Effects Of Nitrogen Addition On Secondary Metabolic Processes Of Pinus Tabulaeformis And Quercus Liaotungensis Seedlings

Under the background of increasing global N deposition,the increase of soil available N will affect the distribution of photosynthetic products in various organs by affecting the physiological processes of plant photosynthetic process,endogenous hormone pattern and secondary metabolism,and ultimately affect plant growth.In this article,the seedlings of two major species,Pinus tabuliformis and Quercus liaotungensis in the Ziwuling forest area of Loess Plateau were selected as the study objects.Based on the continuous 2-year N-pot experiment,set 0?N0?,3?N3?,6?N6?,12?N12?g·N·m^-2·yr^-1 four treatments,studied the growth characteristics of N seedlings,soil physical and chemical properties and the effects of primary and secondary metabolism,and the interrelationship between the above factors.The main conclusions are as follows:?1?With the increase of N application,the growth strategies and tolerance to N level of Pinus tabulaeformis and Quercus liaotungensis seedlings were different.Nitrogen application promoted the accumulation of biomass in Pinus tabulaeformis.The biomass of N12 treatment was 1.86 times that of N0.However,the biomass difference between the treatments of Quercus liaotungensis was not significant.The aboveground biomass and underground biomass of Pinus tabulaeformis and Quercus liaotungensis increased with the increase of nitrogen application,but the growth rate of Pinus tabulaeformis was greater than that of Quercus wutaishanica.There was a threshold value in the stem-leaf ratio of Pinus tabulaeformis,and the ratio of Pinus tabulaeformis to stem was the highest when N3 was applied.When the nitrogen application was increased,the stem-leaf ratio of Pinus tabulaeformis was significantly decreased?P<0.05?,while the stem of Quercus liaotungensis was treated with N6,The leaf ratio takes the maximum value.With the increase of the amount of N applied,the fine root/thick root values of the two plants showed a decreasing trend,which was consistent with the optimal allocation hypothesis.Nitrogen application reduced the root-shoot ratio of Pinus tabulaeformis seedlings as a whole,and the minimum value was obtained in N12;the difference in treatments of Quercus liaotungensis was not significant.?2?With the increase of N application,the soil organic carbon of Pinus tabulaeformis and Quercus liaotungensis increased first and then decreased,and the total nitrogen was not significantly different.There was no significant difference in nitrate nitrogen in Pinus tabulaeformis under different N levels.The maximum value was taken and significantly different from the other treatments?P<0.05?.The soil pH decreased with the increase of N application,but the difference of treatment was not significant.?3?Overall,N3 and N6 treatments promoted increased levels of growth hormones in the stems,finest roots and fine roots of Pinus tabulaeformis.The content of gibberellinin leaves,finest roots and fine roots is June>August>October.With the increase of N application,the content of GA₃ in leaves and stems decreased first and then increased.The roots of stems and roots of different diameters?the finest roots,fine roots and coarse roots?increased by 12.9%and 13.2%,respectively,compared with N0 12.9%,64.1%,4.6%,14.3%.The auxin content was higher overall in the N3 and N6 treatments except for the leaves.Except for leaves,the content of abscisic acid increased with the increase of nitrogen application.In October,the N12 in different diameter grades was higher than that of N0treatment,72.9%,53.3%,72.7%,respectively.The accumulation of ABA.The results of w?ZR+GA₃+IAA?/w?ABA?were compared and showed that the ratio of N3 and N6 was higher than that of leaves and roots under different nitrogen treatments,It indicated that the growth potential of Pinus tabulaeformis was stronger.?4?Except for leaves,the total soluble sugar content of the organs of Pinus tabulaeformis was higher than that of N0 and N12 treatments,and the maximum value was obtained in N6;the soluble sugar of Quercus liaotungensis rice had no obvious rule with the increase of nitrogen.The starch content of various organs of Pinus tabulaeformis and Quercus liaotungensis was overall in October>June>August,and in June,Pinus tabulaeformis had lower values in N3 and N6 treatments;the total N0 and N3 treatments in different organs were not significant.The starch content in the roots is the lowest.?5?Nitrogen application had different effects on the total phenolic content of Pinus tabulaeformis and Quercus liaotungensis.Except for N0 treatment,the total phenolic content of the organs of Pinus tabulaeformis was gradually reduced in June,and the lowest value was obtained in N12 and significantly different from other treatments;The total phenolic content in the leaves and the finest roots was the highest,and the total phenolic content in the stems was the lowest.The total phenolic content in the organs of Pinus tabulaeformis and Quercus liaotungensis in different growth stages was October>August>June.The tannin content of Pinus tabulaeformis was highest in August,and the maximum value of Quercus wutaishanica in October,and the response of the two to nitrogen treatment was not obvious,and the content in leaves and finest roots was higher.?6?Secondary metabolites depended on the availability of carbohydrates.Pinus tabulaeformis and condensed tannins were significantly positively correlated with soluble sugars in fine roots and leaves?P<0.01?.The synthesis of total phenols and condensed tannins is coordinated by hormones.Total phenol and condensed tannin were significantly positively correlated with w?IAA+GA₃+ZR?/w?ABA?ratio in stems.The carbon to nitrogen ratio is not significantly related to total phenol and condensed tannins and does not support the carbon/nutrition balance hypothesis.Correlation analysis showed that the biomass of leaves,stems and fine roots were significantly positively correlated with ZR and w?ZR?/w?ABA?.The above results indicate that global N deposition may affect the growth of plants in forest ecosystems by affecting the endogenous hormone content of plants and affecting the distribution of carbohydrates in plant growth and defense.