| The white pollution has become more and more serious, led to cropsgrowth was damaged and yield decreased in some areas north of china in recent years.Many scholars have study on the prevention and controlling of white plastic pollution,and given some proposals to solve the problem. The research and application on theenvironmental degradable mulch film (EDMF) provides an available way for solvingwhite pollution in field. EDMF can be broken down into smaller bits or powderedresidues called Low Molecular Weight Polyethylene (LMWPE) in short period; thisprocess is accompanied by molecular weight decreased. These residues are difficult toidentify mixed in soil so that EDMF is thought to solve the white pollution completely.However, LMWPE is hard to degrade completely because of strong hydrophobic. Thereare few studies on residues in soil whether are harmful to crop growth and soilmicro-environment or not, so it is unclear that how these residues might affect cropsgrowth and soil micro-environment, which is the urgent problem to be solved.Furthermore, full biodegradable film which is made up of polyvinyl alcohol (PVA) anddibutyl phthalate (DBP) brings new problem, that is PVA, DBP have adverse to cropgrowth, physiological and its cell toxicity effect or not because compared withpolyethylene (PE) these residues are absorbed easily by plant roots, which is the currentproblem also need to investigate. Solving those two problems above is valuable asreference for promoting EDMF.In this study, different molecular weight (M1=2000, M2=5000, M3≥100000) anddifferent dosages0.04241g·kg-1(A),0.21205g·kg-1(B),0.4241g·kg-1(C),2.1205g·kg-1(D),4.2410g·kg-1(E) of LMWPE potted into loam, sand, clay and seeded wheat under naturalconditions to simulated the environment which EMDF is degraded in field. Mainagronomic indexes were measured in tillering stage, jointing stage, booting stage,flowering stage, filling stage and maturing stage, and components of yield were measured in maturing stage, the photosynthetic parameters and fluorescence kinetics were measuredthough CARIS-2Photosynthetic measurement system and FMS-2pulse modulationfluoremeter, physiological and biochemical indexes such as pigment content, leaf nitratereductase activity and soluble protein, soluble phosphorus content of wheat weremeasured to investigate the effects of EDMF degradation residues in soil on crop growth.Meanwhile, soil samples were collected during every wheat growth period,7kinds of keyenzymes activities related C, N, P, S element metabolism and oxidation-reduction of soilwere measured to explore the effect of LMWPE on soil micro-environment. In addition,broad bean roots were treated with different concentrations of DBP and PVA solution inlaboratory, the root growth were measured as well as antioxidant enzymes system.Micronucleus, chromosome mutation and DNA fragmentation of the tip cell weremeasured.There are3chapters in this paper to elaborate the effects of LMWPE on crop growthand soil enzymes activities, and the effects of DBP and PVA on broad beans radiclegrowth, antioxidant enzymes system and cell toxicity effect. The results showed that:(1) The effects of LMWPE on growth and metobolism of wheat in potted loam.Multivariate analysis of variance showed that the effects of different molecular weightLMWPE on wheat agronomic traits was not significant in tillering stage, jointing stage;but the effects on stem length, tiller numbers, spike numbers, kernels per spike weresignificant in booting stage, filling stage and maturing stage. For example, the LMWPEwhich molecular weight more than100000was reduced tiller numbers, spike numbers,1000-grains weight, etc. The effects of different cumulants of LMWPE were notsignificant in every growth period. Thus, it could be concluded that LMWPEs added insoil were not harmful on wheat growth and yield.The chlorophyll content, quantum efficiency of PS Ⅱ, Gs, Pn,etc were increasedsignificant under the treatments of LMWPE which molecular weight lower than5000. So,low molecular weight LMWPEs added in loam could promote wheat photosynthesis.Wheat photosynthesis was inhibited under treated by LMWPE which molecular weightmore than5000or cumulants more than2.1205g·kg-1.The effects of different molecular weight LMWPE on wheat leaves NR activitieswere not significant in filling to flowering periods in loam, NR activities were inhibitedwith high cumulants (more than4.2410g·kg-1) of LMWPE in filling stage and bootingstage. The soluble protein content of wheat leaves was increased with different molecularweight LMWPE treatments in jointing stage, while the effects of cumulants of LMWPE were not significant.The effects of LMWPE on wheat leaf phosphorus metabolism were similar tonitrogen metabolism. The phosphorus contents of wheat leaves were increased with lowermolecular LMWPE treatments, it was decreased when the molecular weight more than100000. The phosphorus contents of wheat leaves were increased with low cumulants (＜0.4241g·kg-1) LMWPE treatments, while were decreased with high cumulants (＞4.2410g·kg-1).(2) The effects of LMWPE on key enzymes activities in different texture of soil.Multivariate analysis of variance showed that the effects of different molecular andcumulants of LMWPE on key soil enzymes activities were all significant in differenttexture soils in every growth period of wheat. It could be determined than the effects ofdifferent molecular weight LMWPE were stronger than cumulants in the same period ofwheat growth. The effects of different molecular weight LMWPE on7key enzymesactivities were all significant in3kinds of texture soil in growth periods of wheat, but theeffects were different for different enzymes. Sucrase activities were increased by treatedwith different molecular weight LMWPE, while urease, acid phosphatase, aryl sulfatase,dehydrogenase and peroxidase activities were decreased in potted loam; sucrase, urease,protease, acid phosphatase, aryl sulfatase, dehydrogenase and peroxidase activities weredecreased in sand; protease, aryl sulfatase, dehydrogenase and peroxidase activities wereincreased, sucrase, urease and acid phosphatase activities were decreased in clay.(3) The effects of DBP and PVA on broad bean root growth, activities ofanti-oxidation enzyme system and the micronucleus rate of broad bean root tips.The roots growth were inhibited significantly and appeared the symptom such asshading with different concentrations of DBP or PVA. The soluble protein and prolinecontents were changed significantly; it might be that the stress of DBP or PVA on broadbean roots was obvious. SOD activities of broad bean roots were increased, PODactivities, CAT activities were inhibited. The balance of active oxygen metabolism andanti-oxidant enzyme system was broken, and caused young root of broad bean oxidativedamage. The micronucleus rates were increased significantly, the frequency ofchromosome aberration was increased, mitosis index was decreased, and normal mitosiswas inhibited. |
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