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Carbon dioxide (CO2) emissions from forest ecosystems originate largely from soil respiration, and microbial heterotrophic respiration plays a critical role in determining organic carbon (C) stock. This study investigated the impacts of successive nitrogen (N) and phosphorus (P) fertilization after 9 years on soil organic C stock; CO2 emission; and microbial biomass, community, and function in a Chinese fir plantation. The annual fertilization rates were (1) CK, control without N or P fertilization; (2) N50, 50 kg N ha-1; (3) N100, 100 kg N ha-1; (4) P50, 50 kg P ha-1; (5) N50P50, 50 kg N ha-1 + 50 kg P ha-1; and (6) N100P50, 100 kg N ha-1 + 50 kg P ha-1. The N100P50 treatment had the highest cumulative soil CO2 emissions, but the CK treatment had the lowest cumulative soil CO2 emissions among all treatments. The declines of soil organic C (SOC) after successive 9-year fertilization were in the order of 100 kg N ha-1 year-1 > 50 kg N ha-1 year-1 > CK. Compared to the CK treatment, successive N fertilization significantly changed soil microbial communities at different application rates and increased the relative gene abundances of glycoside hydrolases, glycosyl transferases, carbohydrate-binding modules, and polysaccharide lyases at 100 kg N ha-1 year-1. Relative to P fertilization alone (50 kg P ha-1 year-1), combined N and P fertilization significantly altered the soil microbial community structure and favored more active soil microbial metabolism. Microbial community and metabolism changes caused by N fertilization could have enhanced CO2 emission from heterotrophic respiration and eventually led to the decrease in organic C stock in the forest plantation soil. KEY POINTS: • N fertilization, alone or with P, favored more active microbial metabolism genes. • 100 kg N ha-1 fertilization significantly changed microbial community and function. • N fertilization led to a "domino effect" on the decrease of soil C stock.

Carbendazim is a highly effective benzimidazole fungicide and is widely used throughout the world. The effects of carbendazim contamination on the biology and environment should be paid more attention. We reviewed the published papers to evaluate the biological and environmental risks of carbendazim residues. The carbendazim has been frequently detected in the soil, water, air, and food samples and disrupted the soil and water ecosystem balances and functions. The carbendazim could induce embryonic, reproductive, developmental and hematological toxicities to different model animals. The carbendazim contamination can be remediated by photodegradation and chemical and microbial degradation. The carbendazim could enter into human body through food, drinking water and skin contact. Most of the existing studies were completed in the laboratory, and further studies should be conducted to reveal the effects of successive carbendazim applications in the field.

Successive mineral fertilization might have side effects on soil environmental quality, such as aggregate structure, contamination, and enzyme activity. To gain a more comprehensive understanding of the influences of mineral fertilization on biotic and abiotic properties of forest soils, we investigated the effects of successive nitrogen and phosphorus fertilization on physical structures, contaminant contents, and microbial communities of forest soils with different sampling depths. Mineral nitrogen (N) and phosphorus (P) were applied, alone or together, at different rates to provide nutrients to economic tree species (Chinese fir) in a forest plantation since 2011. Surface soil samples were taken at different sampling depths, and soil aggregate, contaminant content, and microbial properties were determined and comprehensively linked. Our results showed that successive fertilization, sampling depths, and their interactions had negligible impacts on soil aggregate ratios and cadmium (Cd) and arsenic (As) contents. Contrastingly, soil β-glucosidase, phosphate, and fungal and actinomycetal biomass were significantly affected by the mineral fertilization, and sampling depth was a key factor determining the responses of microbial communities to the mineral fertilization. In the surface (0–20 cm) soils, abiotic properties had resistance to different fertilization and sampling depths, but biotic properties were markedly or significantly affected by the mineral fertilization or sampling depths. Simultaneously, sampling depths should be considered to reveal the impacts of managements on microbial properties in the surface forest soils.

Repeated and high-dose carbendazim applications have caused serious soil carbendazim contamination, and eco-friendly and economical approaches have been suggested to promote carbendazim removal in agricultural soil. Spent mushroom substrate (SMS) is a special recycled resource after harvesting mushrooms and can be utilized in contaminated soil amendment. The SMS application into agricultural soil might increase antibiotic resistance gene abundances, and the health risks of SMS application might be reduced with reasonable management to adjust the related electron transport of soil nitrification or denitrification. In this study, the SMS and nitrification inhibitor dicyandiamide were used to remediate agricultural soil contaminated with the carbendazim, and the carbendazim contents, soil microbial biomass, activities and community and human disease genes were determined. Compared to the control treatment, the combined applications of SMS and dicyandiamide significantly decreased soil carbendazim content by 38.14% but significantly enhanced soil β-glucosidase, chitinase, arylsulfatase, urease and electron transfer system activities. The relative abundances of Proteobacteria and Actinobacteria were increased by 11.0% and 8.2% with the SMS application, respectively. The carbendazim residues were negatively correlated with the soil pH, electron transfer system activities and relative abundances of Proteobacteria and Actinobacteria. The relative abundances of human disease genes were also dramatically increased with the SMS application, but compared to the SMS alone, extra dicyandiamide application significantly reduced the relative abundances of human disease genes in soils. The SMS applications into fungicide-contaminated soils could generate double-edged sword effects of facilitating fungicide dissipation but leading to potential health risk increase, while applying the dicyandiamide with SMS might be an effective strategy to decrease the negative effect of health risk.

There are growing trends of combined contaminations in agricultural soils, and therefore it is urgently needed to remediate contaminated soils with eco-friendly approaches. This study aimed to evaluate the effects of Medicago sativa L. (alfalfa) planting, alone or together with biochar additions, on contaminant removals and bacterial properties in an agricultural soil contaminated by heavy metal and organic fungicide. The treatments in this study included: the control (CK), alfalfa planting (AP), alfalfa planting +1.5% biochar addition (w/w) (AP + 1.5B), alfalfa planting +3.0% biochar addition (AP + 3.0B), and alfalfa planting +6.0% biochar addition (AP + 6.0B). Relative to the alfalfa planting only, extra biochar additions increased alfalfa biomass and heavy metal cadmium (Cd) phytoextraction. The alfalfa planting, alone or together with biochar additions, significantly decreased soil iprodione concentrations. After 90 days of remediation, bacterial 16S rRNA gene abundances of the AP, AP + 1.5B, AP + 3.0B and AP + 6.0B treatments were 1.69, 3.84, 3.34 and 3.13 times as great as that obtained from the CK treatment, respectively. The AP + 1.5B treatment had the highest richness estimators and Shannon diversity index, but the AP + 6.0B treatment had the lowest invsimpson diversity index among the five treatments. The relative abundances of Bacteroidetes and Nitrospirae were enhanced by the alfalfa phytoremediation, alone or together with biochar additions. Our results suggest that the alfalfa has promising potentials in the remediation of co-contaminated soil and in the increases of soil bacterial biomass and community diversity. Simultaneously, biochar is beneficial to enhance Cd phytoextraction, however, biochar addition rate would need to be optimized.

Rhizosphere and fertilization might affect soil microbial activities, biomass, and community. This study aimed to evaluate the impacts of Phyllostachys edulis (moso bamboo) rhizospheres on soil nutrient contents and microbial properties in a moso bamboo forest with different fertilizer applications and to link soil microbial activities with abiotic and biotic factors. The experiment included three treatments: (1) application of 45% slag fertilizer (45%-SF); (2) application of special compound fertilizer for bamboos (SCF); and (3) the control without any fertilizer application (CK). Simultaneously, bulk soils and 0.5, 2.5, 4.5, and 6.5-year-old (y) bamboo rhizosphere soils were selected. Soil nutrient contents were analyzed. Microbial activities were evaluated based on the activities of soil enzymes including β-glucosidase, urease, protease, phosphatase, and catalase. The total microbial biomass and community were assessed with the phospholipid fatty acids (PLFAs) method. In the CK and SCF treatments, organic matter contents of rhizosphere soils were significantly higher than those of bulk soils. Soil β-glucosidase, urease, protease, phosphatase, and catalase activities in rhizosphere soils were higher than those of bulk soils, with the sole exception of β-glucosidase of 0.5 y rhizosphere soil in the 45%-SF treatment. Compared with the CK treatment, fertilizer applications tended to increase soil total PLFAs contents and changed soil microbial community. Moso bamboo rhizospheres did not significantly increase the total microbial biomass. In the SCF treatment, the Shannon index of bulk soil was significantly lower than those of rhizosphere soils. Our results suggested that both rhizospheres and fertilizer applications could change the soil microbial community structures and that moso bamboo rhizosphere could increase microbial activity rather than biomass in the forest soils with different fertilizer applications.

Background: Phyllostachys edulis (moso bamboo) is a key source of non-wood forest products. Clarifying the linkage among bamboo growth, soil nutrient and core microbe can expand the horizon on nutrient management practices and functional endophytic and rhizospheric microbes.Results: In this study, young (0.5-yr), mature (2.5-yr and 4.5-yr) and old (6.5-yr) bamboo plants were selected in a moso bamboo field, and above-ground tissues, below-ground roots (rhizomes) and rhizospheric soils were sampled. The bamboo biomass, soil properties and endophytic microbes were determined and quantify their comprehensive relationships. Bamboo ages had negligible impacts on the bamboo height, diameter at breast height and above-ground biomass. Organic matter and nitrogen (N) contents in the rhizospheric soil of the 0.5-yr bamboo were significantly higher than those of the other three age groups. The rhizospheric soil of the 6.5-yr bamboo had the lowest N mineralization rate and urease activity. Significant differences in bacterial and fungal communities were found in the above-ground tissues but not in the rhizospheric soils associated with plants of different ages. Bacterial and fungal community structures in the above-ground tissues were significantly different from their counterparts in the rhizospheric soils. Conclusions: Bamboo ages significantly affected N transformation rates, functional gene abundances and urease activities of rhizospheric soils and endophytic bacterial community structures. However, niche differentiations outweighed ages in shaping the whole microbial communities of bamboo aboveground tissues, roots and rhizospheric soils. In the future, moso bamboo management should consider balanced applications of ammonium-N and other nutrients and utilisations of Chytridiomycota to stimulate moso bamboo growth.

Bacteria play determining roles in forest soil environment and contribute to essential functions in the cycling of nitrogen (N) and phosphorus (P). Understanding the effects of different fertilizer applications, especially successive fertilization, on soil properties and bacterial community could reveal the impacts of fertilization on forest soil ecology and shed light on the nutrient cycling in forest system. This study aimed to evaluate the impacts of successive mineral N (NH4NO3) and P (NaH2PO4) fertilization at different rates, alone or together, on soil bacterial biomass and communities at 0–5, 5–10, and 10–20 cm. Compared with the control, N fertilization decreased soil pH, but P alone or with N fertilization had negligibly negative impacts on soil pH. Different mineral fertilizer applications, alone or together, showed no significant effects on soil organic matter contents, relative to the control treatment. Bacterial biomass remained stable to different fertilizations but decreased with sampling depths. Sole N or P fertilization, rather than combined fertilizations, significantly changed soil bacterial community structures. Our results demonstrated that mineral N or P fertilization alone significantly affected bacterial community structures rather than biomass in the plantation soils. • Impacts of successive mineral fertilization on soil bacteria were determined. • Mineral fertilization showed negligible impacts on bacterial biomass. • N additions stimulated Chloroflexi relative abundances. • Mineral N or P fertilization significantly altered bacterial community structure.

As an anthropogenic disturbance, prescribed burning may alter the biogeochemistries of nutrients, including nitrogen (N) cycling, in forest ecosystems. This study aimed to examine the changes in N mineralization, nitrification and denitrification rates following prescribed burning in a suburban forest located in subtropical Australia and assess the interactive relationships among soil properties, functional gene abundances and N transformation rates. After a prescribed burning event, soil pH value increased, but soil labile carbon and mineral N contents decreased. Net N mineralization rates, potential nitrification rates and ammonium-oxidizing archaea and bacteria (AOA and AOB) amoA gene abundances in the soils all increased after 3 months of the prescribed burning. However, the abundances of different functional genes related to denitrification changed differently after the prescribed burning. The net N mineralization rates could be best described by soil abiotic properties, rather than functional gene abundances. In contrast, potential denitrification rates were positively related to soil nirK gene abundances. Potential nitrification rates could be influenced by both soil chemical and microbial properties. The results revealed that the prescribed burning might increase N mineralization and nitrification rates in the forest soil.

Silicon (Si) offers beneficial effect on plants under cadmium (Cd) stress such as promoting plant growth and increasing resistance to heavy metal toxicity. In this study, a pot experiment was performed to study the role of Si in alleviating Cd toxicity in tobacco (Nicotiana tabacum L.) plants on a yellow soil taken from Guiyang, China. Nine treatments consisting of three concentrations of Cd (0, 1, and 5 mg kg−1) together with three Si levels (0, 1, and 4 g kg−1) were established. Plant growth parameters, Cd concentration, and the malondialdehyde (MDA), chlorophyll, and carotenoid contents were determined 100 d after transplanting of tobacco seedlings. Application of exogenous Si enhanced the growth of tobacco plants under Cd stress. When 5 mg kg−1 Cd was added, Si addition at 1 and 4 g kg−1 increased root, stem, and leaf biomass by 26.1%–43.3%, 33.7%–43.8%, and 50.8%–69.9%, respectively, compared to Si addition at 0 g kg−1. With Si application, the transfer factor of Cd in tobacco from root to shoot under both 1 and 5 mg kg−1 Cd treatments decreased by 21%. The MDA contents in the Si-treated tobacco plants declined by 5.5%–17.1% compared to those in the non-Si-treated plants, indicating a higher Cd tolerance. Silicon application also increased the chlorophyll and carotenoid contents by 33.9%–41% and 25.8%–47.3% compared to the Cd only treatments. Therefore, it could be concluded that Si application can alleviate Cd toxicity to tobacco by decreasing Cd partitioning in the shoots and MDA levels and by increasing chlorophyll and carotenoid contents, thereby contributing to lowering the potential health risks of Cd contamination.

Phytoremediation with biochar addition might alleviate pollutant toxicity to soil microorganism. It is uncertain to what extent biochar addition rate could affect activities of enzymes related to soil nitrogen (N) mineralization and alter fungal community under the phytoremediation. This study aimed to reveal the effects of Medicago sativa L. (alfalfa) phytoremediation, alone or with biochar additions, on soil protease and chitinase and fungal community and link the responses of microbial parameters with biochar addition rates. The alfalfa phytoremediation enhanced soil protease activities, and relative to the phytoremediation alone, biochar additions had inconsistent impacts on the corresponding functional gene abundances. Compared with the blank control, alfalfa phytoremediation, alone or with biochar additions, increased fungal biomass and community richness estimators. Moreover, relative to the phytoremediation alone, the relative abundances of phylum Zygomycota were also increased by biochar additions. The whole soil fungal community was not significantly changed by the alfalfa phytoremediation alone, but was indeed changed by alfalfa phytoremediation with 3.0% (w/w) or 6.0% biochar addition. This study suggested that alfalfa phytoremediation could enhance N mineralization enzyme activities and that biochar addition rates affected the responses of fungal community to the alfalfa phytoremediation.

Harvest residues contain large stores of carbon (C) and nitrogen (N) in forest plantations. Decomposing residues can release labile C and N into soil and thus provide substrates for soil bacterial communities. Previous studies showed that residue retention could increase soil C and N pools and activate bacterial communities in the short term (≤ 10 years). The current study examined the effects of a long-term (19-year) harvest residue retention on soil total and water and hot water extractable C and N pools, as well as bacterial communities via Illumina MiSeq sequencing. The experiment was established in a randomised complete block design with four replications, southeast Queensland of Australia, including no (R0), single (R1, 51 to 74 t ha−1 dry matter) and double quantities (R2, 140 t ha−1 dry matter) of residues retained. Generally, no significant differences existed in total C and N, as well as C and N pools extracted by water and hot water among the three treatments, probably due to negligible amounts of labile C and N released from harvest residues. Soil δ15N significantly decreased from R0 to R1 to R2, probably due to reduced N leaching with residue retention (P

This study evaluated the effects of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) and fungicide iprodione on net nitrification rates and abundances of functional genes related to nitrification and denitrification in an agricultural soil. Single DMPP application or repeated iprodione applications decreased net nitrification rates in the test soil. However, when the DMPP and iprodione were applied together, they could generate antagonistic effects on the inhibitions of net nitrification rates. Repeated iprodione applications reduced ammonia-oxidizing archaea and bacteria (AOA and AOB) amoA gene abundances, while DMPP application decreased AOB amoA gene abundances only. The abundances of narG and nirK genes were negatively affected by repeated iprodione applications. Our results demonstrated that combined applications of DMPP and iprodione could generate antagonistic effects on the inhibitions of net nitrification rates and discrepant impacts on the abundances of functional genes related to soil denitrification.

Agrochemical applications may have unintended detrimental effects on soil microorganisms and soil health. However, limited studies have been conducted to evaluate the effects of repeated fungicide applications and interactive effects of different agrochemical applications on soil microorganisms. In this study, an incubation experiment was established to evaluate the potential influences of the fungicide iprodione and the nitrification inhibitor 3, 4-dimethylpyrazole phosphate (DMPP) on soil enzyme activities and bacterial properties. Weekly iprodione applications decreased the activities of all enzymes tested, and DMPP application inhibited soil urease activity. Compared with the blank control, bacterial 16S rRNA gene abundance decreased following repeated iprodione applications, but increased after DMPP application. After 28 days of incubation, the treatment receiving both iprodione and DMPP application had higher bacterial 16S rRNA gene abundance and Shannon diversity index than the treatment with iprodione applications alone. Repeated iprodione applications significantly increased the relative abundance of Proteobacteria, but decreased the relative abundances of Chloroflexi and Acidobacteria. Simultaneously, bacterial community structure was changed by repeated iprodione applications, alone or together with DMPP. These results showed that repeated iprodione applications exerted negative effects on soil enzyme activities, bacterial biomass and community diversity. Moreover, relative to iprodione applications alone, additional DMPP application could alleviate the toxic effects of iprodione applications on bacterial biomass and community diversity.

Camellia (Camellia oleifera Abel.) plantation often needs fertilizer application to ensure fruit yield, and camellia fruit yield might be affected by soil phosphorus supply and microbial community and function. However, a large fraction of applied phosphorus is lost through leaching and runoff, which may cause eutrophication risks in waterbodies. Intensive management of phosphorus fertilization based on the comprehensive balance among fruit yield, soil nutrient and microbial property is required to quantify appropriate phosphorus fertilization rate. In this study, a camellia plantation located in southern China was selected, and four different fertilization treatments were established: control without P fertilizer (P0); 114.5 kg phosphorus pentoxide ha−1 applied as sodium dihydrogen phosphate (P1); 229.0 kg phosphorus pentoxide ha−1 (P2) and 343.5 kg phosphorus pentoxide ha−1 (P3). The fruit yields of P1, P2 and P3 treatments were approximately 1.5, 2.0 and 2.0 times of that measured from the P0 treatment, respectively. Bacterial community richness estimators and diversity indices in the P2 treatment were significantly higher than those in the P3 treatment. Relative abundances of Bacteroidetes, Planctomycetes, Verrucomicrobia and Eremiobacterota were significantly affected by the phosphorus fertilization. The gram-negative bacterial relative abundance was significantly lower in the P3 treatment than in the other treatments. Relative to the P2 treatment, the P3 treatment had significant decreases in soil pH, bacterial community diversity and gram-negative bacterial relative abundance, which might offset the stimulation of higher phosphorus supply for fruit yield. Based on the comprehensive balance among fruit yield, fertilization input cost, soil environment impact and microbial property, 229.0 kg phosphorus pentoxide ha-1 fertilization is appropriate for this camellia plantation. Future phosphorus fertilization in the camellia plantation should consider the comprehensive balance among yields, soils and microbial properties.

Nitrogen (N) limitation is one of the major constrain factors for biochar in improving plant growth, the same for elevated atmospheric carbon dioxide (CO 2 ). Hence, we hypothesized that (1) biochar would induce the same plant responses as elevated CO 2 under N-poor conditions; (2) elevated CO 2 would decrease the potential of biochar application in improving plant growth. To test these hypotheses, we assessed the effects of pinewood biochar, produced at three pyrolytic temperatures (650, 750 and 850 °C), on C and N allocation at the whole-plant level of three plant species (Austrostipa ramossissima, Dichelachne micrantha and Isolepis nodosa) grown in the N poor mine spoil under both ambient (400 μL L −1 ) and elevated (700 μL L −1 ) CO 2 concentrations. Our data showed that biochar addition (1) significantly decreased leaf total N and δ 15 N (P < 0.05); (2) decreased leaf total N and δ 15 N more pronouncedly than those of root; and (3) showed more pronounced effects on improving plant biomass under ambient CO 2 than under elevated CO 2 concentration. Hence, it remained a strong possibility that biochar addition induced the same plant physiological responses as elevated CO 2 in the N-deficient mine spoil. As expected, elevated CO 2 decreased the ability of biochar addition in improving plant growth. Refereed/Peer-reviewed

This study aimed to assess the effects of biochar on improving nitrogen (N) pools in mine spoil and examine the effects of elevated CO2 on soil carbon (C) storage. The experiment consisted of three plant species (Austrostipa ramossissima, Dichelachne micrantha, and Lomandra longifolia) planted in the N-poor mine spoil with application of biochar produced at three temperatures (650, 750, and 850 °C) under both ambient (400 μL L−1) and elevated (700 μL L−1) CO2. We assessed mine spoil total C and N concentrations and stable C and N isotope compositions (δ13C and δ15N), as well as hot water extractable organic C (HWEOC) and total N (HWETN) concentrations. Soil total N significantly increased following biochar application across all species. Elevated CO2 induced soil C loss for A. ramossissima and D. micrantha without biochar application and D. micrantha with the application of biochar produced at 750 °C. In contrast, elevated CO2 exhibited no significant effect on soil total C for A. littoralis, D. micrantha, or L. longifolia under any other biochar treatments. Biochar application is a promising means to improve N retention and thus, reduce environmentally harmful N fluxes in mine spoil. However, elevated CO2 exhibited no significant effects on increasing soil total C, which indicated that mine spoil has limited potential to store rising atmospheric CO2.

Nitrification inhibitors that impact soil nitrifying microorganisms have been widely applied in agricultural soils to enhance the efficiency of nitrogen fertilizers. However, little is known about their combined impact with other chemical applications, such as fungicides, on soil fungi. This study specifically examined the effects of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP), alone or together with the fungicide iprodione, on fungi biomass and community in a typical farmland soil. Four treatments were set: (1) control of zero agrochemical applications (CK), (2) a single DMPP application (DAA), (3) repeated iprodione applications (4×IPR), and (4) combined applications of DMPP and iprodione (DAA+4×IPR). The agrochemicals were applied at the recommended intervals, and the soil samples were incubated in the dark for 28 days. During the incubation, soil sample DNA was extracted, and the effects of DMPP and iprodione applications on soil fungal internal transcribed spacer (ITS) abundances were determined with quantitative PCR (qPCR). At the end of the incubation, Illumina MiSeq method was employed to assess soil fungal community diversity and structure. DMPP application had a negligible effect on fungal ITS abundance. However, repeated iprodione applications significantly decreased fungal ITS abundances. After 28 days of incubation, the fungal ITS abundances in the 4×IPR and DAA+4×IPR treatments were 43.6 and 56.2% of that measured from the CK treatment, respectively. Shannon indices of fungal communities demonstrated the treatment-induced gradients, with the DAA+4×IPR treatment harboring the highest Shannon index. Fungal community structures following the DAA and 4×IPR treatments remained overlapping with that in the CK treatment, but repeated iprodione applications markedly enriched the family Teratosphaeriaceae. Relative to the CK treatment, fungal community structure in the DAA+4×IPR treatment was significantly changed, with the families Cephalothecaceae, Hypocreaceae, and Cordycipitaceae harboring a linear discriminant analysis value >3. DMPP application had negligible effects on soil fungal biomass, community diversity, and structure, potentially indicating that the DMPP is “bio-safe.” Conversely, repeated iprodione applications significantly decreased fungal ITS abundances. Moreover, the family Teratosphaeriaceae could be further investigated as a potential biomarker of the impacts of iprodione on soil fungi. The combined applications of DMPP and iprodione stimulated the Shannon diversity index and markedly changed soil fungal community structure.

The riparian zone is a spatially fluctuating ecotone between terrestrial and aquatic ecosystems and has key ecological functions, due to specific geographic conditions and seasonal environmental changes. The comprehensive functions of vegetation cover and microbial community in riparian zones might generate positive consequences for nutrient cycling. In this study, four different vegetation-covered soils in a riparian zone on the Yangtze River was selected. Soil nutrient concentration and microbial properties, including nitrogen (N) and phosphorus (P) cycling and microbial community structure, were analyzed, and the relationships among soil nutrient concentrations, microbial properties and vegetation covers were also linked. Vegetation covers increased soil NH4+-N supply by enhancing N mineralization and positively affected available N retention through inhibition of soil nitrification. Plant species outweighed plant biomass in determining soil microbial properties related to P mineralization, including phosphatase activities and functional gene abundances. Vegetation covers significantly increased Acidobacteria and Mortierellomycota relative abundances. Soil bacterial and fungal communities had opposing responses to the impacts of plant species richness and biomass. In the riparian zone, plant species outweighed plant biomass in promoting soil N and P mineralization, and vegetation covers, regardless of plant species, improved available nutrient supplies and retentions and shaped soil microbial community.

Knowledge of the impacts of prescribed burning on ecosystem functions could help to improve forest management practices. However, relative to forest safety and aesthetic values, changes in soil properties and processes after prescribed burning are not well understood. This study aimed to quantify changes in soil microbial communities and greenhouse gas emissions following prescribed burning in a subtropical suburban forest. The soil microbial communities were determined with the Illumina sequencing methods. Carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) emissions were quantified under three different soil water contents, and net greenhouse gas emissions were derived from emissions of the three gases after 7 days of incubation and expressed in CO2-equivalent. Prescribed burning had negligible impacts on soil bacterial and fungal community diversities but significantly changed soil microbial community structures. Compared to the unburnt soil, the relative abundances of Chloroflexi increased by 86% and 119% one month and three months after the prescribed burning, respectively. However, the relative abundances of Mortierellomycota decreased by 94% one month after prescribed burning. At different soil water contents, The CO2 and N2O emissions during a 7-day laboratory incubation did not differ consistently or significantly between the soils collected before/after the prescribed burning. Simultaneously, there were no significant changes in net greenhouse gas emissions from soil in association with the prescribed burning. The results revealed that relative to the unburned soils, prescribed burning caused minor alterations in net soil greenhouse gas fluxes, despite short-term evident changes in soil microbial community structures.

Plastic film mulching has played an important role in Chinese agriculture, especially in vegetable production, but large amounts of film residues can accumulate in the soil. The present study investigated the effects of plastic film residues on the occurrence of soil PAEs and microbial activities using a batch pot experiment. PAE concentrations increased with increasing plastic film residues but the soil microbial carbon and nitrogen, enzyme activities and microbial diversity decreased significantly. At the end of the experiment the PAE concentrations were 0-2.02 mg kg(-1) in the different treatments. Soil microbial C and N, enzyme activities, AWCD value, and Shannon-Weaver and Simpson indices declined by about 28.9-76.2%, 14.9-59.0%, 4.9-22.7%, 23.0-42.0% and 1.8-18.7%, respectively. Soil microbial activity was positively correlated with soil PAE concentration, and soil PAE concentrations were impacted by plastic color and residue volume. Correlations among, and molecular mechanisms of, plastic film residues, PAE occurrence and microbial activity require further study.

Chlorothalonil (CTN) has received much attention due to its broad-spectrum antifungal function and repeated applications in agriculture production practice. An incubation experiment was conducted to study the accumulating effects of CTN repeated application on soil microbial activities, biomass, and community and to contrast the discrepancy of effects in contrasting soils. Different dosage CTN (5 mg kg−1, T1, and 25 mg kg−1, T5) was applied into two contrasting soils at 7-day intervals. Soil samples were taken 7 days after each application to assess soil enzyme activities and gene abundances. At the end of incubation, the soil samples were also taken to analyze microbial communities in the two test soils. Soil fluorescein diacetate hydrolysis (FDAH) and urease activities were inhibited by CTN repeated applications. After 28 days of incubation, bacterial 16S rRNA gene abundances in T1 and T5 treatments were significantly lower than those in the CK treatments (46.4 and 36.6 % of the CK treatment in acidic red soil, 53.6 and 37.9 % of the CK treatment in paddy soil). Archaeal 16S rRNA gene abundances of T1 and T5 treatments were observed the similar trends (56.1 and 40.8 % of the CK treatment in acidic red soil, 45.6 and 43.7 % of the CK treatment in paddy soil). Repeated applications at 25 mg kg−1 exerted significantly negative effects on the Shannon-Weaver, Simpson and McIntosh indices. Microbial activity, biomass, and functional diversity were significantly inhibited by repeated CTN application at the higher dosage (25 mg kg−1), but the inhibitory effects by the application at the recommended dosage (5 mg kg−1) were erratic. More emphasis needs to be placed on the soil type and cumulative toxicity from repeated CTN application when assessing environmental risk.

The widespread and increasing application of chlorothalonil (CTN) raises concerns about its non-target impacts, but little information is available on the effect of CTN on the key functional genes related to soil nitrogen (N) cycling, especially in the case of repeated applications. In the present study, a microcosm incubation was conducted to determine CTN residues and the impacts on the abundances of key functional genes related to N cycling after repeated CTN applications. The results demonstrated that repeated CTN applications at the recommended application rate and five times the recommended rate led to the accumulation of CTN residue in soil at concentrations of 5.59 and 78.79 mg kg − 1 , respectively, by the end of incubation. Real time PCR (RT-PCR) revealed that repeated CTN applications had negative effects on the chi A and apr A gene abundances. There were significantly negative correlations between CTN residues and abundances of AOA and AOB genes. In addition, the abundances of key functional genes involved in soil denitrification were declined by repeated CTN applications with the sole exception of the nos Z gene. This study suggests that repeated CTN applications could lead to the accumulation of CTN residue and generate somewhat inconsistent and erratic effects on the abundances of key functional genes related to soil N cycling.

Forest ecosystems greatly affect the global carbon (C) budget. Because subtropical regions typically have wet and dry seasons that are likely to differ in their effects on soil respiration, our estimates of carbon dioxide (CO2) emissions from subtropical soil would be improved by consideration of both wet and dry seasons rather than wet seasons alone. In this 10-year study, we determined soil respiration rates (SRRs) and soil properties in a typical subtropical forest in southern China, and we quantified the relationships between SRRs and soil abiotic and biotic properties during the dry and wet seasons. During the 10 years, soil organic carbon contents, microbial biomass, and fine root biomass were generally higher in the wet season than in the dry season. Microbial biomass C and fine root biomass were positively associated with precipitation in dry seasons but negatively associated with precipitation in wet seasons. The SRRs of wet season were consistently and significantly higher than the counterparts of dry season, with the average SRR being 5.94 ± 0.32 μmol CO2 m−2 s−1 in the wet season and 1.56 ± 0.41 μmol CO2 m−2 s−1 in the dry season. In the wet and dry seasons, cumulative CO2 emissions were positively correlated with microbial biomass C and fine root biomass, but the abiotic and biotic factors explaining variation in SRR differed in the wet and dry seasons. Most of the variation in SRRs was explained by fine roots in the wet season but by fine roots, microorganisms, and soil pH in the dry season. The results revealed that the precipitation generated significantly positive effects on the cumulative CO2 emissions in the dry seasons and that the fine root was the crucial factor contributing to the SRRs in wet and dry seasons.

Sunflower broomrape (Orobanche cumana Wallr.) is a weedy root parasite that causes huge damage to sunflower (Helianthus annuus L.). Trap crop can stimulate parasitic seed germination without attachment in trap crop, and it was considered as economic methods for controlling the parasite. In this study, co-culture and pot experiments were conducted to assess the allelopathic activity of maize (Zea mays L.) to stimulate broomrape seeds germination and to evaluate the performance of maize rotation for reducing sunflower broomrape infection. All the tested maize cultivars could induce sunflower broomrape germination, and the most active maize cultivar was N314, which induced approximately 40% broomrape seeds germination. Rotation of maize significantly reduced broomrape infection on subsequent sunflower and increased sunflower biomass. After cultivated N314 for 3 years, broomrape attachment on sunflower was the lowest (0.8 attachment plant&minus, 1), and the dry mass of sunflower shoot (28.7 g plant&minus, 1) was approximately twice higher than the sunflower without previous crop. The effectiveness of broomrape management was significantly different among various maize cultivars. Meanwhile, the differences among cultivars were decreased with the years of maize cultivated prolonged. Our results confirmed that maize was significantly effective in reducing the sunflower damage caused by sunflower broomrape and suggested that maize rotation could be included in the integrated management of sunflower broomrape.

A bacterial strain ZY1 capable of utilizing PCBs as its carbon source was isolated from the root nodules of Chinese milk vetch (Astragalus sinicus L.). The strain was identified as Mesorhizobium sp. according to its physiological-biochemical properties and the analysis of its 16S rRNA gene sequence. When the initial OD600 was 0.15, 62.7% of 15 mg L(-1) 3,3',4,4'-TCB in a liquid culture was degraded by Mesorhizobium sp. ZY1 within 10 days. Mesorhizobium sp. ZY1 also greatly increased the biotransformation of soil PCBs. Pot experiments indicated that the soil PCB concentrations of a single incubation of strain ZY1 (R) and a single planting of A. sinicus (P) decreased by 20.5% and 23.0%, respectively, and the concentration of PCBs in soil treated with A. sinicus and strain ZY1 decreased by 53.1%. We also observed that A. sinicus-Mesorhizobium sp. ZY1 treatment (PR) improved plant biomass and the concentration of PCBs in plants compared with a single A. sinicus planting treatment (P). The results suggest that the synergistic association between A. sinicus and PCBs-degrading Mesorhizobium sp. ZY1 can stimulate the phytoextraction of PCBs and the rhizosphere microflora to degrade PCBs, and might be a promising bioremediation strategy for PCB-contaminated soil.

Di-(2-ethylhexyl) phthalate (DEHP) is a high-molecular-weight phthalate ester (PAE) that has been widely used in the manufacture of polyvinylchloride and contributes to environmental pollution. The objectives of the present study were to isolate a DEHP degrader that can utilize DEHP as a carbon source and to investigate its capacity to biodegrade DEHP in both liquid culture and soil. A bacterial strain WJ4 was isolated from an intensively managed vegetable soil, which was contaminated with PAEs. The strain WJ4 was affiliated to the genus Rhodococcus and was able to remove DEHP from soil effectively. A period of only 7 d was required to degrade about 96.4% of DEHP (200 mg L −1 ) in the liquid culture, and more than 55% of DEHP (1.0 g kg −1 ) in the artificially contaminated soil was removed within 21 d. Furthermore, Rhodococcus sp. strain WJ4 had a strong ability to degrade DEHP without additional nutrients in liquid minimal medium culture and DEHP-contaminated soil and to degrade the homologue of DEHP in both liquid culture and soil. Strain WJ4 represents a novel tool for removing PAEs from contaminated soils and it may have great potential for application in the remediation of environmental pollution by PAEs.

A chlorothalonil (CTN)-degrading bacterial strain H4 was isolated in this study from a contaminated soil by continuous enrichment culture to identify its characteristics and to investigate its potential for remediation of CTN in contaminated soil. Based on the morphological, physiological and biochemical tests and 16S rDNA sequence analysis, the strain was identified as Stenotrophomonas sp. After liquid culture for 7 d, 82.2% of CTN was removed by strain H4. The isolate could degrade CTN over a broad range of temperatures and pH values, and the optimum conditions for H4 degradation were pH 7.0 and 30 °C. Reintroduction of the bacteria into artificially contaminated soil resulted in substantial removal of CTN (> 50%) after incubation for 14 d. Soil samples treated by H4 showed significant increases (P < 0.05) in soil dehydrogenase activity, soil polyphenol oxidase activity, average well-color development obtained by the Biolog Eco plateTM assay and Shannon-Weaver index, compared with the control. Strain H4 might be a promising candidate for application in the bioremediation of CTN-contaminated soils.

Nitrogen (N) limitation is one of the major constrain factors for biochar in improving plant growth, the same for elevated atmospheric carbon dioxide (CO

Apart from the contaminant removal, the remediation of agricultural soil should also pay more attention to soil nutrient retention and biogeochemical cycling. This study aimed to evaluate changes of soil properties, potential nitrification rates (PNRs), and functional gene abundances and link their relationships after remediating co-contaminated agricultural soil with Medicago sativa L. (alfalfa) planting, alone or together with biochar application. Compared with the control (CK), alfalfa planting, alone or together with biochar application, could significantly increase soil organic matter (SOM) contents and discrepantly affect soil pH values. The PNRs of the amended treatments were significantly higher than that of the CK. Moreover, alfalfa plantings also enhanced the abundances of functional genes related to soil nitrification and denitrification, with the sole exception of nosZ gene. Stepwise regression analysis revealed that the PNRs were best described by the gene abundance ratios of AOB amoA/nifH and nirS gene abundances. Compared with the CK, alfalfa planting, alone or with biochar application, could restore nitrogen cycling in the co-contaminated agricultural soil and enhance the PNRs via decreasing contaminant bio-availabilities and increasing SOM contents and gene abundance ratios of AOB amoA/nifH.

Purpose: Re-establishment of soil nitrogen (N) capital is a priority in mine rehabilitation. We aimed to evaluate the effects of biochar addition on improving mine spoil N pools and the influence of elevated CO 2 concentration on mine rehabilitation. Materials and methods: We assessed the effects of pinewood biochar, produced at three temperatures (650, 750 and 850 °C, referred as B 650 , B 750 and B 850, respectively), on mine spoil total N concentrations with five different plant species, including a tree species (Eucalyptus crebra), N-fixing shrubs (Acacia floribunda and Allocasuarina littoralis) and C 3 and C 4 grasses (Austrodanthonia tenuior and Themeda australis) incubated at ambient (400 μL L −1 ) and elevated (700 μL L −1 ) atmospheric CO 2 concentrations, as well as the effects of elevated CO 2 on mine rehabilitation. Results and discussion: Soil total N significantly improved following biochar incorporation under all plant species (P < 0.05) except for T. Australis. E. crebra had the highest soil total N (0.197%, 0.198% and 0.212% for B 650 , B 750 and B 850 , respectively). Different from the negligible influence of elevated CO 2 on soil properties under the grasses and the N-fixing shrubs, elevated CO 2 significantly increased soil water and hot water extractable organic C (WEOC and HWEOC, respectively) and decreased total C under E. crebra, indicating that the nutrient demands were not met. Conclusions: Biochar addition showed the potential in mine rehabilitation in terms of improving soil N pool, especially with E. crebra. However, it would be more difficulty to rehabilitate mine spoils in future with the rising atmospheric CO 2 concentration. Refereed/Peer-reviewed

Understanding the relationships among bamboo growth, soil microbial community and phosphorus (P) fertilization may shed new light on the optimization of P application rate and ecological function of P nutrient in forest ecosystem. This study aimed to evaluate the impacts of P fertilizations (25 and 50 kg P ha−1) on Phyllostachys edulis (Moso bamboo) growths, soil nutrient contents and microbial properties at different altitudes (300 and 800 m) and to link Moso bamboo growths with abiotic and biotic factors. Compared with the blank control, P fertilizations alone generated negligible impacts on the increases of Moso bamboo biomass and soil available P contents. Bacterial and fungal community diversities kept relatively stable after P fertilizations. Contrastingly, relative to the control, 25 kg P ha−1 application significantly enhanced the relative abundance of Proteobacteria and changed bacterial community structure at low altitude. At low and high altitudes, 50 kg P ha−1 applications significantly increased the relative abundances of Ascomycota. The Moso bamboo growth might be stimulated by the increases of soil total nitrogen, available P, Proteobacteria and Ascomycota. Our results demonstrated that P fertilization alone significantly changed soil bacterial community structure but generated negligibly stimulating role in the increase of Moso bamboo biomass.

Agrochemical applications may have side effects on soil biochemical properties related to soil nitrogen (N) mineralization and thus affect N cycling. The present study aimed to evaluate the effects of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) and fungicide iprodione on soil neutral protease (NPR), alkaline protease (APR), chitinase (CHI), and their functional genes (nprA, aprA, and chiA) related to soil N mineralization. The following four treatments were included: blank control (CK), single DMPP application (DAA), weekly iprodione applications (IPR), and the combined applications of DMPP and iprodione (DI). Compared with the CK treatment, DMPP application significantly inhibited the CHI activity in the first 14 days of incubation, and iprodione applications, particularly when applied alone, decreased the NPR, APR, and CHI activities. Relative to the IPR treatment, extra DMPP application had the potential to alleviate the inhibitory effects of iprodione on the activities of these enzymes. DMPP application significantly increased aprA gene abundances after 14 days of incubation. However, repeated iprodione applications, alone or with the DMPP, decreased nprA and chiA gene abundances. Relative to the CK treatment, DMPP application generated negligible effects on the positive/negative correlations between soil enzyme activities and the corresponding functional gene abundances. However, the positive correlation between the CHI activity and chiA gene abundance was changed to negative correlation by repeated iprodione applications, alone or together with the DMPP. Our results demonstrated that agrochemical applications, particularly repeated fungicide applications, can have inadvertent effects on enzyme activities and functional gene abundances associated with soil N mineralization.

Broad-spectrum fungicide chlorothalonil (CTN) is successively applied into intensive agriculture soil. However, the impacts of successive CTN applications on soil nitrification and related microorganisms remain poorly understood. A microcosm study was conducted to reveal the effects of successive CTN applications on soil nitrification and functional genes involved in soil nitrogen (N) cycling. The CTN at the dosages of 5 mg kg−1 dry soil (RD) and 25 mg kg−1 dry soil (5RD) was successively applied into the test soil at 7-day intervals which resulted in the accumulations of CTN residues. After 28 days of incubation, CTN residues in the RD and 5RD treatments were 3.14 and 69.7 mg kg−1 dry soil respectively. Net nitrification rates in the RD and 5RD treatments were lower than that obtained from the blank control (CK). Real-time PCR analysis revealed that AOA and AOB amoA gene abundances were significantly decreased by CTN applications. Moreover, CTN applications also discrepantly decreased the abundances of functional genes involved in soil denitrification, with the exception of nosZ gene. Principal component analysis further supported the observation that successive CTN applications could result in enhanced ecological toxicity.

Phthalate esters (PAEs) are suspected of having adverse effects on human health and have been frequently detected in soils and vegetables. The present study investigated their occurrence and composition in plastic film greenhouse soil-vegetable systems and assessed their potential health risks to farmers exposed to these widespread pollutants. Six priority control phthalates, namely dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DnBP), butyl benzyl phthalate (BBP), di-(2-ethylhexyl) phthalate (DEHP) and di-n-octyl phthalate (DnOP), were determined in 44 plastic film greenhouse vegetables and corresponding soils. Total PAEs ranged from 0.51 to 7.16mgkg(-1) in vegetables and 0.40 to 6.20mgkg(-1) in soils with average concentrations of 2.56 and 2.23mgkg(-1), respectively. DnBP, DEHP and DnOP contributed more than 90% of the total PAEs in both vegetables and soils but the proportions of DnBP and DnOP in vegetables were significantly (p0.05) higher than in soils. The average concentrations of PAEs in pot herb mustard, celery and lettuce were3.00mgkg(-1) but were2.50mgkg(-1) in the corresponding soils. Stem and leaf vegetables accumulated more PAEs. There were no clear relationships between vegetable and soil PAEs. Risk assessment indicates that DnBP, DEHP and DnOP exhibited elevated non-cancer risk with values of 0.039, 0.338 and 0.038, respectively. The carcinogenic risk of DEHP was about 3.94×10(-5) to farmers working in plastic film greenhouses. Health risks were mainly by exposure through vegetable consumption and soil ingestion.