[Objective]The aim was to screen the marine microorganisms with strong antagonism to the agricultural disease fungi.[Method]Five kinds of agricultural disease fungi were selected as screening models,and the isolated strains were screened by Petri dish antagonism.The active strains were rescreened,and the strain with highest activity was selected to optimize the fermentation process.[Result]There were 21 strains of marine bacteria that had antagonistic effects in the initial screening.The bacteriostasis effect of MB133 strain on the plate ofP yricularia oryzae was most obvious after rescreening.The bacteriostasis effects of MB025,MB026 and MB133 strains on Sclerotinia sclerotiorum,Colletotrichum capsic and Botrytis cinerea were also found.The optimum fermentation process of MB133 strain was as followed:the optimum liquid amount was 12%,and the optimum inoculation amount was 2.0%,the optimum medium was pH 7.0.[Conclusion]This research has laid the resource base for the pop-ularization and application of agricultural antibiotics.

The accumulation of some harmful elements in greenhouse vegetables has caused a serious threat to human health. Comparing tests with cucumber (Cucumis sativus L.) and tomato (Lycopersicon esculentum) were conducted between greenhouse (GH) and open field (OF) cultivation with objective to determining the effects of greenhouse cultivation on transport and distribution of Cu, Zn, Fe, Mn, Pb, and Cd in soil–vegetable system. The results showed that Cd, Mn and Zn contents in most tissues of the vegetables in GH were significantly higher than those in OF, Fe contents reduction occurred in all parts of GH plants, while Pb contents decreased only in aboveground parts of GH plants. Most elements bioaccumulated in GH vegetable roots, except Fe, but exhibited lower transportation from root to aboveground parts in GH than in OF. Fe fractions extracted with ethanol and acid expressed significantly higher percentages in some parts of GH vegetables than in OF vegetables. Element interactions between Fe, Cd and Mn were significant and played an important role on metal elements transportation in vegetables. In conclusion, greenhouse cultivation could threaten vegetable production safety through changing the transportation of most metals in soil–vegetable system.

Migration and transformation of heavy metals in plants depend largely on their chemical forms.A simple two-step sequential extraction procedure was proposed to divide heavy metals into ethanol-extractable fraction,hydrochloric acidextractable fraction and the residue according to their activities in plants.The standard material(tea)was tested to validate the recovery and precision of the simplified extraction method.The sum of three fractions of Cu,Pb,Zn,Cd,Fe and Mn accounted for 82% to 116% of total metals with 16 repeating measurements,which showed that the recoveries can meet the requirements of fraction analysis.And for the relative standard deviation of content of each fraction in 16 repeating measurement,except that the ethanol-extractable fraction and residue of Zn,Pb and Cd were between 32% and 57%,the rest were less than 20%,indicating good precisions for fraction analysis.10 pieces of plant samples including cucumber roots,stems,leaves and fruits picked at vegetable production bases were tested by the extraction procedure to test the practicality of the method,and results showed that for the roots,stems,leaves and fruits of different plants samples,the sum of three fractions of the 6 elements accounted for 84.6% to 106% of the total heavy metals,showing a good recovery for fraction analysis.

Plastic film mulching(FM) is one of the commonly used agricultural practices worldwide in crop production.It significantly alters soil hydrothermal properties and processes such as conserving soil moisture,modifying soil chemical and physical environment,and affecting the forms of elements.Soil nitrogen plays an important role in providing necessary nutrients for crops and thus enhancing crop productivity.Its forms and transport in soil-crop systems are expected to be strongly influenced by FM.In this paper,field experiments were conducted during the winter of 2009—2010 to study the effects of FM on soil physicochemical and microbial properties,and subsequently on the distribution and translocation of nitrogen in a soil-lettuce system.The experimental plots were located in eastern China where it is typically rather moist in winter.Lettuce was grown in the plot soil and sampled following a 50-day growth.Compared to unmulching(UFM),FM had little influence on soil moisture,soil pH and urease.By comparison,FM decreased soil organic matter content by 6.0%,soil total nitrogen by 1.3% and soil NO-3-N by 10.4%,respectively,while increased soil NH+4-N by 6.5%.The one-way analysis of variation(ANOVA) showed that only soil organic matter and total nitrogen were significantly different between FM and UFM.Other soil properties were not statistically different between the two practices.In FM treatment,denitrifier accounted for 77.8—96.2% of the total nitrogen physiological microorganisms,and ammonifier,nitrite bacteria and nitrifier accounted for 1.8—16.5%,0.6—5.1% and 0.4—2.8%,respectively.As such,FM decreased ammonifier by 28.2% and increased nitrite bacteria,nitrifier and denitrifier by 119.8%,26.7% and 48.7%,respectively,as compared to UFM.In lettuce grown in the mulched soil,nitrogen was distributed the most in leaf while the least in root.While FM decreased total nitrogen in root by 2.8%,it increased total nitrogen in stem and leaf by 10.5% and 6.8%,respectively.This indicates that FM facilitated the translocation of nitrogen from root to above-ground parts.The calculated bioaccumulation factor(BCF) of total nitrogen in root,which is expressed as the ratio of nitrogen in lettuce root to that in soil,showed that FM decreased BCF by 1.5%,indicating that FM treatment decreased the total nitrogen in root.The average translocation factors TF1(TF of total nitrogen from root to stem)and TF2(TF of total nitrogen from root to leaf) were higher in FM treatment than in UFM treatment.Lower BCF may thus have resulted from higher translocation factors in FM.However,the influences of FM on the BCF of total nitrogen in root and the TFs of total nitrogen in root,stem and leaf of lettuce were statistically insignificant.This may be due to the abundance of moisture in the experimental location that FM and UFM could not be significantly distinguished in terms of BCF and TFs.The correlation analyses indicated that soil organic matter was positively significantly correlated(P0.05)with total nitrogen in soil,while nitrite bacteria had a significant negative correlation(P0.05)with urease,NH+4-N and inorganic nitrogen.