| Roots system is the key tache of linking soli and fruit tree. The function and development of roots system changed when the condition of soil changed, and the growth of aboveground plants changed fartherly. So it is very important to study the effect of soil nutrient space on the roots system of fruit tree for pomology and soli management.1. Effect of hypoxia stress on hydroponically grown M. hupehensis Rehd. seedlings was studied. Concentration of dissolved oxygen in nutrient solution indicated the hypoxia stress. The physiological characteristics of M. hupehensis Rehd. seedlings including biomass of plant, root activity, respiratory rate, enzyme activities involved in nitrogen metabolism in the root system were measured separately. The results showed that the seedlings'growth and root respiration rate decreased with the concentration of dissolved oxygen in nutrient solution reduced. But the inhibitory effect of hypoxia stress on root respiratory rate decreased at the end of the trial. Root activity increased rapidly and then decreased quickly;, while activities of nitrate reductase (NR) and glutamine synthethase (GS) were increased with concentration of dissolved oxygen in nutrient solution decreased.The activity of glutamate dehydrogenase (NADH-GDH) was inhibited firstly and then was promoted. Therefore, M. hupehensis Rehd. seedlings adjusted respiration consumption and metabolic pathway to stand against hypoxia stress.2. The method of controlling dissolved oxygen concentration in nutrient solution was used to study the effect of hypoxia stress on physiological characteristics of cherry seedlings ( Prunun cerasus×P.canescens). The effect mechanisms of calcium and nitrogen on cherry seedling physiology under hypoxia were studied as well. The main results were as the followings:(1) Cherry seedlings had active response to resist hypoxia stress. Physiological changes of cherry seedlings included the increase of proline content, root activity and the activities of SOD, POD, CAT, NR, GS. NADH-GDH activity increased in the middle time of treatment. But the protected function was destroyed with the hypoxia stress going on, and the activities of SOD and POD in leaves and roots decreased after treatment for 2 days , the activities of CAT and NR decreased after 4 days, the root activity, GS and NADH-GDH activities decreased after 6 days. At the end of treatment, the content of chlorophyll, photosynthesis rate, the soluble protein content, the synthetical and metabolizing abilities, the root activities and root respiration rate decreased, which resulting from the cell being short of energy, and the absorb ability of root decreased; O2.- productive rate, H2O2 content, MDA content increased and these induced the destroy to membrane. At last, the biomass of cherry seedlings decreased.(2) Exogenous application of Ca2+ in nutrient solution could relieve hypoxia stress in cherry seedling. The content of chlorophyll and the function of photosynthesis were higher than the hypoxia treatment when exogenous Ca2+ was applied in nutrient solution. The activities of protective enzymes were induced, and the O2.- productive rate, H2O2 and MDA content decreased and the harm of hypoxia stress was relieved; It can supply enough energy to cell because the root activities and root respiration rate increased. The activities of enzymes involved in nitrogen metabolism (NR, GS) in cherry root system were increased, which supplying NAD+ to glycolytic pathway and promote the electron transfer. At last, the harm to mitochondria was relieved and the restrain to growth was alleviated. Applicatiion of Ca2+ at consentration of 10 mmol·L-1 was advisable. However, calcium deficiency showed the opposite results.(3) Exogenous nitrogen application in nutrient solution could relieve hypoxia stress to cherry seedling, which maybe owing to the increase of NR activity. The materials for plant metabolizing were abundant and the synthesis of some enzymes was ensured; The content of chlorophyll, photosynthesis rate, soluble protein and proline content increased. The electron transfer was promoted, the ROS and MDA content decreased, and the activities of protective enzymes (SOD, POD, CAT) increased, as a result, the harm to mitochondria and membrane was relieved. The activities of NR and GS increased, which resulting in the decline of ammonium harm. Application 22.5 mmol·L-1 NO3- in nutrient solution was better than at 15 mmol·L-1. However, the effect of nitrogen deficient treatment had the opposite result.3. To give some useful references to apple production, a pot culture experiment was conducted to investigate the effects of soil with different bulk densities (1.1, 1.3 and 1.5g/cm3) on the biomass, root growth and metabolism of Malus hupehensis Rehd. seedlings.. The results were showed as below:The root development of Malus hupehensis Rehd. seedling was inhibited as the soil compaction increasing, including the underground fresh weight and dry weight, the length of root and number of lateral roots, the total mass and area of primary roots and fine roots. However, the height of plant,overground fresh mass and dry mass were the largest in the slightly compacted soil (1.3g/cm3).The root activity, respiration rate of primary roots decreased as the soil compaction increasing. The respiration rate of fine roots increased when the soil compaction increased. The NO3--N content in leaf and root system increased. However, the NH4+-N content in leaves and root systems of Malus hupehensis Rehd. were highest in treatment B, the C treatment take the second place and the treatment A was the lowest. The NR activity in leaves and the GS activity in roots were in the following order: A>B>C. The NR activity in roots and the GS activity in leaves were B>A>C. All these results showed that nitrogen metabolism can be affected by soil compaction, and the function of absorbing and utilizing nutrients were effected ulteriorly.4. A pot culture experiment was conducted to investigate the effects of clay combined with organic fertilizer on the photosynthesis, root architecture, root activity and root respiration rate of Malus hupehensis Rehd.seedlings. Effects of soil changing on the biological and physiological characteristics of Malus hupehensis Rehd. roots were also studied . The main results were as the followings:(1) The content of chlorophyll, net photosynthetic rate, plant height, diameter of stem,overground fresh mass and underground fresh weight in the clay add organic fertilizer treatment were higher than that of in clay and loamy soil, and the treatment B (clay: organic fertilizer =2:1)was higher than treatment A (clay: organic fertilizer =3:1). The length and area of primary roots and fine roots in treatment B were the highest. In treatment A, only the area of primary roots was lower than loamy soil treatment and the others were higher than clay and loamy soil. The root activity and respiration rate of primary roots and fine roots in treatment B were the highest, followed by treatment A .(2) Theoverground fresh mass, underground fresh weight, angle of lateral roots of treatment A (from clay to loamy soil) were higher than treatment C (from clay to clay), and lower than treatment B (from loamy soil to clay). The diameter of taproots was higher than treatment B and lower than treatment C and treatment D (from loamy soil to loamy soil); The number of lateral roots and the mass, area, length, diameter of inner fine roots were the lowest. However, the mass, area, length, diameter of outer fine roots were higher than treatment B and lower than treatment D. The aboveground resh mass, underground fresh weight, taproot diameter of treatment B were the lowest, however, the number of lateral roots was the most; The mass, area, length, diameter of inner fine roots were the highest. However, the mass, area, length of outer fine roots were the lowest, the diameter of outer fine roots was higher than treatment C. The order of root activities of inner fine roots were D>B>A>C. The order of root activities of outer fine roots were D>A>C>B. The NO3--N content of outer fine roots were C>D>B>A , and the NH4+-N content were C>D>A>B. The NR and GS activities of outer fine roots in treatment A were the highest, treatment D was the second, treatment C was the third , and treatment B was the lowest.
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