Flux Changes And Distribution Characteristics Of Carbon And Water In Chinese Fir Plantation In Huitong

Forest ecosystem plays an important role in terrestrial carbon and water cycle,which is of great significance for mitigating global climate change and promoting the sustainable utilization of carbon and water resources.In this paper,the Chinese fir plantation in Huitong,Hunan Province is taken as the research object.The eddy correlation system,meteorological gradient observation system and hydrological observation system are used to locate the observation data of carbon and water flux and its components.Combined with literature and mathematical model,the dynamic change characteristics of each component of carbon and water cycle in Chinese fir plantation in Huitong from 2008 to 2019 at the annual and interannual scales and its relationship with environmental factors are studied.The change of water use efficiency and the characteristics of carbon and water distribution were analyzed,which provided a theoretical basis for predicting the response and feedback of carbon and water cycle of Chinese fir plantation to climate change.The main research results are as follows:(1)The carbon storage of stand and litter increases year by year,and the carbon storage of organs is dry>root>leaf>branch.Understory vegetation carbon storage decreases year by year,and herbaceous carbon storage is more but the proportion decreases year by year.Soil carbon storage first increases and then decreases with the increase of forest age,mainly distributed in 0～20 cm,and decreases with the increase of soil depth.(2)The annual variation of productivity and respiration show a single peak curve,and the minimum monthly mean and maximum monthly mean are in January and July,respectively.The average annual differences of total primary productivity(GPP),net ecosystem productivity(NEP)and net primary productivity(NPP)are 194.72,26.94 and 60.65 gC·m-2 mon-1,respectively.The average annual differences of ecosystem respiration(RE),autotrophic respiration(RA)and heterotrophic respiration(RH)are 167.78,134.05 and 35.35 gC·m-2mol-1,respectively.GPP,NPP and NEP fluctuated between years,with the lowest values in 2011(1482.70,412.68,104.15 gC·m-2a-1)and the highest values in 2015(2249.89,918.37,561.72 gC·m-2a-1).RE,RA and stem respiration fluctuated,The variation of RH,leaf and root respiration are relatively stable.The maximum values of RE,RA and stem respiration are in 2019(1719.30,1396.80,797.74 gC·m-2a-1),the maximum value of RH is in 2014(336.73 gC·m-2a-1),and the maximum values of leaf respiration and root respiration are in 2015(405.49,227.97 gC·m-2a-1).(3)The average annual variation of precipitation,evapotranspiration(ET),interception evaporation,transpiration and underground runoff is a unimodal curve,and the fluctuation of soil evaporation and surface runoff is small.Among them,the minimum monthly mean of atmospheric precipitation and forest precipitation is in January(50.7,37.7 mm),the maximum is in May(217.3,182.2 mm),the minimum monthly mean of ET and transpiration is in December(35.1,15.6 mm),the maximum is in May(154.1,114.1 mm),the maximum monthly mean of interception evaporation and underground runoff is in June(36.2,82.3 mm),the minimum is in November(9.8 mm)and February(11.3 mm).The interannual variation show that precipitation,ET,transpiration and underground runoff show an upward trend from 2009 to 2015,and a downward trend from 2015 to 2018.Interception evaporation,soil evaporation and surface runoff have little fluctuation.(4)On monthly scale,GPP shows significant linear relationship with temperature(Ta)and precipitation(P)(p<0.001),and significant quadratic polynomial relationship with PAR and VPD(p<0.001).NPP and NEP show extremely significant linear relationships with Ta,PAR and VPD,respectively(p<0.001),and NPP shows significant linear relationships with P(p<0.01).Both RE and RA show extremely significant quadratic polynomial relationship with Ta and VPD(p<0.001),and extremely significant linear relationship with P(p<0.001).Moreover,RE shows extremely significant quadratic polynomial relationship with PAR,and RA shows extremely significant linear relationship with PAR(p<0.001).RH and soil respiration show extremely significant linear relationships with Ta(p<0.001),PAR and VPD(p<0.001),and RH shows extremely significant linear relationships with P(p<0.001)and soil respiration shows significant linear relationships with P(p<0.05).ET and transpiration show extremely significant linear relationships with P and Ta(p<0.001),extremely significant quadratic polynomial relationships with PAR(p<0.001),and significant quadratic polynomial relationships with VPD(p<0.05).At the annual scale,GPP shows a significant linear relationship with P and VPD(p<0.05).RE only have a very significant linear relationship with VPD(p<0.001),RA have a very significant linear relationship with VPD(p<0.001)and a significant linear relationship with Ta(p<0.05),and soil respiration only have a significant linear relationship with P(p<0.05).ET and transpiration show extremely significant linear relationship with P(p<0.001),and significant linear relationship with VPD(p<0.05).(5)The average water use efficiency of Chinese fir plantation is(2.17±0.30)gC·kg-1H2O,and the average annual variation is high in autumn and winter but low in spring and summer.The lowest and highest monthly mean values are in May(1.36 gC·kg-1H2O)and October(5.52 gC·kg-1H2O),respectively.The minimum and maximum values are in 2008(1.83 gC·kg-1H2O)and 2009(2.83 gC·kg-1H2O),respectively.(6)The carbon and water distribution characteristics of Chinese fir plantation are as follows:GPP,NPP and NEP are 1969.68,743.03 and 403.49 gC·m-2a-1,respectively.RE is 1566.19 gC·m-2a-1,of which RA and RH account for 78.32%and 18.4%,respectively.Total carbon storage is 109.72 t·hm-2,soil carbon storage account for 78.05%.Forest carbon storage is 20.52 t·hm-2,stem,branch,leaf and root account for 56.38%,9.80%,13.74%and 20.08%respectively.Understory vegetation carbon storage is 2.37 t·hm-2,shrub and herb account for 31.65%and 68.35%respectively.Litter carbon storage is 1.19 t·hm-2.The precipitation is 1288.1 mm,and the surface runoff and underground runoff are 8.72 mm and 357.79 mm,respectively.ET is 920.06 mm,transpiration,interception evaporation and soil evaporation account for 65.53%,25.99%and 8.48%respectively.In summary,the annual and interannual variations of carbon and water cycle components in Chinese fir plantation and their relationships with environmental factors are different.GPP,RA,precipitation and transpiration are the most important carbon and water input and output items in Chinese fir plantation.