Why Multiplex?

LI-8100 Multiplexer in field

Soil CO2 flux (FCO2) is usually the largest component of ecosystem respiration. It is also important for understanding soil carbon sequestration potential and soil carbon dynamics. FCO2 has a strong temporal variation over the course of a day or a season because of changes in soil temperature, soil moisture, above-ground vegetation physiological activities, and other driving variables. It also shows a strong spatial variation because of high heterogeneity of soil properties in the field. Studies in the literature on temporal variation are often limited to weekly, or even monthly measurements. Spatial variation studies are often limited to survey types of measurements with one chamber. Therefore, the best solution to calculate FCO2 is to use a multiple chamber system.

Below we present data from a study that indicates the importance of continuous measurements at multiple locations for understanding the spatial and temporal changes in Soil CO2 Flux. The following study shows data in a corn/soybean rotation field over two growing seasons using a 16 chamber multiplexed LI-8100 System.

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Time series of 16-chamber Soil CO2 flux data (FCO2) and coefficient of variation (CV) (A). 16 chamber mean FCO2 + std and mean soil temperature at 5 cm deep (B). Date were obtained with a 16-chamber multiplexing system. Results show CV of 20-30%from 16 locations and a strong temperature-dependant diurnal pattern of FCO2

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The coefficient of variation (CV = std dev / mean) shows large seasonal trends. Two phenomena are clear from the results:

a. Middle season has lower CV than that of early and late season, probably due to relatively uniform soil temperature from well-developed canopy and high rate of FCO2

b. Rain events greatly increase CV. This was due to the large difference in residue from location to location. Rainfall enhanced the FCO2 at locations with residue and suppressed FCO2 at locations with little or no residue because of the increase in resistance of gas transport in the soil surface layer after rain events.

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Based on the continuous FCO2 dataset from 2006, we analyzed the magnitudes of errors in total seasonal FCO2 when the measurements were obtained with different time intervals. Results show that weekly measurements could have ±5% error in total soil CO2 flux estimation as compared with continuous measurements. Biweekly or monthly measurements could have ±13% or ±25% errors, respectively.

These illustrations show the importance of long-term multiplexed datasets.

The LI-8100A Automated Soil CO2 Flux System configured with the LI-8150 Multiplexer is ideal for making mulitplexed CO2 flux Measurements.

LI-8100A Automated Soil CO2 Flux System

LI-8100A Automated Soil CO2 Flux System

  • Measures CO2 exchange from soils
  • Multiplexed configuration available for larger sampling area
  • Useful for survey or long-term measurements
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