Deciphering soil amendments and actinomycetes for remediation of cadmium (Cd) contaminated farmland.

Soil heavy metal pollution is one of the most serious environmental problems in China, especially cadmium (Cd), which has the most extensive contaminated soil coverage. Therefore, more economical and efficient remediation methods and measures are needed to control soil Cd contamination. In this study, different amendments (biochar (B), organic fertilizer (F), lime (L)) and actinomycetes (A) inoculants were applied to Cd contaminated farmland to explore their effects on wheat growth. Compared with Control, all treatments except A treatment were able to significantly increase the underground parts dry mass of wheat, with the highest increase of 57.19 %. The results showed that the B treatment significantly increased the plant height of wheat by 3.45 %. All treatments increased wheat SOD activity and chlorophyll content and reduced the MDA, which contributes to wheat stress resistance under Cd contamination. F, L and AF treatments can significantly reduce the Cd content in wheat above- and underground parts by up to 56.39 %. Soil amendments can modify the physical and chemical properties of the soil, which in turn affects the absorption of Cd by wheat. Moreover, the addition of soil amendments significantly affects the composition and structure of the rhizospheric soil bacterial community at the wheat jointing stage. The application of organic fertilizer increases the richness and diversity of the bacterial community, while lime makes it significantly decreases it. T-test and microbiome co-occurrence networks show that actinomycetes could not only effectively colonize in local soil, but also effectively enhance the complexity and stability of the rhizosphere microbial community. Considering the practical impact of different treatments on wheat, soil microorganisms, economic benefits and restoration of soil Cd contamination, the application of organic fertilizer and actinomycetes in Cd contaminated soil is a more ideal remediation strategy. This conclusion can be further verified by studying larger repair regions and longer consecutive repair cycles to gain insight into the repair mechanism.

Negative effects of poly(butylene adipate-co-terephthalate) microplastics on Arabidopsis and its root-associated microbiome.

The degradable plastic poly(butylene adipate-co-terephthalate) (PBAT) is considered a potential replacement for low-density polyethylene (LDPE) as the main component of mulch film. However, it is not clear whether PBAT is harmful to the plant-soil system. Thus, we determined the effects of LDPE microplastics (LDPE-MPs) and PBAT microplastics (PBAT-MPs) on the growth of Arabidopsis. The inhibitory effect of PBAT-MPs was greater than that of LDPE-MPs on the growth of Arabidopsis. Transcriptome analysis showed that PBAT-MPs severely disrupted the photosynthetic system of Arabidopsis and increased the expression levels of genes in drug transport-related pathways. PBAT-MPs increased the relative abundances of Bradyrhizobium, Hydrogenophaga, and Arthrobacter in the bulk soil and rhizosphere soil. The abundances of Variovorax, Flavobacterium, and Microbacterium increased in the plant root zone only under PBAT-MPs. Functional prediction analysis suggested that microorganisms in the soil and plant root zone could degrade xenobiotics. Furthermore, the degradation products from PBAT comprising adipic acid, terephthalic acid, and butanediol were more toxic than PBAT-MPs. Our findings demonstrate that PBAT-MPs may be degraded by microorganisms to produce chemicals that are highly toxic to plants. Thus, biodegradable plastics may pose a great risk to the environment.

Biodegradability of polyethylene mulching film by two Pseudomonas bacteria and their potential degradation mechanism.

Wasted polyethylene (PE) products caused pollution has become a global issue. Researchers have identified PE-degrading bacteria which have been considered as a sustainable alleviation to this crisis. However, the degradation mechanism employed by currently isolated bacteria is unclear and their degradation efficiencies are insufficient. More importantly, there is little research into bacteria capable of degrading PE mulching film to solve "white" pollution in agriculture. We determined the PE degradation efficiency of two Pseudomonas, identified by 16S rDNA analysis, and elucidated their potential mechanisms through whole genome sequencing. During an 8-week period, PE mulch lost 5.95 ± 0.03% and 3.62 ± 0.32% of its mass after incubated with P. knackmussii N1-2 and P. aeruginosa RD1-3 strains, respectively. Moreover, considerable pits and wrinkles were observed on PE.The hydrophobicity of PE films also decreased, and new oxygenic functional groups were detected on PE mulch by Fourier Transform Infrared Spectrometry (FTIR). Complete genome sequencing analysis indicated that two Pseudomonas strains encode genes for enzymes and metabolism pathways involved in PE degradation. The results provide a theoretical basis for further research that investigates the mechanism driving the degradation and metabolism of discarded PE in the environment.

Above- and belowground biodiversity drives soil multifunctionality along a long-term grassland restoration chronosequence.

Restoring degraded land is an efficient strategy for improving biodiversity and ecosystem functioning. However, the effects of aboveground and belowground biodiversity on multiple ecosystem functions (multifunctionality) during ecological restoration are not well understood. Here, the relationships between plant and microbial communities and soil multifunctionality were assessed in a 30-year natural grassland restoration chronosequence on the Loess Plateau, China. Soil multifunctionality, in relation to the carbon, nitrogen, phosphorus, and sulfur cycles, was quantified. Soil bacterial and fungal communities were analyzed by high-throughput sequencing using the Illumina HiSeq platform. The results showed that soil multifunctionality was significantly increased with the increasing period of grassland restoration. Plant and bacterial diversity, rather than fungal diversity, were significantly and positively correlated with soil multifunctionality based on single functions, averaging, and multiple threshold approaches. Random forest and structural equation modeling analyses showed that soil multifunctionality was affected by both biotic and abiotic factors. Plant diversity and bacterial community composition had direct effects, whereas plant community composition had both direct and indirect effects on soil multifunctionality. Restoration period and soil pH indirectly affected soil multifunctionality by altering plant and bacterial communities. This work demonstrates the importance of aboveground and belowground biodiversity in driving soil multifunctionality during grassland restoration. The results provide empirical evidence that conserving biodiversity is crucial for maintaining ecosystem functions in restored areas.