| Corp root, an important organ for absorbing water and nutrients and synthesizing growth substances regulation, has a direct influence on crop growth and yield. However, due to the less advanced root study techniques, the research about crop root system was not so thorough as that about the aerial parts of the crop, which suggested that the study on the root is very important for the further improvement of the yield. Therefore, the root morphology, the biological responses of root under stress, and the effect of cultural techniques on root system and yield of grain crops (millet, spring wheat, winter wheat, sorghum and broomcom millet) were studied on the Experimental Farm of Shanxi Agricultural University by pot culture, soil column culture, water cultivation experiments and field experiment. The results were shown as follows:1) The root weight of different grain crops all decreased with soil depth, showing a 'T' type in different soil depth. The decrease followed the exponential regression Y= A.e~-bx, but different crop had different 'b' value. The 'b' of sorghum was the lowest, showing its weight decreases was more slowly as the depth increases. For the same crop, the' b' value became lower as the crop grew, which indicated that the crop has more amount of depth root at later stage. The root length of different grain crops also showed the 'T' style in different soil depth at earlier stage, but showed " 8" style at later stage. At the earlier stage the root length decreasing followed the exponential regression Y= A.e~-bx, but at the later stage the distribution of root length along profile of soil could be expressed as multinomial Y=ax3+bx2+cx+d. The increasing of root weight, total root length, aerial parts weight all accorded with Logistic growth curve. There were many similar spatial distribution among millet, broomcom millet, sorghum and spring wheat root system, such as the 1st to 3rd whorl adventitious roots trended towards depth, the later growing adventitious root trended horizontally, and the last growing adventitious root to depth again. Root system distribution formed in "two groups", that is, in vertical correspondence with that of leaves.2) Drought stress could lead to the sharp increase of the content of MDA and of the ratio between root and canopy, but the dry weight of root, total root length, nodal root numbers, root activity, the SOD and POD activity of root, the total and active absorbing area of winter wheat root decreased significantly with drought treatment regardless of fertilizing or not. Manure supply reduced the effect of drought in a certain extent by promoting root growth, improving root physiological characteristics, enhancing the yield, the water use efficiency and drought resistance.3) The growth of millet root system can be significantly influenced by its growth density. The results showed that the root amount per plant had little difference among the population before the jointing stage of millet, but the difference became marked in the middle and later stages, while the root amount in a unit soil volume had great difference among the population in the early stages, but little difference was observed in the later stage. Heavy colony could cause the growth peak of root amount, total root length, total and active absorbing areas to reach earlier, however, the millet roots under high density senesced much earlier than those under low density, and the root depth was smaller than the contrast. Little colony remarkably increased the root depth at later growth stage, so it could improve the obtaining of water and nutrition from depth soil at later growth stage, prolong leaf function period of millet and increase the yield. Colony was a decisive factor of quantity in crop growth, and individual crop in colonies of different density may result in the difference of quality. The coordinated growth of colony and individual is the guarantee for a successful output.4) Limitation of the root growing space greatly affected sorghum growth, and decreased "plant height, leaf area, the activity of SOD and POD of flag leaf, total root length, total absorbing area, the weight of root and above ground, nutrient uptake and yield, but the restriction obviously increased the root active absorbing area and root activity. Fertilization stimulated root growth, increased root absorbing area and activity, promoted nutrient uptake, and therefore increased crop yield and decreased the detrimental effects resulting from the limitation of root growing space.5) Waterlogging could lead to the increased quantity of roots. However, under long-term (20-30d) waterlogging stress, the weight and activity of sorghum root decreased significantly. Waterlogging stress can stimulate POD and SOD activity, but with the extent of stress, the activity of SOD turned to be restrained, and then, decreased sharply. At the same time, the content of MDA increased significantly. Thereafter, the sorghum root under waterlogging senesced much earlier than those under control. The result also showed long-term (20d) waterlogging could lead to the increase of quantity of roots at every growth stage and the activity of POD increase at seedling, returning-green, jointing and booting stage. However, the weight and activity of root, the green leaf area, the N, P and total chlorophyll content of leaf, and the activity of SOD decreased significantly, and the content of MDA increased sharply at the same time. Compared with the control group, the waterlogging stress could lead the yield of wheat to decrease 5.2%, 20.8%, 43.1%, 61.8%and 68.3% separately at the stage of seedling, returning-green, jointing, booting and filling.6) Compared with the control group, the spring wheat seedling under sewage irrigation had small height and root length. And numbers of root, the root vigor, fresh and dry weight of aerial parts and rootdecreased drastically; and the MDA content of root increased dramatically. Sewage irrigation stress also stimulated POD and SOD activities, but with the extended stress, the activities of SOD turned to be restrained, yet decreased dramatically. The spring wheat seedling under disposed sewage irrigation hasnt shown significant difference with the control group. Both high and low root zone temperature stress could stimulate wheat root POD and SOD activities, but with the extended stress, the activities of SOD turned to be restrained, yet decreased dramatically also. High root zone temperature stress lead to the root length, root weight, root activity and root active absorbing area decreased sharply, however the plant height and the weight of aerial parts increased to a certain extent. The detrimental effect on aerial parts of low root zone temperature was heavier than that on root. The wheat roots were not passively tolerant to stress, but actively regulated their physiological metabolic processes, and increased their SOD and POD activity, so that plant injury by the environmental stress could be reduced.7) Low nutrition stress (low nitrogen, low phosphorus, low potassium) could lead to the drastic decrease of the plant height, root length, root numbers, root activity, root dry weight, the activity of SOD and POD of root, total root length, total absorbing area, and active absorbing area and of spring wheat. Jiachun 2 was most tolerant to low concentration of N in the genotypes, and Jiachun 1 was most tolerant to low concentration of P in the genotypes, and Jiachun 4 was most tolerant to low concentration of K in the genotypes. Total N uptake was significantly and positively correlated to root dry weight, total root length, root activity, total uptake area and active uptake area under low nitrogen stress. This indicated that genotypes with large root systems were able to obtain more N from low N medium. When N was not a limiting factor for plant growth, root morphology became less important in N uptake. The result also showed that the morphological and physiological characters were significantly different among three wheat genotypes, and that as the concentration of N, P, K decreased, the variations of corresponding parameters increased. The morphological and physiological characters of roots could be reference to screen N, P, and K efficient uptake of wheat.8) This experiment showed that P, N, and organic fertilizer could improve broomcorn millet root growth obviously in immature soil. In the treatment with K fertilizer alone, the yield of broomcorn millet was not significantly enhanced, however, combined P-K or N-K fertilization to broomcorn millet significantly enhanced its yield and root growth. The effect of P fertilization was significantly higher than that of N or K fertilization on root growth and yield. The dry weight of root, total root length, secondary root numbers, root activity, SOD activity of root, height of plant and aerial parts dry weight of broomcorn millet decreased significantly with drought treatment regardless of fertilizing or not. After the drought was released, root weight accumulated rapidly. It indicated that root system was sensitive to the changing soilenvironment than the aboveground part. However, no matter how rapidly the weight of root accumulated after drought released, the part of dry weight increased could not compensated that of decreasing during the period of drought treatment. Rewatering after drought during jointing stage had compensatory effects more than during booting stage. The booting stage of broomcorn millet was a sensitive stage to water deficit. The application of fertilization can greatly increase the growth of broomcorn millet, enhance the yield, the water use efficiency and drought resistance, and therefore improve the effect of drought in a certain extent.9) The root system distribution changed with fertilization depth. Fertilization in a depth of 50~100cm could lead to the increase of root weight, root vigor of sublayer, flag leaf area and net photosynthesis ratio, meanwhile it sustained the activities of SOD and POD in root system at a high level. Therefore, the content of MDA in wheat root system decreased, and the senescence of wheat delayed. The study also showed that super-deep (150cm) application of fertilizer has an inductive effect to root growing downwards also, but the total root weight and yield decreased sharply. It is considered that the depth (50~100cm) of fertilization could be used as an index for delaying senescence and increasing yield.10) Seed soaking with the chemical regulators increased the total root length, leaf area, root vigor and the activity of SOD and POD, and this increase under water stresses or salt stresses was remarkably higher than that under normal condition. And it decreased the detrimental effects resulting from the stress. Soaking seeds with FA or MET or rare earths could play an important role in raising healthy wheat seedlings.11) Uniconazole treatment inhibited the growth of shoot and promoted the growth of root simultaneously. It led to the increase of the diameter of stem, the number of tillers and root, the dry weight and activity of root, and the total root length, but decreased the height of plant at the same time. Uniconazole treatment decreased the leaf area of foxtail millet at seedling stage, but increased the leaf area of foxtail millet at jointing stage and booting stage. The senesce process of foxtail millet plant could be adjusted by Uniconazole treatment by prolonging the slow decline phase of leaf area per plant and root activity, increasing SOD and POD activity in root and flag leaf after anthesis, inhibiting malondialdehyde (MDA) accumulation and membrane peroxidization in some extent. Uniconazole treatment increased grains weight and the ears of per pot. Within the range of 15-120mg/kg concentration, the seed soaking in Uniconazole solution can make the foxtail millet seed yield increase obviously. Among them, .the 30mg/kg concentration got the best result.12) Cutting different root group (seminal root, adventitious root or different deep root system) could influence the crop growth, yield and its composition factors significantly. Yield reduction by root cutting... |
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