Seasonal Pattern And Response To Soil Nitrogen Supply Of Fine Root Production In N-fixing And Nonfixing Tree Species

Fine roots(diameter <5 mm)are important organs that affect the growth and development of trees.They are responsible for the nutrients and water absorption.Growth of fine roots effect on the C/N cycle,global carbon cycle,and the forest production.Nitrogen deposition and fertilization is one of the important issues,the dynamic changes of fine roots in this context of forest ecosystem carbon cycle has an important role.In this research,nitrogen fixation species(Albizia kalkora and Robinia pseudoacacia)and non-nitrogen fixation species(Pinus massoniana and Cunninghamia lanceolata)under different site conditions were studied.Under nitrogen fertilizer treatment,the annual growth dynamics of fine roots in different soil layers were observed and analyzed by micro-root canal technique.The specific test results are:(1)Annual growth dynamics of fine roots of nitrogen fixation and non-nitrogen fixation trees under different site conditions were researched.The total root length,total root surface area,root average diameter and total root volume have the obvious seasonal dynamics.The peaks are always found in the July to September,then that will gradually decreased until December.Then the growth rate will increase slowly in the next year.It have not the seasonal dynamics in the greenhouse,the fine roots keep stable growth.(2)The rule of increase nitrogen fertilizer on fine root production: The application of nitrogen fertilizer reduced the fine root production of the four tree species of wild plots.On the contrary,it increased the production of fine roots in greenhouse.There was a negative correlation between the annual root production of nitrogen fixation and non-nitrogen fixation species and the content of nitrogen in field plots.And the difference between the two nitrogen fixation species fertilization area and the control area was lower than that of two non-nitrogen fixation species.Application of nitrogen fertilizer increased fine roots production of two kinds of tree species in greenhouse may be due to different growth environment,different age and production methods.(3)The results of fine root dynamics among different soil depth of two classes of trees showed: two classes of trees among different soil depth have the same patterns of fine root dynamics in fertilized and controlled plots.All of them have the peaks in the July to September,then that will gradually decreased until December.The growth rate will increased slowly in the next year.The length,surface area,diameter and volume of fine root were all increased with soil depth increased.20-40 cm depth soil were conducive to fine root growth.(4)The results of fine root dynamics among different soil plots showed: Albizia kalkora's fine roots grow better than the other tree species in the field.Then the controlled plots grow better than the fertilized in Albizia kalkora plantation.We didn't find the edge species in the greenhouse.The results showed that there are obviously seasonal patterns of the fine root growth in nitrogen fertilized plots.And the increase in nitrogen fertilizer slows down the growth of fine roots.However,greenhouse material has no seasonal change in response to nitrogen supply.And fertilization is beneficial to the growth of fine roots.The growth of fine roots in different soil layers is consistent but the number of fine roots in the deep soil is more favorable for the growth of fine roots.These results will provide the necessary reference for further understanding the change mechanism of fine root dynamics of nitrogen-fixing and non nitrogen-fixing species in different ecological environment,the distribution of fine roots and the C cycle of forest underground.