Study On Soil Respiration Monitoring Based On Combined Measurement Of CO₂ And Moisture In Soil Profile

Soil is the largest carbon pool in terrestrial ecosystems and it is also an important factor in studying the global carbon balance.Soil respiration may constitute up to about three-quarters of total ecosystem respiration which has an important impact on the global carbon cycle and climate change.We can have a deeper understanding of soil CO₂ emissions by exploring the changes of soil respiration at different depths.Therefore,this study uses the concentration gradient method as the basic principle to develop a CO₂ flux monitoring system,which collects CO₂ concentration,moisture and temperature values at soil vertical depths of 3 cm,10 cm and 18 cm,respectively.And then estimates the soil CO₂ flux by Fick’s first law.Firstly,this study analyzes the current research on soil CO₂ flux monitoring.After that,the principle of the concentration gradient method to calculate the CO₂ flux is introduced.The hardware and software design of the soil CO₂ flux monitoring system is completed based on this principle.In order to realize real-time remote monitoring of data,a CO₂ flux model conversion and display platform based on the idea of Internet of Things is designed.Then,the experiment verifies that the CO₂ flux monitoring system has good stability.Finally,this system was used for data collection in four time periods in a year at the Gongqing Forest Farm in Shunyi,Beijing.Based on the concentration gradient method and using five gas diffusion models to process the collected data,soil CO₂ fluxes for four time periods were obtained.At the same time,compared with the measured data of LI-8100 equipment,the applicability of 5 gas diffusion models was analyzed and evaluated.The results show that Moldrup model is the most suitable,followed by Millington-Quirk model,while those of the Penman,Marshall and Penman-Millington-Quirk models are inappropriate.Compared with LI-8100,the calculated results of Moldrup model have smaller errors,which the mean absolute error is 0.076μmol·m^-2s^-1,and the mean relative errors is 4.51%.Compared with other soil CO₂ flux measuring instruments on the market,this system not only realizes the vertical monitoring of the soil,but also has a lower cost.Which can provide important technical support for deepening soil respiration research.