Turnover of fine roots and mycorrhizae and their relationship with continuous measurements of soil respiration

Belowground processes, such as soil respiration, root and mycorrhizae turnover, are heterogeneous in space and time. Much of the difficulties with measuring these processes are the technical limitations to continuously measure their changes. We installed fifteen minirhizotron tubes coupled with soil temperature, moisture and solid-state CO2 sensors in an area of 160 m2 of a temperate forest at the San Jacinto James Reserve in southern California. Minirhizotron images were taken in all tubes during four consecutive days every second or third week of 2006. During the same year we calculate soil respiration based on continuous measurements of CO2 gradients and diffusivity. We found rapid turnover times with an average lifespan of fine roots, rhizomorphs and hyphae of 9.7, 11.2 and 8.1, respectively. Lifespan of fine roots from minirhizotron images were lower than the radiocarbon (14C) age (5 to 8 years) of fine roots <1cm. The mean annual respiration rate of all locations was 2.6 micro mol CO2/m2/s but we observed unexpected mean annual variation up to 83% at small spatial scales. We observed that root counts were correlated with soil respiration but counts of hyphae and rhizomorphs in the minirhizotron images were not. Temperature and soil moisture influenced soil respiration and turnover of roots and mycorrhizae. Wireless sensor networks are an alternative technology tested at the James Reserve, CA to study belowground processes.