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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.

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.

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 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

Carbon dioxide (CO2) enrichment and increased nitrogen (N) deposition can change microbial activity and dissolved organic carbon (DOC) turnover, consequently affecting carbon sequestration in soils. However, we do not have much available information on the relationship between soil DOC and microbial activity under CO2 enrichment and N addition in semi-arid agroecosystems. Using free air CO2 enrichment (FACE), soybean and winter wheat were grown in the field under ambient CO2 (350 μmol mol−1) and elevated CO2 (550 μmol mol−1) conditions subjected to two N fertilizer regimes (132 and 306 kg N ha−1 year−1). Rhizosphere soils and bulk soils at three depths, 0–10, 10–20 and 20–40 cm, were collected to determine water extractable organic matter (WEOM) characteristics with fluorescence spectroscopy and parallel factor analyses of excitation/emission matrix, as well as five extracellular enzymes activities. All significant effects were observed in the topsoil (0–10 cm): elevated CO2 decreased water extractable organic carbon concentration of the rhizosphere soils and bulk soils by 8.5 and 10.1 %, respectively. Furthermore, elevated CO2 changed the composition and structure of soil WEOM by increasing the plant- and microbial-derived components in the rhizosphere and solubilizing soil organic matter (SOM). The activities of β-1,4-glucosidase, cellobiohydrolase, phenol oxidase, and peroxidase were stimulated by elevated CO2 in the rhizosphere soils and bulk soils. Our findings suggest that the stimulation of microbial activity elicited by elevated CO2 increased the turnover of labile WEOM and the solubilization of SOM in the topsoils, which could be adverse to the accumulation and stability of soil carbon in the semi-arid agroecosystems in northern China.

The natural abundance of nitrogen (N) stable isotopes (δ15N) has the potential to enhance our understanding of the ecosystem N cycle at large spatial scales. However, vegetation and soil δ15N patterns along climatic and edaphic gradients have not yet been fully understood, particularly for high-altitude ecosystems. Here we determined vegetation and soil δ15N in alpine grasslands on the Tibetan Plateau by conducting four consecutive regional surveys during 2001–2004, and then examined their relationships with both climatic and edaphic variables. Our results showed that both vegetation and soil N in Tibetan alpine grasslands were more 15N-enriched than global averages. Vegetation δ15N did not exhibit any significant trend along the temperature gradient, but decreased significantly with an increase in precipitation amount. In contrast, soil δ15N did not vary with either mean annual temperature or precipitation. Our results also indicated that soil δ15N exhibited a slight increase with clay content, but decreased with soil carbon:nitrogen ratio. A general linear model analysis revealed that variations in vegetation δ15N were dominantly determined by climatic variables, whereas soil δ15N was related to edaphic variables. These results provide clues for potential climatic and edaphic regulations on ecosystem N cycle in these high-altitude regions.

A novel circuit technique for enhancing the phase-margin of the recycling folded cascode amplifier is presented. Compared to the conventional recycling folded cascade, using a high-speed current mirror, the proposed amplifier offers the advantage of cancellation of the first non-dominant pole, allowing the phase-margin to be enhanced without affecting the bandwidth. The proposed amplifier was implemented in CSMC standard 0.18 μm CMOS process. Simulation results show that the phase-margin enhancement of 20° is achieved without limiting the bandwidth.

This letter is to present a transconductance enhanced recycling structure for folded cascode amplifier. The proposed structure introduces a positive feedback path to achieve a significant boost in transconductance without increasing power or area consumption. A folded cascode amplifier using the proposed structure was implemented in SMIC standard 65 nm CMOS process. Simulation results show that the proposed amplifier achieves 400% improvement in gain-bandwidth and 16.6 dB boost in DC gain compared to the conventional folded cascode.

To assess the effects of atmospheric N deposition on the C budget of an alpine meadow ecosystem on the Qinghai–Tibetan Plateau, it is necessary to explore the responses of soil-atmosphere carbon dioxide (CO2) exchange to N addition. Based on a multi-form, low-level N addition experiment, soil CO2 effluxes were monitored weekly using the static chamber and gas chromatograph technique. Soil variables and aboveground biomass were measured monthly to examine the key driving factors of soil CO2 efflux. The results showed that low-level N input tended to decrease soil moisture, whereas medium-level N input maintained soil moisture. Three-year N additions slightly increased soil inorganic N pools, especially the soil NH 4 + -N pool. N applications significantly increased aboveground biomass and soil CO2 efflux; moreover, this effect was more significant from NH 4 + -N than from NO 3 − -N fertilizer. In addition, the soil CO2 efflux was mainly driven by soil temperature, followed by aboveground biomass and NH 4 + -N pool. These results suggest that chronic atmospheric N deposition will stimulate soil CO2 efflux in the alpine meadow on the Qinghai–Tibetan Plateau by increasing available N content and promoting plant growth.

From July 2008 to August 2008, 72 leaf samples from 22 species and 81 soil samples in the nine natural forest ecosystems were collected, from north to south along the North-South Transect of Eastern China (NSTEC). Based on these samples, we studied the geographical distribution patterns of vegetable water use efficiency (WUE) and nitrogen use efficiency (NUE), and analyzed their relationship with environmental factors. The vegetable WUE and NUE were calculated through the measurement of foliar delta(13)C and C/N of predominant species, respectively. The results showed: (1) vegetable WUE, ranging from 2.13 to 28.67 mg C g(-1) H(2)O, increased linearly from south to north in the representative forest ecosystems along the NSTEC, while vegetable NUE showed an opposite trend, increasing from north to south, ranging from 12.92 to 29.60 g C g(-1) N. (2) Vegetable WUE and NUE were dominantly driven by climate and significantly affected by soil nutrient factors. Based on multiple stepwise regression analysis, mean annual temperature, soil phosphorus concentration, and soil nitrogen concentration were responding for 75.5% of the variations of WUE (p

CO2 efflux was estimated using different regression methods in static chamber observation from an alpine meadow on the Qinghai-Tibetan Plateau. The CO2 efflux showed a seasonal pattern, with the maximun flux occurring in the middle of July. The temperature sensitivity of CO2 efflux (Q10) was 3.9, which was at the high end of the range of global values. CO2 emissions calculated by linear and nonlinear regression were significantly different (p < 0.05). Compared with the linear regression, CO2 emissions calculated by exponential regression and quadratic regression were 12.7% and 11.2% larger, respectively. However, there were no significant differences in temperature sensitivity values estimated by the three methods. In the entire growing season, the CO2 efflux estimated by linear regression may be underestimated by up to 25% compared to the real CO2 efflux. Consequently, great caution should be taken when using published flux data obtained by linear regression of static chamber observations to estimate the regional CO2 flux in alpine meadows on the Qinghai-Tibetan Plateau.

The natural abundance of 15N (δ15N) in plants and soils is an ideal tool for assessing ecosystem N dynamics. However, many of the mechanisms driving the variability of foliar and soil δ15N values within and across ecosystems are still unclear. In this study, we analyzed the patterns of N concentrations and δ15N values in leaves, bulk soils and soil mineral N as well as soil N turnover rates across four temperate and boreal forest ecosystems along a mountain transect. The results showed that plant species and soil properties directly controlled soil δ15N patterns and climate factors (air temperature and precipitation) indirectly affected foliar δ15N patterns. Foliar N concentrations varied consistently with the concentrations of soil available N and soil NO3−-N, whereas foliar δ15N was most closely associated with the δ15N of soil NH4+, the most abundant form of N in soil solution. 15N enrichment in surface mineral soil in high elevation forests was mainly attributed to 15N-enriched organic N accumulation. Furthermore, the foliar enrichment factor (ep/s = δ15Nfoliage−δ15Nsoil) was significantly correlated with N transformation and loss rates, and was negatively correlated with the ratio of NH4+ to total inorganic N. These results suggest that foliar δ15N value and foliar N concentration together accurately reflect the N availability of forest ecosystems. Foliar ep/s can act as an integrated proxy to reflect the status of N cycling within or across forest ecosystems. Soil nitrification and species’ NH4+ to NO3− uptake ratios are key processes controlling foliar δ15N patterns in N-limited forest ecosystems. Our findings improve the mechanistic understanding of the commonly observed variability in foliar and soil δ15N within and across forest ecosystems.

Understanding forest carbon cycling responses to atmospheric N deposition is critical to evaluating ecosystem N dynamics. The natural abundance of 15 N( d 15 N) has been suggested as an efficient and non-invasive tool to monitor N pools and fluxes. In this study, three successional forests in southern China were treated with four levels of N addition. In each treatment, we measured rates of soil N mineralization, nitrification, N2O emission and inorganic N leaching as well as N concentration and d 15 N of leaves, litters and soils. We found that foliar N concentration and d 15 N were higher in the mature broadleaf forest than in the successional pine or mixed forests. Three-year continuous N addition did not change foliar N concentration, but significantly

Chronic atmospheric nitrogen deposition affects the cycling of carbon (C) and nitrogen (N) in forest ecosystems, and thereby alters the stable C isotopic abundance of plant and soil. Three successional stages, disturbed, rehabilitated and mature forests were studied for their responses to different nitrogen input levels. N-addition manipulative experiments were conducted at low, medium and high N levels. To study the responses of C cycling to N addition, the C concentration and 13C natural abundances for leaf, litter and soil were measured. Labile organic carbon fractions in mineral soils were measured to quantify the dynamics of soil organic C (SOC). Results showed that three-year continuous N addition did not significantly increase foliar C and N concentration, but decreased C/N ratio and enriched 13C in N-rich forests. In addition, N addition significantly decreased microbial biomass C, and increased water soluble organic C in surface soils of N-rich forests. This study suggests that N addition enhances the water consumption per unit C assimilation of dominant plant species, restricts SOC turnover in N-poor forests at early and medium successional stages (thus favored SOC sequestration), and vice versa for N-rich mature forests.

Four images of 1991 AVHRR, 2003 and 2007 MODIS were used to extract waterlogging inundated water of three years, and three inundated water maps were overlaid to estimate waterlogging affected frequency. Based on wa-terlogging affected frequency, waterlogging hazard of pixel scale was assessed. According to the weighed score of area percentage of different waterlogging affected frequency in 13 counties/cities of Lixiahe region, waterlogging hazard rank of every county/city was assessed. Waterlogging affected frequency map and 1km×1km grid landuse map were used to assess waterlogging risk of pixel scale; and then waterlogging risk rank of every county/city was assessed by the similar method by which waterlogging hazard rank of every county/city was assessed. High risk region is located mainly in core zone of Lixiahe hinterland, medium risk region is adjacent to high risk region, and low risk region is located in the most outlying area of risk zone and mainly in south to middle part of Lixiahe region. Xinghua and Gaoyou belong to high risk city, Jiangyan belongs to medium risk city, and the other counties/cities have low or lower waterlogging risk. The method of assessing waterlogging risk in this paper is simple and applicable. This paper can provide guidance for the waterlogging risk analysis in broader area of Huaihe River Basin.

Soil organic C (SOC) content can increase by managing land use practices in which the rates of organic C input exceed those of organic C mineralization. Understanding the changes in SOC content of Black soils (mainly Typic Halpudoll) in northeast China is necessary for sustainable using of soil resources there. We used the RothC model to estimate SOC levels of Black soils under monoculture cropping corn in a long-term fertilization trial at Gongzhuling, Jilin Province, China. The model outputs for the changes in SOC were compared with measured data in this long-term fertilization/manure trial. The sound performance of model in simulating SOC changes suggests that RothC is feasible with Black soils in the temperate climatic region of northeast China. The modeled and measured results indicated that the treatment without fertilizer/farmyard manure (FYM) addition led to a continuous decline in SOC during the study period and N and NPK fertilization were inadequate to maintain the SOC levels in the plow layer (upper 20 cm) unless FYM was added under the current conventional management associated with no above-ground crop residues returning into the soil. Soil organic carbon could follow the same path of decline if the same management practices are maintained. Model results indicate that returning above-ground crop residues to the soil from 2002 to 2022 would increase SOC by 26% for the treatment without fertilization addition, 40% for N treatment, 45% for NPK treatment, and 38% and 46% for N and NPK treatments with FYM addition, compared to the levels in the corresponding treatments in 2002. The simulation results suggest that the RothC model is a feasible tool to assess SOC trend under different management practices, and returning above-ground crop residues into the soil would lead to a remarkable increase in SOC of Black soils in the region.

Atmospheric nitrogen (N) deposition, an important component in the global N cycle, has increased sharply in recent decades in China. Here, we constructed national-scale inorganic N wet deposition (Ndep) patterns in China based on data from 280 observational sites and analysed the effects of anthropogenic sources and precipitation on Ndep. Our results showed that the mean Ndep over China increased approximately 25%, from 11.11 kg ha(-1) a(-1) in the 1990s to 13.87 in the 2000s. Ndep was highest over southern China and exhibited a decreasing gradient from southern to western and northern China. The decadal difference in Ndep between the 1990s and 2000s was primarily caused by increases in energy consumption and N fertiliser use. Our findings conformed that anthropogenic activities were the main reason for the Ndep increase and provide a scientific background for studies on ecological effects of N deposition in China.