| Deficiency of nutrients in soil can limit the growth of plants.Trees develop strategies to adapt to various nutrient environment through long-term evolution.Seedlings is the most vulnerable stage of tree life and affected by the environment easily.Sensitivity of seedlings to environment is of great value for their population establishment.The coniferous tree Pinus tabulaeformis and the deciduous tree Quercus mongolica seedlings were fertilized 50,250,and 500 mg Peters Professional(20%N+8.7%P+16.5%K+micronutrients)per seedling accumulatively to set three fertility levels of low,medium and high.The fertilizer was water soluble and added once a week from 30 March to 27 July exponentially.Seedling growth,root morphology,mineral nutrients,non-structural carbon(NSC)were measured at the end of the growing season.Seedlings were afforested at the beginning of second growing season.Survival rate and growth of the seedlings were measured at next two growing seasons.How seedlings morphology,root morphology,nutrients and NSC storage,field performance of P.tabulaeformis and Q.mongolica responsed to fertility level were studied respectively,and compared the responses of two species.The study aimed to explore how the two species were influenced by soil fertility and the mechanism of them adapt to soil fertility.The results showed that:(1)The response of P.tabulaeformis seedlings to the change of fertility was stronger than Q.mongolica.Soil fertility significantly affected the growth of P.tabulaeformis seedlings.Seedlings was biggest at high fertility level,with seedling height,root-collar diameter(RCD),and individual biomass of 7.4 cm,2.25mm,and 0.897 g,respectively 1.4,1.2,and 1.7 times at low fertility level.Growth of Q.mongolica responded weakly to fertility.Seedling height,RCD,and biomass were 9.7?10.0cm,3.10?3.27mm and3.057?3.530g.Only RCD increased significantly at high fertility level.(2)Root morphology of P.tabulaeformis and Q.mongolica seedlings responded significantly as soil fertility changed.At high fertility soil,length,surface area,and volume of P.tabulaeformis coarse root increased significantly,reached 2.4cm,1.8cm~2,and 0.1cm~3,which increased by 128.18%,318.45%,and366.67%than the minimum on low soil fertility.The length of fine roots decreased significantly as fertility became better,it was 744.18cm at low fertility,and increased by 24.70%at high fertility.The specific root length and specific surface area responded negatively to fertility,which were 26.4m/g and 218.7cm~2/g at low fertility,respectively,and increased by 23.80%and 53.53%at high fertility.The size of coarse root of Q.mongolica did not change significantly with the change of fertility.The length and surface area of fine root had significantly negative responses to fertility levels.The fine root length and surface area of Q.mongolica seedlings reached 1401.6cm and 65.3cm~2 on low-fertility soil,increased by 148.71%and56.73%respectively than at high fertility level.The specific root length of Q.mongolica also responded negatively to the changed fertility.It was 4.8 m/g in low-fertilization environment,which increased by127.78%than it at higher fertilization.(3)Mineral nutrient contents of both P.tabulaeformis and Q.mongolica seedlings responded positively to the improvement of the fertility level.P.tabulaeformis stored the most nutrients at the high fertility level,and nitrogen content,phosphorus content and potassium content of individual plant were 17.2 mg,4.4 mg and 13.1 mg,and compared with low fertility level they increased by 304.47%,209.33%and255.66%,respectively.Nitrogen content of Q.mongolica increased significantly and reached maximum at high fertility level,it was 35 mg per plan and 62.33%more than at lower fertility level.Phosphorus content was 9.2?12.1mg and potassium content was 22.8?28.9mg,both the two did not changed significantly.The percentage of storage in organs for P.tabulaeformis and Q.mongolica and their responses to fertility levels were different.P.tabulaeformis allocated the most nitrogen,potassium and starch to root when the fertility was poor,while stored the most nitrogen and potassium to needles when the soil was fertile.Specially,P.tabulaeformis always stored the most amount of phosphorus in root.Q.mongolica stored more than 90%of the mineral nutrients and non-structural carbon in root,which was not affected by soil fertility.(4)Winter and spring were the key periods for declining of seedlings survival rates.In the first growing season,P.tabulaeformis and Q.mongolica survived well,with survival rates of the two species were greater than 90%.After experience of cold and physiological drought during winter and spring,survival rates of P.tabulaeformis seedlings dropped sharply to 53.6%?67.1%,a drop of up to 27.1%?36.4%.At the end of the second growing season,the survival rates were 42.1%?60.7%.During the second growing season,the survival rates decreased by 6.4%to 11.4%.Fertilization in nursery was beneficial to increase the survival rates of P.tabulaeformis.The resistance to environmental stress of Q.mongolica was stronger than that of P.tabulaeformis.After cold and physiological drought in winter and spring,the survival rates of Q.mongolica dropped to 80.0%?82.9%,a decrease of 8.3%?10.4%,the decline was one third of the pine.At the end of the second growing season,the survival rates of Q.mongolica seedlings were 78.3%?80.8%,a decrease of 1.7%?2.1%.Fertilization in nursery did not change the survival rates of Q.mongolica,but increased the above-ground growth during the second growing season.In summary,growth and storage of P.tabulaeformis seedlings responded to soil fertility sensitively than Q.mongolica,indicating that it relies more on external nutrients.Both P.tabulaeformis and Q.mongolica are adaptive for poor soil.The two species improve the ability to absorb nutrients from soil by increasing specific length,specific surface area,length and surface area of fine roots in infertile soil.Storage of evergreen P.tabulaeformis seedlings most in needles and root.More than 90%storage of deciduous Q.mongolica always allocate in root,which are not affected by soil fertility.The field performance of Q.mongolica is better than P.tabulaeformis. |
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