In situ enrichment of sulphate-reducing microbial communities with different carbon sources stimulating the acid mine drainage sediments.

The applications of sulphate-reducing microorganisms (SRMs) in acid mine drainage (AMD) treatment systems have received extensive attention due to their ability to reduce sulphate and stabilize metal(loid)s. Despite great phylogenetic diversity of SRMs, only a few have been used in AMD treatment bioreactors. In situ enrichment could be an efficient approach to select new effective SRMs for AMD treatment. Here, we performed in situ enrichment of SRMs in highly stratified AMD sediment cores using different kinds of carbon source mixture. The dsrAB (dissimilatory sulfite reductase) genes affiliated with nine phyla (two archaeal and seven bacterial phyla) and 26 genera were enriched. Remarkably, those genes affiliated with Aciduliprofundum and Vulcanisaeta were enriched in situ in AMD-related environments for the first time, and their relative abundances were negatively correlated with pH. Furthermore, 107 dsrAB-containing metagenome-assembled genomes (MAGs) were recovered from metagenomic datasets, with 14 phyla (two archaeal and 12 bacterial phyla) and 15 genera. The relative abundances of MAGs were positively correlated with total carbon and sulphate contents. Our findings expanded the diversity of SRMs that can be enriched in AMD sediment, and revealed the physiochemical properties that might affect the growth of SRMs, which provided guidance for AMD treatment bioreators.

Application of biochar and compost improved soil properties and enhanced plant growth in a Pb-Zn mine tailings soil.

This study evaluated the effect of biochar and compost on physiochemical properties, heavy metal content, microbial biomass, enzyme activities, and plant growth in Pb-Zn mine tailings. In this study, a pot experiment was conducted to evaluate the effects of biochar, compost, and their combination on the availability of heavy metals, physicochemical features, and enzyme activities in mining soil. Compared to separate addition, the combined application of biochar and compost was more effective to improve soil pH, soil organic carbon (SOC), total nitrogen (TN), available phosphorus (AP), and potassium (AK). All amendments significantly decreased CaCl2-extractable Pb, Zn, Cu, and Cd. Soil enzyme activities were activated by biochar and compost. Meanwhile, the addition of biochar and compost decreased heavy metal content in plant tissues and increased plant biomass. Pearson's correlation analysis showed that plant biomass was positively correlated with nutrient levels, microbial biomass, and enzyme activities, whereas it was negatively correlated with CaCl2-extractable heavy metals. These results enhance our understanding of the ecological functions of biochar and compost on the restoration of mining soil and reveal the potential benefit of organic amendments on the improvement of mining soil quality.

Functional Guilds, Community Assembly, and Co-occurrence Patterns of Fungi in Metalliferous Mine Tailings Ponds in Mainland China.

Metalliferous mine tailings ponds are generally characterized by low levels of nutrient elements, sustained acidic conditions, and high contents of toxic metals. They represent one kind of extreme environments that are believed to resemble the Earth's early environmental conditions. There is increasing evidence that the diversity of fungi inhabiting mine tailings ponds is much higher than previously thought. However, little is known about functional guilds, community assembly, and co-occurrence patterns of fungi in such habitats. As a first attempt to address this critical knowledge gap, we employed high-throughput sequencing to characterize fungal communities in 33 mine tailings ponds distributed across 18 provinces of mainland China. A total of 5842 fungal phylotypes were identified, with saprotrophic fungi being the major functional guild. The predictors of fungal diversity in whole community and sub-communities differed considerably. Community assembly of the whole fungal community and individual functional guilds were primarily governed by stochastic processes. Total soil nitrogen and total phosphorus mediated the balance between stochastic and deterministic processes of the fungal community assembly. Co-occurrence network analysis uncovered a high modularity of the whole fungal community. The observed main modules largely consisted of saprotrophic fungi as well as various phylotypes that could not be assigned to known functional guilds. The richness of core fungal phylotypes, occupying vital positions in co-occurrence network, was positively correlated with edaphic properties such as soil enzyme activity. This indicates the important roles of core fungal phylotypes in soil organic matter decomposition and nutrient cycling. These findings improve our understanding of fungal ecology of extreme environments.

Remarkable effects of microbial factors on soil phosphorus bioavailability: A country-scale study.

Low soil phosphorus (P) bioavailability causes the widespread occurrence of P-limited terrestrial ecosystems around the globe. Exploring the factors influencing soil P bioavailability at large spatial scales is critical for managing these ecosystems. However, previous studies have mostly focused on abiotic factors. In this study, we explored the effects of microbial factors on soil P bioavailability of terrestrial ecosystems using a country-scale sampling effort. Our results showed that soil microbial biomass carbon (MBC) and acid phosphatase were important predictors of soil P bioavailability of agro- and natural ecosystems across China although they appeared less important than total soil P. The two microbial factors had a positive effect on soil P bioavailability of both ecosystem types and were able to mediate the effects of several abiotic factors (e.g., mean annual temperature). Meanwhile, we revealed that soil phytase could affect soil P bioavailability at the country scale via ways similar to those of soil MBC and acid phosphatase, a pattern being more pronounced in agroecosystems than in natural ecosystems. Moreover, we obtained evidence for the positive effects of microbial genes encoding these enzymes on soil P bioavailability at the country scale although their effect sizes varied between the two ecosystem types. Taken together, this study demonstrated the remarkable effects of microbial factors on soil P bioavailability at a large spatial scale, highlighting the importance to consider microbial factors in managing the widespread P-limited terrestrial ecosystems.

A comprehensive synthesis unveils the mysteries of phosphate-solubilizing microbes.

Phosphate-solubilizing microbes (PSMs) drive the biogeochemical cycling of phosphorus (P) and hold promise for sustainable agriculture. However, their global distribution, overall diversity and application potential remain unknown. Here, we present the first synthesis of their biogeography, diversity and utility, employing data from 399 papers published between 1981 and 2017, the results of a nationwide field survey in China consisting of 367 soil samples, and a genetic analysis of 12986 genome-sequenced prokaryotic strains. We show that at continental to global scales, the population density of PSMs in environmental samples is correlated with total P rather than pH. Remarkably, positive relationships exist between the population density of soil PSMs and available P, nitrate-nitrogen and dissolved organic carbon in soil, reflecting functional couplings between PSMs and microbes driving biogeochemical cycles of nitrogen and carbon. More than 2704 strains affiliated with at least nine archaeal, 88 fungal and 336 bacterial species were reported as PSMs. Only 2.59% of these strains have been tested for their efficiencies in improving crop growth or yield under field conditions, providing evidence that PSMs are more likely to exert positive effects on wheat growing in alkaline P-deficient soils. Our systematic genetic analysis reveals five promising PSM genera deserving much more attention.