Interannual Variation Of Biomass And N And P Of Black Locust Plantations In Zhifanggou Watershed Of Ansai County

In order to understand the biomass and N and P stoichiometry changes of black locust at different stand age in the Loess Plateau,four stand ages of black locust in the forest age were selected for 16,27,33,and 43 years?a?,using the tree ring method to determine the annual tree ring growth width,using the local black locust allometric growth equation to calculate its annual biomass to understand the biomass allocation of various organs during the growth of black locust,and the process of biomass accumulation of black locust in different stand ages;at the same time,through the slicing and processing of tree rings,the changes of N,P and N:P values,and N,P and N:P were analyzed.The relationship between N,P,N:P values and radial growth,the main findings are as follows:?1?During the growth process,the average diameter at breast height?DBH?of the black locust is gradually increased.The average tree height reached the maximum at 33a and then decreases.The density of the black locust plantation generally decreased with the increase of forest age.The N and P concentrations in the topsoil of black locust at 33a were higher than the other three forest ages.With the increase of soil depth,the concentrations of N and P decreased,and the concentration of N decreased mainly in the 0-50cm soil layer,and then the rate of decline was slow.There was no significant difference between different forest ages.The P concentration had been slowly decreasing with the increase of soil depth.Among them,the P concentration of black locust at 33a and 43a had been significantly higher than that in the soil at 16a.?2?The biomass growth of various organs of different ages black locust showed that roots>dry>branches>bark>leaves.In the first 1-2 years after reaching the height of the DBH,the growth of underground biomass of black locust was higher than that of aboveground biomass.In the subsequent growth period,the amount of aboveground biomass growth was higher than that of underground biomass growth,and the black locust at each forest age stage showed a state in which biomass growth increased first and then stabilized.The cumulative biomass of each organ also showed root>stem>branches>bark>leaves at each stage of forest age.In 2010-2013,the growth of black locust biomass in 27a,33a,and 43a showed a significant increase.?3?The plot biomass of the 16,27,33 and 43a black locust forests calculated from the plots of the measured breast diameter data were:51.18,94.89,122.52 and 129.18 t hm^-2,respectively;and the plot biomass of the 16a,27a,33a and 43a black locust calculated from ring width were 49.53,124.80,141.76 and 161.85 t hm^-2,respectively.There was no significant difference in the cumulative biomass calculated by the two methods.?4?The N concentration of the black locust in different forest ages was high in the annual ring elements near the bark.Except for the black locust of 43a,the P concentration of16a,27a and 33a were consistent with the variation of N concentration.The N:P values were consistent in the early stage of tree growth in black locust forests of 16a,27a,and 33a,and gradually decreased in the annual rings near the bark.There was a negative correlation between the N concentration and the radial growth of black locust in different ages.Except for the black locust of 43a,the P concentration of black locust in the other three forest ages also showed a negative correlation with radial growth.Among them,in the locust forest of16a and 33a,the annual ring width and the N and P concentrations showed a significant negative correlation?P<0.01?.