Spatio-temporal Variation Of Carbon Source/Sink Of Vegetation And Its Response To Climate Change In The Hexi Corridor

This study estimated the monthly Net Primary Productivity?NPP?of vegetation in the Hexi corridor from 2001-2016 based on the model of Carnegie Ames Stanford Approach?CASA?to quantify the carbon source of vegetation and evaluate the carbon balance of Hexi corridor and its response to natural elements.We adopted the equation of Heterotrophic Respiration rate and Soil Respiration rate proposed by Bond_Lamberty and Raich to obtain Soil Microbial Respiration?Rh?of this study area.According to the formula NEP=NPP-Rh,we can obtain the monthly Net Ecosysterm Productivity?NEP?as a quantitative index to evaluate the balance of payment of carbon source and carbon sink and analyse the effects of natural factors such as temperature,precipitation and solar radiation on carbon source \ sink.The main conclusions were as follows: 1.The spatial and temporal analysis of net primary productivity?NPP?of vegetation in Hexi corridor based on the CASA model?1?In general,the vegetation NPP of Hexi corridor decreases from southeast to northwest and from east to west.As a whole,the high value of NPP is mainly distributed in the eastern section of Qilian mountains and the oasis farming area in the central plain.The average value of vegetation NPP in the study area for 16 years was 144.80 g C·m^-2·a^-1,and the total value was about 32.62 Tg C·a^-1.?2?The NPP of Hexi corridor was significantly increased from 2001 to 2016?P<0.01?,with an average annual growth rate of 2.62 g C·m^-2·a^-1.The annual total NPP increased from 26.25 Tg C·a^-1 in 2001 to 38.60 Tg C·a^-1 in 2016.?3?Interannual variability of different vegetation NPP is more stable in Hexi corridor.The arbor vegetation NPP is on the high side,shrubs NPP is lower with a certain characteristics of layered.The NPP sorting as follows: forest land > shrub > cultivated land > grassland > bare land sparse vegetation.2.Spatial and temporal analysis of Soil Microbial Respiration?Rh??1?On the whole,Rh in the Hexi corridoris decreasing from southeast to northwest,from east to west in turn.The high value of Rh is mainly distributed in the middle_eastern of study area.The average value of vegetation Rh in the study area for 16 years was 353.53 g C·m^-2·a^-1,and the total value was about 87.46 Tg C·a^-1.?2?The Rh of Hexi corridor was significantly increased from 2001 to 2016?P<0.01?,with an average annual growth rate of 0.43 g C·m^-2·a^-1.The annual total Rh increased from 67.43 Tg C·a^-1 in 2001 to 111.50 Tg C·a^-1 in 2016.3.Spatial and temporal analysis of vegetation carbon source/sink in Hexi corridor?1?The Hexi corridor is a carbon source in 2001-2016,it's ability increases by years and the carbon source area is much larger than the carbon sink area.The carbon storage capacity decreases from the south to the north,and is distributed in the northern region of Qilian mountain and the oasis area of the central plain,and the others are carbon source.?2?The three basins have a carbon source effect for 16 years.Carbon emissions are highest in the Shule River Basin,with a total carbon emissions of 24.24 Tg C·a^-1 in 16 years,and only 0.78 Tg C·a^-1 in carbon storage.?3?The area of carbon sink in 2016 was larger than 2001,and the area increased by about 339.81 km2.The Hexi corridor has a growth trend of 12.23% in the last 16 years.The most significant growth area is in the Qilian mountains and Anxi county.NEP has a large area of decline,mainly in the north and west of Hexi corridor.?4?Interannual variability of different vegetation NEP is more stable in Hexi corridor.The arbor vegetation NEP is on the high side,NEP of meadow is lower with a certain characteristics of layered.The NEP sorting as follows: forest land > shrub > cultivated land > grassland > bare land sparse vegetation.4.Response analysis of vegetation carbon source/sink to various factors in Hexi corridor?1?The carbon source/sink have different correlations with climatic factors in different regionsin the Hexi Corridor.Overall,there was a negative correlation with precipitation,a partial correlation coefficient of-0.89,a negative correlation with temperature,a partial correlation coefficient of-0.53,a positive correlation with solar radiation,and a partial correlation coefficient of 0.00038.In the carbon source area,the three factors are negatively correlated with the vegetation carbon source/sink.?2?Precipitation is the dominant factor which influences carbon source/sink of vegetation in the Hexi corridor and there are different responses of carbon source/sink of vegetation to climate factors in different areas.The dominant factor in the upstream of Hexi corridor is mainly solar radiation.The influence of temperature and precipitation gradually increased and the influence of solar radiation gradually decreased in the middle reaches.The significant factor is mainly precipitation in downstream.In general,Hexi corridor is a carbon source for 16 years,and the role of carbon sources gradually increased.Precipitation is the dominant factor which influences carbon source/sink of vegetation in the Hexi corridor,and its relative contribution is 62.09%,followed by solar radiation and temperature.