| After the death of plant root system,the process of leaching,crushing and decomposition of soil microorganisms can produce carbon dioxide?CO2?,release nutrients and generate complex organic compounds,which play a vital role in plants and soil organisms.There are some problems in previous studies on root decomposition,for example,?1?In some forest ecosystems,a large number of roots grow in litters.However,previous researchers mainly focused on the decomposition of roots in soil layers,but often neglected the decomposition of roots in litters.?2?At present,the litter bag method is widely used in the root decomposition in the study.However,this method isolated roots from semi-decomposed litter leaf,soil and some soil organisms.The method can not truly reflect the decomposition of root system in the natural environment.It may produce certain deviation to estimate the root decomposition rate.?3?The previous research methods for root decomposition were mostly limited to the traditional approach,which was difficult to reflect the difference between absorptive roots and transport roots in the decomposition process.To address the above problems,we took the roots of Schima superba and Cleyera japonica,evergreen broad-leaved trees in the bifengxia reserve,yucheng district,ya'an city,sichuan province,as the research materials,and adopted root order classification and root function classification as the research framework.The roots were divided into grades 1-3?absorptive roots?,4-5?transport roots?and 6?transport roots?.By improving the litter-bag method?i.e.the root mixed with semi-decomposed litter leaf,humus?simulation of the root in the litter layer,humus layer decomposition of natural environment?mix with semi-decomposed litter and leaf litter bag placed in litter layer,mixed with humus litter bag placed in humus layer?,the decomposition of the period of 1 year experiment was carried out.During this period,root litter bags were recovered every 4 months and their residual mass and chemical element content were determined.The following contents were mainly discussed:?1?the difference in the decomposition rate of roots in the semi-decomposition litters?O layer?and humus layer?A layer?;?2?whether the mixing of litters and roots had an effect on root decomposition;?3?whether the mixture of humus and roots has an impact on root decomposition;?4?difference in root decomposition rate between the absorpt group and the transport group.The main results are as follows.?1?In terms of root matrix,there were significant differences in matrix quality between the absorptiive roots?1-3 grade?and the transport roots?4-5 and 6 grade?with S.superba and C.japonica.The content of nitrogen?N?,phosphorus?P?element of 1-3 grade absorptive roots of S.superba and C.japonica was significantly higher than 4-5 and 6 grade transport roots,and the element of kalium?K?,magnesium?Mg?content of S.superba was significantly lower than 4-5 and 6 grade transport roots,the content of carbon?C?and manganese?Mn?element of transport roots there was no significant difference.The contents of C,K,Mg,Mn element of C.japonica absorptive roots was lower than transport roots significantly.The root ash free mass residual rate of the two tree species showed a significant positive correlation with the initial P element content,and a significant negative correlation with mass residual rate of K element,in which the root mass residual rate of S.superba was also significantly negatively correlated with Mg element,and the root mass residual rate of C.japonica was significantly negatively correlated with Mn element.?2?In terms of location effect,the roots of S.superba and red light ratio in traditional littering bag method had no ash mass in layer O There was no significant difference between the residual rate and the root system in layer A(except schima superba 4-5 transport roots,the residual rate of ash free mass in layer O was significant lower than that in the A layer.After decomposition of one year,the average mass loss of S.superba pure roots in the O layer was 25.3%,significantly higher than that in the A layer?20.1%?.The mass loss of C.japonica pure roots in the O and A layer was 18.6%and 17.9%,respectively.In addition,the decomposition coefficient?k?of 1-3 grade absorption pure roots of the two tree species in the O layer is less than that of the pure roots in the A layer,while the 4-5 grade transport pure roots are greater than that of the pure roots in the A layer.?3?In terms of mixing effects,the mixture with semi-decomposed litters and humus soil was significantly accelerated the decomposition of root systems in each layer of the two tree species.The residual rates of C,N,P,K and Mg in 1-3 grade absorption roots of S.superba and C.japonica were all lower than those in the same layer of pure roots after mixing with litters and humus,and the residual rates of Mn in the mixture with litters were higher than those in the same layer of pure roots.The residual rate of C,N and K of S.superba and C.japonica 4-5 grade roots mixed with litters and humus was significantly lower than that in the same layer of pure roots,and the Mn residual rate in the F layer mixed with litters was significantly higher than that in the same layer of pure roots.?4?In terms of the root group effect,the root group effect had a very significant impact on the ash free mass residual rate of the two species.After the decomposition of 1.0 a,the ash free mass residual rates of the 1-3 grade pure roots in the F layer and the H layer of S.superba and C.japonica were significantly higher than that of the 4-5 and 6 grade transport roots.For the mixed roots,the ash free mass residual rate of S.superba and C.japonica 1-3grade roots mixed with litters and humus was significantly than that of grade 4-5 and 6 grade roots.In summary,this study showed that the decomposition rate of roots of two species of traditional litter-bag method in the litter-layer was almost the same as that of the traditional litter-bag method.The decomposition rate of level 1-3 grade absorption roots was significantly higher than that of level 4-5 and level 6 grade transport roots.However,the decomposition rate of two species'roots which mixed with semi-decomposed litters and humus was accelerated?especially the absorption root?.In addition,The level 4-5 and 6grade transport roots of the two tree species showed similar results in mass loss and element dynamics.Because of the traditional litter-bag method isolates the semi-decomposed litters and humus soil from the decomposed root system,this would affecting the decomposition process of root system,and the early decomposition rate of root system?especially the lower root system?is underestimated. |
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