Effect Of Simulated Nitrogen Deposition On Fine Root Decomposition And Nutrient Release In Populus Deltoides And Metasequoia Glyptostroboides Plantations

Fine root is an important part in forest underground ecosystem,which is the core link in the process of carbon and nutrient cycling.Understanding the response of fine root decomposition and nutrient release to nitrogen deposition in forest ecosystems will help us to better manage the forest ecosystem.In this paper,the fine roots of poplar and metasequoia were used as research objects,and the fine root decomposition,nutrient release and their response to simulated nitrogen deposition were studied by using buried bag method.The levels of nitrogen application were respectively N0(0 g·m^-2·^a?-1?),N1(5 g·m^-2·^a?-1?),N2(10 g·m^-2·^a?-1?),N3(15 g·m^-2·^a?-1?)and N4(30 g·m^-2·^a?-1?).The purpose of this study is to discuss the decomposition rate and nutrient release of fine roots with different tree species and different diameter grades and their response mechanisms to different degrees of nitrogen deposition.The results showed that:?1?The decomposition rate of fine roots of poplar was significantly higher than that of metasequoia?p<0.01?.The effect of diameter grades on fine root decomposition was different due to different tree species.0-1mm fine roots of metasequoia decayed faster than 1-2mm fine roots,while 1-2mm fine roots of poplar decomposed faster.?2?The effect of different treatments on the decomposition of fine roots varied with tree species and diameter grades.According to the decomposition coefficients obtained by fitting negative exponential decomposition model,it can be seen that the exogenous N addition inhibited the decomposition of fine roots?0-2mm?of metasequoia except N3 treatment promoted the decomposition of 1-2mm fine roots of metasequoia,while the exogenous N addition promoted the decomposition of fine roots?0-2mm?of poplar except N1 treatment inhibited the decomposition of 1-2mm fine roots of poplar.?3?Under N0,N2,N3 and N4 treatments,the decomposition rate of fine roots was positively correlated with P content,cellulose/N,and negatively correlated with N/P.Under N1 treatment,the decomposition rate of fine roots was positively correlated with P content,and was negatively correlated with C/P and N/P.The initial P content,cellulose/N,C/P,and N/P of fine roots can be used as accurate indicators reflecting fine roots decomposition rate.?4?The C and P release rate of fine roots of poplar was higher than that of metasequoia?p<0.01?.The P release rate of 1-2mm fine roots of metasequoia was higher than 0-1mm fine roots?p<0.05?,and the P release rate of 1-2mm fine roots of poplar was higher than 0-1mm fine roots?p<0.01?.After 1a,the fine roots of poplar and metasequoia showed N enrichment,and the N enrichment of 1-2mm roots of metasequoia was significantly higher than that of 0-1mm?p<0.05?.The Ca remaining pecentage of metasequoia fine roots increased,and that of poplar fine roots decreased.The Mg remaining percentage of 0-1mm fine roots of metasequoia decreased slightly,while that of 1-2mm fine roots increased.The Mg content in the fine roots of poplar decreased,and the release rate of Mg of 1-2mm roots was significantly higher than that of 0-1mm roots?p <0.01?.?5?N1 and N2 treatments significantly inhibited the P release of 0-1mm roots of metasequoia?p<0.05?.N2 treatment significantly promoted the N enrichment of 1-2mm fine roots of metasequoia?p<0.05?;With the increasing of N concentration,the enhancement of Ca enrichment of metasequoia 1-2mm roots was enhanced.The exogenous N addition significantly promoted the C release of 0-1mm fine roots of poplar,and the order of C release rate was as follows: N2>N4>N1>N3>N0;N3 treatment promoted the Ca enrichment of fine roots?p<0.05?.N2 treatment significantly promoted the C release of 1-2mm fine roots of poplar?p<0.05?.?6?The initial C/N ratio of poplar fine roots was higher than that of metasequoia?p<0.01?,and the initial C/N of 1-2mm fine roots was significantly higher than that of 0-1mm fine roots?p<0.01?.The C/N of fine roots decreased with increasing decomposition time.Afer one year,the differrence of C/N of metasequoia fine roots in different N treatments was insignificant,while nitrogen deposition had significantly reduced C/N of fine roots of poplar?p<0.01?.