Effects Of Thinning On The Fine Root Anatomical Structure And Chemical Composition Of Chinese Fir Plantation

The seasonal dynamics of the effects of thinning on the anatomical structure and chemical composition of the 1~5 grade fine root of Chinese fir(Cunninghamia lanceolata)were investigated with 4 thinning intensities(control CK:0%,weak LIT:30%,moderate MIT:50%and intensity HIT:70%)in the Lishui forest farm of Nanjing.Research shows:(1)After thinning,the thickness of the lower root cortex of Chinese fir increased significantly(p<0.05),especially the 1 grade root increased significantly by 30% and 32% in spring and summer respectively.(p<0.05)Thinning has a significant effect on the anatomical structure of fine roots,in which the thinning(p<0.05)increases the thickness of the cortex and the proportion of the cortex,and reduces the diameter of the vascular bundle of the advanced root.(2)Compared with the control group(CK),the weak thinning(LIT)significantly(p<0.05)increased the proportion of the fine root cortex(11%),significantly(p<0.05)decreased by 3,the diameter of the 4 level root vascular bundle was 19%,and the moderate thinning(MIT)increased the low-grade root to root ratio,the average of 12%,and the strong thinning(HIT)significantly(p<0.05)increased 2,3,and 4 level roots.The average proportion of cortex was16%,significantly(p<0.05)decreasing the diameter of high root vascular bundle,with an average of 18%.(3)Compared with the control group(CK),the total nitrogen content of the weak(LIT)thinning(p<0.05)increased 1,2,and 3 lower roots,averaging 19%,21% and 14%,and the thinning had no significant influence on the total nitrogen content of the 4 level root(p>0.05).Compared with the control group,thinning significantly(p<0.05)reduced the total carbon content of 1 and 2 levels,averaging 9.12% and 5.37%,while thinning had no significant effect on the total carbon content of the 5 grade root(p>0.05).(4)Thinning significantly(p<0.05)reduced grade 1 and 2 of root C/N ratio,decreased by 12%(LIT,HIT)and 6%(LIT,MIT,HIT),and had no significant effect on 4 and 5 roots(p>0.05).Weak degree(LIT)and moderate(MIT)thinning significantly(p<0.05)increased the soluble sugar concentration of low roots,with an average of 23% and 27% respectively.(5)Correlation analysis showed that rhizosphere soil temperature,rhizosphere water content and Rhizosphere carbon and nitrogen ratio have significant correlation with the changes of fine root anatomical structure and chemical composition.