Coarse Root Decomposition And Its Control Factors Among 10 Co-Occuring Common Tree Species In A Temperate Forest,Northeast China

Coarse roots(>5 mm)are important functional organs of plants accounting for most of the total root carbon storage,and plays an important role in ecosystem carbon and nutrient cycling,while coarse root decomposition is also a hot spot and difficult point in ecological research.The root decomposition rate is closely related to the diameter of the system,and the root decomposition rate of different diameters is different,resulting in a large difference in nutrient return rate.At present,the research on root system mainly focuses on fine roots(<2 mm),while there is few studies on the pattern of coarse root decomposition and the main factors affecting coarse root decomposition.Its regulatory factors and the mechanism is unclear.In this study,the coarse roots(5-10 mm)of 10 tree species,AM species(Phellodendron amurense,Juglans mandshurica,Fraxinus mandschurica,Acer mono),EM species(Pinus koraiensis,Larix gmelinii,Betula platyphylla,Ulmus davidiana var.japonica,Tilia amurensis and Quercus mongolica)commonly found in the temperate forests of Northeast China were studied by burier-bag method for a period of two years,to explore the dynamic changes of coarse root decomposition and nutrient release and their internal regulatory factors.The results of the study showed that:(1)Among the 10 tree species,the initial chemical composition varies significantly with significant differences,which affected the decomposition of coarse roots.For the tree species that decompose quickly,such as AM species Juglans mandshurica and Phellodendron amurense,they have lower levels of lignin,lignin/nitrogen,and higher levels of sulfur(S),and calcium(Ca);The reverse is true for slower tree species,such as EM species Quercus mongolica,Larix gmelinii,etc.It was explained that the different initial chemical components of different tree species affected the decomposition of coarse roots.(2)With the increase of decomposition time,In the early stage of decomposition,the decomposition rate of coarse root is relatively fast,and in the later stage,the decomposition rate of coarse root is relatively slow.The results of this experiment show that: the annual decomposition coefficients of the coarse roots of AM species(Phellodendron amurense,Juglans mandshurica,Fraxinus mandschurica,Acer mono)were 0.826、0.897、0.477、0.341,EM species(Pinus koraiensis,Larix gmelinii,Betula platyphylla,Ulmus davidiana var.japonica,Tilia amurensis and Quercus mongolica)were 0.358 、 0.264 、 0.244 、 0.593 、0.458、0.227,respectively.During the whole process of coarse root decomposition,the decomposition rate between the 10 tree species was significantly different.The decomposition rate of each tree species from fast to slow is as follows: Juglans mandshurica>Phellodendron amurense>Ulmus davidiana var.japonica>Fraxinus mandschurica>Tilia amurensis>Acer mono>Pinus koraiensis>Betula platyphylla>Larix gmelinii>Quercus mongolica.(3)The concentration of C and N nutrients,as well as the retention rate of C and N in the coarse roots of the 10 tree species,were also different.In the early stage of decomposition,the concentration of endomycorrhizal species C increased,while the concentration of ectomycorrhizal species C showed an overall trend of increase-decrease-increase.In the late stage of decomposition,endomycorrhizal tree species Juglans mandshurica and Acer mono showed a downward-rising trend,while Fraxinus mandschurica and Phellodendron amurense showed an upward-declining trend.During the decomposition process of 10 tree species,the N concentration showed an increasing trend,and the N concentration of endomycorrhizal species was slightly higher than that of ectomycorrhizal species.At different decomposition times,the retention rate of C of the 10 species showed a downward trend,indicating that C was in the release state of the 10 species.The retention rate of N now shows a downward-upwarddownward trend,indicating that N is both released and enriched during the process of crude root decomposition.(4)This experiment indicates that the decomposition rate of coarse roots of 10 tree species was regulated by the contents of different initial chemical components.Experimental studies have found that the mass lossing of AM species coarse root is negatively correlated with manganese(Mn),lignin,and lignin/nitrogen content(P<0.001),but positive correlation sulfur(S)and calcium(Ca)(P<0.001).Experimental studies have found that the mass lossing of EM species coarse root is negatively correlated with carbon: nitrogen ratio,lignin,and ligninnitrogen ratio content(P<0.001),but positive correlation Kalium(K),Phosphorus(P)and hemicellulose(P<0.001).Other chemical indexes determined in this experiment,such as Aluminum(Al),Ferrum(Fe),Magnesium(Mg),Natrium(Na),Zinc(Zn),cellulose,were not significantly correlated with the decomposition rate.