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ispartof: GEODERMA vol:431 status: published

Excess heavy metals, especially copper (Cu) and cadmium (Cd), are common in paddy soils in the red soil hilly areas of southern China. Microorganisms are regulators of soil organic matter accumulation and pollutant transformation. Clarifying the effects of Cu and Cd accumulation on microbial community composition and function is a prerequisite for bioremediation of paddy soil contamination. However, it remains unclear how Cu and Cd contamination affects soil fungal taxonomic attributes and microbial-mediated biogeochemical processes in paddy soils. Here, soil heavy metals, fungal community composition, and soil enzyme activities were determined in paddy fields downstream of a typical mining area in southern China, and the effects of Cu and Cd co-contamination on fungal community diversity and co-occurrence networks, as well as the associations between them were assessed. The concentrations of Cu and Cd in paddy soils decreased from upstream to downstream of the river, and were positively correlated with the Shannon index of fungal communities. Soil Cu and Cd concentrations exhibited a greater impact on the structure and assembly of fungal communities than soil general properties. Increases in soil Cu and Cd concentrations were correlated with drastic changes in the cumulative relative abundance of ecological clusters in fungal co-occurrence networks. Soil Cu and Cd concentrations were positively correlated with the relative abundances of Eurotiomycetes, Pezizomycetes, Ustilaginomycetes, and Kickxellomycetes, respectively, whereas negatively correlated with hydrolase activities related to carbon, nitrogen, and phosphorus cycles. These results confirmed in the field that long-term Cu and Cd enrichment significantly altered the structure and diversity of fungal communities in the subtropical paddy soils, thereby affecting soil nutrient transformation and organic matter accumulation. This can also provide a basis for the bioremediation of heavy metal pollution in paddy soils.

Plant nitrogen (N)-acquisition strategy affects soil N availability, community structure, and vegetation productivity. Cultivated grasslands are widely established to improve degraded pastu...

Background Although soil erosion plays a key role in the carbon cycle, a holistic and mechanistic understanding of the soil erosion process within the cycle is still lacking. The aim of this study was therefore to improve our mechanistic understanding of soil organic carbon (SOC) and soil respiration dynamics through an experiment conducted in an eroding black soil farmland landscape in Northeast China. Results The depositional profiles store 5.9 times more SOC than the eroding profiles and 3.3 times more SOC than the non-eroding profiles. A linear correlation between the SOC and 137Cs (Caesium-137) was observed in our study, suggesting that the SOC decreased with increased soil erosion. Furthermore, the fractions of intermediate C and the microaggregate C were lowest at the eroding position and highest at the depositional position. In the depositional topsoil, the input of labile materials plays a promotional role in soil respiration. Conversely, in the subsoil (i.e., below 10 cm), the potential mineralization rates were lowest at the depositional position—due to effective stabilization by physical protection within soil microaggregates. The field results of soil surface respiration also suggest that the depositional topsoil SOC is prone to be mineralized and that SOC at this depositional context is stabilized at subsoil depth. In addition, the high water contents at the depositional position can limit the decomposition rates and stabilize the SOC at the same time. Conclusions The findings from this study support that a majority of the SOC at footslope is stored within most of the soil profile (i.e., below 10 cm) and submitted to long-term stabilization, and meanwhile support that the depositional profile emits more CO2 than the summit due to its high amount and quality of SOC.

Fertilization is a worldwide practice to maintain and increase crop productivity and improve soil quality in agricultural ecosystems. The interactive mechanisms of long-term fertilization affecting the functional soil organic matter (SOM) fractions, microbial community, and enzyme activities are unclear. We investigated the effects of manure and mineral fertilization on six SOM fractions (non-protected, physically, chemically, biochemically, physical-chemically, and physical-biochemically protected), microbial community structure, and enzyme activities based on a 35-year fertilization experiment. The combined application of manure and mineral fertilizers (NPKM) increased the soil organic carbon (SOC) and total nitrogen (TN) in the biochemically (28.6–43.9%) and physically (108–229%) protected fractions, compared to their content in the unfertilized soil (CK). The total phospholipid fatty acid content, Gram(−) bacteria, and actinomycetes, as well as the activities of α-1,4-glucosidase, β-1,4-N-acetylglucosaminidase, β-1,4-xylosidase, and cellobiohydrolase were highest under NPKM fertilization. The protected SOM fractions (physical, biochemical, physical-chemical, and physical-biochemical) were closely related to microbial community composition (accounting for 67.6% of the variance). Bacteria were sensitive to changes in the physically and biochemically protected fractions, whereas fungi responded more to the changes in the chemically protected fraction. In summary, long-term mineral and organic fertilization has a strong effect on microbial communities and activities through the changes in the functional SOM fractions.

Approximately 50–70% of C stored in soil is derived from the roots or root-associated microorganisms, reflecting their importance for soil organic matter (SOM) formation. Microorganisms are the major driver for SOM decomposition and their activities are modified by the input of labile organics such as root exudates and low molecular weight organic substances derived from litter decomposition. Such short-term changes in the turnover of SOM caused by moderate organic additions into the soil were defined as priming effects (PE). Priming effects can influence global carbon (C) storage in soil and lead to climate feedbacks by accelerating the decomposition of organic matter (OM). In natural ecosystems, input of nitrate (NO3−) and ammonium (NH4+) into the soil can be derived from nitrogen (N) deposition and biological N fixation. Although availability N can alter the magnitude and direction of priming, it remains unclear whether additions of NO3− and NH4+ have distinct effects on the decomposition of OM. Thus, the aims of this study were to investigate the responses of OM decomposition along a decay continuum (i.e. decreasing decomposition degree) to labile C and N inputs and determine the PE induced by the two N forms. Leaf litter, wood litter, organic soil horizon, and mineral soil, with a broad range of C:N ratios were collected along a decay continuum in a typical subtropical forest and incubated for 38 days with 13C labeled glucose and N (NO3−) additions. Based on the very broad range of C:N ratios in OM in soil and inputs of labile C and N, we demonstrated the OM decomposition within a decay continuum as well as PE intensities and the thresholds for the switch of PE directions. In contrast to NH4+ additions, NO3− generally accelerated the decomposition of all OM. Priming of plant litter was dependent on the C:N ratios of the labile inputs. However, leaf litter decomposition was more controlled by N addition than wood litter. Glucose addition greatly increased the priming of OM decomposition, demonstrating energy limitation for microorganisms. Distinct priming patterns were observed between NO3− and NH4+ additions, both for the individual OM types and for all four types of OM. The PE induced by labile C and N inputs can increase or reduce C sequestration depending on C:N stoichiometric ratios of labile inputs. Net C losses caused by PE can be observed in organic soil and plant litter with low C and N additions, but all four OM substrates increased C sequestration under high C addition. Minor differences in priming along the continuum were observed where the OM C:N ratio was below 30 when NO3− was added and where the labile C:N ratio was less than 55 when NH4+ was added. Thus, changes in the composition of deposited N (atmospheric deposition and fertilization) may induce distinct climate feedbacks. Under future climatic conditions by global warming and elevated CO2, more labile C inputs via root exudates could accelerate litter decomposition. Effects of N however, depend on the N form: NH4+ to NO3− due to the energy necessary for microorganisms for NO3- reduction.

Soil microbial communities support a great belowground biodiversity, but our knowledge regarding their spatial patterns and underlying driving mechanisms in small scale is very limited, especially for forest ecosystems. The spatial distributions of microbial community and enzyme activities depending on soil environmental factors were studied using geostatistical tools. 55 soil samples were collected across a 30 m × 40 m plot in a broad-leaved Korean pine mixed forest in the Changbai Mountains. Abundances of total and bacterial PLFAs had stronger spatial dependence than fungal PLFAs. Gram-positive bacteria had stronger spatial dependence than Gram-negative bacteria, suggesting that Gram-negative bacteria are more susceptible to stochastic factors. The proportions of structural variance for the activities of β-1,4-glucosidase (βG), β-1,4-N-acetylglucosaminidase (NAG) and acid phosphatase (AP) were 0.997, 0.519 and 0.966, respectively, suggesting that βG and AP had high spatial dependence. Cross-variogram analysis showed that root biomass played a critical role in structuring the spatial distributions of total and bacterial PLFAs. Fungi had close spatial connection with total nitrogen (TN), particulate organic carbon and root biomass within the ranges of 8.2–13 m. The βG, NAG and AP activities were closely spatially connected to the soil organic carbon and TN and were all spatially correlated with fungal abundance. Overall, microbial community and enzyme activities were patchily distributed at small spatial scales. Close spatial connections between microbial communities, enzyme activities, and root biomass and soil variables help to understand the main drivers of belowground soil biodiversity in the forest.

Steroid estrogens, such as 17β-estradiol (E2), in animal manure pose a potential threat to the aquatic environment. The transport and estrogenicity of estrogens influence the sorption of estrogens to dissolved organic matter (DOM) in animal manure, and composting treatment alters the structure and composition of the manure. The objectives of the present study were to identify the contribution of the molecular composition of DOM of composted manure to the sorption of E2 and then elucidate the dominant mechanisms involved in the interaction of E2 with manure-derived DOM. The excitation–emission matrix (EEM) spectra and atomic force microscopy (AFM) showed that composting significantly altered the chemical composition and structure of DOM. A decrease in the atomic ratios of oxygen (O)/carbon (C) occurred in conjunction with the formation of DOM aggregates in the composted manure, indicating that the hydrophilicity and polarity of the DOM decreased after composting. Composting increased the sorption coefficients (KDOC-E2) for E2 to DOM, and KDOC-E2 was positively correlated with the proportion of the fulvic acid (FA)-like fraction and molecular weight (MW) fractions of the DOM (range of 1.0 × 103–7.0 × 103 Da and 7.0 × 103–1.4 × 104 Da). Specifically, E2 showed a tendency for sorption to medium-sized FA-like molecules of DOM aggregates in composted manure. Hydrophobic forces and π-π binding appeared to be the main mechanisms underlying the aforementioned interaction.

Soil N2O responds differently to various soil variables; moreover these driving variables usually have low explanatory capacity of soil N2O flux variability. Anthropogenic nitrogen (N) deposition inputs to the subtropical plantation forests markedly increase N2O emission from soils, but the relative contribution of deposited NH4+ and NO3− is not well understood. Based on a two-type (NH4Cl and NaNO3) and three-level (0, 40, 120 kg N ha−1 yr−1) N addition experiment, we simultaneously determined soil N2O flux and related soil variables once a week in 2015. Boundary line analysis was used to describe the maximum responses of soil N2O fluxes to different soil variables. Four years of N addition led to significant accumulations of soil NH4+-N and NO3−-N, thereby accelerating soil acidification. Nitrogen addition significantly increased soil N2O fluxes by 4.7–19.3 folds relative to control; moreover, the promotions to soil N2O emission and soil acidification were greater with ammonium-N addition than with nitrate-N addition. The relationships between the maximum soil N2O fluxes and individual soil variables were well fitted to the Gaussian equations, and the optimum values of soil temperature, moisture, pH, and NO3−-N content indicate that nitrification dominated soil N2O production. Overall, our results suggest that exogenous NH4+ input to the subtropical plantation appears to have greater negative effects on soil acidification and N2O emission compared with NO3− input. Boundary line analysis well depicts the shape and magnitude of response functions of soil N2O fluxes against soil variables, which should be incorporated into terrestrial ecosystem process models.

Responses of soil organic carbon (SOC) cycling and C budget in forest ecosystems to elevated nitrogen (N) deposition are divergent. Little is known about the N critical loads for the shift between gain and loss of SOC storage in the old-growth temperate forest of Northeast China. The objective of this study was to investigate the nonlinear responses of SOC concentration and composition to multiple rates of N addition, as well as the microbial mechanisms responsible for SOC alteration under N enrichment. Nine rates of urea addition (0, 10, 20, 40, 60, 80, 100, 120, 140 kg N ha−1 year−1) with 4 replicates for each treatment were conducted. Soil samples in the 0–10 cm mineral layer were taken after 3 years of N fertilization. Soil aggregate size distribution and SOC physical fractionation were performed to examine SOC dynamics. Phospholipid fatty acid (PLFA) technique was used to measure the abundance and structure of microbial community. Three years of N addition led to significant increases in the concentrations of soil particulate organic C and aggregate-associated organic C fractions only. The responses of total N and each labile SOC fraction to the rates of N addition followed Gaussian equations, with the N critical loads being estimated to be between 80 and 100 kg N ha−1 year−1. The change in SOC concentration (ΔSOC) was positively correlated with the changes in aggregate associated OC (r2 > 0.80) and POC concentrations (r2 > 0.50). Significant correlations among the concentrations of labile SOC fractions, the percentages of soil aggregates, and the abundances of microbial PLFAs were observed, which implies a close linkage between microbial community structure and SOC accumulation and stability. Our results suggest that increase in soil moisture and shift of microbial community structure could control the critical N load for the switch between C accumulation and loss. The current N deposition rate (~ 11 kg N ha−1 year−1) to the northeast China’s forests is favorable for soil C accumulation over the short term.

The responses of soil-atmosphere carbon (C) exchange fluxes to growing atmospheric nitrogen (N) deposition are controversial, leading to large uncertainty in the estimated C sink of global forest ecosystems experiencing substantial N inputs. However, it is challenging to quantify critical load of N input for the alteration of the soil C fluxes, and what factors controlled the changes in soil CO 2 and CH 4 fluxes under N enrichment. Nine levels of urea addition experiment (0, 10, 20, 40, 60, 80, 100, 120, 140 kg N ha −1 yr −1 ) were conducted in the needle-broadleaved mixed forest in Changbai Mountain, Northeast China. Soil CO 2 and CH 4 fluxes were monitored weekly using the static chamber and gas chromatograph technique. Environmental variables (soil temperature and moisture in the 0–10 cm depth) and dissolved N (NH 4 + -N, NO 3 − -N, total dissolved N (TDN), and dissolved organic N (DON)) in the organic layer and the 0–10 cm mineral soil layer were simultaneously measured. High rates of N addition (≥60 kg N ha −1 yr −1 ) significantly increased soil NO 3 − -N contents in the organic layer and the mineral layer by 120%-180% and 56.4%-84.6%, respectively. However, N application did not lead to a significant accumulation of soil NH 4 + -N contents in the two soil layers except for a few treatments. N addition at a low rate of 10 kg N ha −1 yr −1 significantly stimulated, whereas high rate of N addition (140 kg N ha −1 yr −1 ) significantly inhibited soil CO 2 emission and CH 4 uptake. Significant negative relationships were observed between changes in soil CO 2 emission and CH 4 uptake and changes in soil NO 3 − -N and moisture contents under N enrichment. These results suggest that soil nitrification and NO 3 − -N accumulation could be important regulators of soil CO 2 emission and CH 4 uptake in the temperate needle-broadleaved mixed forest. The nonlinear responses to exogenous N inputs and the critical level of N in terms of soil C fluxes should be considered in the ecological process models and ecosystem management.

Elevated nitrogen (N) deposition variously affects the soil carbon (C) cycle. It is not clear how deposited NH 4 + and NO 3 − divergently affect the amount and stability of soil organic C (SOC) in the N-limiting forests. A multi-form N addition experiment was conducted in a boreal forest in the Great Khingan mountain in 2010. Three fertilizers, NH 4 Cl, KNO 3 and NH 4 NO 3 , were applied at four rates of 0, 10, 20, and 40 kg N ha − 1 yr − 1 . Solid-state 13 C nuclear magnetic resonance spectroscopy and elemental analysis were used to determine the chemical structure and C contents in bulk soils and/or two density fractions ( − 3 light fraction and > 1.70 g cm − 3 heavy fraction). NH 4 Cl addition significantly decreased the SOC contents in the organic layer by 28.35% to 54.23%, but KNO 3 addition significantly increased the SOC contents in the organic layer and mineral layer by 26.53% and 87.44%, respectively. Nitrogen addition rates significantly influenced the degradability (alkyl-C/O-alkyl-C) and hydrophobicity ((alkyl C + aromatic C)/(O-alkyl C + carboxyl C)) of light and heavy fractions, whereas N addition forms only impacted their aromaticity (aromatic C/(aromatic C + alkyl C + O-alkyl C)). The movement between residue-C and stable humin fraction, as well as the chemical stability of SOM could profoundly affect the storage of SOC under N enrichment. Overall, added NH 4 + and NO 3 − differently affect C sequestration in the N-limiting forest soils. This should be differentiated in the biogeochemical models of C N cycle coupling.

The effects of organic and mineral fertilization on four soil organic matter (SOM) fractions (non-protected, physically protected, chemically protected, and biochemically protected) and microbial community composition were investigated by sampling soil of a 35-year-long fertilization experiment. The SOM fractions were investigated by combined physical and chemical approaches, while microbial community composition was determined by phospholipid fatty acid analysis (PLFA). Organic C (SOC) was primarily distributed within the microaggregate-protected particulate organic matter (iPOM) and the hydrolysable and non-hydrolysable silt-sized (H-Silt, NH-Silt) fractions, which accounted for 11.6–16.9, 23.4–28.9, and 25.4–30.6% of the total SOC content, respectively. The contributions of these “slow” fractions (iPOM, H-Silt, NH-Silt) to the increased SOC were 178–293, 118–209, and 85–109% higher after long-term sole manure or manure in combination with inorganic N fertilization compared with unfertilized soil (control). The combination of manure and mineral fertilizers increased the coarse and fine non-protected C (cPOM and fPOM) contents much more (34.1–60.7%) than did manure alone. PLFAs, bacteria, G (+) bacteria, and actinomycete abundances were the highest in soil with manure, followed by soil treated with manure combined with mineral N. The addition of inorganic and organic fertilization both altered the microbial community composition compared with the control. All SOM fractions contributed to 81.1% of the variance of the PLFAs-related microbial community composition by direct and indirect effects. The change in coarse unprotected particulate organic matter (cPOM) was the major factor affecting soil microbial community composition (p

The responses of nitrous oxide (N2O) emission from forest soils to increasing atmospheric nitrogen (N) deposition are controversial. In this study, our objectives were to explore the response curves of soil N2O flux to multi-level N inputs, as well as to examine the key factors dominating the changes in soil N2O emission caused by N enrichment in the temperate needle-broadleaved mixed forest, Northeast China. The study consists of nine levels of urea addition (0, 10, 20, 40, 60, 80, 100, 120, 140 kg N ha− 1 yr− 1) with 4 replicates for each treatment. Soil N2O fluxes were monitored weekly using the static chamber and gas chromatograph technique. NH4+-N, NO3−-N, total dissolved N (TDN), dissolved organic N (DON), and auxiliary variables (soil temperate and moisture in 0–10 cm depth) were measured at the same frequency to examine the regulation of soil N2O flux. The results showed that high rates of urea inputs (> 60 kg N ha− 1 yr− 1) significantly increased soil NO3−-N concentrations in litter layer and mineral layer (0–10 cm depth) by 120–180% and 56.4–84.6%, respectively. Soil N2O flux increased exponentially with increase in the rates of urea addition by 194% to 334% for the 60 to 140 kg N ha− 1 yr− 1 treatments relative to the control. The critical level of N input for the significant alternation of soil N accumulation and N2O emission was approximately 70 kg N ha− 1 yr− 1. The changes in soil N2O flux elicited by N addition were positively related to those of soil NO3−-N and soil moisture contents. These results suggest that exogenous N input at the rate below the critical load will not significantly promote soil N2O emission over the short term, which is favorable to carbon sequestration of the temperate needle-broadleaved mixed forest, Northeast China.

Key Findings: Combining physical fractionation and pyrolysis&ndash, gas chromatography/mass spectrometry (py-GC/MS) technique can help better understand the dynamics of soil organic matter (SOM). Background and Objectives: SOM plays a critical role in the global carbon (C) cycle. However, its complexity remains a challenge in characterizing chemical molecular composition within SOM and under nitrogen (N) deposition. Materials and Methods: Three particulate organic matter (POM) fractions within SOM and under N treatments were studied from perspectives of distributions, C contents and chemical signatures in a subtropical forest. N addition experiment was conducted with two inorganic N forms (NH4Cl and NaNO3) applied at three rates of 0, 40, 120 kg N ha&minus, 1 yr&minus, 1. Three particle-size fractions (&gt, 250 &mu, m, 53&ndash, m and &lt, 53 &mu, m) were separated by a wet-sieving method. Py-GC/MS technique was used to differentiate between chemical composition. Results: A progressive proportion transfer of mineral-associated organic matter (MAOM) to fine POM under N treatment was found. Only C content in fine POM was sensitive to N addition. Principal component analyses (PCA) showed that the coarse POM had the largest plant-derived markers (lignins, phenols, long-chain n-alkanes, and n-alkenes). Short-chain n-alkanes and n-alkenes, benzofurans, aromatics and polycyclic aromatic hydrocarbons mainly from black carbon prevailed in the fine POM. N compounds and polysaccharides from microbial products dominated in the MAOM. Factor analysis revealed that the degradation extent of three fractions was largely distinct. The difference in chemical structure among three particulate fractions within SOM was larger than treatments between control and N addition. In terms of N treatment impact, the MAOM fraction had fewer benzofurans compounds and was enriched in polysaccharides, indicating comparatively weaker mineralization and stronger stabilization of these substances. Conclusions: Our findings highlight the importance of chemical structure in SOM pools and help to understand the influence of N deposition on SOM transformation.

Nitrogen (N) status has a great impact on methane (CH4) consumption by soils. Modeling studies predicting soil CH4 consumption assume a linear relationship between CH4 uptake and N addition rate. Here, we present evidence that a nonlinear relationship may better characterize changes in soil CH4 uptake with increasing N additions. By conducting a field experiment with eight N-input levels in a Tibetan alpine steppe, we observed a unimodal relationship; CH4 uptake increased at low to medium N levels but declined at high N levels. Environmental and microbial properties jointly determined this response pattern. The generality of the unimodal trend was further validated by two independent analyses: (i) we examined soil CH4 uptake across at least five N-input levels in upland ecosystems across China. A unimodal CH4 uptake-N addition rate relationship was observed in 3 out of 4 cases; and (ii) we performed a meta-analysis to explore the N-induced changes in soil CH4 uptake with increasing N additions across global upland ecosystems. Results showed that the changes in CH4 uptake exhibited a quadratic correlation with N addition rate. Overall, we suggest that the unimodal relationship should be considered in biogeochemistry models for accurately predicting soil CH4 consumption under global N enrichment.

External inorganic and organic nitrogen (N) inputs can contrastingly affect the transformation and availability of N in forest soils. Studies have mainly focused on the effects of inorganic N enrichment, whereas little is known about the effects of organic N input on soil gross N transformation and the underlying microbial mechanisms. Here we conducted a laboratory 15N tracing study in a temperate needle-broadleaved mixed forest with a fertilization rate of 0, 20, 60, and 120 kg urea-N ha−1 yr−1 over three years. We investigated the key drivers of soil N transformation processes using a 15N tracing model in the context of selected soil chemical properties and microbial characteristics. Urea addition did not change soil gross N mineralization rates, while stimulating mineralization of labile organic N (MNlab). Urea addition at a rate of 120 kg N ha−1 yr−1 significantly increased autotrophic nitrification and gross nitrification rates by 88% and 96%, respectively. In contrast, all the three levels of urea addition significantly reduced gross microbial N immobilization by 28% to 52%, leading to an increase in the accumulation of soil NO3−-N in the top 10 cm soil layer by 38% to 88%. The changes in autotrophic nitrification were primarily driven by acid-tolerant ammonia-oxidizing archaea (AOA). Fungi were responsible for the change in heterotrophic nitrification under organic N enrichment. Gross N transformation rates were predominately regulated by AOA and fungal abundances as well as soil NO3−-N content under high level of organic N addition. The response of soil N transformation to exogenous organic N input depended on N addition level with the threshold rate being estimated to be 60–120 kg N ha−1 yr−1. All lines of evidence showed that the temperate needle-broadleaved mixed forest is moving towards an opener microbial N cycle under elevated organic N deposition. Our finding suggests that the effect of organic N input on soil gross N transformation is different from that of inorganic N input, which should be considered in ecosystem process models.

Soil samples from 0 to 100 cm depth were collected in eight sampling sites (Sites A1, B1, C1 and D1; Sites A2, B2, C2 and D2) respectively along two 250-m length of sampling zones (Zone N and Zone S) from the Yellow River channel to a tidal creek in the short-term flooding and seasonal flooding wetland of the Yellow River Delta of China in fall of 2007 and spring of 2008 to investigate spatial and seasonal distribution patterns of total sulfur (TS) and their influencing factors. Our results showed that TS contents in both seasons in surface soil in Zone N increased with increasing distances away from the Yellow River channel except for Site D1 in fall. However, TS contents in both seasons in surface soil in Zone S showed a tendency of increasing and then decreasing with increasing distances away from the Yellow River channel. Relative to spring, the mean TS contents in surface soils were slightly higher in fall in Zone N, whereas an opposite tendency was observed in Zone S. The mean TS stocks were obviously higher in fall with 934.36 g/m(2) and 877.77 g/m(2) compared to those in spring with 729.85 g/m(2) and 696.78 g/m(2) in Zone Nand Zone S, respectively. TS contents and stock generally declined with depth along soil profiles with one accumulation peaks at a soil increment of 40-60 cm. Topsoil concentration factors also indicated that TS had shallower distribution in soil profiles. Soil total carbon (TC), total nitrogen (TN), soil organic matter( SOM), salinity and silt exerted positive loadings on TS, while soil pH and depth exhibited a negative correlation with TS content. (C) 2015 Elsevier B.V. All rights reserved.

A BODIPY-based 1 as a colorimetric fluorescence sensor was synthesized, and its metal sensing property was investigated. 1 displayed high selectivity and sensitivity towards Hg2 + and Cu2 + ions among 15 different metal cations. The addition of Hg2 + and Cu2 + ions into 1 in CH3CN resulted in a significant bathochromic shift of the UV absorption spectra from 533 nm to 560 nm and 593 nm, respectively, changing the corresponding colors from pink to purple and blue. When excited at 530 nm, the fluorescence intensity of 1 was quenched over 75% upon addition of Hg2 + ions, while 1 with Cu2 + ions exhibited significant fluorescence enhancement with a 23 nm red-shift. Based on these results, three logic gates (OR, IMPLICATION, and INHIBIT) were obtained by controlling the chemical inputs.

Ammonia-oxidizers play an essential role in nitrogen (N) transformation and nitrous oxide (N2O) emission in forest soils. It remains unclear if ammonia-oxidizers affect interaction between methane (CH4) uptake and N2O emission. Our specific goal was to test the impacts of changes in ammonia-oxidizing communities elicited by N enrichment on soil CH4 uptake and N2O emission. Based on a field experiment, two-forms (NH4Cl and NaNO3) and two levels (40 and 120 kg N ha−1 yr−1) of N were applied in the subtropical plantation forest of southern China. Soil CH4 and N2O fluxes, the abundance and structure of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) communities were measured using static chamber-gas chromatography, quantitative PCR (qPCR), and terminal-restriction fragment length polymorphism (T-RFLP). Nitrogen addition tended to inhibit soil CH4 uptake, but significantly promoted soil N2O emission; moreover, these impacts were more significant with NH 4 + − N than with NO 3 − − N addition. NH4Cl addition significantly changed ammonia-oxidizer abundance with an increase in AOA and a decrease in AOB. Nitrogen additions significantly decreased the relative abundance of 329 bp and 421 bp of archaeal amoA gene. Negative relationships occurred between soil CH4 uptake and AOA abundance and between soil CH4 uptake and AOA/AOB ratio; however, a positive relationship was found between soil N2O emission and AOA abundance. These results indicate that a shift in abundance and composition of ammonia-oxidizing communities is closely linked to changes in soil CH4 uptake and N2O emission under N enrichment. Furthermore, AOA communities play a contrasting role from AOB communities for regulating the fluctuation between soil CH4 and N2O fluxes.