The significance of ecological safety to the sustaining and development of the Chinese nation as well as the safeguard of the people′s vital interests are expounded on the basis of elaboration of the conception and connotation of ecological safety.Severe environmental pollution,expanding ecological deficits,damage of species resources,recurrence of natural calamities and other critical situations the country is confronted with are analyzed.On such a basis,strategies to safeguard the ecological safety of the country are brought forward,such as standardizing orderly development of the territory,consummating laws,policies and regulations for ecological protection,establishing an ecological monitoring and evaluation system,strengthening environmental supervision and management of resources exploitation,enhancing ecological safety awareness of the nation.

Effect of soil fauna on decomposition of litters in Carex lasiocarpa wetland in Sanjiang Plain was studied with the litter bag technique,through analyzing decomposition rate and component contents of the litters and calorific value of the residue of decomposition.Results indicate that 1) soil fauna accelerated decomposition of the litters and the effect of macrofauna and mesofauna was more significant than that of microfauna;2) it increased concentrations of cellulose,lignin and humic acids and variation of C/N ratio of the litters,which was more significant in 16 mesh-bags than in 250 mesh-bags,suggesting that soil fauna accelerated release of components from the litters;3) the calorific value of the residue of decomposition was significantly different between 16 mesh-bags and 250 mesh-bags,suggesting that energy flow from decomposition of the litter was affected by soil fauna;and 4) soil fauna,however,did not affect much the general tendency of the decomposition,that is to say,soil fauna is not a decisive factor of the decomposition process of the litters.

Main eco-effects of the rice-duck-azolla compound system were studied.Results show that the system improved soil fertility by increasing organic matter,available N,P and K by 7.95%,7.05%,6.47% and 4.46%,respectively,over CK.Besides,it controlled weeds by 98.94%,and reduced significantly infestation of former dominant species of weeds in the paddy fields.As a result,fewer weeds survived and Pielou evenness index rose sharply.It was also quite effective in controlling planthoppers,thus obviously suppressing incidence of rice stripe disease that is spread through planthoppers.Though the system also showed significant effect on controlling of rice sheath blight,it couldn′t put an end to incidence of the disease.As azolla absorbed some organic substances and humus from the water,the rice-duck-azolla system was 8.70% lower than the rice-duck system in COD of the submerging water.Thus the water in the former was more transparent.

A high-efficiency production model(Model A),combination of paddy-lotus rotation with fish/crab rearing in paddy fields,was put forward in light of the local physical conditions,regional advantages and the current agricultural farming structure of Baodi,Tianjin,and its ecological effects were analyzed.With the aid of Ecopath software,comparison in sustainability and net output value of the complex model with four simple models,rearing fish in paddy(Model B),rearing crabs in paddy(Model C),rearing fish and crabs in paddy(Model D),and just planting rice in paddy(Model E),was performed.Results show that in terms of Finn′s index,the five models were in the order of A>B>C>D>E;in terms of sustainability,Model A was superior to the other four,and in terms of net productivity,B/E ratio,O/I ratio and stability,it was 2.63,4.25,2.03 and 3.56 times as much as Model E,respectively.Compared with other four models,Model A is very high in net output value and thus put forth as an optimal ecological farming model for extrapolation in North(China).

With the aid of the technology of analytic hierarchy process and fuzzy pattern recognition,a comprehensive evaluation model is established and used to analyze ecological resilience and ecological load of forest,grassland and farmland ecosystems exposed to the strongest human interference in the Qilian Mountain Nature Reserve,and then of the reserve as a whole.Results show that the Qilian Mountain ecosystem has suffered strong human interference and has been exposed to ecological overload.But within the ecosystem,discrepancies do exist between subsystems in spatial distribution of ecological load.The subsystems of forest and grassland are seriously overloaded while that of farmland is medium overloaded.In terms of spatial distribution of ecological load,the northwest region is more heavier than the southeast;whereas in terms of overloading of subsystems,the subsystems of forest and grassland are less in the southeast than in the northwest,but the subsystem of farmland is more in the southeast than in the northwest.

Investigations were conducted of community structure of the macrobenthos in the Suzhou Creek from April to December in 2005,covering density,biomass,diversity and dominancy of species,and comparison made with the data of macrobenthos collected in 1999,2001 and 2003,in order to explain changes in community structure of the macrobenthos in the Suzhou Creek.Results show that from 2001 to 2005,species diversity of the zoobenthos decreased from 14 to 8,average density decreased from 34 445.1 m^-2 in 1999 to 3 746.6 m^-2 in 2001,and then rose up to 22 770.8 m^-2 in 2005,while biomass decreased from 285.33 g·m^-2 to(31.78) g·m^-2 from 1999 to 2005.From 2001 to 2003,Shannon-Wiener diversity index decreased from 1.20 to 0.49,and Pielou index from 0.67 to 0.40.Dominant species at sites Zhaotun and Huangdu changed from Bellamya aeruginosa in 1999 and 2001 to Limnodrilus hoffmeisteri in 2003 and 2005,while the dominant species at sites Beixinjing and Zhejiangluqiao remained unchanged.According to the changes in community structure of the zoobenthos,the restoration of zoobenthos in the Suzhou Creek can be divided into two phases:fast restoration phase in 1999 and 2001,and slow restoration phase in 2003 and 2005.

Toxic Microcystis blooms have caused extensive ecological damage to aquatic environment.Biological control is recommended to be a potential approach.Chlorella ellipsoidea was screened out for analysis of its inhibiting effect on Microcystis growth.Mixed culture of C.ellipsoidea,a strain isolated from waste water,and Microcystis PCC 7806 was carried out to observe competitive growth of two species.Chlorophyll-a/chlorophyll-b ratio was used as an indicator to estimate percentage of C.ellipsoidea in the mixed culture.Results show that C.ellipsoidea grew faster than Microcystis at either 20 or 30 ℃in BG-11 medium.In water from a Microcystis blooming lake,C.ellipsoidea displayed stronger competitiveness over Microcystis.The same phenomenon was observed under low light intensity.No evidence was found that C.ellipsoidea produced any toxic substance that inhibits Microcystis.To compare two organisms in ability to use nutrients,absorptions of nitrogen and phosphorus were measured.Results show that C.ellipsoidea absorbed more phosphorus obviously than Microcystis in BG-11,although they were the same in nitrogen absorption.When N concentration in BG-11 was reduced to onetenth,a low nitrogen condition,C.ellipsoidea still absorbed more nitrogen and phosphorus than Microcystis,demonstrating that C.ellipsoidea is more capable of absorbing nutrients,thus resulting in the growth inhibition of Microcystis in mixed culture.It is,therefore,feasible to make use of the superiority of C.ellipsoidea in interspecies competition for growth to control Microcystis bloom.

Corn gluten peptides were prepared by four different kinds of proteases and their respective root-inhibiting activities on smoothscale kyllinga(Kyllinga brevitolia var.leiolepis) were evaluated in Petri dish bioassay when they were 0.5,1.0,2.0 and 5.0 mg·mL^-1 in concentration.Results show that they all demonstrated root-inhibiting activity,which increased with their concentration.Herbicidal activities of peptides prepared by alcalase and Papain were significantly higher than those prepared by flavourzyme and neutrase.The peptides varied in bioactivity with molecular weight.Peptides small in molecular weight(<5 000 u) exhibited higher herbicidal activity than those large in molecular weight.

Seven strains of phosphorus solubilizing bacteria were screened out of red soils under different land use patterns and cultured for determination of characteristics,growth rate and phosphorus solubilizing capability.Results show that their HD/CD ratios ranged from 1.47 to 3.45,and their phosphorus solubilization rate in broth culture were in the range between 11.27 and 136.27 mg·L^-1,showing they were all quite high in phosphorus solubilizing capacity.Strain CY06 was the highest among the seven,and moreover it seemed to be more efficient in solubilizing AlPO₄ than in other insoluble phosphates.So,it is a promise microbial resource for development of high efficiency biological phosphorus fertilizer.

After foliar application with 10 mmol·L^-1 CaCl₂ each day for the first week,Kosteletzkya virginica seedlings were moved into an incubator,kept at 40 ℃ and monitored periodically for related physiological indices.Results show that Ca²⁺ could lower contents of proline and soluble sugar,prevent seedlings from withering and decreasing in root activity.Besides,Ca²⁺ could inhibit the increase of membrane permeability,improve the activity of Ca²⁺-ATPase.Thus,Ca²⁺ improves the tolerance of K.virginica seedlings to heat. 

Effect of addition of dissolved organic matter （DOM） on nitrification in fluvo-aquic soil was studied.The soil used in the experiment was collected from Suqian,Jiangsu.The experiment had three treatments different in DOM addition rate,220,440 and 880 mg·L^-1,respectively.Results show that addition of DOM inhibited nitrification to a certain extent.After 16 days of incubation,nearly 100% of NH⁺₄-N in CK had changed into NO^-₃-N.Compared with CK,the three treatments,DOC220,DOC440 and DOC880,decreased by 7.83%,13.60% and 19.12%,respectively in nitrification,and hence the decrease in NH⁺₄-N concentration in the treatments was much slower than in CK.The addition of DOM,however,increased nitrite accumulation significantly.In CK,NO^-₂-N concentration peaked on D 12 in incubation,up to 67.83(mg·L^-1),whereas in Treatment DOC220,DOC440 and DOC880,it did on D 12,14 and 16,and 21.17%,33.91% and 59.90% higher,respectively.The addition of DOM also decreased the production rate of NO^-₃-N.The maximum concentration of NO^-₃-N,143.61 mg·L^-1,in CK was found on D 16,while only 41.97,78.09 and 91.30 mg·L^-1 in Treatment DOC220,DOC440 and DOC880 respectively,much lower than in CK.In order to eliminate the effect of extraneous nitrogen brought in with the addition of DOM,comparison was made of effects of DOM addition and application of（NH₄）₂SO₄ as the sole nitrogen source on nitrification in soils with same initial nitrogen concentration.Results also show increase in NO^-₂-N accumulation and decrease in NO^-₃-N production,which indicate that the organic carbon and low molecular organic compounds in DOM affected the process of nitrification.The findings of the experiment implied a high risk of NO^-₂-N accumulation existed in environments high in organic matter content,which may have some bad effects on the health of the terrestrial and aquatic systems.

Two typical soils（meadow marsh soil and humus marsh soil）,located in zones different in moisture regime in Calamagrostis angustifolia wetland of the Sanjiang Plain were selected for study of horizontal movement of nitrate nitrogen（NO^-₃-N） with KNO₃ as tracer.Results show that NO^-₃-N concentration and the movement rate were significantly and negatively related to the distance of NO^-₃-N horizontal movement in the two typical soils（P<0.01）,showing a first-order exponential decay curve.NO^-₃-N horizontal movement was mainly controlled by concentration gradient,soil water potential gradient and soil matric potential;But the rate of the movement was significantly and positively related to soil moisture content（P<0.05）,showing an exponential growth curve,and so was the concentration of NO^-₃-N in horizontal movement with the diffusion rate of soil water（P<0.01）,showing a Boltzmann curve in the 0-20 cm soil layers and exponential growth curves in other soil layers.In conclusion,meadow marsh soil is more propitious to horizontal movement of NO^-₃-N than humus marsh soil,which is attributed to the significant differences in physical properties（grain composition and porosity,etc.） between the two typical soils,and hydraulic conditions might be important factors leading to formation of the two soils different in physical properties.

Based on the data of the second national soil survey in China,coupling characteristics and spatial variation of soil organic carbon(SOC) and total nitrogen(TN) in the plow layers of paddy and upland fields were studied.Results show that SOC and TN contents were higher in paddy fields than in upland fields by 47.8% and 45.5%,respectively,but spatial variation of SOC and TN were found higher in upland than in paddy fields.Soil organic carbon and total nitrogen ratio((C/N)) was about 10.8 in paddy fields,higher than 9.9 in upland fields.The highest C/N ratio value was found in the paddy fields in Northeast China while the lowest in the upland fields in Northwest China and East China.Meanwhile,results also show significant regional variation of C/N ratio in upland fields,but little significant variation in paddy fields.Correlation analysis shows that SOC was significantly and positively correlated with TN,with correlation coefficients being all higher than 0.8 in paddy and upland fields except for in North China.Moreover,the correlation coefficients may decrease along with the length of agricultural land use.The findings above indicate that there exist close coupled relationship between SOC and TN and distinct regional variation in the plow layer of farmland under different land use patterns.To understand these coupled characteristics will greatly contribute to improvement of regional farmland productivity and agro-ecosystem environment,and as reference to the technique selection and policy making for carbon sequestration in farmland soils in China.

Thirteen soil profiles and 38 soil samples from the plow layers of some randomly chosen crop fields in Yixing were collected in an experiment to study variation of total selenium in soils and soil profiles.The soil samples were digested in HNO^-₃-HClO₄-HF（V∶V∶V=8∶1∶2） solution and concentrations of total Se were determined with atomic fluoresce spectroscope.Total Se of the tested top soil samples ranged from 0.33 to 2.25 μg·g^-1 and over 80% of the top soil samples exceeded 0.45 μg·g^-1,the critical value for Se-rich soils.While Se accumulation in top soil was observed in all the soils tested,total Se varied with depth in soil profile,differed from soil to soil,and affected by land use.Total Se in dry croplands tended to be lower than in paddy fields and higher in soils rich in SOM and iron oxyhydrates.Statistical data show dominance of SOM in Se binding and accumulation in the studied soils.The findings here evidence that the area is high in top soil Se.However,translocation of Se from soil to plant or food crops needs further studies.

Desorption kinetics of Cu(II) and Pb(II) in two paddy soils and effects of citric and tartaric acids on desorption of Cu(II) and Pb(II) were investigated with a batch method.Results show that although much more Pb(II) than(Cu(II)) was adsorbed by the soils,more Cu(II) than Pb(II) was desorbed in either single metal system or bi-metal system.The findings suggest that the greater the adsorption affinity of a soil for a heavy metal,the more difficult the desorption of the heavy metal from the soil.The Elovich equation (Q_t =a+blnt) can be used to fit the kinetics data with fairly satisfactory results,which indicates that the desorption rate of Cu(II) and Pb(II) decreased sharply with the time going on.Constant b in the Elovich equation can be used to compare desorption rates in different systems.The desorption rate of Cu(II) was greater than that of Pb(II).The presence of citric and tartaric acids increased desorption of heavy metals in both quantity and rate,especially Cu(II). The effect of citric acid was greater than that of tartaric acid.

Through field investigations and pot trials,it was found that As and Cd was low in mobility in tea plant.Most of the As and Cd absorbed by the plant is fixed in feeder roots and only a small amount is transported to above ground parts.Distribution of As and Cd,based on their concentrations per unit dry matter,in tea plants growing on un-contaminated soil,is in the order as feeder roots>stems or main roots>old leaves>young leaves.When tea plants were growing on polluted soils,simulated by addition of salts of these two metals,feeder roots possibly acted as both buffer and defense,inhibiting As and Cd from moving up to above ground parts.The concentration of Cd from 6 to 20 mg·kg^-1 in soil was significantly and negatively correlated with chlorophyll content,photosynthetic rate,transpiration rate and biomass production rate of tea plants,whereas the concentration of As from 50 to 200 mg·kg^-1 was first negatively,but late little correlated.

Effects of environmental conditions and microbes on degradation of iodosulfuron-methyl-sodium were studied by simulation in laboratory.Results show that bio-degradation of iodosulfuron-methyl-sodium played a leading role,with its rate positively related to temperature,moisture content and organic matter level of the soil,but inversely to initial concentration of iodosulfuron-methyl-sodium.

Paddy soil samples applied with different rates of P fertilizer were incubated and examined for changes in contents of OlsenP and CaCl₂-P at different time periods.Results show that in 200 days,soil Olsen-P decreased by about 50% in all the treatments.When P application rate was low,the content of CaCl₂-P was low and did not varied much.But when P application rate exceeded 400 kg·hm^-2,the content of CaCl₂-P rose rapidly.With the increasing P application rate,the proportion of the applied P entering into the P pool of residual P was decreasing,whereas those into the pools of dissolved P and Olsen-P were increasing,so the probability of P losing into water that may induce non-point pollution is increasing.The "change point" value of Olsen-P content that can indicate soil P loss into surface runoff and rapid increase in P content in subsurface drainage is 81.3 mg·kg^-1,and the corresponding P application rate is about 524 kg·hm^-2.So,if P application is above 500 kg·hm^-2,the possibility of soil P loss in different ways is increasing.

Forms and contents of N pollutants in groundwater in a typical small watershed in the hilly area of the Central Sichuan Basin were monitored for a year.Results show that nitrate was the main form of nitrogen in groundwater in the watershed.The content of nitrate-nitrogen in 54.5% of the monitored wells was found above 10 mg·L^-1（drinking water standard of WHO）,and 27.3% approaching 10 mg·L^-1,suggesting that nitrate pollution had occurred in a large area in the hilly region of the Central Sichuan Basin.Land use is the main contributor of NO₃^--N content in the groundwater,and precipitation and well depth are also affecting factors.In slope cropland of purple soil,nitrate accumulated in the plow layer moving down into subsurface flow could be the major source of the higher content of nitrate in the groundwater.

Comparison of ADIs(acceptable daily intake) of rare earths elements proposed at different times reveals that the ADIs proposed recently are much lower than those in the past,reflecting that rare earth elements do have biotoxic effects.Based on the findings that agricultural products containing higher rare earth elements residues may enter human body through food chain,potential environment risks of their agricultural application and wastes from rare earth refineries are discussed and potential food safety issues are analyzed.