C,N,P Stoichiometric Characteristics Of Populs Tomentosa Under Different Irrigation And Nitrogen Coupling

This study aimed to explore the effects of irrigation and nitrogen application on the stoichiometric characteristics of C,N and P in various organs of Populus tomentosa Carriere during dormancy.The fast-growing high-yield Populus tomentosa clonal S86 plantation with 10-year continuous irrigation and nitrogen application rate was selected.The soil water content was adjusted to 45%,60%,75%of field capacity by irrigation and the nitrogen application was 0,101.6,203.2,304.8 kg hm-2,and in total there were 12 treatments with 3 replicates.At the end of October 2016,when the tree growth entered the dormant period,determinated tree height and DBH,and a sample tree was selected from each plot and fell down to sample roots,stems and branches for the determination of C,N and P content.The results are as follows:(1)The content of C and P in the stems and branches of Populus tomentosa was significantly higher than that of roots(P<0.05);The content of N was significantly different among organs and showed in the order of branch>root>stem.The C:N was significantly different among organs and stem>root>branch;The C:P was not significantly different among organs;The N:P was significantly different among organs and branch>root>stem.(2)Irrigation had no significant effect on C content in all organs.Nitrogen application significantly reduced root C content;Irrigation,nitrogen application and their interaction significantly affected the N content of root,stem and branch.Irrigation and nitrogen application significantly increased the N content of various organs,and the N content of various organs of Populus tomentosa increased significantly under high water content and high nitrogen application rate.(3)Irrigation and nitrogen application significantly reduced C:N in various organs of Populus tomentosa,which had no significant effect on C:P and significantly increased N:P content.(4)The stand volume of Populus tomentosa was negatively correlated with C content in roots and C:N in organs,and positively correlated with N content and N:P in organs.It indicated that C:N and N:P could be used as physiological indicators to reflect the growth rate of Populus tomentosa.Among them,the stand volume of Populus tomentosa was most closely correlated with nutrient element content and measurement ratio in roots.This study shows that Irrigation and nitrogen application promote N uptake,thereby increasing the N content of all organs;Irrigation and nitrogen application reduce C:N ratio and increase the growth rate of Populus tomentosa;although this area is suitable for Populus tomentosa,fast-growing and high-yield timber plantation may still be restricted by N.Irrigation and nitrogen application are two important cultivation measures to improve the timber yield of Populus tomentosa plantation.