DETERMINING ROOT ACTIVITY DISTRIBUTION BY MEASURING SURFACE CARBON-DIOXIDE FLUXES

Methods for determining root characteristics and distributions are time consuming and tedious. Indirect approaches could decrease the effort required to obain information on root distributions. The objectives of this study were to measure soil surface CO2 flux and to relate these measurements to root properties. Two chambers to measure CO2 fluxes at the soil surface were tested for use in root activity studies. One chamber was a 0.75-L cylinder and the other was a 7. 1-L cubic chamber. The bottom edges of both chambers were inserted 1 to 2 cm into the surface soil. The increase in CO2 concentration in the chambers was measured with infrared gas analyzers. The following were used to evaluate the applicability of the approach for root studies: (i) test of the relationship between CO2 surface fluxes and root characteristics (length, area, mass, and number) in the root zone of a mature almond (Prunus amigdalus Batsch. cv. Butte) orchard and a corn (Zea mays L.) field, and (ii) evaluation of temperature and solar radiation effects on CO2 soil surface flux. The results showed that surface CO2 fluxes were proportional to the logarithm of root characteristics, i.e., large changes in root characteristics were associated with small changes in flux. Soil temperature had a distinct effect on measured CO2 surface flux. There was a clear diurnal cycle for Soil surface CO2 fluX, which peaked near solar noon and maximum solar radiation. Acceptable correlations between the major root characteristics and surface CO2 flux suggest that this approach can provide vital information on root activity.