Assessing global-warming induced soil organic matter and iron oxides depletion: Empirical insights into sorption and uptake of atrazine by plants.

Recent pesticide use is alarmingly high and unregulated in several parts of the world. Pesticide fate in soil is controlled by sorption processes which affect the subsequent transport and chemical reactivity in the environment, as well as uptake by plants. Sorption processes are dependent on soil composition and properties, but these are beginning to be affected by global warming-linked factors leading to soil depletion. Thus, it is vital to decipher soils' response, especially in the sub-Sahara (SS), to the depletion of some inherent components in the presence of pesticides. This was ascertained by monitoring a model pesticide (atrazine) sorption and desorption on whole SS soil (WS), and the same soil whose organic matter (OMR) and iron oxides (IOR) were substantially depleted, as well as studying atrazine uptake from these soils by fast-growing vegetables. Organic matter depletion enhanced equilibrium in OMR. Sorption was enhanced at lower ambient pH, higher initial atrazine concentration, and higher temperature. Hysteresis was low resulting in high desorption. Overall, atrazine desorption of ≥65 % was observed; it was higher in OMR (≥95 %) since SOM enhanced hysteresis. Though sub-Saharan soils are rich in iron oxides, SOM played a significantly higher role in sorption than iron oxides in this soil. This result suggests a high potential for atrazine to leach into the aquifer in the sub-Saharan. Atrazine uptake experiment by waterleaf and spinach showed that it could be detected in soil after 63 d, and its presence significantly affected the growth of both vegetables especially in soils with depleted SOM and iron oxides, and at high (100 µg/kg) atrazine spiking. Spinach may be a higher atrazine accumulator than waterleaf. It may be concluded that waterleaf and spinach grown on atrazine-contaminated soils, especially on SOM/iron oxide-depleted soils, are likely to accumulate atrazine.

Impacts of soil type and drought stress on growth and cesium accumulation in Napier grass.

In our previous study, the decontamination efficiency of cesium-137 (137Cs) by Napier grass (Pennisetum purpureum Schum.) in the field was shown to be variable and often influenced by natural environmental factors. To elucidate the factors influencing this variable 137Cs-decontamination efficiency, we investigated the influences of soil type and drought stress on Cs accumulation using cesium-133 (133Cs) in Napier grass grown in plastic containers. The experiment was performed using two soil types (Soil A and B) and three different soil moisture conditions: well-watered control (CL), slight drought stress (SD), and moderate drought stress (MD). Overall, our results indicate that soil type and drought have a significant impact on plant growth and 133Cs accumulation in Napier grass. Plant height (PH), tiller number (TN), leaf width (Wleaf), and dry matter weight of aboveground parts (DWabove) and root parts (DWroot) in Soil B were greater than those in Soil A. Drought stress negatively affected chlorophyll fluorescence parameters (maximal quantum efficiency of photosystem (PS) II photochemistry and potential activity of PS II), PH, TN, Wleaf, DWabove, DWroot, and total 133Cs content (TCs), but it had a positive effect on 133Cs concentration. The 133Cs concentration in the aboveground parts (Csabove) was increased by MD approximately 1.62-fold in Soil A and 1.11-fold in Soil B compared to each CL counterpart. The TCs in the aboveground parts (TCsabove) decreased due to drought by approximately 19.9%-39.0% in Soil A and 49.9%-62.7% in Soil B; however, there was no significant effect on TCsabove due to soil type. The results of this study indicate that soil moisture is a key factor in maintaining Napier grass 137Cs-decontamination efficiency.

Impacts of land use/land cover and soil property changes on soil erosion in the black soil region, China.

Soil erosion (SE) is seriously threatening grain production and the ecological environment in the black soil region. Understanding the impact of changes in land use/land cover (LULC) and soil properties on SE is critical for agricultural sustainability and soil management. However, the contribution of soil property changes to SE is often ignored in existing studies. This study analyzed changes in LULC and soil properties from 1980 to 2020 in the black soil region, China. Then, the revised universal soil loss equation was used to explore the spatiotemporal changes of SE from 1980 to 2020. Finally, the contribution of LULC change and soil property change to SE was separated by scenario comparison. The results showed that cropland increased (by 24,157 km2) at the expense of grassland and forest from 1980 to 2020. Sand in cropland decreased by 21.95%, while the silt, clay, and SOC increased by 21.37%, 1.43%, and 15.38%, respectively. Soil erodibility in cropland increased greatly (+9.85%), while in forest and grassland decreased (-6.05% and -4.72%). LULC change and soil properties change together aggravated SE in the black soil region. LULC change and soil property change resulted in a 22% increase in SE, of which LULC change resulted in a 14% increase, and soil property change resulted in an 8% increase. Agricultural development policy was the main reason driving LULC change. The combination of LULC change, climatic factors, and long-term tillage resulted in changes in soil properties. Ecosystem management and policy can reduce SE through vegetation restoration and soil improvement. This study can provide important references for soil conservation and agricultural development in the black soil region.

Amendment with controlled release urea increases leaf morpho-physiological traits, grain yield and NUE in a double-cropping rice system in southern China.

BACKGROUND: Understanding of mechanisms that underpin high-yielding cropping systems is essential for optimizing management practices. Currently, the contribution of plant traits such as leaf area, chlorophyll content and intercepted photosynthetically active radiation (PARi ) to yield and nitrogen use efficiency (NUE) are not fully understood. In addition, the understanding of how canopy traits are affected by nitrogen (N) management practices is unclear. The present study aimed to determine the effect of amendment with controlled release urea (CR), common urea or no urea on NUE and plant eco-physiological characteristics in a 2-year field study in a double rice cropping system. RESULTS: Regulation of N release through amendment with CR significantly increased grain yield, NUE and leaf morpho-physiological attributes. CR coupled with common urea (at comparable total N rates) increased leaf area index (LAI), relative chlorophyll content index (CCI) and PARi , leading to higher grain yield and NUE (increased 24.4% and 25.3% in early and late rice, respectively) compared to local farming practice. Structural equation model (SEM) analysis showed that differences in N application, between CR and common urea, directly accounted for differences observed in soil nutrient, PARi and NUE rather than yield components. Additionally, compared to traditional yield determinants, LAI and PARi (between booting and filling stage) are capable of predicting and explaining grain yield by 0.69 and 0.92 of R2 in early and late rice, respectively. CONCLUSION: Leaf morpho-physiological traits are important for developing N management practices to increase NUE and improve food security for paddy agriculture in southern China. © 2022 Society of Chemical Industry.

Spatial Distributions, Compositional Profiles, Potential Sources, and Intfluencing Factors of Microplastics in Soils from Different Agricultural Farmlands in China: A National Perspective.

More attention has been paid to ubiquitous microplastics (MPs). As a major food producer, the situation of MPs in China's farmland is of even greater concern. Spatial distributions, characteristics, and compositions of MPs in five types of agricultural lands with representative crops were investigated by collecting 477 soil samples from 109 cities in 31 administrative regions of mainland China. To better control MPs in farmland, nearly 400 field questionnaires were obtained, and meteorological conditions, soil properties, and other statistics were collected to quantify potential sources and determine influencing factors. The average abundances of MPs was 2462 ± 3767 items/kg in the agricultural soils, and MP abundance in the greenhouses, farmlands with film mulching, and blank farmlands from four integrated physical geographic regions were determined. The contributions of agricultural films, livestock and poultry manures, irrigation water, and air deposition to MPs in farmlands have been calculated. Influencing factors, such as recovery method, plowing frequency, meteorological conditions, and part of soil properties, were significantly correlated with the abundances of MPs in the agricultural soils (p < 0.05), while mulching age mainly affected MPs in the greenhouses (p < 0.05). This study provides basic scientific data for decision-making and further analysis.

Biochar alleviating heavy metals phytotoxicity in sludge-amended soil varies with plant adaptability.

Recycling sewage sludge (SS) to soil potentially causes soil heavy metal (HM) pollution and plant phytotoxicity. Biochar plays an important role in alleviating HM phytotoxicity, and responses vary with the feedstocks and usage of biochar. However, the effect of plant adaptability on biochar-mediated alleviation is poorly understood. Here, SS-derived biochar (SB) and rice straw-derived biochar (RB) applied at rates of 1.5% and 3% (W/W, SB1.5, SB3, RB1.5, and RB3) were used to improve the properties of soil amended with SS at 50% (W/W). Alleviation of phytotoxicity by biochar was further analyzed with SS-sensitive plant Monstera deliciosa and SS-resistant plant Ruellia simplex. Results revealed that both SB and RB significantly decreased the soil's bulk density and increased water retention. They also changed soil organic matter content and HMs fractionation. The addition of SB or RB alleviated the SS phytotoxicity, and they significantly promoted the growth and the root morphology and physiological index of M. deliciosa. But for R. simplex, these significant changes only synchronously occurred in SB3 treatment. The alleviation in M. deliciosa was more prominent and more closely connected with soil property changes than in R. simplex. Also, more soil property predictors were observed to play an important role in M. deliciosa growth than in R. simplex growth. These results indicated that biochar alleviating HMs phytotoxicity in SS-amended soil is associated with the changes of soil property. Moreover, the alleviation varies more prominently with plant adaptability than with biochar feedstocks and usage.

Effects of different growth patterns of Tamarix chinensis on saline-alkali soil: implications for coastal restoration and management.

OBJECTIVE: To better understand the wetland restoration, the physicochemical property and microbial community in rhizosphere and bulk soil of the living and death Tamarix chinensis covered soil zones were studied. RESULTS: There were differences between growth conditions in the levels of soil pH, salinity, SOM, and nutrient. The living status of T. chinensis exhibited higher capacity of decreasing saline-alkali soil than the death condition of plants, and the living T. chinensis showed higher uptake of N, P, and K as compared with the death samples. Proteobacteria, Bacteroidota, and Chloroflexi were the predominant bacterial communities as revealed via high-throughput sequencing. CONCLUSIONS: It is great potential for using halophytes such as T. chinensis to ecological restore the coastal saline-alkali soil. This study could contribute to a better understanding of halophyte growth during the coastal phytoremediation process, and guide theoretically for management of T. chinensis population.

Derivation of human health risk-based thresholds for lead in soils promote the production of safer wheat and rice.

A reliable and accurate soil threshold helps prevent excessive dietary Pb intake risks to consumers of locally grown wheat and rice crops. Based on a three-year investigation of 206 wheat fields and 358 rice fields throughout China, this study aimed to improve the soil protection guidelines by investigating Pb accumulation in soil-wheat and soil-rice systems and by assessing Pb exposure risks through the soil-grain-human pathway. A site-specific bioconcentration factor (BCF, ratio of Pb concentration in plant to that in soil) was calculated and used to assess grain Pb intake risks instead of a generic BCF value to reduce data uncertainty. In addition to soil pH, cation-exchange capacity exerted a major influence on the Pb BCF variations in wheat, whereas the organic carbon dynamics affected the BCF variations in rice. Once normalized BCF against those soil variables, the distributions of BCF were log-normal in nature. Optimizing the pH and cation-exchange capacity of wheat soils would help protect 49.8% of local adults from excessive Pb dietary intake. The scenario soil thresholds linked to soil variables and grain Pb intake risks were then derived and validated by independent data from field surveys and published articles. Poor production practices in the wheat fields under study included using soils with low fertility.

Low-Temperature Thermal Desorption Effectively Mitigates Accumulation of Total Mercury and Methylmercury in Rice (Oryza sativa L.).

For maximally reserving soil fertility, two critical parameters (i.e. time and temperature) of low-temperature thermal desorption (LTTD) were initially optimized to remediate the mercury-contaminated soil from a mercury mining area. The effect of LTTD on soil properties was investigated, and the bioaccumulation of total mercury (THg) and methylmercury (MeHg) in rice (Oryza sativa L.) were researched via a pot experiment. Results indicated that the physicochemical properties and fertility of the soil after LTTD still meet the requirements of rice growth. Moreover, the concentrations of THg and MeHg in the remediated soil were decreased by 94.1% and 98.8%, respectively. Further, the bioavailability of Hg in soil was significantly reduced. More importantly, the concentrations of THg and MeHg in the seed of rice plant cultivated on the remediated soil were decreased by 57.6% and 80.2%, respectively. Overall, LTTD technology could efficiently remediate Hg-contaminated soil and be a promise remediation strategy.

Global gross nitrification rates are dominantly driven by soil carbon-to-nitrogen stoichiometry and total nitrogen.

Soil gross nitrification (GN) is a critical process in the global nitrogen (N) cycle that results in the formation of nitrate through microbial oxidation of ammonium or organic N, and can both increase N availability to plants and nitrous oxide emissions. Soil GN is thought to be mainly controlled by soil characteristics and the climate, but a comprehensive analysis taking into account the climate, soil characteristics, including microbial characteristics, and their interactions to better understand the direct and indirect controlling factors of GN rates globally is lacking. Using a global meta-analysis based on 901 observations from 330 15 N-labeled studies, we show that GN differs significantly among ecosystem types, with the highest rates found in croplands, in association with higher pH which stimulates nitrifying bacteria activities. Autotrophic and heterotrophic nitrifications contribute 63% and 37%, respectively, to global GN. Soil GN increases significantly with soil total N, microbial biomass, and soil pH, but decreases significantly with soil carbon (C) to N ratio (C:N). Structural equation modeling suggested that GN is mainly controlled by C:N and soil total N. Microbial biomass and pH are also important factors controlling GN and their effects are similar. Precipitation and temperature affect GN by altering C:N and/or soil total N. Soil total N and temperature drive heterotrophic nitrification, whereas C:N and pH drive autotrophic nitrification. Moreover, GN is positively related to nitrous oxide and carbon dioxide emissions. This synthesis suggests that changes in soil C:N, soil total N, microbial population size, and/or soil pH due to anthropogenic activities may influence GN, which will affect nitrate accumulation and gaseous emissions of soils under global climate and land-use changes.

Responses of soil organic carbon stock to animal manure application: A new global synthesis integrating the impacts of agricultural managements and environmental conditions.

Enhancing soil organic carbon (SOC) through applying animal manure is of interest for both sustaining cereal production and mitigating greenhouse gas (GHG) emissions. Previous syntheses showed that manuring-induced SOC changes varied substantially with agricultural managements and environmental conditions, while their significance and relative importance to such variability are still largely uncertain. Here, we presented a new synthesis using an updated and balanced database integrating the manuring-induced SOC stock changes and their plausible explanatory factors in 250 observations at global 120 sites. Manure application increased SOC stock by 7.41 ± 1.14 (95% confidence interval, CI) and 8.96 ± 1.83 (95% CI) Mg C ha-1 , respectively, compared to their mineral fertilized (REF-min) and unfertilized (REF-zero) references. Of which approx. 72% and 34% were directly contributed by manure-C input, respectively. Following the IPCC (Intergovernmental Panel on Climate Change) approach, these changes corresponded to the manuring-induced SOC change factors of 1.27 ± 0.04 (95% CI) and 1.40 ± 0.08 (95% CI), respectively. Basing on a balanced database, we identified the amount of manure-C input as the most important factor to the global variations in the resultant SOC stock changes. More importantly, our integrative analysis distinguished the significance of soil properties (e.g., soil pH and initial SOC content) in regulating the efficiency of manure application in enhancing SOC stock. These results indicate that, at the similar rate, applying manure could sequestrate much more carbon in alkaline soils than in neutral and acidic soils. By integrating the impacts of agricultural managements and environmental conditions, our findings would help to develop region-specific tailor-made manure application measures in agriculture and to refine the SOC change factors for regional GHG inventories.

Soil potentials to resist continuous cropping obstacle: Three field cases.

Continuous cropping has become the most common system in intensive, modern agricultural production; however, obstacles often appear in continuous cropping patterns after a few years of use. There have been several studies about the impacts of continuous cropping on soil microbial, but few about differences between soil experiencing continuous cropping obstacles and those where such obstacles had been resisted. Here, after ten or twenty years of continuous tobacco cropping, we collected soil samples investigating discrepancies in soil property and bacterial community between soils experiencing continuous cropping obstacles and soils where the obstacles were resisted providing insight into preventing and controlling continuous cropping obstacles. Results showed that soil organic matter (SOM), available phosphorus (AP), total nitrogen (TN), nitrate-N (NO3--N), and bacterial diversity of samples where continuous cropping obstacles had been resisted were significantly higher than those where continuous cropping obstacles were present. Besides, SOM, AP, TN, and Ammonium-N (NH4+-N) considerably affected the bacterial community. Among all variables, NH4+-N explained the largest proportion of bacterial community variation. Molecular ecological networks were used to putatively identify keystone taxa, including Acidobacteria Gp1, Acidobacteria Gp2, Acidobacteria Gp16, and WPS-1_genera_incertae_sedis. Their relative abundance significantly changed between the two conditions. Overall, our results indicate that decreases in soil nutrient content and bacterial diversity, and significant changes in some keystone taxa abundances may be important factors leading to increased soil-borne diseases and reduced tobacco production potential or quality. Thus, during agricultural production, we could regulate the stability of the soil-crop-microbial ecological system via crop rotation, intercropping, or the use of specialized bio-fertilizers and soil conditioners to mitigate continuous cropping obstacles.

Soil microbial community composition in a paddy field with different fertilization managements.

Microbes play vital roles in soil quality; however, their response to N (nitrogen) and P (phosphorus) fertilization in acidic paddy soils of subtropical China remains poorly understood. Here, a 10-year field experiment was conducted to evaluate the effects of different fertilization treatments on microbial communities by Illumina MiSeq sequencing. The results showed that different fertilization treatments did not exert a significant effect on microbial alpha diversity, but altered soil properties, and thus affected microbial community composition. The microbial communities in the T1 (optimized N and P fertilizer) and T2 (excessive N fertilizer) treated soils differed from those in the T0 (no N and P fertilizer) and T3 (excessive P fertilizer) treated soils. In addition, the bacterial phyla Proteobacteria, Chloroflexi, and Acidobacteria, and the fungal phyla Ascomycota and Basidiomycota dominated all the fertilized treatments. Soil total potassium (TK) concentration was the most important factor driving the variation in bacterial community structure under different fertilization regimes, while the major factors shaping fungal community structure were soil TN and NO3--N (nitrate N). These findings indicate that optimization of N and P application rates might result in variations in soil properties, which changed the microbial community structure in the present study.

Plant and soil properties mediate the response of soil microbial communities to moderate grazing in a semiarid grassland of northern China.

Even though a growing amount of information about the effects of livestock grazing on soil microbial communities have accumulated in literature, less is known about the combined response of plants, soil properties, and their interactions with soil microbes. In this study, we used a seven-year controlled grazing experiment to quantify the response of plant and soil properties and their interactions with soil microbial communities to moderate grazing in a semiarid grassland of Northern China. Our results showed that moderate grazing reduced the richness and diversity of soil microbial communities, as well as weakened community interactions. However, bacterial communities and their linkages were more stable under moderate grazing than fungal communities. Changes in aboveground plant biomass, soil water content, NO3--N, and NO3/NH4 ratio dominated grazing effects on soil bacterial communities, while fungal communities were mainly influenced by plant N, soil NO3--N, and NO3/NH4 ratio. Changes in the plant community composition played a key role in driving the composition of the fungal community. Our results provide a new insight into the response of soil microbes to moderate grazing, and suggest that above- and belowground communities should be considered to be precise indicators of the state and characteristics of the grassland ecosystem.

Impact of Biochar on Soil Properties, Pore Water Properties, and Available Cadmium.

Some effects of biochar on soil properties (such as pore water DOC) are not very clear. The changes of soil properties [cation exchange capacity (CEC)], pore water properties [pH, dissolved organic carbon (DOC), and Cd concentration (CPW-Cd)], Cd concentration measured by diffusive gradients in thin films (CDGT-Cd), and available Cd content (Cd in weak acid extractable state and reducible state, CBCR-Cd) determined by the BCR sequential extraction procedure over time after biochar addition were studied by soil incubation and potted corn experiments with five soils from a mining area. The results showed increases of 20.3%-64.6% in CEC and 0.34-1.02 in pH (both p < 0.05) in the soil incubation after adding biochar. The DOC concentration was reduced by 8.2%-33.2% (p < 0.05). CPW-Cd, CDGT-Cd, and CBCR-Cd decreased by 14.2%-47.2%, 15.3%-47.9%, and 22.3%-61.4%, respectively. During the corn cultivation phase, CEC increased by 5.1%-29.0%, and DOC concentration decreased by 10.4%-41.3% (p < 0.05). CPW-Cd, CDGT-Cd, and CBCR-Cd decreased by 5.9%-22.4%, 7.2%-25.1%, and 10.5%-64.8%, respectively. Biochar effectively increased the biomass of corn roots and reduced the concentration of Cd in the roots. Biochar altered the properties of soil and pore water, reduced the bioavailability of Cd in soil, and mitigated the harm to corn caused by Cd.

Ecological criteria for zinc in Chinese soil as affected by soil properties.

The increasing accumulation of zinc (Zn) in agricultural soils has led to the need to assess the potential risk of this element for terrestrial organisms. However, the soil ecological criteria in agricultural soil as a function of soil properties have been sparsely reported. In the present study, we derived the ecological criteria (expressed as predicted no effect concentration (PNEC)) for Zn in soils, based on ecotoxicity data for 19 terrestrial species in Chinese soils, the effect of soil properties on Zn ecotoxicity, differences in species sensitivity, and differences between laboratory and realistic field conditions. First, all ecotoxicity data of Zn for terrestrial organisms in Chinese soils were collected and filtered with given criteria to obtain reliable database. Second, the ecotoxicity data were normalized using Zn ecotoxicity predictive models to eliminate the effect of soil properties on Zn ecotoxicity, and corrected with leaching and aging factors to minimize the differences in Zn ecotoxicity under laboratory and field conditions. Then, species sensitivity distribution (SSD) curves were generated with a Burr Ⅲ function based on corrected ecotoxicity data. The concentration of Zn in soil that provides ecological safety for (100 - x)% of species (HCx), was calculated from the SSD curve and HC5 was used for estimation of PNEC. Finally, we developed the predictive models for HCx by quantifying the relationship between the Zn HCx and soil properties. Results showed that soil pH was the most crucial factor affecting Zn HCx values, with HC5 values varying from 38.3 mg/kg in an acidic soil to 263.3 mg/kg in an alkaline calcareous soil. Both the two-factor (soil pH and OC) and the three-factor (soil pH, OC and CEC) models predicted HCx values well, with determination coefficients (R2) of 0.941-0.959 and 0.978-0.982, respectively. This study provides a scientific and reliable basis for the improvement of ecological risk assessment and the establishment of soil environmental quality standards.

Effect of green garlic/cucumber crop rotation for 3 years on the dynamics of soil properties and cucumber yield in Chinese anthrosol.

BACKGROUND: Long-term drastic anthropic inputs in conventional monoculture systems cause negative plant-soil feedback that will largely affect sustainable cucumber cultivation. The inclusion of multicropping in intensive cropping systems could reduce the detrimental effects of continuous cropping obstacles. The present study investigated the dynamics of soil microbial communities, soil enzyme activities and cucumber yield under plastic tunnel cultivation for three successive growing seasons (2013, 2014 and 2015). RESULT: In the amended crop rotation system, soil pH decreased with increasing number of cropped garlic bulbs. The soil electrical conductivity significantly changed during the entire growth period and increased with increasing number of incorporated garlic bulbs. The level of soil organic matter content increased in the last year (2015). Soil catalase activity was generally induced by the treatments of 10, 15, 20 and 25 garlic bulbs, and soil invertase activity was also enhanced by all the treatments in the last year. Similarly, fungal species richness dramatically increased under these crop rotation systems. In this study, we found the highest cucumber yield under the cropping treatment of 20 garlic bulbs. CONCLUSION: The results indicate that the green garlic/cucumber cropping system is a sustainable and efficient cropping system for cucumber production and can improve the soil environment to a certain extent. © 2019 Society of Chemical Industry.

Impact of dichlorprop on soil microbial community structure and diversity during its enantioselective biodegradation in agricultural soils.

Enantioselective biodegradation of racemic dichlorprop in two soils was investigated in the laboratory. Chiral separation of racemic dichlorprop was achieved by using HPLC with Phenomenex Lux Amylose-2. The first-order kinetic model fitted well the dissipation data of racemic dichlorprop and its pure R- and S-enantiomers. S-dichlorprop was preferentially degraded in both soils and enantioselectivity was affected by soil pH. The half-lives (DT50) of S-dichlorprop were 8.22 days in soil A and 8.06 days in soil D, while R-dichlorprop was more persistent with DT50 of 12.93 days in soil A and 12.38 days in soil D, respectively. Dichlorprop dissipated faster in soil D with lower organic matter content. In sterilized soils, neglected dissipation was observed and enantiomer fraction values remained constant, indicating that the enantioselective degradation was mainly controlled by soil microorganisms. Soil microbial community structure and diversity was assessed by Illumina MiSeq sequencing of 16S rRNA genes from dichlorprop and no dichlorprop contaminated microcosms. Compared with controls, dichlorprop application had no significant effect on microbial community structures at phylum level, but increased bacterial diversity and dichlorprop degradation related taxa in both soils. S-dichlorprop preferential degradation might be attributed to the S-enantiomer preferred degraders in the family of Sphingomonadaceae.

Effects of Elevated Ozone Concentrations on Root Characteristics and Soil Properties of Elaeocarpus sylvestris and Michelia chapensis.

The increasing concentration of surface ozone (O3) was observed during recent decades in the world, which affects tree roots and forest soils. Meanwhile, the impact of ozone on tree roots is greatly affected by soil condition. However, there is a lack of knowledge about the possible effects of ozone on tree roots and soil processes. In this study, The influences of surface ozone (O3) stress on the root biomass, morphology, nutrients, soil properties, and soil enzyme activity of Elaeocarpus sylvestris and Michelia chapensis seedlings were examined at four O3 concentrations (charcoal-filtered air, 1 × O3 air, 2 × O3 air, and 4 × O3 air). Elevated O3 concentrations were found to significantly increase the root C content, N content, C/P ratio, and N/P ratio, and significantly decrease the root biomass, number of root tips, and root C/N ratio of both species. The soil organic matter content, pH, total N content, and urease and catalase activities of both species tended to increase. The limitation in root growth and responses in the root structure of E. sylvestris induced by elevated O3 concentrations led to increased bulk density and decreased soil porosity and void ratio. These profound effects of O3 concentrations on the roots and soil characteristics of these two species underscore the importance of research in O3 science.

Identification of potential electrotrophic microbial community in paddy soils by enrichment of microbial electrolysis cell biocathodes.

Electrotrophs are microbes that can receive electrons directly from cathode in a microbial electrolysis cell (MEC). They not only participate in organic biosynthesis, but also be crucial in cathode-based bioremediation. However, little is known about the electrotrophic community in paddy soils. Here, the putative electrotrophs were enriched by cathodes of MECs constructed from five paddy soils with various properties using bicarbonate as an electron acceptor, and identified by 16S rRNA-gene based Illumina sequencing. The electrons were gradually consumed on the cathodes, and 25%-45% of which were recovered to reduce bicarbonate to acetic acid during MEC operation. Firmicutes was the dominant bacterial phylum on the cathodes, and Bacillus genus within this phylum was greatly enriched and was the most abundant population among the detected putative electrotrophs for almost all soils. Furthermore, several other members of Firmicutes and Proteobacteria may also participate in electrotrophic process in different soils. Soil pH, amorphous iron and electrical conductivity significantly influenced the putative electrotrophic bacterial community, which explained about 33.5% of the community structural variation. This study provides a basis for understanding the microbial diversity of putative electrotrophs in paddy soils, and highlights the importance of soil properties in shaping the community of putative electrotrophs.