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Based on the long-term fertilization experiments, effects of various fertilization practices on the soil organic carbon (SOC) and total nitrogen (TN) in the surface (0-20 cm) and subsurface (20-40 cm) black soil in northeast China were studied. Results showed that, compared with the CK, long-term application of organic manure, especially the combination of mineral fertilizers and organic manure significantly increased the organic SOC and TN in the surface soil. Application of mineral fertilizers plus organic manure with conventional (NPM) and high application (N2P2M2) rate increased SOC significantly by 24. 6% and 25.1% , and TN by 29.5% and 32.8%, respectively. However, there was no significant difference among the treatments for SOC and TN at the subsurface. Compared with the CK (CKh), mineral fertilizer plus organic manure (NPM and N2P2M2) did not only increase the soil microbial biomass carbon (SMBC) and nitrogen (SMBN) , dissolved organic carbon (DOC) and nitrogen (DN), but also significantly increased the ratio of SMBC and DOC to SOC, SMBN and TN to TN. Application of the NPM and N2P2M2 increased the value of SMBC/SOC by 0.36 to 0.59 and SMBN/TN by 1.21 to 1.95 percentage points, respectively. The value of DOC/SOC and DN/TN ranged from 0.53% to 0.72% and 1.41% to 1.78%, respectively. This result indicated that SMBC, SMBN, DOC, DN and SMBC/ SOC, SMBN/TN, DOC/SOC, DN/TN were more sensitive than SOC and TN to long-term fertilization in the soil profile, and were better indicators for the impact of long-term fertilization soil fertility. The concluded that the application of manure especially manure plus mineral fertilizers can increase soil nutrients activity in the surface and subsurface black soil, acting as a helpful practice to improve soil fertility and the ability of nutrient supply, while it may cause potential environment pollution on carbon and nitrogen loss in the agroecosystem.

In order to clarify the effects of soil properties on the stabilization process of the cadmium (Cd) added, 11 different soils were collected and incubated under a moisture content of 65%-70% at 25 degrees C. The changes of available Cd contents with incubation time (in 360 days) in Cd and Cd-Pb contaminated treatments were determined. The stabilization process was simulated using dynamic equations. The results showed that after 1.0 mg x kg(-1) Cd or 500 mg x kg(-1) Pb + 1.0 mg x kg(-1) Cd were added into the soil, the available Cd content decreased rapidly during the first 15 days, and then the decreasing rate slowed down, with an equilibrium content reached after 60 days' incubation. In Cd-Pb contaminated soils, the presence of Pb increased the content of available Cd. The stabilization process of Cd could be well described by the second-order equation and the first order exponential decay; meanwhile, dynamic parameters including equilibrium content and stabilization velocity were used to characterize the stabilization process of Cd. These two key dynamic parameters were significantly affected by soil properties. Correlation analysis and stepwise regression suggested that high pH and high cation exchange capacity (CEC) significantly retarded the availability of Cd. High pH had the paramount effect on the equilibrium content. The stabilization velocity of Cd was influenced by the soil texture. It took shorter time for Cd to get stabilized in sandy soil than in the clay.

Bio-availability of Cu and Zn fixed by phosphate in contaminated soils with application of nutrients were measured by pot experiment. It was simulated for the third national standardization of copper and zinc polluted soils by adding copper and zinc nitrate into red and paddy soils, respectively and together. Phosphate amendment was added to the soils to fix Cu and Zn, then added KCl and NH4Cl or K2SO4 and (NH4)2SO4 fertilizers following to plant Ryegrass, which was harvested after 40 d. Available Cu/Zn content in soils and biomass, Cu/Zn content in the shoot of Ryegrass were determined. Results showed that, compared with no nutrient application, adding KCl and NH4 Cl/K2SO4 and (NH4)2SO4 to polluted red and paddy soils increased the available Cu and Zn content in red soil significantly. The increasing order was KCl and NH4 ClK2SO4 and (NH4)2SO4. Especially in single Zn polluted red soil, the available Zn content increased by 133.4% in maximum. Although adding K2SO4 and (NH4)2SO4 could promote the growth of Ryegrass on red soil, and the largest increasing was up to 22.2%, it increased Cu and Zn content in the shoot of Ryegrass for 21.5%-112.6% remarkably. These nutrient effects on available Cu and Zn were not significantly in paddy soil. It was suggested that application of nitrogen and potassium fertilizers to soils could change the bioavailability of Cu/Zn. So it is necessary to take full account of the nutrient influence to the heavy metal stability which fixed by phosphate in contaminated soils when consider contaminated soils remediation by fertilization.

The aging processes of copper and zinc in single and combined metal-contaminated typical soils of China, red soil, paddy soil and cinnamon soil, were studied. The results showed that available copper and zinc (metals extracted by 0.01 mol x L(-1) CaCl2 ) decreased rapidly at initial stages, and then reduced slowly, where the turning point occurred at about 90 d. The difference in aging of copper and zinc was insignificant whether in single metal-contaminated soils or in combined metal-contaminated soils, suggested there were similar chemical behaviors between copper and zinc. The aging processes of copper and zinc in red soil, paddy soil and cinnamon soil fitted best a second-order equation (R2 = 0.9940-0.9999, p0.0001), whereas parabolic diffusion equation has less goodness of fit. It indicated that the transformation from availability to unavailability of metals, i.e. aging, was not completely controlled by diffusion, but controlled by the interactions from surface nucleation/precipitation, occlusion by organic matter, and diffusion, etc. The aging of copper and zinc in soils was significantly affected by pH. In soils with low pH such as red soil, the ratio of available metals was higher and the aging rate was slower [constant of rate, k2 4.36x10(-3)-7.05x10(-3) kg x (mg x d)(-1)]; whereas in soils with high pH, for example in cinnamon soil, the ratio of available metals was lower and the aging rate was faster [k2 1.095x10(-2)-1.377x10(-2) kg x (mg x d)(-1)]. That is, the aging rate of metals in soils increased obviously with increasing pH.

Effects of four kinds of potassium fertilizer (KH2PO4, K2SO4, KNO3 and KCl) in its conventional application rate as K, 0.11 g x kg(-1) on the Pb absorption by rape and speciation of Pb in paddy soil were examined by pot trial. Results showed that the Pb content in rape decreased with using KH2PO4 and K2SO4, and in the second season of pot trial for KH2PO4 treatment, Pb content in rape shoots under Pb1 (300 mg x kg(-1)) and Pb2 (500 mg x kg(-1)) level decreased by 35.6% and 45.4% respectively compared with control treatment. Applied KNO3 in soil also decreased Pb content in rape shoots to some extent, but KCl had adverse effect. At lower Pb level (300 mg x kg(-1)), KH2 PO4 and K2SO4 caused Pb in soil transformed from non-residual fractions to residual fraction substantially and for higher Pb level (500 mg x kg(-1)) only KH2PO4 application had similar effect. Under two contaminated Pb levels, exchangeable and carbonate fraction Pb in soil by using KCl were all enhanced, which indicated that KCl could promote the phytoavailability of Pb. As thus one of the most important mechanisms of potassium fertilizers influencing Pb phtoavailability was changing the speciation of Pb in soil.

A model was developed based on the theories of physiological ecology and turnover dynamics of organic carbon in wetland ecosystem. It aimed to illustrate the process and characteristics of carbon cycling and its potential changes under climate change scenarios in wetland ecosystems. The key environmental parameters to determine the effects of temperature, water-logging, and freeze-thaw were gained from the results of incubation experiments. Effects of CO2 fertilizing on the carbon sequestration and plant cover on organic carbon mineralization were also taken into account in this model. It was verified by the conventional observed meteorologic data in temperate and subtropical wetland ecosystems. Sensitivity analysis and prediction under climate change scenarios by this model were also discussed. There were significant correlations between the simulated and observed values of sediment respiration in temperate wetlands in Northeast China. It was estimated that the annual net carbon sequestration rate was about 104 g x m(-2) in permanently water-logged wetland ecosystems and 76 g x m(-2) in the seasonally water logged ones in temperate northeast China. The simulated value of the accumulated organic carbon density was within the changing range of the investigated data. The model was sensitive to the change of parameters of CO2 concentration and temperature. The potential changes in carbon cycling characteristics were also predicted under assumed climate change scenarios of A1B and A1FI. It indicated that the exchange of carbon between the atmosphere and the wetland ecosystem became more active under climate change scenario of warming and increased CO2 concentration assuming no changing of hydrological condition. The net primary production (NPP) and the organic carbon density in temperate wetland ecosystems would increase under the scenario of doubled CO2 concentration and less than 2.5 degrees C increment of temperature. In this case wetland ecosystem would act as a net carbon sink of the atmosphere. However, it had no advantage to the carbon sequestration and accumulation in wetland ecosystems under the more warming scenarios. Under these more warming scenarios, the amount of increased NPP resulted from CO2 fertilizing and warming could not compensate the carbon loss from the accelerated respiration caused by warming. The organic carbon accumulated in seasonally water-logged wetland even would decrease under the assumed scenarios.

Amendments are widely applied in agricultural soils to improve soil quality and crop yield. Effects of three amendments, lime, manure, and sepiolite on cadmium (Cd) and zinc (Zn) bioavailability in contaminated paddy soils were studied by pot experiment with cultivating rape. There were eight treatments, including lime, manure, and sepiolite separately applied and combined with others in contaminated soil. The biomass yield of rape was investigated after harvest. The amounts of absorbed Cd and Zn in harvested rape with application amendments were determined. Besides soil pH, different forms of Cd and Zn in the conducted soils were also measured. Results showed that the yield of rape increased after amendments application. The treatment of lime and manure co-application showed the highest increasing yield by more than 170% comparing with no amendments application in the eight treatments. The amount of absorbed Cd and Zn in rape decreased after the three amendments application. Lime application showed the best effect to decrease the heavy metal content in rape when amendments were separately applied. However, sepiolite could hardly decrease the content in rape after separately applied in contaminated soil. It was mainly due to the decrease of exchangeable Cd and Zn, which was available for rape, after lime application. Soil pH in these treatments increased in response. Accordingly, the carbonate combined and the Fe-Mn oxide fractions, which were unavailable in soil for rape, increased greatly. The uptake coefficient of Cd was higher than that of Zn. It indicated that Cd was more movable in soil and lime application could obviously decrease the uptake coefficient. The remediation efficiency was significantly improved in the treatment of co-application with lime and manure in Cd-Zn contaminated paddy soil. Compared with control (CK), it increased 13.5 times for Cd and 2.4 times for Zn, respectively.