Effects Of Nitrogen Application And Water Addition On Fine Root Biomass And Morphological Characteristics Of Dominant Species In Warm Temperate Forests

The dramatic increase in atmospheric nitrogen deposition and rapid changes in global rainfall patterns affect the balance and stability of forest ecosystems through complex interactions.Fine roots refer to plant roots with a diameter of ≤ 2 mm,which are the main organs for plants to absorb nutrients and water,and are also the most active part of the underground ecological process of forest ecosystems.Regarding the effects of nitrogen deposition and water addition on the biomass and morphological characteristics of fine roots,most of the relevant studies that have been carried out have been carried out by the methods of understory nitrogen application and understory water addition,ignoring the interception effect of forest canopy on nitrogen and rainwater.In addition,previous studies have usually been on a single forest layer or a single tree species,and there are few studies on the response of different forest layer species to nitrogen application and water addition,so the experimental results may be biased.In this study,this study relied on the field control experimental platform of "Canopy Simulation of the Impact of Nitrogen Deposition and Precipitation on Forest Ecosystem" established in Jigongshan National Nature Reserve established by the National Field Scientific Observation and Research Station of Dabieshan Forest Ecosystem in Henan Province,simulating the atmospheric nitrogen deposition and atmospheric rainfall enhancement process,and carried out canopy nitrogen application and canopy water addition treatment for evergreen deciduous broadleaved mixed forests in warm temperate zone.Three dominant arbor species: Liquidambar formosana Hance.,Quercus acutissima Carruth.,Quercus variabilis Bl.,and three shrub dominant species: Lindera glauca Bl.,Acer buergerianum Miq.,and Celtis sinensis Pers.were selected as the experimental research objects,analyzed the effects of nitrogen application(N),water addition(W),nitrogen application and simultaneous water addition(N+W)on the functional traits of fine roots of dominant species of evergreen deciduous broadleaved mixed forest in warm temperate zone,including fine root biomass,fine root morphological characteristics and fine root stoichiometric components,and constructed the influence path of nitrogen application and water addition on functional diversity and biomass of plant communities.The main results are as follows:(1)The fine root biomass of arbor dominant species and shrub dominant species respond differently to nitrogen and water addition.Nitrogen application and water addition tended to reduce the fine root biomass of the dominant species of trees and increase the fine root biomass of the dominant species of shrubs.Due to the different characteristics of fine roots of tree species,the interaction of nitrogen and water may have both a promoting effect and an inhibitory effect on the fine root biomass of arbor dominant species and shrub dominant species.There were significant seasonal differences in the fine root biomass of the dominant species of trees,while there were no significant seasonal differences in the fine root biomass of the dominant species of shrub.The fine root biomass of the dominant species of trees showed the highest seasonal dynamic trend in the non-growing season,followed by the growing season,and the lowest at the end of the growing season,while the fine root biomass of the dominant species of shrub showed no obvious seasonal dynamic trend.(2)The effects of nitrogen application on the morphological characteristics of fine roots of arbor dominant species and shrub dominant species were different.Nitrogen application increased the average diameter of fine roots of the dominant species of Arbor,and decreased its specific root length and specific root area.Conversely,nitrogen application inhibited the growth of the average diameter of the dominant shrub species,but promoted the increase of their specific root length and specific root area.Water addition had negative effects on the specific root length and specific root area of fine roots of arbor dominant species and shrub dominant species.In addition,the morphological characteristics of the fine roots of the dominant shrub species showed a trend of seasonal dynamic changes.(3)Under nitrogen application and water addition,there was no significant change in the total carbon content of fine roots of the dominant tree species and the dominant shrub species.For the fine roots of the dominant species of Arbor,nitrogen application,water addition and nitrogen application plus water addition treatment had basically no effect on the total nitrogen content.For the fine roots of the dominant shrub species,the water addition treatment and nitrogen application plus water addition treatment tended to increase the total nitrogen content,which increased the total nitrogen content of the fine roots of Lindera glauca Bl.and Celtis sinensis Pers.,and decreased the total nitrogen content of Acer buergerianum Miq.(4)In general,nitrogen application tends to reduce the functional diversity of plant communities,and water addition tends to increase the functional diversity of plant communities,that is,under nitrogen application conditions,the utilization range of functional space and resource utilization efficiency of community species will decrease,and the ecological niche complementarity between species is weak,while under water addition conditions,the functional space utilization range of species increases,and the distribution of species in functional space tends to be scattered and evenly distributed.(5)Nitrogen application and water addition have both direct and indirect effects on plant functional diversity and fine root biomass.Both nitrogen application and fine root stoichiometry had negative effects on the functional diversity of plant communities,and the effects were significant(P<0.05).Nitrogen application has a negative effect on biomass,while water addition has a positive effect on biomass.The stoichiometric components had a negative effect on biomass and the effect was significant(P<0.05).In summary,nitrogen addition had a negative effect on the fine root biomass of the dominant species,and tended to reduce the fine root biomass.Water addition had a positive effect on the fine root biomass of dominant species,and tended to increase fine root biomass.The morphological characteristics and stoichiometry components of the fine roots of arbor dominant species and shrub dominant species had different responses to nitrogen application and water addition.In addition,nitrogen application and water addition had negative effects on the functional diversity of plant communities,and nitrogen application had a significant impact on it.The above results are due to the adaptive strategies adopted by plants in response to environmental changes,which have certain reference value for understanding the ecological functions of forest ecosystem roots,and are of great significance for further exploring the process of underground ecology of forest ecosystems under the background of global climate change.