DETERMINING ROOT ACTIVITY DISTRIBUTION BY MEASURING SURFACE CARBON-DIOXIDE FLUXES

Methods for determining root characteristics and distributions are tim e consuming and tedious. Indirect approaches could decrease the effort required to obain information on root distributions. The objectives o f this study were to measure soil surface CO2 flux and to relate these measurements to root properties. Two chambers to measure CO2 fluxes a t the soil surface were tested for use in root activity studies. One c hamber 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 su rface soil. The increase in CO2 concentration in the chambers was meas ured with infrared gas analyzers. The following were used to evaluate the applicability of the approach for root studies: (i) test of the re lationship 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, a nd (ii) evaluation of temperature and solar radiation effects on CO2 s oil surface flux. The results showed that surface CO2 fluxes were prop ortional to the logarithm of root characteristics, i.e., large changes in root characteristics were associated with small changes in flux. S oil temperature had a distinct effect on measured CO2 surface flux. Th ere was a clear diurnal cycle for Soil surface CO2 fluX, which peaked near solar noon and maximum solar radiation. Acceptable correlations b etween the major root characteristics and surface CO2 flux suggest tha t this approach can provide vital information on root activity.