| In order to study the effect of different water stress on the plant growth and developmentstatus, the changes of soil moisture, stem flow rate and stem diameter in2-year old apple trees(Malus pumila Mill. cv. Kangmutian), an experiment with two different stock-scions anddifferent water stresses was carried out in a waterproofed shelter from April to November in2011. The pot experiment was designed in two factors random block to discuss the law ofwater requirement and evaluate the drought resistance. There were two different stock-scionswhich were Malus pumila Mill. cv. Kangmutian/Malus hupehensis pamp Reld. and Maluspumila Mill. cv. Kangmutian/M26/Malus hupehensis pamp Reld.. And there were four watertreatments which were70-85%(CK, normal water quantity),55%-70%(LWS, light waterstress),40%-55%(MWS, moderate water stress),25%-40%(HWS, high water stress) ofmaximum field carrying capacity, respectively. The main research results were as followed:1. Under water stress, the plant heights of KM and KP young apple trees weresignificantly reduced by9.29%and6.27%,17.22%and8.91%,26.59%and14.43%than thecontrol group, respectively; the stem diameters of KM and KP young apple trees weresignificantly inhibited by11.57%and9.36%,20.31%and26.11%,24.23%and28.49%thanCK, respectively; the leaf areas per plant of KM and KP young apple trees were significantlyreduced by60.72%and27.04%,76.45%and46.46%,68.13%and85.53%than CK,respectively; the root length of KM and KP young apple trees were significantly inhibited by22.91%and13.77%,33.83%and29.45%,41.36%and40.54%than CK, respectively; thelength and diameter of young shoots KM and KP young apple trees had not significantdifference between normal irrigation and water stress. Along with the prolonging of waterstress time, the plant height, stem diameters, length and diameter of young shoots were slowlyincreased and leaf area per plant was decreased after a gradual increase. KM roots grew fast inthe early period and then its growth became gradually slow at the later stage, whereas, KProots were always shown a rapid growth. The growth potential of KP was higher than KMunder the same water conditions.2. With the water stress time going on, the aboveground biomass, underground biomass,total biomass and the root-shoot ratio of two different stock-scion young apple trees in different water conditions presented a gradual increase trend, and the biomass accumulationrate became gradually slow and the root-shoot ratio became gradually higher with the enhanceof water stress. The root-shoot ratios of KM and KP under water stress were increased by5.16%and16.90%,15.50%and24.10%,29.31%and36.71%than CK, respectively. Theroot-shoot ratio of KP was6.01%~18.18%higher than KM under the same water treatment.3. The stem water potential and leaf water potential can represent the water status in vivoand soil water regime of two different stock-scion young apple trees. As the water stress timebecame longer and its extent increased, the stem and leaf water potential gradually reduced.The stem water potential was higher-0.20~-0.10Mpa than leaf water potential at everycorresponding moment of the same treatment. The variation trend of stem water potential andleaf water potential were similar with that of soil water potential, which all showed a tendencyto decrease, but there was a lag effect relative to soil water potential.4. The diurnal changes of sap flow rate on two different stock-scion young apple treesunder different water treatments were mono-peak curves. Whether normal irrigation or waterstress, the sap flow rate of the apple trees generally started a launch at7:30am reached themaximum at about12:30and finally ended at about17:30pm. The sap flow peak of KM underlight water stress was3.24%lower than normal irrigation, while it was46.70%and11.84%higher than normal irrigation under moderate and severe water, respectively. The sap flowpeak of KP under light water stress was30.17%higher than normal irrigation, while it was4.10%and17.48%lower than normal irrigation under moderate and severe water stress,respectively, and the peak decreased as water stress became serious. The day-to-day variationof sap flow rate on two different stock-scion young apple trees under different watertreatments obviously showed a alternative circadian rhythm. The sap flow peak was higherunder light water stress, followed by normal irrigation, moderate water stress and severewater stress, and varied slightly in different dates. Under the same water conditions, the sapflow peak of KM was20.99,20.78,18.66, and14.05g·h-1·cm-2higher than that of KP,respectively.5. The diurnal changes of stem diameter on two different stock-scion young apple treeswere divided into three stages: contraction phase, expansion phase and increment phase. Thestem diameter under normal irrigation was highest, followed by light water stress and moderate water stress. Under the same water treatment, the stem diameter of KM was1.63mm,0.59mm and1.34mm higher than that of KP, respectively. The day-to-day variationof stem diameter on two different stock-scion young apple trees existed significant differenceunder different water conditions. When normal irrigated, the stem diameter graduallyincreased in the early stage and then decreased slowly during the late stage. While the stemdiameter presented a gradual decrease trend under water stress and the growth of stemdiameter was significantly inhibited with the enhance of water stress. The maximum dailytrunk shrinkage (MDS) under different water treatment had a similar variation trend, andMDS of low soil water content was mostly larger than that of high soil water content. Inaddition, the daily radial stem growth (DRSG) of high soil water content was larger than thatof low soil water content during water treatment stage, and the change relationship betweenMDS and DRSG was a opposite tendency.6. Based on responses of two different stock-scion young apple trees to water deficit, wedetermined the relationship between sap flow (SF), DRSG and MDS, Ψstem with the linearregression and nonlinear regression and defined reference values for MDS and Ψstem. Thereference values for MDS and Ψstem of KM were0.22mm and-1.02MPa, respectively. Thereference values for MDS and Ψstem of KP were0.23mm and-1.17MPa, respectively.7. Drought resistance of two different stock-scion young apple trees was assessed underwater stress conditions with drought index. KP showed good resistance under light waterstress, and its resistance weakened and even death with water stress became serious. KMshowed some resistance only under light water stress, but its drought index reached73.33%and82.22%under moderate and severe water stress, respectively. |
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