| Study were carried out on the dynamic changes of root growth and development, numbers of rhizosphere microbe and activities of soil enzymes, uptake, distribution, redistribution of nutrients, photosynthesis and senescence in maize under different soil bulk densities at special soil layers. The results were as follows:1. Subsoil bulk density had effect on the growth and physiological characteristic of maize root. As the subsoil bulk density reduced, numbers, weight, length and activities of root were extremely reduced. Root growth had a compensative effect on soil physical properties. For instance, More and larger root grew in the top soil layer with smaller soil bulk density when soil bulk density unfavorable to the root growth in the deep soil layer was large enough, but such effect was limited to make up for the negative effect made by larger bulk density. Total root weight and gaseous root decreased as subsoil compaction increased, and maize root could not penetrate into soil layer with bulk density 1.6g/m3 in this experiment.2. Subsoil bulk density had a greater effect on number rhizosphere microbe (bacterium, actinomycetes, fungi),soil microbial biomass C, N and activities of soil enzymes( Invertase, Urease ,Protease ,Catalase , Phosphatase ) .For example number of rhizosphere microbe , soil microbial biomass C,N and activities of soil enzymes were improved rapidly under low soil bulk density, and then nitrogen and phosphors could be relatively fully used. During the growth of maize, the dynamics change of rhizosphere microbe was consistent with soil microbial biomass and soil enzyme activities, amounting to their maximum at silking stage, and decreased gradually after that. In the same soil layer, such indexes were larger in the lower soil bulk density than those in the higher soil bulk density. The results also indicated that close correlation was observed among soil microbial biomass, number of soil microbe and soil enzyme activities.3 The activity of SOD and content of MDA were affected by subsoil bulk density, the results showed that the activity of SOD was lower as soil bulk density became larger. Contrary to the change of the content of MDA. Among different treatments, T224 was the best one, T266 was the worst one. In the course of maize growth, the activity of SOD was lower and lower, the content of MDA was higher and higher.4 Within the certain range of bulk density, the accumulation of nitrogen, phosphors and potassium in the above-ground parts reduced significantly with subsoil bulk density increase. Both nitrogen,49phosphors and potassium staying in the growth center and nutrients redistributed to the kernel declined, too. In soil layers with larger bulk density suitable to the com growth, more nutrients were redistributed to kernel part, and then the yield improved.5 In different subsoil bulk density conditions, there existed difference in daily changes among photosynthetic rate (Pn) ,the content of CO2 in the cell(Ci), maximal photochemical efficiency of PSII in the darkness (Fv/Fm), actual photochemical efficiency of PSn in the light (4>PSII), photochemical quenching co-efficient (qP) and non-photochemical quenching (NPQ). Pn and NPQ were lower in the weak light, and reached maximum values at noon in the daily changes while the values of Ci, Fv/Fm, 4>PSn amount to minimum at the midday and larger in the morning or the dusk. Such indexes as Pn , Fv/Fm and 4>PSn became continuously low with maize growth . On the other hand, the values of Ci and NPQ became higher. There are lower values of Fv/Fm, 4> PSII, qP, Pn and higher Ci and NPQ in the larger subsoil bulk density treatment compared with in the lower bulk density treatment. In all treatments the changes of Fv/Fm, 4>PSII, qP, Pn were T224>T244>T226>T246>T266, contrary to the change of NPQ and Ci.6 Finally, leaf area index ,yield component factors and yield of maize were significantly different among all the treatments, leaf area index, grain number per spike ,1000 kernel weight and yield declined as subsoil bulk dens...
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