| There is a characteristic fruit tree native on southwest China that is Rosa roxburghii Tratt.,and it is a widely cultivated fruit tree species in Karst area of Guizhou province.The extensive distribution of karst areas in Guizhou is non-zonal calcareous soil.The availability of phosphorus and nitrogen in soil is very low,which is caused by the causes of the formation of calcareous soil and the environmental chemical effects of a large amount of free calcium carbonate in the soil.This result has become the main nutritional obstacle of plant growth on calcareous soil.Rosa roxburghii is facing serious problem of nutrient stress,such as low nitrogen and phosphorus stress in production.So far,the effect of low nitrogen and phosphorus stress on the growth and related physiological characteristics of Rosa roxburghii are unclear.The adaptation strategies and related physiological mechanisms in roots of Rosa roxburghii on low nitrogen and phosphorus stress are not yet understood.In this study,we took Rosa roxburghii Tratt seedlings of'Guinong 5'as materials,selected the Hoagland and Arnon nutrient solution formula and used the method of sand culture matrix,and took the 210 mg·L-11 middle nitrogen level,the 45 mg·L-1 middle phosphorus level and the middle combination level of 210 mg·L-11 nitrogen and 45mg·L-1 phosphorus as a contrast to studied the effect of nitrogen and phosphorus stress on the root system of Rosa roxburghii seedlings and interaction with endogenous hormones contents in roots.The indexes of growth and root morphological characteristics,the activity of acid phosphatase?Apase?,nitrate reductase?NR?and glutamine synthetase?GS?in roots,the activity of root system,the type and content of low molecular organic acid in roots,the contents of nutrient elements in the whole plant,the contents of endogenous hormone in roots were determined at five different supply nitrogen levels(70,140,210,280 and 350 mg·L-1),five different supply phosphorus levels(5,25,45,65 and 85 mg·L-1)and five different combinations levels of nitrogen and phosphorus(N70+P5?N140+P25?N210+P45?N280+P65?N350+P855 mg·L-1).We studied the growth and root morphology of Rosa roxburghii seedlings and their main physiological responses under different nitrogen and phosphorus levels.This study also analyzed the relationship between root morphological changes and endogenous hormone contents under different supply nitrogen and phosphorus levels,and explored the regulation of endogenous hormones in the root morphological changes of Rosa roxburghii under different supply nitrogen and phosphorus levels.Revealed the adaptive strategies of Rosa roxburghii seedlings in responded to low nitrogen and low phosphorus stress.The following results are obtained.1.With the increase of nitrogen and phosphorus levels,the plant height,base diameter,biomass of shoots,roots and whole plant of Rosa roxburghii seedlings increased significantly under different nitrogen and phosphorus levels.The growth of Rosa roxburghii seedlings was the best and the above growth indexes was the largest under the three conditions including that nitrogen supply level of 350 mg·L-1,phosphorus supply level of45 mg·L-1,the combinations levels of nitrogen and phosphorus was 280 mg·L-1?N?and 65 mg·L-1?P?.With the supply level of phosphorus was above 45 mg?L-1 than and the combinations levels of nitrogen and phosphorus was above the 280 mg·L-1?N?and 65 mg·L-1?P?than,the growth of Rosa roxburghii seedlings was significantly inhibited,and the growth indexes decreased significantly.The root shoot ratio of Rosa roxburghii seedlings was increased with the decreased of nitrogen level,phosphorus level and the combination level of nitrogen and phosphorus.2.The main root length,amount of total root tips,total root length,total root volume,total root surface area,average diameters,number and length of first order,secondary and tertiary lateral root,density of first order lateral root of Rosa roxburghii seedlings obviously increased under different nitrogen levels treatments.The above root morphological indexes of Rosa roxburghii seedlings were obviously reduced under the phosphorus supply level was below or above 45 mg·L-1 and the combination level of nitrogen and phosphorus was lower than or higher than 280 mg·L-1?N?+65 mg·L-1?P?.With the decrease of nitrogen and phosphorus level,the density of secondary and tertiary lateral root and the density and length of root hairs increased significantly.The density of s secondary and tertiary lateral root and the density and length of root hairs of Rosa roxbunghii seedlings reached the largest at 70 mg·L-11 low nitrogen level,and 5 mg·L-1 low phosphorus level and the low combination level of 70mg·L-11 nitrogen and 5 mg·L-1 phosphorus.Increased the density of s secondary and tertiary lateral root and the density and length of root hairs of Rosa roxbunghii seedlings was an adaptation strategy of root system adaptation to low nitrogen and phosphorus stress.3.With increasing the nitrogen supply level,the contents of IAA and ABA in roots of Rosa roxburghii seedlings gradually decreased,the contents of ZR and GA1+3 in roots of Rosa roxburghii seedlings gradually increased.With increasing the phosphorus supply level and the combination level of nitrogen and phosphorus,the contents of IAA,ZR and ABA in roots of Rosa roxburghii seedlings gradually decreased.The contents of GA1+3in roots of Rosa roxburghii seedlings decreased significantly at the phosphorus supply level was below or above45 mg·L-1 and the combination level of nitrogen and phosphorus was lower than or higher than 280 mg·L-1?N?+65mg·L-1?P?.The ratio of GA1+3/ABA,ZR/IAA and(IAA+GA1+3+ZR)/ABA in roots was decreased by decreasing the nitrogen supply level alone and simultaneously decreasing the level of nitrogen and phosphorus.The ratio of GA1+3/ABA and ZR/IAA in roots was decreased under the phosphorus supply level was below or above 45 mg·L-1.With increasing the phosphorus supply level,the ratio of IAA/ABA in roots of Rosa roxburghii seedlings gradually decreased,the contents of ZR and GA1+3 in roots of Rosa roxburghii seedlings gradually increased,but it did not affect the ratio of GA1+3/ABA and(IAA+GA1+3+ZR)/ABA in roots.4.Under the conditions of different nitrogen and phosphorus supply levels,there was a significant positive correlation between the plant height,base diameter,biomass of over ground part and root and whole plant,main root length,amount of total root tips,total root length,total root volume,total root surface area,average diameters,length and number of first order,secondary and tertiary lateral root,density of first order lateral root and the contents of GA1+3+3 in roots of Rosa roxburghii seedlings,and there was a significant positive correlation between the density of secondary and tertiary lateral root,density and length of root hair and the contents of IAA and ABA in roots of Rosa roxburghii seedlings.The high contents of GA1+3 in roots of Rosa roxburghii seedlings played a positive role in promoting the growth,root elongation and lateral root formation of Rosa roxburghii seedlings.The high contents of IAA and ABA in roots of Rosa roxburghii seedlings could increase the density of secondary and tertiary lateral root,the density and length of root hair.Significant quadratic nonlinear regression relationship was found between the main root length,amount of total root tips,total root length,total root volume,total root surface area,average diameters,length and number of first order,secondary and tertiary lateral root,density of first order lateral root of Rosa roxbunghii seedlings at different phosphorus supply levels and different combination of nitrogen and phosphorus and the contents of IAA,ABA and ZR in roots,and its shown that too low or too high of IAA,ABA and ZR in roots could inhibited lateral root formation when the phosphorus supply level was below or above 45 mg·L-1,and the combination level of nitrogen and phosphorus was lower than or higher than 280 mg·L-1?N?+65 mg·L-1?P?.5.Increasing nitrogen level could enhance the activity of NR and GS in roots and root activity of Rosa roxbunghii seedlings.The activity of NR and GS in roots and root activity gradually of Rosa roxbunghii seedlings weakened at the phosphorus supply level was below or above 45 mg·L-1,and the combination level of nitrogen and phosphorus was lower than or higher than 280 mg·L-1?N?+65 mg·L-1?P?.The activity of Apase in roots was strongest at 70 mg·L-11 low nitrogen level,5 mg·L-1 low phosphorus level and the low combination level of 70mg·L-11 nitrogen and 5 mg·L-1 phosphorus.The activity of Apase in roots of Rosa roxbunghii seedlings increased significantly with the increase of nitrogen and phosphorus levels.Reducing the level of nitrogen and phosphorus increased significantly the content of small organic acids including oxalic acid,malonic acid,malic acid,citric acid,succinic acid,tartaric acid and acetic acid in the roots of Rosa roxbunghii seedlings.Under low phosphorus stress,the activity of Apase was enhanced and the content of small molecular organic acids were the important physiological adaptation strategies for Rosa roxbunghii to reply with low phosphorus stress.6.Low or high nitrogen and phosphorus supply levels had adverse effects on the absorption of nutrient elements of Rosa roxbunghii seedlings.With increaseing the phosphorus supply level and the combination level of nitrogen and phosphorus,the contents of Zn obvious decreased.The contents of N,P,K,Mn,Cu and B gradually increased at the phosphorus supply level was below or above 45 mg·L-1 and the combination level of nitrogen and phosphorus was lower than or higher than 280 mg·L-1?N?+65 mg·L-1?P?.The contents of K decreased significantly and the contents of N,P,Ca,Mg,Mn,Cu and B in Rosa roxbunghii seedlings obvious increased. |
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