| In recent years,the area of artificial forest has increased rapidly.However,with the continuous planting of artificial forest,resulted in simple plantation structure,few forest tree species,and poor plantation management,all of them make the problem of soil fertility decline becoming more and more prominent.The factors that contribute to the decline of plantations are comprehensive,the irrational disturbance and destruction of human activities to the soil ecosystem of plantations is the primary cause.In this study,in order to find out the restrictive nutrient elements of plantation,explore the effect of adding exogenous nitrogen and phosphorus elements on soil fertility,and finally understand the nutrient distribution pattern and internal circulation mechanism of plantation ecosystem,we chose the middle age Larix principis-rupprechtii Mayr as the research object,combining with long-term fertilization and ecological stoichiometry theory,deeply explored the correlations between Larix principis-rupprechtii Mayr needles and soil carbon,nitrogen,phosphorus content and stoichiometric ratio.The results were as follows:(1).The effect of different fertilizations on the needles carbon content of Larix principis-rupprechtii Mayr was not significant,but it affected the needles nitrogen and phosphorus content in different degrees,and then the stoichiometric ratio of needles carbon,nitrogen and phosphorus was changed,especially the mass ratio of needle N:P.Fertilization treatment N1,N2,N1 P and N2 P increased the needle N:P in different degrees,except for treatment P.Among them,the needles N:P ratio of treatments N1,N2 and N2 P was significantly higher than this of the control(CK),and treatment N2 P was the optimal way to improve soil fertility.(2).Application of phosphorus combined with nitrogen fertilizer(treatment N1 P and N2P)significantly affect the soil carbon,nitrogen,phosphorus content and stoichiometric ratio,and they are better than other treatments.All fertilization treatments reduced the mass ratio of soil C:N in different degrees,but increased the mass ratio of soil C:P and N:P.In addition to fertilization treatment P,the soil C:P ratio is higher than the average value of soil C:P ratio in China and in different ecosystems of the world under other treatments.It indicated that this area showed soil phosphorus deficiency.Moreover,according to the correlation analysis of soil indexes,we knew that the correlation between soil C:P ratio and soil phosphorus was not significant under treatment N1 P and N2 P.It showed that combining phosphorus with nitrogen fertilizer could improve the status of soil phosphorus deficiency.Soil C:N and N:P ratio significantly increased under different fertilization treatments.And the correlations between soil C:P,N:P ratio and soil nitrogen were significant.It indicated that plant growth was susceptible to nitrogen limitation in this region,and fertilization treatments could improve the status of soil available nitrogen deficiency.In a word,fertilization treatments played a positive and effective role in soil fertility,especially the treatment N1 P and N2 P.(3).According to the correlation analysis of needle and soil carbon,nitrogen,phosphorus content and stoichiometric ratio,it showed that there was not only a certain relationship between them,but also some differences.Overall,correlations between stoichiometric were higher than nutrition elements.The content of needle carbon,nitrogen and phosphorus,and the mass ratio of needle C:N and C:P were higher than soil.Besides,the mass ratio of needle N:P is less than soil N:P ratio.These differences between soil and needle represented a competitive and interactional relationship between plant nutrient requirement and soil nutrient supply.Carbon is stable in plants,so the global ecosystem mainly affects the mass ratio of carbon,nitrogen and phosphorus by changing the content of plants nitrogen and phosphorus,and then regulates the plant growth and development. |
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