Microplastics affect activity and spatial distribution of C,N, and P hydrolases in rice rhizosphere

Microplastics provide a new ecological niche for microorganisms,and the accumulation levels of microplastics(MPs)in terrestrial ecosystems are higher than those in marine ecosystems.Here,we applied the zymography to investigate how MPs–polyethylene[PE],and polyvinyl chloride[PVC])at two levels(0.01%and 1%soil weight)impacted the spatial distribution of soil hydrolases,nutrient availability,and rice growth in paddy soil.MPs increased the above-ground biomass by 13.0%–15.5%and decreased the below-ground biomass by 8.0%–15.1%.Addition of 0.01%and 1%MPs reduced soil NH4+content by 18.3%–63.2%and 52.2%–80.2%,respectively.The average activities of N-and P-hydrolases increased by 0.8%–4.8%and 1.9%–6.3%with addition of MPs,respectively.The nutrient uptake by rice plants and the enzyme activities in hotspots increased with MP content in soil.The accumulation of MPs in paddy soil could provide an ecological niche that facilitates microbial survival,alters the spatial distribution of soil hydrolases,and decreases nutrient availability.

Exogenous rare earth element-yttrium deteriorated soil microbial community structure

In this study, we selected yttrium as the representative of REEs to investigate the impacts of exogenous yttrium on soil physicochemical properties and microbiota. The results showed that exogenous yttrium has no significant effect on soil physical properties but a significantly negative impact on soil chemical properties. The results of high-throughput sequencing demonstrate that exogenous yttrium significantly decreases the number of OTUs, ACE, Chao 1, and Shannon indices while increases the Simpson index（P 〈 0.05）, indicating the low soil microbial diversity. The relative abundances of soil microbes are significantly changed at phylum and genus level. Principal component analysis（PCA） showed the significant difference of microbial community between yttrium treatments（YCl_3-250 and YCl_3-500） and non-yttrium treatment（CK） and the similarity of that between YCl_3-250 and YCI_3-500. Proteobacteria and Bacteroidetes are found to be the most tolerant phyla to exogenous yttrium while Verrucomicrobia the most sensitive phylum. Redundancy analysis（RDA） results suggest that exogenous yttrium affects soil microbiota only through changing the soil chemical properties but not soil physical properties, and C/N ratio is the key environmental factor.

Effect of N and P fertilization on the allocation and fixation of photosynthesized carbon in paddy soil

Potted rice seedlings independently treated with N,P,and NP were continuously^(13)CO_(2) labeled to investigated the influence of N and P application on the contribution of photosynthesized C to the rhizosphere versus bulk soil and particulate organic matter(POM)versus mineral fraction(MIN).N and NP enhanced net assimilated^(13)C on day 14(D14),with maximum C assimilation occurring on day 22(D22)under NP.Aboveground biomass retained more^(13)C than belowground biomass for all treatments.^(13)C incorporation into the rhizosphere exceeded that in bulk soil,with the maximum(6-10%)found under N addition.Newly assimilated^(13)incorporated into POM increased in the rhizosphere under N and NP conditions,whereas MIN remained largely unaffected.^(13)C-MBC proportion in the total microbial biomass C(MBC)pool revealed that N and NP stimulated microbial activity to a greater degree than P.The main portion of^(13)C in the rhizosphere and bulk soil was found in POM on D14,which decreased over time due to microbial utilization.Contrastingly,root-derived ^(13)C in the MIN remained unchanged between sampling days,which indicates that the stabilization of rhizodeposits in this fraction might be the potential mechanism underlying SOM sequestration in paddy soils.

Legacy effect of elevated CO_(2) and N fertilization on mineralization and retention of rice (Oryza sativa L.) rhizodeposit-C in paddy soil aggregates

Rhizodeposits in rice paddy soil are important in global C sequestration and cycling.This study explored the effects of elevated CO_(2) and N fertilization during the rice growing season on the subsequent mineralization and retention of rhizodeposit-C in soil aggregates after harvest.Rice(Oryza sativa L.)was labeled with ^(13)CO_(2) under ambient(400 ppm)and elevated(800 ppm)CO_(2) concentrations with and without N fertilization.After harvest,soil with labeled rhizodeposits was collected,separated into three aggregate size fractions,and flood-incubated for 100 d.The initial rhizodeposit-^(13)C content of N-fertilized microaggregates was less than 65%of that of non-fertilized microaggregates.During the incubation of microaggregates separated from N-fertilized soils,3%–9%and 9%–16%more proportion of rhizodeposit-^(13)C was mineralized to ^(13)CO_(2),and incorporated into the microbial biomass,respectively,while less was allocated to soil organic carbon than in the non-fertilized soils.Elevated CO_(2) increased the rhizodeposit-^(13)C content of all aggregate fractions by 10%–80%,while it reduced cumulative ^(13)CO_(2) emission and the bioavailable C pool size of rhizodeposit-C,especially in N-fertilized soil,except for the silt-clay fraction.It also resulted in up to 23%less rhizodeposit-C incorporated into the microbial biomass of the three soil aggregates,and up to 23%more incorporated into soil organic carbon.These results were relatively weak in the silt-clay fraction.Elevated CO_(2) and N fertilizer applied in rice growing season had a legacy effect on subsequent mineralization and retention of rhizodeposits in paddy soils after harvest,the extent of which varied among the soil aggregates.