| In face of the prominent problems of the current water crisis and environmental degradation, how to reduce the amount of irrigation water and improve water use efficiency of plants in itself to maintain the arid and semi-arid ecosystem balance will be a crucial question in future. In recent years, there are some hot research projects about the response of the plant water hydraulic conduction, hydraulic resistance and other physiological elements to a variety of environmental factors. Especially, partial root-zone alternate drip irrigation which is widely studied and applied indeed plays an important role in improving the relationship between soil water condition and in enhancing the water use efficiency of irrigation. In our country the majority of orchards are located in arid and semi-arid regions. The contradiction of nutrient supply and salt stress of soil is outstanding and these two factors always have an important influence on fruit trees. Thus, the studies on the root water uptake and water transport in plants in this condition not only enrich the water transport theories, but also have significances in determining the regulation mechanism of partial rootzone irrigation and in providing services to the orchards production in water shortage regions.In this paper,young apple tree is used as experimental material. Partial root-zone alternate drip irrigation and the response of the environmental factors on the mechanism of water transport are studied and analysed systematicly by pot and field plot experiments. The main conclusions are showed as follow:1. By studying effects of different drip irrigation patterns of root zone and watering treatments on young apple tree growth and root hydraulic conductivity, it shows that there is a positive correlation between root hydraulic conductivity and root dry mass and water potential. partial root-zone alternate drip irrigation repeatedly stimulates root rapid growth are important reasons for the increase root hydraulic conductivity. Using partial root-zone alternate drip irrigation pattern may help to optimize dry matter even distributed to every organs, increase its ratio of stem diameter and plant height and root-shoot, so seedlings healthy index is greatly enhanced. Thus, strengthened the roots to absorb and transport watering capability which impelled the transmission efficiency of root hydraulic signal and the ability of regulating water balance of seedling could be enhanced.Root biomass and root hydraulic conductivity could be enhanced by increasing the amount of irrigation. When the irrigation quota increased from 20 mm to 30 mm each time, root hydraulic conductivity of partial root-zone alternate drip irrigation treatment has the largest increase, shows: ADI(17.34%)>FDI(12.27%)>CDI(3.36%). When the amount of irrigation water in partial root-zone alternate drip irrigation treatment is saved by 33% , dry mass of lateral roots is only reduced by 6.33%, but the ratio of stem diameter and plant height, and root-shoot ratio , seedlings healthy index are enhanced by 0.27%, 19.46% and 11.74% respectively. Alternate drip irrigation treatment of growth conditions and root hydraulic conductivity are higher than the fixed drip irrigation.2. By studying effects of drip irrigation patterns of partial root zone and watering treatments on young apple tree hydraulic resistance, it shows, Correlation analysis shows, there is a negative correlation between and leaf stomatal conductance, while there is a positive correlation between hydraulic resistance and leaf area. The increase of leaf hydraulic resistance under alternate drip irrigation treatment play an important role in reducing water loss of leaf transpiration, and By decreasing root resistance and resistance of lateral branch and master rod, thus the partial rootzone irrigation raises crop storage water adjustment function , enhances the capacity of osmotic adjustment and increases the resistant ability to drought. So the alternate drip irrigation enhances the capacity of the environment adaptability.The root resistance, shoot resistance, resistance of lateral branch and master rod of young apple tree are decreased by increasing watering quantity, while the resistance from leaf to petiole are raised by increasing watering quantity. In 20 mm and 30 mm irrigating quota, the hydraulic resistance from leaf to petiole of alternate drip irrigation were increased by 17.89% and 24.58% respectively compared with that of conventional drip irrigation treatment. In the premise of saving 33% of the water supply, compared with conventional drip irrigation treatment, the average hydraulic resistance from leaf to petiole in alternate drip irrigation and fixed drip irrigation are increased by 19.65% and 24.34% respectively, but the average resistance of lateral branch and master rod are reduced by 4.61% and 13.02%, respectively. For the reason that the partial rootzone irrigation increases the hydraulic resistance from leaf to petiole through the decrease of the stomata conductance, leaf area, and thus decreases the leaf blade luxurious transpiration dehydration, and raises plant's water use efficiency.Hydraulic resistances of different components and their contributions to whole-plant resistance by studying show: Root resistance to account for the largest proportion of whole-plant resistance, accounting for 62.28 %, followed by shoot resistance, accounting for 37.72%, in turn resistance from leaf to petiole and resistance of lateral branch and master rod, accounting for 19.9% and 17.82%, respectively. So it shows that within the hydraulic resistance of each organ in the whole plant, the root system is the main organ of hindering water transport and leaves is the main organs of hindering water consumption.3. By studying effects of different drip irrigation patterns of root zone and watering treatments on young apple tree physiological characteristics and water use efficiency, it shows that when ADI and FDI save 33.3% of irrigation water the average root hydraulic conductivity only reduce 5.81% and 14.7%, but the average total water use efficiency and irrigation water use efficiency are enhanced by 16.31% and 14.48%,40.52% and27.65% respectively, which indicates that root hydraulic conductivity plays an important role in improving water use efficiency under partial root-zone irrigation strategies.4. By analyzing daily and seasonal changes of young apple tree stem sap flow and hydraulic conductivity and its relationship with environmental factors under partial root zone irrigation, some conclusions are obtained:(1) Hydraulic conductivity in each organs of young apple tree have a obviously seasonal variation. With the growing season goes on, the variation trend of root hydraulic conductivity, shoot hydraulic conductivity, hydraulic conductivity of lateral branch and master rod, and hydraulic conductivity from leaf to petiole increase at first and then decrease; while the trend of master rod hydraulic conduction, lateral branch and master rod hydraulic conduction gradually increase with the growing season goes on.(2) The curve fitting result of daily changes of root hydraulic conductivity is a quadratic parabolic equation. All drip irrigation treatments have a Maximum value at around 12:00 and the Maximum value of daily root hydraulic conductivity in the conventional drip irrigation is obtained; at around 18:00 the minimum value is obtained and it is appeared in fixed drip irrigation treatment; when its value go back to the level of 8:00 at about 16: 00. Under three drip irrigation patterns, daily change of the hydraulic conductivity from leaf to petiole is shown as a bimodal curve and it obtains its peak at 12:00 and 16:00 respectively. Maximum value of the hydraulic conductivity from leaf to petiole is obtained at 12:00 and the minimum is obtained at 14:00. Under three drip irrigation patterns, the maximum and minimum values decrease in order of its performance: CDI> ADI> FDI.(3) There is a positive correlation between shoot hydraulic conductivity of its each organs and its corresponding dry matter. The master rod hydraulic conduction and its dry weight have a high correlation coefficient showing that the master rod dry weight can be a better factor to estimate its hydraulic conduction capacity and the formula is: kmr = 0.5406Wmr + 0.9721, R2 = 0.6377. There is a linear positive correlation between root hydraulic conductivity and root zone soil moisture and also soil temperature showed a positive correlation with root hydraulic conductivity. That the partial root zone drip irrigation pattern improves the root zone soil temperature also plays an important role in enhancing root hydraulic conductivity. At different measured time, the relationship of the decision coefficient of root hydraulic conductivity and root zone soil moisture is: R2(Aug)(0.6949)>R2(Oct)(0.5391)>R2(Jun)(0.1551)>R2(Dec)(0.0428). It obtains the maximum and minimum values in August and December respectively. Thus, there is a close relationship between root hydraulic conductivity and root zone soil moisture relations, seasonal changes.(4) In different weather conditions, the stem sap flux of conventional drip irrigation treatment is significantly greater than the other two treatments; Under different drip irrigation patterns, the seasonal variation trends of young apple tree stem sap flux are related to atmospheric temperature seasonal variation. No matter it is sunny days or rainy days, the stem sap flow diurnal variation of each treatment show a single peak curve, but the diurnal variation of stem sap flux show a multi-peak curve when the weather becomes cloudy. It shows that there is a positive correlation between stem hydraulic conductivity and diumal stem sap flux, the relationship of their correlation coefficient is: CDI (0.98) > ADI (0.93) > FDI (0.82).5.By analyzing effects of drip irrigation patterns of partial root zone and fertilization treatments on hydraulic conductivity characteristics of young apple tree, we achieve the following conclusions: in the premise of saving 50% of irrigation water by alternate drip irrigation and fixed drip irrigation compared with conventional irrigation treatment and compared with no fertilizer treatment , root growth rate of alternate drip irrigation treatment is higher than conventional drip irrigation treatment, but leaf dry weight of alternate drip irrigation treatment have a larger drop. Thus alternate drip irrigation treatment's plants can maintain the lower transpiration rate of per unit absorbing area. Root hydraulic conductivity plays an important role in improving water and fertilization use efficiency under alternate drip irrigation treatment, not only enhances the capacity of water-saving regulation and control, but also improves the water and fertilization transmission capacity.Although the average root hydraulic conductivity of the conventional drip irrigation treatment is higher than alternate drip irrigation and fixed drip irrigation, the average root hydraulic conductivity shows decreases in this order compared with no fertilizer treatment: ADI(5.14 times)>CDI(4.74 times)>FDI(4.04 times).This indicates that effects of fertilization on alternate drip irrigation treatment is the largest. Transpiration and evapotranspiration of alternate drip irrigation and fixed drip irrigation treatment reduce 34.4% and 71.27% respectively compared with the conventional drip irrigation treatment. Growth condition of alternate drip irrigation treatment and root hydraulic conductivity are higher than the fixed drip irrigation.With the increase of the amount of fertilizer, seedling growth, healthy index of seedling and root hydraulic conductivity improves. the average root hydraulic conductivity of three drip irrigation patterns shows decreases in this order compared with no application fertilizer treatment: N2P2 (7.37 times) >N1P1 (6.7 times) >P2 (4.82 times) >P1 (3.72 times) >N2 (2.98 times) >N1 (2.11 times). Application of mixture of nitrogen and phosphorus promotes rapid growth of young apple tree and increases the root hydraulic conductivity greatly, makes the dry matter to distribute more balanced to each organs, improves the healthy index of seedling. Judging from the effect of single fertilization,application nitrogen promotes fast shoot growth and application phosphorus promotes root rapid growth, making the root hydraulic conductivity improves more significant than only application nitrogen. Although application phosphorus reduces the amount of total dry matter, the phosphorus has a positive effect on the root-to-shoot and diameter-high ratio larger, so application phosphorus also increases the healthy index of seedlings. It can clearly be seen that the beneficial effect of alternate drip irrigation should be better materialized under appropriate fertilization.6. By analyzing effects of drip irrigation patterns of partial root zone and salt treatments on growth and root hydraulic conductivity of young apple tree. Results shows that the dry root zone of alternate drip irrigation and fixed drip irrigation treatment hinder the absorption of salt ions, which reduces the damage of salt ions to the root system. Compared to CDI treatment, ADI and FDI treatment reduced irrigation water by 50%. Under higher NaCl concentrations (S2 and S3) levels, ADI treatment decrease from leaf to petiole hydraulic conductivity by 33.56% and 44.26%, while the root hydraulic conductivity of alternate drip irrigation treatment increased by 1.13% and 10.91%, respectively. At the same time,the growth and hydraulic conductance of alternate drip irrigation treatment are all higher than fixed drip irrigation treatment.This indicates that the root hydraulic signal transmission efficiency of alternate drip irrigation treatment, the ability of seedlings regulating water balance and resistance stability to salt-stress could be enhanced.With the increase of the salt concentration, the young apple tree growth blocked, photosynthetic rate, stomatal conductance and transpiration rate are greatly decreased, hydraulic conductivity significantly reduced. However, alternate drip irrigation treatment is less affected. As the salt concentration increased from S1 to S2 to S3 and compared with no salt treatment,the average decreasing range of root hydraulic conductivity and from leaf to petiole hydraulic conductivity under three drip irrigation patterns shows: CDI (48.06% and 38.18%) > ADI (40.57% and 29.65%) > FDI (32.82% and 21.22%). The relationship between hydraulic conductivity of young apple tree and their dry matter shows that there is a logarithmic relationship between them, but the relationship between other organ's hydraulic conductivity and its dry weight shows a linear positive correlation, however, it shows that there is a power relations between from leaf to petiole hydraulic conductivity and leaf blade dry weight and stomatal conductance.From the above analysis, we know that hydraulic conductivity of plants is closely related to the environment in which plants grows. water-saving irrigation in fruit trees, using alternate partial rootzone irrigation patterns not only helps to regulate roots and shoots growth of fruit trees and optimize dry matter even distributed to every organs, increase its ratio of stem diameter and plant height and root-shoot, so seedlings healthy index is greatly enhanced, but also has a greater impact on fruit water and fertilization absorption and transmission, especially, partial root-zone alternate drip irrigation repeatedly stimulates root rapid growth are important reasons for the increase root hydraulic conductivity. And alternate drip irrigation treatment's plants can maintain the lower transpiration rate of per unit absorbing area. Thereby alternate partial rootzone irrigation plays an important role in improving water and fertilization use efficiency and regulating and controlling water consumption of the shoots. So we can conclude that alternate partial rootzone irrigation is conducive to improve the environment adaptability and the capacity of water-saving regulation and control and it shows wide application prospect not only in arid and semi-arid areas, but also in the saline area. |
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