Effcets Of Fertilization On Nutrient Content And Ecoological Stoichiometry Characteristics In Larix Principis-rupprechtii Mayr Plantation

The North China larch is main afforestation species of middle mountains above in north China, one of the important species used in fast-growing plantation, which can resistant to bad weather and plays an important role in water and soil conversation, forest region ecosystem formation and maintenance. But in recent years, there are many problems in North China larch plantation development, such as single tree species, the structure of community is simple, poor stability, low productivity, frequent harm of wind throw and snowbreak, the serious problem of disease and insect pests, degradation of plantation quality. These problems seriously affect the sustainable development of North China larch and management. Nitrogen and phosphorus are not only the basics elements for plant growth but also the main limiting factor in plant growth of terrestrial ecosystem. Nitrogen and phosphorus fertilization can change the North China larch on soil nutrients absorption and utilization, thus affecting the growth of North China larch plantation. In this study, we collected the 23-year-old North China larch plantation as the research object in Qinling, which is conducted by nitrogen and phosphorus fertilization experiment for four consecutive years, determined the contents of organic carbon, total nitrogen, total phosphorus, total potassium in fine roots,stems,needles and the contents of organic carbon, available nitrogen, available phosphorus, available potassium in soil. Effects of fertilization on contents and ecological stoichiometry of C, N, P, K in different organs be analyzed and the impact of fertilization on soil nutrient content in North China larch plantation and their seasonal variations be explored. The aim of this study is also to explicit the nutrient resorption efficiency of N, P, K and discuss internal relation of nutrient resorption efficiency and C, N, P, K ecological stoichiometry characteristics, in order to provide theoretical basis of study of nutrient uptake, utilization and restoration mechanism. The main results were as follows:(1) Nitrogen and phosphorus fertilization can have a significance influence on the needles、stems and roots nitrogen, phosphorus and potassium content in the larch, but has no significant influence on organic carbon content. Both nitrogen treatment and the combination of N and P treatment increased the carbon organic content of 3.32% and 5.43%. The N2 treatment has improved the nitrogen content of needles and roots and the most significant effect is N 150 kg·hm-2 + P 75 kg·hm-2 fertilizer rate; the needles and roots phosphorus content also increased by phosphorus fertilization and the combination of N and P treatment, all of above showed that there are some degree of N and P limited of North China larch land. Nitrogen and phosphorus fertilization has no significant influence on potassium content. The North China larch carbon, nitrogen, phosphorus and potassium content show obvious seasonal variations, among them organic carbon have the minimum seasonal variability while total potassium have the maximum seasonal variability. The needles and roots can be a good characterization of nutrient deficiency, July and August is the best for diagnosis of nutrient deficiency.(2) Nitrogen and phosphorus fertilization has a significant influence on soil organic carbon content. The combination of N and P treatment obviously increased the soil organic carbon, available nitrogen and phosphorus content, single N and P fertilization respectively increased the soil available nitrogen and phosphorus content, all of them indicate that fertilizer can improve the soil nutrient availability. Single P fertilization also increased the content of available potassium. Both soil organic carbon and available nutrient have obviously seasonal variability, the maximum is available nitrogen and the minimum is available phosphorus.(3) Nitrogen and phosphorus fertilizer significantly influenced the ecological stoichiometric ratio in North China larch, to judge the nutrient limitation well, single N fertilization and the combination of N and P treatment significantly improved the C:N、N:K and N:P in needles and improved the P content of needles. The single P fertilization and the combination of N and P treatment significantly reduced the C:P while increased the P:K, and showed that fertilizer could improved the P content in needles. On the basis of nutrient limitation judgement theory, the growth of the North China larch limited by N.(4) The stem nutrient can’t represent the nutrient limitation and not obviously response the fertilization. The fertilization has no significant influence on C:N, N:K and C:K of stem, but single P fertilization decreased N:P and increased P:K. The ecological stoichiometrics of roots nutrient can reflect the nutrient absorption and utilization. Single N fertilization and the combination of N and P treatment significantly improved the C:N and N:K,Single P fertilization and the combination of N and P treatment significantly decreased C:P but improved P:K Nitrogen and phosphorus fertilizer significantly improved the use efficiency of N and P and growth rate of fine roots.(5) The soil available nutrient has a close correlation with the carbon, nitrogen, phosphorus and potassium content in needles, stem and roots of North China larch, and the soil available nutrient content obviously affected the growth of North China larch. Both the nutrient resorption efficiency of N and P higher than the global average, the fertilizer also reduced its nutrient resorption efficiency. So it indicated that the soil need more nitrogen and phosphorus from another perspective.