Effects Of Nitrogen Addition On Fine Root Production And Fine Root Morphology Of Metaseguoia Glyptostroboides And Populus Deltoides According To In-growth Cores Method

Nitrogen deposition is a hot topic issue of global change.Fine root is critical in the belowground nutrition cycling in forest ecosystem.Understanding the response patterns and feedback mechanisms of forest ecosystems associated with this continued,increased nitrogen deposition and rapid nitrogen cycle is vital for the maintenance of forest ecosystem health and productivity.In this study,13-year-old poplar and 21-year-old metasequoia were selected as the research object.A total of 5 nitrogen concentration treatments(N0=0 g·m^-2·a^-1,N1=5 g·m^-2·a^-1,and N2=10 g·m^-2·a^-1,N3=15 g·m^-2·a^-1,N4=30 g·m^-2·a^-1)were set up,and the fine root production and morphology of two tree species were studied by in-growth soil core method.The distribution characteristics of fine root production and morphology in different soil layers and different root orders of different tree species,and their responses to different levels of nitrogen deposition were discussed.The main findings are as follows.?1?In natural state,with the increase of soil depth,the fine root production of metasequoia and poplar decreased significantly,and the vertical distribution of fine root production in each root order rank also showed a vertical distribution,that is,significantly decreased with the increase of soil depth.The fine roots production at all levels in the same soil layer decreased significantly with the increase of root order.Root diameter and root length were increased and the special root length and root length density decreased with root order increasing gradually in the metasequoia and poplar plantation.The average root diameter of each root order of metasequoia and poplar increased with the depth of soil layer.The root length,the special root length and the root length density decreased with the increase of soil depth.The root length,the special root length and the root length density in the 20-30cm and 30-40cm soil layers were significantly smaller than that in the 0-10cm soil layer.The vertical distribution of fine root production and fine root morphological changes of Metasequoia and poplar trees both favor fine root growth and nutrient uptake.?2?Nitrogen addition resulted in fine root growth reduction in metasequoia and poplar planation.High nitrogen concentration significantly reduced the total production of fine root of metasequoia plantation,and the total root production in N2,N3 and N4 plots of poplar plantation and in N3 and N4 plots of metasequoia were significantly smaller than that of N0 control,while the low nitrogen concentration?N1 and partial N2 treatment?had no significant difference with the control plots?N0?in the total root production of two tree species.The high concentration of exogenous nitrogen input allows soil nutrients to maintain root physiological functions for a longer period of time,resulting in reduced root production.Therefore,increased nitrogen deposition will have an adverse effect on the growth of trees.?3?Exogenous nitrogen input significantly reduced the fine root production in surface soil?0-10cm and 10-20cm?of two tree species,and decreased the fine root production significantly with the increase of nitrogen concentration,and the exogenous nitrogen input had no significant influence on root production in the deeper soil?20-30cm and 30-40cm?.The input of exogenous nitrogen had a significant effect on the 1th²th order root production of metasequoia and the1th³th order root production of poplar in the 0-20cm soil,and the increase of fine root production with the nitrogen input significantly decreased;basically,there was no significant effect on the 3th⁴th fine root production of the two tree species.?4?The addition of exogenous nitrogen significantly increased the average diameter of the first or second order roots of the metasequoia in 0-20cm and of the poplar in 0-30cm soil layer.The root length,the special root length and the root length density of the first or second order roots were significantly reduced.The morphological indexes of the first or second order roots in N3and N4 plots were significantly different from those of the control,but the nitrogen addition had no significant influence on the morphological indexes of the root order of the metasequoia and poplar at the 30-40cm soil layer.The input of exogenous nitrogen mainly affects the production and morphology of fine roots in surface soil,and the high concentration of nitrogen treatment will inhibit the growth of fine roots,which will affect the growth and development of trees.Therefore,the application of excessively high concentration of nitrogen fertilizer should be avoided in the practical application of forestry production.