Effects Of Planting Density And Spacing Configuration On Nonstructural Carbohydrates Of Poplar Forests In Northern Jiangsu

Non-structural carbohydrate（NSC）is an important substance in tree growth process,and its distribution and dynamics suggest the situation of carbon supply during the certain period of trees.Quantification of NSC pools at the individual and stand level would allow us to effectively assess the carbon sequestration potential of trees.In this thesis,we collected poplar organ（leaves,branches,stems,coarse roots and fine roots）samples in each trial of density and spacing configuration trial forests（high density 400 plants/hm²:3.0m×8.0m,5.0m×5.0m;low density 278plants/hm²:4.5m×8.0m,6.0m×6.0m,3 replicate plots in each trial）in northern Jiangsu province from July 2018 to December 2019.We then measured the content of NSC and its components（soluble sugar and starch）in different organs under each planting trial.Then we estimated the soluble sugar,sarch and total NSC stocks at the individual and the stand level using the biometric equations.Furthermore,we investigated the seasonal dynamics and distribution characteristics of carbohydrates in poplar plantations with different stand density and spacing configuration.The main findings of the study were as followed:1.In general,soluble sugar,starch and total NSC in all organs showed seasonal dynamics of being depleted in the growing season and accumulated in the late of growing season.In spring（March-May）,NSC in poplar leaves showed an increasing trend,while most other organs showed a decreasing trend.The distribution of soluble sugars content in each organ was in the order of leaves>branches>coarse roots>fine roots>stems.The distribution of starch content in each organ was coarse roots>stems>branches>fine roots>leaves.2.The soluble sugar,starch and total NSC storage of poplar in this study were 15.14±4.51kg,40.54±11.10kg and 55.68±14.63kg at the individual plant level,respectively.The average contribution of NSC storage in each organ to the whole plant NSC storage was 1.82%for leaves,23.19%for branches,56.25%for stems,17.62%for coarse roots and 1.91%for fine roots.In addition,branches and stems were the major carbon storage organs of poplar.Stand density and spacing configuration significantly affected individual poplar soluble sugar,starch and total NSC storage in the individual level.Overall,whole-tree soluble sugar,starch,and total NSC reserves of individual poplar were greater in the low-density（278 plants/hm²）stands than in the high-density（400 plants/hm²）stands.While when under the same density,the soluble sugar,starch and total NSC storage in poplar were significantly higher under square configuration than under the rectangular configuration.3.At the stand level,the average soluble sugar,starch and total NSC stocks were 0.20kg Cm^-2,0.53kg Cm^-2 and 0.73kg Cm^-2,respectively.The stand density（278 plants/hm²-400plants/hm²）did not significantly affect the total NSC storage.Nonetheless,the total NSC storage were significantly larger in square configuration than in the rectangular configuration at the same density（P<0.05）.There are significant seasonal dynamics of soluble sugar,starch and total NSC in all organs of poplar in northern Jiangsu province.When the planting density ranges between 278 plants/hm²-400 plants/hm²,the lower density could be favorable for NSC storage in the individual level Moreover,under the same density conditions,the square configuration would be more likely to improve the carbon sequestration potential of poplar at the individual and the stand level.