Optimization of Robot System on Determining Upland Soil N2 Emission as Compared to Other Methods
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National Natural Science Foundation of China (Nos. U20A20113, 42177303) and Scientific Instrument and Equipment Development Project of CAS (No. YJKYYQ20170058)

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    Abstract:

    【Objective】The massive application of nitrogen fertilizer to agricultural soils plays an important role in ensuring the world’s food supply. However, it also leads to a large amount of reactive nitrogen(N) entering the environment, which strongly interferes with the biogeochemical cycle of N and causes a series of ecological and environmental problems. As the last step of N cycling, denitrification is the predominant pathway, converting reactive N into inert N(i.e., N2). However, measuring soil N2 production from denitrification is a major challenge in terrestrial ecosystems because of the high atmospheric background N2 concentration. Recently, direct methods for measuring N2emission rates have been developed. Among them, robotized incubation and analyzing system(Robot system) which is based on N2 free headspace(i.e., helium environment) have been widely used for measuring N2 emission in pure denitrifying culture or soil, due to its advantage on platform construction and high throughput for N2 determination. Nevertheless, frequent sampling with the small-diameter steel needle is required during the operation and determination of the Robot system, which inevitably causes leakage of N2. This seriously interferes with the determination of low N2 emission rates(i.e., background N2 flux in upland soil). Therefore, to enable the Robot system to measure background N2 emission rate in upland soil without exogenous substrate, the leakage rate of the system must be further reduced.【Method】In this study, helium-washed rubber septa, solutions prepared by helium-washed distilled water and destructive sampling treatments were explored to optimize the Robot system aiming at reducing the N2 leakage therein. Additionally, results of soil N2 emission determined by the optimized Robot system were compared with those of acetylene inhibition technique(AIT) and Robotized continuous flow incubation system(RoFlow system).【Result】Our results showed that the N2 leakage rate of the Robot system could be remarkably reduced by optimizing with helium-washed septa, solutions prepared by helium-washed distilled water and destructive sampling treatments. The N2 leakage rate was reduced to 0~0.78 μL·L-1·h-1 by the aforementioned treatments. Under similar treatments, the N2 emission rate measured by the acetylene inhibition method was highest, followed by the RoFlow system, and the Robot system had the lowest results. Furthermore, the optimized Robot system was capable of determining upland soil N2 emissions in response to carbon and N addition, which also had the smallest standard error(0.003~0.045 mg·kg-1·d-1) compared with the AIT method(0.34~3.29 mg·kg-1·d-1) and RoFlow system(0.41~1.02 mg·kg-1·d-1).【Conclusion】Overall, the optimized Robot system is characterized by low N2 leakage, effective response to substrate addition and good consistency in determining soil N2 emission. In the future, it will have a favorable application in investigating background N2 emissions and the associated mechanism of upland soil.

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LI Chenglin, WEI Zhijun, WU Min, SHAN Jun, YAN Xiaoyuan. Optimization of Robot System on Determining Upland Soil N2 Emission as Compared to Other Methods[J]. Acta Pedologica Sinica,2023,60(3):694-704.

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History
  • Received:September 27,2021
  • Revised:March 03,2022
  • Adopted:May 07,2022
  • Online: May 19,2022
  • Published: May 28,2023