Wantai Yu

Atmospheric organic nitrogen deposition: analysis of nationwide data and a case study in Northeast China.

The origin of atmospheric dissolved organic nitrogen (DON) deposition is not very clear at present. Across China, the DON deposition was substantially larger than that of world and Europe, and we found significant positive correlation between contribution of DON and the deposition flux with pristine site data lying in outlier, possibly reflecting the acute air quality problems in China. For a case study in Northeast China, we revealed the deposited DON was mainly derived from intensive agricultural activities rather than the natural sources by analyzing the compiled dataset across China and correlating DON flux with NH4(+)-N and NO3(-)-N. Crop pollens and combustion of fossil fuels for heating probably contributed to summer and autumn DON flux respectively. Overall, in Northeast China, DON deposition could exert important roles in agro-ecosystem nutrient management and carbon sequestration of natural ecosystems; nationally, it was suggested to found rational network for monitoring DON deposition.

The combined effect of sulfadiazine and copper on soil microbial activity and community structure

Elevated concentrations of heavy metals and antibiotics often coexist in agricultural soils due to land application of large amounts of animal manure. The experiment was conducted to investigate the single and joint effects of different concentrations of sulfadiazine (SDZ) (10mgkg-1 and 100mgkg-1) and copper (Cu) (20mgkg-1 and 200mgkg-1) on soil microbial activity, i.e. fluorescein diacetate (FDA) hydrolysis, dehydrogenase (DHA) and basal respiration (BR), microbial biomass and community structure estimated using phospholipid fatty acids (PLFA), and community level physiological profiles (CLPP) using MicroResp™. High concentration of SDZ or Cu significantly reduced microbial activity during the whole incubation period, while the inhibiting effect of low concentration of SDZ or Cu was only visible within 14 days of incubation. The total PLFA concentration was reduced by SDZ and/or Cu, which resulted from reduced bacterial and actinomycetic biomass. The addition of SDZ and/or Cu decreased the bacteria:fungi ratio, whereas only the addition of high Cu concentration significantly decreased Gram+:Gram- ratio. The addition of Cu obviously inhibited the dissipation of SDZ, which could affect the combined effects of both on microbial activity, biomass and community structure. Principal component analysis of the CLPP and PLFA data clearly revealed the notable effects of SDZ and/or Cu on soil microbial community structure.

Interactive effects of sulfadiazine and Cu(II) on their sorption and desorption on two soils with different characteristics.

Antibiotics and heavy metals often coexist in soils due to land application of animal wastes and other sources of inputs. The aim of this study is to evaluate the interaction of Cu(II) and sulfadiazine (SDZ) regarding to their sorption and desorption on Brown soil (BS, luvisols) and Red soil (RS, Udic Ferrosols) using batch experiments. The presence of Cu(II) significantly enhanced sorption of SDZ on BS at pH>5.0, and this trend increased with increasing pH, which was mainly ascribed to the formation of ternary complexes of Cu-SDZ-soil and/or SDZ-Cu-soil. In contrast, Cu(II) only slightly increased SDZ sorption on RS at pH<5.0 due to the decrease of equilibrium solution pH, whereas it hardly affected SDZ sorption at pH>5.0 because RS had high oxides contents and low affinity for Cu(II). In addition, Cu(II) inhibited SDZ desorption from BS but promoted SDZ desorption from RS, which was related to their different sorption mechanisms. The presence of SDZ exerted no significant effect on the sorption of Cu(II) on the two soils at pH<6.5 because of its low sorption coefficients (Kd), while slightly decreased Cu(II) sorption at pH>6.5 by forming water-soluble complexes. Furthermore, SDZ had little effect on Cu(II) desorption from the two soils at natural pH. These results indicate that soil characteristics strongly influence the interactions of Cu(II) and SDZ on their sorption and desorption on soils.

Toxicity of sulfadiazine and copper and their interaction to wheat (Triticum aestivum L.) seedlings

A pot experiment was carried out to investigate the single and combined effect of different concentrations of sulfadiazine (SDZ) (1 and 10mgkg-1) and copper (Cu) (20 and 200mgkg-1) stresses on growth, hydrogen peroxide (H2O2), malondialdehyde (MDA), antioxidant enzyme activities of wheat seedlings and their accumulation. High SDZ or Cu level significantly inhibited the growth of wheat seedlings, but the emergence rate was only inhibited by high SDZ level. The presence of Cu reduced the accumulation of SDZ, whereas the effect of SDZ on the accumulation of Cu depended on their concentrations. Low Cu level significantly increased the chlorophyll content, while high Cu level or both SDZ concentrations resulted in a significant decrease in the chlorophyll content as compared to the control. Additionally, H2O2 and MDA contents increased with the elevated SDZ or Cu level. The activities of superoxide dismutase, peroxidase and catalase were also stimulated by SDZ or Cu except for the aerial part treated by low Cu level and root treated by high SDZ level. The joint toxicity data showed that the toxicity of SDZ to wheat seedlings was generally alleviated by the presence of Cu, whereas the combined toxicity of SDZ and Cu was larger than equivalent Cu alone.

Potential risk of cadmium in a soil-plant system as a result of long-term (10 years) pig manure application

Animal manure may be a primary source of cadmium (Cd) to Chinese farmlands because abnormally high values of Cd were observed in various manures. In this study, we evaluated the potential risk of Cd in soil-plant (maize and soybean) system as a result of the long-term (10 years) application of pig manure (PM). During 10 years, the loading rate of Cd through PM application ranged from 26.33–131.50 g/ha/year, while the crops removal rate of Cd was relatively small in comparison to the quantity of Cd supplied by PM application (1.03–4.36 g/ha/year). The PM ap plication significantly increased total Cd concentration in soil. Although the Cd levels did not exceed the Chinese soil quality criteria (1.0 mg/kg dry matter (DM)), it would only take less than two years to reach this limit at high PM application rate. The same trend was also observed for the Cd concentration in maize and soybean. More seri ously, Cd concentration in grain of soybean was higher than the threshold values for animal and human ingestion (0.2 mg/kg DM). Based on a mass balance calculation, we found that atmospheric deposition was also an important source of Cd in the experimental area (10.27 g/ha/year). Moreover, the application of PM enhanced the leaching loss of Cd, but they were still fairly small (0.34–0.73 g/ha/year).

The relationship between soil nutrient properties and remote sensing indices in the Phaeozem region of Northeast China

This study analyzed the relationships between soil nutrient characters and remote sensing image of the farmland in the Phaeozem region of Northeast China by GIS and canonical correlation analysis. The results showed that the two sets of variables, i.e. remote sensing indices and soil nutrient indices, had significantly correlative relationship (P<0.05) and the first canonical variable of remote sensing indices (W1) was significantly correlated with the first canonical variable of soil nutrient properties (V1) (r=0.72). In other words, it was a feasible and efficient way to estimate soil fertilizer level by analyzing remote sensing indices. SDI ( SWIR Difference Index ) dominated W1 and V1 was directly influenced by SOC, nitrogen, potassium and coarse sand. At the same time, it indicated that SDI had significant relationship with SOC and total N, and SDI was the best index among all the remote sensing indices for evaluating soil nutrient status.

Spatial Heterogeneity of SOM Concentrations Associated with White-rot Versus Brown-rot Wood Decay

White- and brown-rot fungal decay via distinct pathways imparts characteristic molecular imprints on decomposing wood. However, the effect that a specific wood-rotting type of fungus has on proximal soil organic matter (SOM) accumulation remains unexplored. We investigated the potential influence of white- and brown-rot fungi-decayed Abies nephrolepis logs on forest SOM stocks (i.e., soil total carbon (C) and nitrogen (N)) and the concentrations of amino sugars (microbial necromass) at different depths and horizontal distances from decaying woody debris. The brown-rot fungal wood decay resulted in higher concentrations of soil C and N and a greater increase in microbial necromass (i.e., 1.3- to 1.7-fold greater) than the white-rot fungal wood decay. The white-rot sets were accompanied by significant differences in the proportions of the bacterial residue index (muramic acid%) with soil depth; however, the brown-rot-associated soils showed complementary shifts, primarily in fungal necromass, across horizontal distances. Soil C and N concentrations were significantly correlated with fungal rather than bacterial necromass in the brown-rot systems. Our findings confirmed that the brown-rot fungi-dominated degradation of lignocellulosic residues resulted in a greater SOM buildup than the white-rot fungi-dominated degradation.

Priming effects on labile and stable soil organic carbon decomposition: Pulse dynamics over two years

Soil organic carbon (SOC) is a major component in the global carbon cycle. Yet how input of plant litter may influence the loss of SOC through a phenomenon called priming effect remains highly uncertain. Most published results about the priming effect came from short-term investigations for a few weeks or at the most for a few months in duration. The priming effect has not been studied at the annual time scale. In this study for 815 days, we investigated the priming effect of added maize leaves on SOC decomposition of two soil types and two treatments (bare fallow for 23 years, and adjacent old-field, represent stable and relatively labile SOC, respectively) of SOC stabilities within each soil type, using a natural 13C-isotope method. Results showed that the variation of the priming effect through time had three distinctive phases for all soils: (1) a strong negative priming phase during the first period (≈0–90 days); (2) a pulse of positive priming phase in the middle (≈70–160 and 140–350 days for soils from Hailun and Shenyang stations, respectively); and (3) a relatively stabilized phase of priming during the last stage of the incubation (>160 days and >350 days for soils from Hailun and Shenyang stations, respectively). Because of major differences in soil properties, the two soil types produced different cumulative priming effects at the end of the experiment, a positive priming effect of 3–7% for the Mollisol and a negative priming effect of 4–8% for the Alfisol. Although soil types and measurement times modulated most of the variability of the priming effect, relative SOC stabilities also influenced the priming effect for a particular soil type and at a particular dynamic phase. The stable SOC from the bare fallow treatment tended to produce a narrower variability during the first phase of negative priming and also during the second phase of positive priming. Averaged over the entire experiment, the stable SOC (i.e., the bare fallow) was at least as responsive to priming as the relatively labile SOC (i.e., the old-field) if not more responsive. The annual time scale of our experiment allowed us to demonstrate the three distinctive phases of the priming effect. Our results highlight the importance of studying the priming effect by investigating the temporal dynamics over longer time scales.

Effects of Long-Term Fertilization Regimes on N2-Fixing Bacteria in a Luvisol Soil of Northeast China

Long-term fertilization significantly inhibited the free-living N2-fixation rate (FNR) mainly because of the increased NO3–-N. DGGE profiles and redundancy analysis (RDA) plots clearly revealed that long-term fertilizations changed the community structures of N2-fixing bacteria (NFB) due to differences in N availability and pH. In addition, the differences in community composition were correlated with the changes in process rates for NFB (P < 0.05).

Seasonal Changes in Various Soil Organic Carbon Pools with Different Soil Amendments

In a sustainable agriculture farming systems experiment, the dynamics of soil organic carbon (OC), carbon/nitrogen (C/N) ratio and labile organic carbon pool in soil amended with maize stalk (MS), rice straw (RS) and alfalfa (AF) were studied from August 2005 to August 2006. The results showed that organic material with low N content decomposed slowly, while that with absolutely high N content depressed decomposition rate. After one year’s decomposition, the humification process of organic materials was basically complete. Soil labile carbon content was dramatically improved compared with the control after the addition of organic materials to the soil. The leached DOC was highly correlated with micro-organisms activity and MBC was highly dependent on N incorporation.