicators characterizing the impact of external disturbances on the soil environment, providing a theoretical foundation for the effective utilization of soil microbial resources, thereby achieving the goal of environmental protection and health promotion.

Microalgae biomass as a conditioner and regulator of soil quality and fertility.

Characteristics of an acid soil cultivated with Urochloa brizantha cv. Marandu were evaluated in relation to two types of fertilization: a conventional one, chemical based on nitrogen and potassium, and a biofertilizer, based on microalgae biomass. The results were compared among three treatments, control, conventional, and biological fertilization, with seven replications each. The study evaluated microalgae community, total carbon and nitrogen contents, mineral nitrogen, and enzymatic activity. Chlorella vulgaris showed the highest organism density, which can be explained by its rapid growth and high resistance. The highest species diversity was detected in the control 1,380,938 org cm-3 and biological 1,841,250 org cm-3 treatments, with the latter showing a higher density of cyanobacteria, especially Pseudanabaena limnetica with 394,554 org cm-3. The soil treated with chemical fertilization showed higher nitrate (9.14 mg NKg-1 NO3--N) and potassium (52.32 mg dm-3) contents. The highest levels of sulfur (21.73 mg dm-3) and iron (96.46 mgdm-3) were detected in the biological treatment. The chemical treatment showed higher activity of the enzymes acid phosphatase, acetylglucosaminidase, and sulfatase, while α-glucosidase and leucine aminopeptidase stood out in the biological treatment. Soil properties were not significantly affected by the treatments. The use of microalgae biomass derived from wastewater treatment from milking parlors was evaluated and presented as a promising biofertilizer for agriculture, following the line of recovering nutrient-rich wastes. In this sense, although many challenges need to be overcome, the results suggest that microalgal-based fertilizers could lead to low-impact agriculture.

Leaf litter chemistry and its effects on soil microorganisms in different ages of Zanthoxylum planispinum var. Dintanensis.

BACKGROUND: Leaf litter is the products of metabolism during the growth and development of plantation, and it is also an important component of nutrient cycling in plantation ecosystems. However, leaf litter chemistry and its effects on soil microorganisms in different ages, as well as the interactions between chemical components in leaf litter have been rarely reported. Based on this, this paper took Zanthoxylum planispinum var. dintanensis (hereafter Z. planispinum) plantations of 5-7, 10-12, 20-22, and 28-32 years old as the objects. By using one-way ANOVA, Pearson correlation analysis and redundancy analysis, we investigated leaf litter chemistry and its effects on soil microorganisms in different ages, and to reveal internal correlation of various chemical components in leaf litter, which can provide a scientific basis for the regulation of soil microbial activity in plantations. RESULTS: The variation of organic carbon with plantation age was more stable compared to total nitrogen and phosphorus of leaf litter. Nitrogen resorption was stronger than phosphorus resorption efficiency in Z. planispinum, and resorption efficiencies of leaf nitrogen and phosphorus for different ages were lower than the global average. Total nitrogen was highly significantly positively correlated with lignin, and total potassium was significantly positively correlated with tannin, suggesting the increase of inorganic substances in leaf litter would promote the accumulation of secondary metabolites. The leaf litter chemical traits explained up to 72% of soil microorganisms, where lignin was positively correlated with fungi and negatively correlated with bacteria, indicating that fungi are able to decompose lower quality litter and can break down complex and stable organic compounds more rapidly than bacteria. The nutrient elements carbon and nitrogen in the leaf litter and their interrelationship also have a great impact on soil microorganisms, because carbon is not only the element that provides energy, but also the element with the largest content in the microbiota. CONCLUSIONS: The sustained increase in inorganic nutrients of leaf litter did not favor the decomposition of secondary metabolites, but rather inhibited the degradation of leaf litter. The significant positive effect of the leaf litter chemistry on soil microorganisms indicates the important role of leaf litter in promoting nutrient cycling in Z. planispinum plantations.

Grazing practices affect soil microbial networks but not diversity and composition in alpine meadows of northeastern Qinghai-Tibetan plateau.

Livestock grazing is the primary practice in alpine meadows and can alter soil microbiomes, which is critical for ecosystem functions and services. Seasonal grazing (SG) and continuous grazing (CG) are two kinds of different grazing practices that dominate alpine meadows on the Qinghai-Tibetan Plateau (QTP), and how they affect soil microbial communities remains in-depth exploration. The present study was conducted to investigate the effects of different grazing practices (i.e., SG and CG) on the diversity, composition, and co-occurrence networks of soil bacteria and fungi in QTP alpine meadows. Soil microbial α- and ß-diversity showed no obvious difference between SG and CG grasslands. Grazing practices had little impact on soil microbial composition, except that the relative abundance of Proteobacteria and Ascomycota showed significant difference between SG and CG grasslands. Soil microbial networks were more complex and less stable in SG grasslands than that in CG grasslands, and the bacterial networks were more complex than fungal networks. Soil fungal diversity was more strongly correlated with environmental factors than bacteria, whereas both fungal and bacterial structures were mainly influenced by soil pH, total nitrogen, and ammonium nitrogen. These findings indicate that microbial associations are more sensitive to grazing practices than microbial diversity and composition, and that SG may be a better grazing practice for ecological benefits in alpine meadows.

River water influenced by shale gas wastewater discharge for paddy irrigation has limited effects on soil properties and microbial communities.

The processes of hydraulic fracturing to extract shale gas generate a large amount of wastewater, and the potential impacts of wastewater discharge after treatment are concerning. In this field study, we investigated the effects of the irrigation of paddy fields for 2 consecutive years by river water that has been influenced by shale gas wastewater discharge on soil physicochemical properties, microbial community structure and function, and rice grain quality. The results showed that conductivity, chloride and sulfate ions in paddy soils downstream of the outfall showed an accumulative trend after two years of irrigation, but these changes occurred on a small scale (<500 m). Two-year irrigation did not cause the accumulation of trace metals (barium, cadmium, chromium, copper, lead, strontium, zinc, nickel, and uranium) in soil and rice grains. Among all soil parameters, the accumulation of chloride ions was the most pronounced, with concentrations in the paddy soil at the discharge site 13.3 times higher than at the upstream control site. The use of influenced river water for paddy irrigation positively increased the soil microbial diversity, but these changes occurred after two years of irrigation and did not occur after one year of irrigation. Overall, the use of river water affected by shale gas wastewater discharge for agricultural irrigation has limited effects on agroecosystems over a short period. Nevertheless, the possible negative effects of contaminant accumulation in soil and rice caused by longer-term irrigation should be seriously considered.

Responses of maize (Zea mays L.) seedlings growth and physiological traits triggered by polyvinyl chloride microplastics is dominated by soil available nitrogen.

As a burgeoning pollutant, microplastics (MPs) has elicited global concern. However, ecological effects and mechanisms of MPs on plant-soil system are still poorly understood. In the present study, the impacts of polyvinyl chloride microplastics (PVC-MPs) on maize (Zea mays L.) seedlings growth and physiological traits and soil properties were discussed through a 30-day pot experiment. Results showed that PVC-MPs had greater toxicity effect on seedlings shoot biomass than root biomass. To defense the impact of PVC-MPs, the superoxide dismutase and catalase activities in seedlings leaf were stimulated. Moreover, the adhesion of MPs on soil particles increased, and soil microorganism, enzymes, and nutrients were altered significantly with increasing content of PVC-MPs. Notably, soil nitrate nitrogen decreased significantly with increasing content of PVC-MPs, whereas soil ammonium nitrogen was promoted under lower contents (0.1% and 1%) of PVC-MPs. Redundancy analysis indicated that soil nitrate nitrogen and ammonium nitrogen can explain 87.4% and 7.7% of variation in maize seedlings growth and physiological traits, respectively. These results display that maize seedlings shoot is more susceptible to the impact of PVC-MPs and soil available nitrogen is the primary limiting factor on maize seedlings growth and physiological traits triggered by PVC-MPs. Impacts of PVC-MPs on maize seedlings growth and physiological traits by nitrogen depletion lead to the possible yield and economic loess and potential risks due to the over use of nitrogen fertilizers.

Effect of Lysinibacillus isolated from environment on probiotic properties and gut microbiota in mice.

Soil microorganisms (SM) are primarily involved in organism degradation, plant nitrogen nutrient immobilization, host microorganisms and oxidation. However, research on the effect of soil-derived Lysinibacillus on the intestinal microbiota spatial disparity of mice is lacking. To test the probiotic properties of Lysinibacillus and the spatial disparity on mice intestinal microorganisms, hemolysis test, molecular phylogenetic analysis, antibiotic sensitivity testing, serum biochemical assays and 16S rRNA profiling were applied. The results showed that Lysinibacillus (LZS1 and LZS2) was resistant to two common antibiotics, Tetracyclines and Rifampin, and sensitive to other antibiotics among the 12 antibiotics tested and negative for hemolysis. In addition, the body weight of group L (treatment of Lysinibacillus, 1.0 × 108 CFU/d for 21days) mice was significantly greater than that of the control group; serum biochemical tests showed that the TG and UREA were significantly lower in group L. The spatial disparity of intestinal microorganisms in mice was significant, treatment of Lysinibacillus (1.0 × 108 CFU/d for 21days) reduced the intestinal microbial diversity and decreased the richness of Proteobacteria, Cyanobacteria and Bacteroidetes in mice. Furthermore, Lysinibacillus treatment enhanced Lactobacillus and Lachnospiraceae richness and significantly reduced 6 bacterial genera in jejunum community, reduced 8 bacterial genera, but increased bacteria at the 4 genera level in cecum microorganisms. In conclusion, this study demonstrated spatial disparity of intestinal microorganisms in mice and probiotic potential of Lysinibacillus isolated from soil.

Extraction of active, contaminant degrading enzymes from soil.

Soil microorganisms play critical roles in the degradation of micro-and nano-pollutants, and the corresponding proteins and enzymes play roles in pollutant recognition, transportation, and degradation. Our ability to study these pathways from soil samples is often complicated by the complex processes involved in extracting proteins from soil matrices. This study aimed to develop a new protein soil extraction protocol that yielded active, intracellular enzymes from the perchlorate degradation pathway, particularly perchlorate reductase. An indirect method, which focused on first separating the cells from the soil matrix, followed by cell lysis and enzyme extraction, was evaluated. The optimized indirect method achieved a final extraction efficiency of the active enzyme and total protein of 15.7 % and 3.3 %, respectively. The final step of separating enzymes from residual soil components resulted in the highest activity and protein losses of 67.7 % ± 14.8 % and 91.8 % ± 1.8 %, respectively. Five buffers, each at different concentrations (0.01 M, 0.05 M, and 0.1 M), were tested to enhance enzyme extraction efficiency. The best extractant requires careful consideration between the highest activity and the quality of the recovered enzymes. Coextraction of humic substances could be minimized by using 0.1 M as compared to 0.01 M and 0.05 M of sodium pyrophosphate; however, this resulted in less recovered activity compared to lower extractant concentrations.

Population Response of Rhizosphere Microbiota of Garden Pea Genotypes to Inoculation with Arbuscular Mycorrhizal Fungi.

This study of a legume's rhizosphere in tripartite symbiosis focused on the relationships between the symbionts and less on the overall rhizosphere microbiome. We used an experimental model with different garden pea genotypes inoculated with AM fungi (Rhizophagus irregularis and with a mix of AM species) to study their influence on the population levels of main trophic groups of soil microorganisms as well as their structure and functional relationships in the rhizosphere microbial community. The experiments were carried out at two phenological cycles of the plants. Analyzes were performed according to classical methods: microbial population density defined as CUF/g a.d.s. and root colonization rate with AMF (%). We found a proven dominant effect of AMF on the densities of micromycetes and actinomycetes in the direction of reduction, suggesting antagonism, and on ammonifying, phosphate-solubilizing and free-living diazotrophic Azotobacter bacteria in the direction of stimulation, an indicator of mutualistic relationships. We determined that the genotype was decisive for the formation of populations of bacteria immobilizing mineral NH4+-N and bacteria Rhizobium. We reported significant two-way relationships between trophic groups related associated with soil nitrogen and phosphorus ions availability. The preserved proportions between trophic groups in the microbial communities were indicative of structural and functional stability.

Long-term manipulation of mean climatic conditions alters drought effects on C- and N-cycling in an arable soil.

Climate is changing and predicted future scenarios include both changes in long-term mean climatic conditions and intensification of extreme events such as drought. Drought can have a major impact on soil functional processes; soil microorganisms, key to these processes, depend on water and temperature dynamics. Consequently, feedback mechanisms regarding microbially mediated carbon and nitrogen cycling in soils may be affected. There are indications that microbial exposure to increasingly unfavorable environmental conditions influences their stress responses. Here, the long-term field experiment Hohenheim Climate Change (HoCC) provided a research platform to explore how microbial exposure to long-term reduced water availability and soil warming modifies microbially driven soil processes, especially gas fluxes from soil, both during drought and after rewetting. The HoCC experiment is an agroecosystem in which the soil microbiome has been exposed to reduced annual mean precipitation and elevated temperature since 2008. Treatment levels were chosen based on a realistic future climate scenario. In June 2019, we exposed this system to a drought period of four weeks. We found that even after 11 years, warming remained a driver of CO2 and N2 O fluxes across the different soil moisture conditions in our drought experiment. Importantly, however, microbial exposure to long-term reduced water availability limited the stimulatory effect of warming on gas fluxes during drought and after rewetting. Our results were neither related to a legacy effect within overall microbial biomass carbon levels nor a shift towards enhanced fungal abundance. We found no indications that extracellular enzyme activities or microbial substrate availability explained the gas flux dynamics observed in our drought experiment. Our study indicates that soil warming promotes gaseous C and N loss even under extreme drought conditions. We suspect, however, that a shift in microbial function following long-term water limitation can hamper the enhancing effect of warming on soil gas fluxes.

Do the respiration pulses induced by drying-rewetting matter for the soil-atmosphere carbon balance?

We show that the explosive microbial and biogeochemical dynamics triggered by rewetting dry soil in laboratory experiments also has relevance in intact ecosystems. This highlights an opportunity to use predictions derived from laboratory studies to provide targets in ecosystem-scale biogeochemical studies.

Effects of heavy metals on microorganisms and enzymes in soils of lead-zinc tailing ponds.

Taking the soil around the lead-zinc tailings pound in the upper reaches of the Hanjiang River in Shaanxi Province as the research object, with tailings pond as the center, seven different belt zones were divided outwards, the contents of Pb, Cu, Zn, V, Ni, Cd in soil were analyzed, as well as soil basic respiration (SBR), microbial biomass carbon (MBC), microbial metabolic quotient (MMQ), and the activities of catalase, urease, cellulase, invertase and neutral phosphatase were also determined. The purpose was to reveal the intrinsic relationship between soil microbial, enzyme activities and heavy metal pollution, and to establish the characterization system of enzyme activities, soil heavy metal pollution degree, as well as microbial parameters. The results showed that: (1) The potential ecological risk index of six heavy metals was ranked as Cd > Cu > Pb > Ni > Zn > V. Cd was a high potential ecological risk, Cu was a medium potential ecological risk, and Zn, Pb, V and Ni were low potential ecological risk. The comprehensive evaluation result of Hakanson's potential ecological hazard index showed that, Zone I was of high potential risk level, Zone II, III and IV were of medium risk level, and Zone V, VI and VII were of low level. (2) Microbial biomass carbon (MBC) had a significant negative correlation or extremely significant negative correlation with 6 heavy metals, and microbial metabolic quotient (MMQ) had a significant positive correlation or extremely significant positive correlation with 6 heavy metals. MBC and MMQ were effective microbiological indexes to measure the quality status of soil, while SBR was not. (3) Catalase, cellulase, sucrase and neutral phosphatase activity had significant negative correlation with the contents of 6 heavy metals, and they could replicate the pollution degree of substantial metals in the soil. However, urease had no significant correlation with the contents of 6 heavy metals, which could not reflect the pollution degree of soil heavy metals.

Increasing acid rain frequency promotes the microbial community dissimilarities of forest soil rather than agricultural soil in southern China.

Soil microbial community drives the terrestrial carbon (C) cycling by C sources metabolism (i.e., organic C decomposition), however, the microbial response to changing acid rain frequency remains less studied, thus hampering global warming projection. Here, we manipulated a simulated experiment to decipher the impact of acid rain frequency (0, 30%, and 100%) on microbial community and C sources metabolism in the agricultural and forest soils of southern China, based on the phospholipid fatty acids (PLFAs) analysis and BIOLOG method, respectively. We found that changing acid rain frequency did not affect the microbial biomass and community structure of agricultural soil during the whole experiment period, while the 30% and 100% acid rain frequencies significantly decreased the microbial biomass, and altered the microbial community structure of forest soil at the early stage. However, changing acid rain frequency did not influence the microbial C sources metabolism in the agricultural soil, but 30% acid rain frequency significantly reduced the microbial utilization of carboxylic acids in the forest soil. Moreover, increasing acid rain frequency promoted the microbial community dissimilarities of forest soil. The microbial community structure and C sources utilization of agricultural soil were significantly related to soil available phosphorus content, while that of forest soil correlated with the soil available potassium content and temperature. Changes in soil environmental condition, soil acidification parameters and soil nutrients explained most of the variance of microbial community and C sources utilization (81% and 57%, respectively) in the forest soil, whereas great uncertainties of microbial community and C sources utilization existed in the agricultural soil with the explanatory proportion being 20% and 10%, respectively. Our findings suggest that the microbial community of forest soil is more sensitive to changing acid rain frequency than that of agricultural soil in a short term. These results support the prediction of microbes-driven C cycling dynamics in specific soil ecosystems in the context of changing acid rain frequency.