| Apple is one of the four fruits with the bigget cultivating area in the world, although it ranks first in the world in both cultivated area and production, the apple production area mainly distributed in arid and semi-arid lands in China, drought is the important factor that affect high yield and quality of apple. Roots are the main organs that absorb water and nutrients, which feel first and then occured physiological and biochemical reactions under soil water stress to adapt to the changeable environment, and transmit signals to overground parts. The growth, metabolize, activity changes of roots directly affect the growth and development of overground parts. Field experiment was conducted with 8-year-old Changfu-2 apple trees as test materials to evaluate the effects of different irrigation patterns, i.e, 3/4, 1/2, 1/4 alternate partial root-zone irrigation,1/2 fixed partial root-zone irrigation, conventional border irrigation and non-irrigation on root water physiological characteristics of red Fuji apple. The main results were as follows:1.The highest soil volumetric water content was appeared under conventional border irrigation in all period of different irrigation conditions,the yearly average was 23.20%, which had no significant difference with irrigation area of 1/2 alternate fixed root-zone irrigation, and significantly higher than that of others; the yearly average soil volumetric water contents of the 3/4,1/2,1/4 alternate partial root zone irrigation were 19.66%,19.80%,19.98% respectively, there were no significant difference among them, but they were significant lower than that of conventional border irrigation and irrigation area of 1/2 fixed partial root-zone irrigation; the yearly average soil volumetric water contents of no irrigation area of 1/2 fixed partial root-zone irrigation and non-irrigation were15.58% and 15.83% respectively, and very significant lower than that of others.2. Daily average stem sap flow flux rate of red Fuji apples in July and August were 6.82 cm·h-1,6.12 cm·h-1respectively, and significant higher than that of other months. Stem unit area sap flow flux of conventional border irrigation was 7.907 kg/(cm2·d) ,which was the highest and had no significant difference with 3/4 alternate partial root-zone irrigation; 3/4 alternate partial root-zone irrigation had no significant difference with 1/2 alternate partial root-zone irrigation and 1/2 fixed partial root-zone irrigation; Stem unit area sap flow flux of non-irrigation was 4.857 kg/(cm2·d), which was the lowest and had no significant difference with 1/4 alternate partial root-zone irrigation. There was positive correlation between stem sap flow and soil volumetric water content.3.The largest root quantity of every types in each grid(20cm×20cm) at the soil depth of 0～20cm,20cm～40cm,40cm～60cm,60cm～80cm were happened under 1/2 alternate partial root-zone irrigation, 3/4 alternate partial root-zone irrigation, 3/4 alternate partial root-zone irrigation, non-irrigation respectively. The minimum of every root types in each grid at the soil depth of 0～20cm, 20cm～40cm, 40cm～60cm were all happened under non-irrigation, the number of them were 47.3,94.2,67.8, and the minimum root amount at the soil depth of 60cm～80cm was 25.5,which appeared under 3/4 alternate partial root-zone irrigation. The roots with diameter<2mm were the most, and diameter>5mm were the least in each grid(20cm×20cm)at the four soil depths of every irrigation conditions. In the 0～20cm depth, the maximum root amounts with diameter<2mm were appeared under1/2 alternate partial root-zone irrigation, which was 127.7; the most root amounts in diameter from 2mm to 5mm were appeared under irrigation area of 1/2 fixed partial root-zone irrigation, the number of that was 19.3; The most roots with diameter>5mm were happened under1/4 alternate partial root-zone irrigation, the number of that was 0.8. In the soil depth of 20cm～40cm, the maximum roots with diameter<2mm were appeared under 3/4 alternate partial root-zone irrigation, which was 123.1; the most roots in diameter from 2mm to 5mm were appeared under 3/4 alternate partial root-zone irrigation, the number of that was 20.2; The maximum root amount with diameter>5mm was happened under conventional border irrigation, the number of that was 12.5. In the soil depth of 40cm～60cm, the maximum root amount with diameter<2mm were appeared under 1/2 alternate partial root-zone irrigation, which was 76.8; the maximum root amount with diameter from 2mm to 5mm was appeared under 3/4 alternate partial root-zone irrigation, the number of that was 10.4; The maximum root amountwith diameter>5mm was happened under conventional border irrigation, the number of that was 8.7. In the soil depth of 60cm～80cm, the maximum root amount with diameter<2mm was appeared under no irrigation area of 1/2 fixed partial root-zone irrigation, which was 40.6; the maximum root amount in diameter from 2mm to 5mm was appeared under non-irrigation, the number of that was 6.8; The maximum root amount with diameter>5mm was happened under no irrigation area of 1/2 fixed partial root-zone irrigation, the number of that was 4.6. The total root dry weight of every types under 3/4 alternate partial root-zone irrigation was 57.3 mg·cm-3,which was the largest and 1.34 times compared to conventional border irrigation; The lowest of total root dry weight of every types was 24.8 mg·cm-3,which was under non-irrigation. The largest root dry weight with diameter<2mm was under 1/2 fixed partial root-zone irrigation, which was 16.1 mg·cm-3, the most root dry weight in diameter from 2mm to 5mm was appeared under1/4 alternate partial root-zone irrigation, which was 14.3 mg·cm-3; The most root dry weight with diameter>5mm was happened under 3/4 alternate partial root-zone irrigation, and that of 28.1 mg·cm-3. Under different irrigation conditions, the root hair length of conventional border irrigation was 0.118mm, it was the least length and there had no significant difference with 1/2 fixed root-zone irrigation; the root hair lengths of 3/4 ,1/2, 1/4 alternate partial root-zone irrigation were 0.233,0.244,0.290mm respectively, they were significant higher than than that of 1/2 fixed root-zone irrigation, conventional border irrigation and non-irrigation, the root hair length of 1/4 alternate partial root-zone irrigation was the longest among them and it was 2.50 times compared to conventional border irrigation. The root hair densities under no irrigation of 1/2 fixed root zone irrigation and non-irrigation were 159.2 bar/mm3,164.3 bar/mm3, both of them were significant lower than that of others; the root hair densities of 3/4 ,1/2, 1/4 alternate partial root-zone irrigation were 269.2 bar/mm3,287.5 bar/mm3,249.1 bar/mm3 respectively, and they were significant higher than that of others, the root hair density under no irrigation of 1/2 alternate partial root-zone irrigation was 291.5 bar/mm3, it was the biggest and 1.58 times compared to conventional border irrigation. Moderate drought could accelerate the growth of roots.4.Under different irrigation conditions, irrigation area of 1/2 fixed root-zone irrigation and conventional border irrigation had the complete cytoarchitecture, the nucleus was intact, the nuclear membrane was clear, nucleus cytoplasm was thick and uniform, but the cytoarchitecture obvious changed under no irrigation of 1/2 fixed root-zone irrigation and non-irrigation, such as cell structure was incomplete, cell cytoplasm concentration reduced, cell inclusions degraded seriously, plasmolysis obviously, plasma membranes retracted. The cell structure of root system had high integrity under 3/4,1/2,1/4 alternate partial root-zone irrigation, except no irrigation area of 1/4 alternate partial root-zone irrigation, which was incomplete and the karyotheca dissociated.5.Under different irrigation conditions, the average root activity which under 3/4 alternate partial root-zone irrigation was the highest in all the period, that was 236.39μg/(g·h), and had no significant difference with that of 1/2 alternate partial root-zone irrigation and conventional border irrigation. The average ABA and IAA contents under non-irrigation were 5.977μg·g-1,1.073μg·g-1respectively, they were significant higher than that of others; the average ABA and IAA contents in all period under 3/4,1/2,1/4 alternate partial root-zone irrigation and 1/2 fixed root-zone irrigation were1.97μg·g-1,2.45μg·g-1,2.36μg·g-1,3.41μg·g-1and0.51μg·g-1,0.58μg·g-1,0.69μg·g-1,0.72μg·g-1respectively,among them, the average ABA and IAA content of 3/4 alternate partial root-zone irrigation were significantly lower than other partial root-zone irrigations, there existed significant negative correlations among root ABA and IAA contents and the soil volumetric water contents. Root GA3 and ZT contents under conventional border irrigation were the hightest in all period among the different irrigation patterns, and the contents of them were 38.90μg·g-1,0.831μg·g-1; the average GA3 and ZT contents in all period under 3/4,1/2,1/4 alternate partial root-zone irrigation and 1/2 fixed root-zone irrigation were34.2μg·g-1,32.5μg·g-1,31.7μg·g-1,28.1μg·g-1and 0.64μg·g-1,0.61μg·g-1,0.60μg·g-1,0.52μg·g-1respectively, the average GA3 and ZT contents under 3/4 alternate partial root-zone irrigation were significant lower than that of other partial root-zone irrigations, there was no no significant difference beteen 1/2 alternate partial root-zone irrigation and 1/4 alternate partial root-zone irrigation; root GA3 and ZT contents under no irrigation areas of 1/2 fixed root-zone irrigation and non-irrigation decreased gradually with the treated time going on, and there existed positive correlations among root GA3 and ZT contents and soil volumetric water content. Root proline and soluble sugar contents under non-irrigation were the hightest in all period of different irrigation patterns, the average contents of them were 45.00μg·g-1,879.1μg·g-1, the proline and soluble sugar contents under no irrigation areas of 1/2 fixed root-zone irrigation and non-irrigation increased gradually with the treated time going on, and the highest of them were all appeared at fruit maturing.The root SOD,POD,CAT activities under conventional border irrigation were the lowest in all period, and the average activities of SOD,POD,CAT were 21.99 OD·g-1,45.25 OD·g-1,8.48 mg·g-1 respectively, they were increased gradually with the irrigated volume reduced under 3/4,1/2,1/4 alternate partial root-zone irrigation; the activities of SOD,POD,CAT under no irrigation areas of 1/2 fixed root-zone irrigation and non-irrigation were significant higher than that of others, and gradually increased with the treated time going on, the maximum of SOD activity under no irrigation areas of 1/2 fixed root-zone irrigation and non-irrigation was appeared at fruit swelling period, the activities of them were 95.75 nmol·g-1,108.29 nmol·g-1 respectively, but the maximum of POD,CAT activities appeared at fruit maturing period, and that of them were up to 130.13 OD·g-1,134.62 OD·g-1 and 30.72 mg·g-1,29.37 mg·g-1 respectively. Under different irrigation conditions, the root MDA content and relative conductivity under non-irrigation were the highest in all period, the average numbers of them were 8.9 nmol·g-1,39.9%, they were increased gradually with the treated time going on; the average MDA content and relative conductivity in all period under 3/4,1/2,1/4 alternate partial root-zone irrigation and 1/2 fixed root-zone irrigation were 5.22 nmol·g-1, 5.27nmol·g-1, 6.51nmol·g-1, 6.39nmol·g-1 and 18.43%, 20.69%, 19.39%, 23.15% respectively, the root MDA content under 1/2 alternate partial root-zone irrigation had no significant difference with 3/4 alternate partial root-zone irrigation, and there were no significant difference among 3/4,1/2,1/4 alternate partial root-zone irrigation in root relative conductivity.The root soluble protein contents under conventional border irrigation were lowest during all the periods except fruit swelling period, which up to the maximum at fruit swelling period, that was 1.437 mg·g-1; the average root soluble protein contents in all periods under 3/4,1/2,1/4 alternate partial root-zone irrigation and 1/2 fixed root-zone irrigation were1.74 mg·g-1,1.69 mg·g-1,1.82 mg·g-1,1.79 mg·g-1 respectively,there was no significant difference beteen 3/4 and 1/2 alternate partial root-zone irrigation. There had the highest ABA content in the meristem cells and elongation zone cells of the apple tree root tissue, and there were less ABA content in the root cap cells and root hair zone cells, the ABA content of root cells could increased obviously under the drought stress, and the meristem cells and elongation zone cells were most sensitive to drought stress, in addition, ABA transfered from nucleus and cytoplasm to cell wall, plasmalemma and karyotheca gradually, moreover, there existed more ABA content in cytoplasm of catheter cells.6. Under different irrigation conditions, shoots length under 3/4 alternate partial root-zone irrigation had no significant difference with conventional border irrigation in all period, and they were significant higher than that of others after the end of June; Shoot lengths under conventional border irrigation, 3/4, 1/2, 1/4 alternate partial root-zone irrigation, 1/2 alternate fixed root-zone irrigation and non-irrigation were up to 58.35cm,56.53cm,47.13cm,39.15cm,45.31cm,35.60 cm respectively on Sep.17th, the shoot length under conventional border irrigation was the longest, there was no significant difference compared to 3/4 alternate partial root-zone irrigation, there was no significant difference between 1/2 alternate partial root-zone irrigation and 1/2 alternate fixed root-zone irrigation. Fruit volumes of conventional border irrigation, 3/4, 1/2, 1/4 alternate partial root-zone irrigation, 1/2 alternate fixed root-zone irrigation and non-irrigation were up to 258.4 cm3,244.2 cm3,240.4 cm3,209.5 cm3,215.8 cm3,169.6 cm3 respectively on Sep.17th,there was no significant difference of fruit volumes between 3/4 alternate partial root-zone irrigation and 1/2 alternate partial root-zone irrigation, and they were significant higher thanthat of 1/4 alternate partial root-zone irrigation and 1/2 alternate fixed root-zone irrigation.7. Under different irrigation conditions, the highest fruit yield per plant was appeared under conventional border irrigation,which was 80.12 kg, there was no significant difference of that with 3/4 alternate partial root-zone irrigation. Fruit yield per plant of 1/2 alternate partial root-zone irrigation reduced by 7.10% compared to conventional border irrigation, but had no significant difference compared with 3/4 alternate partial root-zone irrigation; Fruit yield per plant of 1/4 lternate partial root-zone irrigation reduced by 18.41% compared to conventional border irrigation. The highest soluble sugar content was appeared under 1/4 alternate partial root-zone irrigation and that was 13.84%, there was no significant difference with 1/2 alternate partial root-zone irrigation. The maximum of titratable acid content was appeared under conventional border irrigation,which was 0.3268% and very significant higher than that of 1/2 alternate partial root-zone irrigation and 1/2 alternate fixed root-zone irrigation, titratable acid content under 1/2 alternate partial root-zone irrigation was the lowest. Sugar-acid ratio under 1/2 alternate partial root-zone irrigation was the highest, which was 44.56, and had no significant difference with 1/4 alternate partial root-zone irrigation.
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