Responses Of Fine Root Turnover In Broad-leaved Korean Pine Forest To Nitrogen Increase And Water Reduction

Fine roots are the key link between plant and soil ecological processes,and are also the main organ for the underground part of forest to obtain resources.Fine root dynamics play an important role in regulating carbon circulate in terrestrial ecosystems.In the context of global climate change(such as nitrogen deposition increased and change of rainfall pattern),Fine roots can change their dynamic and morphological characteristics in response to changes in the external environment,thereby affecting the carbon cycle of ecosystems.At present,there are different conclusions about the response of fine root dynamics and morphology to nitrogen addition and precipitation reduction,and most of the experiments are carried out in the growing season.In this study,the broad-leaved Korean pine forest in Changbai Mountain was selected as the research object.Four treatments were selected,including control(CK),nitrogen addition(N),precition reduction(W),nitrogen addition and precition reduction(NW),and each treatment was repeated three times.In two years of observation period,Minirhizotron was used to measure the fine root dynamics and morphology of broad-leaved Korean pine forest in Changbai Mountain in response to environmental change.The purpose of this study is to provide data support for understanding and predicting how the dynamics of temperate forest fine roots respond to global climate change.Through two years of observation,the study found that:(1)The annual production of fine roots decreased under the treatments of nitrogen addition,precipitation reduction and the interaction of nitrogen and water,but the effect on the annual mortality was different between years.Compared with the first observation period,the average annual fine root production of the control,precipitation reduction、nitrogen addition and interaction of nitrogen and water decreased by 25.62 %,20.74 %and 38.62 % respectively,while the nitrogen addition treatment increased by 122.10 %.The average annual mortality of fine roots increased by 12.17 %(CK),128.90 %(N),122.18 %(W)and 65.93 %(NW)respectively.(2)The annual production and mortality of fine roots in different soil layers of different treatments had obvious vertical distribution.In the first observation period,the maximum annual production and mortality of control,precition reduction and the interaction of nitrogen and water treatments appeared in 10-20 cm soil layer,and the minimum appeared in 30-40 cm soil layer.The maximum value of annual production and mortality of nitrogen addition treatment appeared in 20-30 cm soil layer.In the second observation period,the maximum value of annual fine root production and the minimum value of annual mortality appeared in 20-30 cm soil layer.The distribution trend of other treatments is consistent with that of the last observation period.(3)The seasonal dynamics of the monthly average production and mortality of the fine roots are all multi peak distribution,and the distribution law of the maximum and minimum values is different.In the second observation period,the three treatments(N,W,NW)significantly increased the annual turnover rate of fine roots.(4)In the first observation period,nitrogen addition,precipitation reduction and the interaction of nitrogen and water did not significantly change the annual average turnover rate of fine roots and the annual turnover rate of each soil layer.The fine root turnover in10-30 cm soil layer was increased by nitrogen addition treatment,while that in 20-30 cm soil layer was increased by precipitation reduction and nitrogen water interaction treatment.(5)The annual average diameter of fine roots was significantly increased by nitrogen addition treatment.Precipitation reduction treatment did not significantly affect the annual average diameter of fine roots.Nitrogen water interaction treatment only significantly reduced the annual average diameter of fine roots at the bottom layer in the second observation period.Three treatments(N,W,NW)significantly reduced the monthly average living root surface and number of living fine roots.