Effects Of Nitrogen And Phosphorus Fertilization On Growth Of Machilus Pauhoi And Pinus Massoniana Seedlings

Machilus pauhoi and Pinus massoniana are evergreen broad-leaved and coniferous trees which are grown in the subtropical South China. They are widely cultivated and have economic timber values, as well as ornamental values. Nitrogen (N) and phosphorus (P) are two essential nutrient elements in the terrestrial ecosystem, usually affect or limit plant growth. Carrying on the research about plants growth in the different nutrient condition and absorption situation is benefit for improving the production of these two species better. Therefore, in this paper, seedlings of Machilus pauhoi and Pinus massoniana are selected as our study objective, analyzing the growth condition, leaf N, P content, N:P ratio, soil nutrient and their relations of seedlings in different measurement periods through different concentration of N, P addition experiment (including controlled treatment), in order to exploring how the growth of the two seedlings make response to the different nutrient environment and responding mechanism. Specific conclusions are as follows:(1) Overall(mean values of different measurement periods), with N or P treatments can both increase the content of this elements in the leaves,and content of N, P appeared increasing trend with the concentration of fertilization. Meanwhile, N and P addition also can promote mutual absorption of N, P elements in leaves, showing synergistic reaction; but in high N or P treatments would result in mutual retraining absorption of leaf N and P, indicating that in the excess nutrients condition, N, P existed antagonistic effect for plant growth. The seedlings of Machilus pauhoi and Pinus massoniana with the same N and P addition treatments, there were some certain differences of N, P content, which that of Machilus pauhoi was higher than that of Pinus massoniana.(2) Leaf N、P content of seedlings had certain seasonal periodicity changes. From March to November, leaf N, P content showed the tendency of increasing first and then decreasing. In March, seedlings had grown, but seedlings from growth stasis period to the beginning of growthing season this moment, and nutrient demand was low; then in the stage of rapid growth, leaf N, P content had increased,and growth tended to be more stable, leaf nutrients declined.(3) N, P addition can influence growth rate of Machilus pauhoi and Pinus massoniana seedlings. At growth peak period, high N and P level of treatments could promote relative growth rate of ground diameter and plant height of seedlings significantly. However, high level treatments would restrain the growth of seedlings in stable periods, middle N, P level should be adapted. Both of the growth rate of ground diameter and plant height appeared seasonal growth rhythm differences. From beginning to end of the experiment, growth rates of three measurement periods, growth rate presented low-high-low status. And in the growing season, plant height of seedlings under high N treatment grew fastest, much greater significantly than other groups. But in the rest periods of growth, the differences with various levels of N, P addition treatments which effected seedlings growth was not obvious, indicating that in this phase, the demand for nutrients was little or has already saturated, caused the luxury of nutrient absorption. This would improve internal nutrient content of seedlings, rather than growth of plant.(4) Coupling relationships between growth rate and leaf N, P content and N:P ratio of Machilus pauhoi and Pinus massoniana seedlings, suggesting that the growth of plants was the external embodiment of nutrients utilization and distribution. Within treatments, leaf N(P) content and growth of ground diameter and plant height were all positive related, yet the correlation with another element was not explicit, showing that rapid growth makes leaf N, P content change with different speed. Besides, plant height grew in step with ground diameter of seedlings under N or P treatments.(5) As a whole, soil N:P ratio had certain indication function on leaf N, P content, and that of Machilus pauhoi was more evident than that of Pinus massoniana seedlings. Furthermore, the imbalance of soil nutrients would make another one become restrictive element which limited plant growth under certain kind of N or P fertilization. At the same time, fertilization intensified the nutrient limitation due to relative shortage of soil nutrient in our experiment plot.(6) Fertilization could significantly influence soil pH value. Both N and P addition could decreased soil pH value, and resulted in soil acidification, reduced soil quality. Moreover, applying N fertilizer made soil acidification more serious than P fertilizer. And from March to July, the range of decline of soil pH value was greater than that from July to November, that might relate to precipitation, temperature and litterfalls in different periods.