Effects Of Nitrogen Deposition And Canopy Nitrogen-water Interaction On Seasonal Dynamics Of Fine Root Characteristics In Warm Temperate Forests

Global changes?such as nitrogen?N?deposition and changes in rainfall patterns?have severely affected the structure and function of forest ecosystems.As the main organ for underground nutrient absorption of vegetation,the production and turnover of fine roots play an important role in nutrient cycling in forest ecosystems.In addition,fine roots are most active and sensitive to environmental changes.At present,there are many studies on the response of fine roots to N deposition and changes in rainfall patterns,but there is no conclusion yet.And most of the experiments were carried out based on the N application method under the forest,ignoring the ecological processes such as N absorption,adsorption,and retention by the canopy.This experiment relies on the field experimental control platform of canopy simulated N deposition in Jigongshan?JGS?Nature Reserve,Xinyang City,Henan Province.Canopy?CAN?and understory?UAN?addition N at different concentrations(25 kg ha^-1yr^-1 and 50 kg ha^-1yr^-1),canopy addition of low concentration N?CN25?,canopy rainfall enhancement?+ 30% local rainfall,CW?and N-water interaction?CN25 × CW,CNW?explore the seasonal dynamics of fine root biomass and morphology.Compared with traditional understory N addition,this study more realistically simulates atmospheric N deposition and provides a more realistic scientific basis for predicting the impact of future environmental changes on the structure and function of forest ecosystems.The research results and conclusions are as follows.1.Effects of different concentrations of N on biomass and morphology of fine roots in canopy and understory:?1?Different N addition methods and concentrations had no significance difference in fine root biomass at different periods?p > 0.05?.CAN increased while UAN reduced total fine root biomass,only CN50 had a significant effect?CK = 148.7±36.2 g/m²,CN50 = 255.3±34.7 g/m²,p < 0.05?.UAN increased the specific root length?SRL?and the specific root surface area?SRA?during the growing season,but decreased the root tissue density?RTD?,while CAN did the opposite.At the end of the growing season,UN25 significantly increased SRL and SRA and decreased RTD?p < 0.05?,which were 49.4%,45.4%,and-36.4%,respectively.In the non-growing season,CN25 significantly reduced SRL and SRA?p <0.05?,which were-34.5% and-25.3%,respectively.CN25 and UN25 significantly increased RTD?p <0.05?,which were 28.7% and 32%,respectively.?2?There was no significant difference in fine root biomass in the experimental treatment,which may be related to the local natural N deposition rate.CAN and UAN have different effects on fine root biomass.The available N concentration on fine roots may be different due to the N application method.Fine root morphology responded differently in different seasons.It may be due to the fact that vegetation more actively adapts to seasonal changes and changes in soil nutrients by changing fine root morphology.2.Effects of canopy N-water interaction on fine root biomass and morphology:?1?CN25,CW and CNW have no significant difference on fine root biomass in different periods?p > 0.05?.CNW decreased?CK = 148.7±36.2 g/m²,CNW = 146.2±19.6 g/m²?while both CW and CN25 increased?CN25 = 171.3±25.4 g/m²,CW = 188.5±36.9 g/m²?total fine root biomass,but neither was significant?p > 0.05?.CW significantly increased the seasonal difference in fine root biomass?p <0.05?.During the growing season,CNW significantly increased SRL and SRA?p <0.05?,which were 13% and 34.5%,respectively.CNW decreased RTD but not significantly?p> 0.05?.At the end of the growing season,CW significantly reduced RTD?-28.2%,p <0.05?and increased SRL and SRA but not significantly?p> 0.05?.In the non-growing season,CN25 significantly reduced SRL and increased RTD?-34.5%,28.7%,p <0.05?.CW significantly reduced SRL and SRA?-42.4%,-40.4%,p <0.05?and increased RTD but not significantly?p> 0.05?.N-water interactions had significant effects on total fine root biomass and fine root morphology during the non-growing season?p <0.05?.However,single factor N or water treatment had no significant effect on biomass and morphology.?2?CNW reduced the total biomass of fine roots.It may be because of the rain enhancement at the same time of N application,the N passing through the canopy was quickly washed away by the rain to the ground,which reduced the canopy interception effect.This results in a significant increase in soil available N and inhibits the growth of fine roots.N-water interactions have different effects on fine root morphology in different seasons.Indicating that vegetation can actively adapt by changing the fine root morphology when facing seasonal and environmental changes.In this experiment,CAN was closer to true atmospheric N deposition than UAN.Different N application methods have different effects on fine roots,both in biomass and morphology.Indicating that UAN cannot effectively reflect the effect of N deposition on fine roots.Increased rainfall has a significant impact on the seasonal dynamics of fine root biomass.This indicates that rainfall may be the limiting factor for fine root growth in this area.The effects of N-water interactions on fine roots are complex,but their internal mechanisms are unclear.