| The carbon cycle of forest ecosystem is an important part of global carbon cycle,and the study of its carbon flux can help us understand the operation process and mechanism of forest ecosystem.In global flux observation,eddy covariance technique has become a recognized standard observation method,it can be on the high precision time quickly capture the atmosphere,land carbon flux variation signal interface,but it also has the limitation of the application,such as in a mountainous area under the condition of complex topography,irregular atmospheric turbulence activities,in the night,the atmosphere with high stability,turbulence when activity is weak,all can lead to flux measurement error.So now for mountain forest carbon flux in the process of simulation and study is less.It is very necessary to put forward a kind of long-term continuous observation technology of carbon flux,as a supplementary study in complex terrain condition and under the condition of the atmospheric stability.This study selected typical side Berlin in Beijing mountain area as the research object,through the use of stable isotope techniques,the system of CO2 flux in Beijing mountain Platycladus orientalis forest ecological system is studied and the simulation process of split.This study on forest ecosystem atmospheric CO2 concentration and the ?13C value of the observation,describes its characteristics and the relationship between environmental factors and at the same time,the binary mixture model are used to get the forest ecosystem in Beijing mountain area of atmospheric ?13C values influence the quantitative relationship.By the analysis of the isotope characteristics of different components of Platycladus orientalis forest ecosystem,the proportional relationship between different flux,and combined with soil respiration flux,completed the carbon flux of the forest ecological system of the separation and quantitative analysis,the mountain forest system photosynthesis,respiration fluxes in the year of 2017 and the net carbon flux.At the same time,the use of isotope method in the research institute is analyzed and compared with the model.The main results are as follows:(1)In 2017,the variation range of CO2 concentration in the mountainous area of Beijing is 366.07?720.04?mol mol-1,and the vertical distribution is decreasing from the ground to the canopy.The variation range of the ?13C value in the forest is-19.78?-3.48‰,and its vertical distribution is rising from the ground to the canopy,which is contrary to the change of CO2 concentration.CO2 concentration(y)and ?13C values are given as follows:y=0.0365+ 5.1462 x,R2=0.554(p<0.001),Keeling Plot relation is:y=7643.6 x-28.394,R2=0.563,the isotopic added value in Beijing mountain forest to atmosphere in 2017 is about 28.394 ‰.(2)Atmospheric stability has obvious day and night changes.It is stable in the night atmosphere and weak in turbulence.In daytime,the atmosphere is unstable and turbulence is strong.At night,we use the atmospheric stability as a filter,can effectively improve the accuracy of forest ecosystem nighttime breathing isotope values,for the accurate expression of forest ecological system flux split and simulation provides the basis.In the daytime,with the use of atmospheric stability as a screening condition,because the data is removed too much,the uncertainty of the daily net carbon flux isotope value of the forest ecosystem will increase.(3)Research by building the mean fitting equation with the use of the growing season,overcome the Keeling intercept discrete problems in growing season change:two methods as the ?canopy value the overall change in the growing season are showing up,first the trend of decrease after,and the result is very close,but by its correlation with environmental factors can be found using the equation as simulated?canopy value as compared to using average fixed value calculated ?canopy value,more sensitive response to environmental factors.(4)Forest ecosystem underground part(soil respiration)flux shows mono peak variation during the year,the average in the growing season is:2.93?mol m-2·s-1,The mean of forest ecosystem overground part flux is 1.61?mol·m-2·s-1,The mean of respiratory flux in the ecosystem 4.29?mol·m-2·s-1,The mean of daytime photosynthetic flux is 8.76?mol·m-2·s-1,The mean value of daily net carbon flux is-4.23?mol·m-2·s-1,Total net carbon flux during the growing season-0.12?mol·m-2·s-1?(5)Through the uncertainty analysis of flux analysis process:For net carbon flux:when the error of atmospheric CO2 concentration increases by 10 ?mol·mol-1,the net carbon flux will be overestimated by 2.7%;when the error of atmospheric ?13C value increases by 1‰,the net carbon flux will be underestimated by 8.59%;the error of the soil respiration flux on the net carbon flux is non-linear,and when the soil respiration flux error increases by 0.2 and 0.5?mol·m·-2·s-1,respectively,the net carbon flux will be underestimated by 8.64%and 46%,respectively;when the stomatal conductance error of CO2 canopy increased by 0.01 mol·m·-2·s-1,the net carbon flux will be overestimated by 17.66%;when the error of ?13Cn-eco increased by 1‰,the net carbon flux will be overestimated by 3.45%;when the error of ?13Cd-net increased by 1‰,the net carbon flux will be overestimated by 8.21%;when the error of?canopy increased by 1‰,the net carbon flux will be underestimated by 8.21%.For photosynthetic flux:when the error of atmospheric CO2 concentration increases by 10?mol·mol-1,the net carbon flux will be overestimated by 2.5%;when the error of atmospheric ?13C value increases by 1‰,the net carbon flux will be underestimated by 8.09%;when the soil respiration flux error increases by 0.5?mol·m-2·s-1,the net carbon flux will be underestimated by 0.38%;when the stomatal conductance error of CO2 canopy increased by0.01 mol·m·-2·s-1,the net carbon flux will be overestimated by 16.3%;when the error of ?13Cn-eco increased by 1‰,the net carbon flux will be overestimated by 0.84%;when the error of ?13Cd-net increased by 1‰,the net carbon flux will be overestimated by 7.62%;when the error of ?canopy increased by 1‰,the net carbon flux will be underestimated by 8.10%.For respiration flux:Atmospheric CO2 concentration,atmospheric ?13C value,?13Cd-net and ?canopy do not affect the simulation of respiratory flux;when the soil respiration flux error increases by 0.5?mol·m·-2·s-1,the net carbon flux will be overestimated by 19%;the error of ?13Cn-eco on the net carbon flux is non-linear,and when the error of ?13Cn-eco increased by 1‰ and 2‰,respectively,the net carbon flux will be underestimated by 27.1%and 44%,respectively.(6)For the whole growth season,CWC-S and CWC-L were used in the application of stomatal conductance:the mean value of the difference between CWC-L and CWC-S was 0.45‰.The mean value of the difference between CWC-L and CWC-S was 2.67%,and the total value of CWC-L was higher than that of CWC-S,the relationship between them could be described by y=0.6581x+6.5016,R2=0.6478;CWC-S method and CWC-L method were used in the application of photosynthetic flux:the mean value of Fp-cwc-L and Fp-cwc-s was 0.27‰.The mean value of Fp-cwc-L and Fp-cwc-s was-3.77%,and the sample points were basically distributed on the 1:1 line,with a very good linear relationship:y=0.9971x+0.2435,R2=0.9883.(7)FP method,CWC-S method and CWC-L method to obtain the canopy photosynthetic discriminant on the daily change law of the change trend is unified,leaf soluble sugar of days change and atmospheric CO2 than days change in the ?13C values are not enough to affect trends.FP method,CWC-S method and CWC-L method of photosynthetic flux on the daily change law of the change trend is also unified,three different methods to obtain the canopy photosynthetic discriminant difference of photosynthetic flux variation trend.Three kinds of methods,mutual verification results are good,no obvious difference between photosynthetic flux:y=0.9941x1-0.0901,R2=0.9872,y=0.9961x2-0.3417,R2=0.997,with y for Fp-FP(?mol·m-2·s-1),x1 for Fp-CWC-s(?mol·m-2·s-1),x2 for Fp-cwc-L(?mol·m-2·s-1).It is indicated that the difference between the photosynthetic discrimination obtained by these three methods will not have a significant effect on the photosynthetic flux,and the simulation results of FP method in this study are verified. |
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