| Root litter as the main component of underground litters,its death and decomposition are important links of carbon(C)turnover and nutrient cycling in forest ecosystem.Most of the previous root decomposition studies used the diameter-level method,ignoring the differences caused by the variable in root forms and functions.These studies paid more attention to the root decomposition at the surface soil,and paid less attention to the root decomposition at litter layer and deep soil.To address the above problems,our study took three evergreen broad-leaved tree species in the Bifengxia Nature Reserve in Ya’an City,Sichuan Province,namely Schima superba,Cleyera japonica and Eurya loquaiana as the research materials.The roots of these three evergreen broad-leaved tree species were divided into grades 1-3(absorptive roots),4-5(transport roots),and 6(transport roots)combining the research framework of root branch-order classification and root function classification.By the litter-bag method to place the roots in the litter layer,0-10 cm,20-30 cm,and 40-50 cm soil layers in order to simulate root decomposition,and then litter bags were recovered every 4 months.We studied the mass loss and the release status of elements and components of different functional root groups at different soil layers,mainly to discuss the decomposition differences between absorptive roots and transport root and between different soil layers.The two-year decomposition test yielded the following main results:(1)The absorptive roots and transport roots of the three tree species were significantly different in the initial chemical properties(except C content).The nitrogen(N),phosphorus(P),calcium(Ca),and natrium(Na)contents of absorptive roots were significantly higher than transport roots,and the contents of kalium(K),magnesium(Mg),manganese(Mn)and the contents of total phenol and condensed tannin were higher in transport roots.At different soil layers,the initial Mn contents of the roots of the three tree species were linearly correlated with the decomposition coefficients.The initial Mn content played an important role in root decomposition.(2)At the litter layer,the decomposition of the absorptive roots of the three tree species were significantly slower than transport roots and the decomposition coefficients of1-3 grade absorptive roots were less than 4-5 and 6 grade transport roots.One of the reasons for this phenomenon may be that the initial Mn contents of transport roots were significantly greater than absorptive roots.However,no consistent results had been seen in other soil layers,and the difference in decomposition between root groups at other soil layers requires longer experimental time to verify.(3)During the decomposition process,the percentages of initial mass remaining of the three tree species was as follows: litter layer <0-10 cm <20-30 cm <40-50 cm.The root decomposition rates of the three tree species were extremely different between different soil layers.With the deepening of the soil layer,the root decomposition coefficient decreases significantly,and the decomposition coefficient of litter layer was about 2.4times that of the 40-50 cm soil layer.(4)In the process of decomposition,the P residual rates of absorptive roots of the three tree species were significantly smaller than transport roots,the Mn residual rates of transport roots were significantly smaller than absorptive roots,and the C residual rates of6 grade transport roots were the lowest.The N residual rates of absorptive roots in Schima superba and Cleyera japonica were lower than transport roots.The total phenolic and condensed tannin residual rates of absorptive roots of the three tree species were significantly higher than transport roots.In general,the elements and components with higher initial content were also released more during the decomposition process,resulting in lower residual rates.In summary,our study showed that the root decomposition coefficients of the three tree species were linearly correlated with the initial Mn contents of root,and the initial Mn content of root was an important factor in predicting the root decomposition rate.The initial Mn contents of transport roots of the three tree species were significantly higher than absorptive roots,which was one of the reasons why transport roots at litter layer decomposed faster than absorptive roots.The soil layer has a very significant effect on root decomposition,and as the deepening of the soil layer,the root decomposition coefficient decreased significantly.The absorptive roots and transport roots of the three tree species were significantly differet in initial element contents and component contents.The element and component with higher initial content was also released more during decomposition,resulting in a lower residual rate. |
