Development of Methods for in situ Observation of Roots and Folsomia candida (Willem) (Collembola: Isotomidae) in Greenhouse Soil Columns
Past investigations have suggested that roots, microbes, and Collembola within the rhizosphere are functionally linked (reviews in Box and Hammond et. al. 1990; Edwards et. a1. 1988; Fitter et. a1. 1985). However, these studies may not have fully assessed the magnitude of collembolan activity because past techniques were often inadequate. Recent advances in documenting root demographics in situ using minirhizotrons (MR.) have led to new speculations regarding collembolan distribution. Collembola, originally thought to populate only the upper 30 cm of the soil, were found by Snider et. al. (1990) at depths of up to 1 m in the rhizospbere of deep-rooted crops; the dominant soil arthropod in these Michigan agroecosystems was Foisomia candida (Willem) (Collembola: Isotomidae). This was an important discovery in agricultural ecology because it gave a new perspective on the actual size of collembolan populations and possible root/collembolan interactions in below-ground system functioning. In the present study, a method for observing roots and Collembola in situ was explored. It was concluded that collembolan population studies in soil columns can be effective if the following factors are taken into consideration: 1. Care must be taken in construction of the column; specifically, MR tube insertion needs to be done in such a way that sufficient contact between the surface of the tubes and soil is ensured. 2. Time Domain Reflectometry (IDR) measurements, which determine volumetric water content (soil moisture), must be done at regular time intervals. 3. The age of the Collembola at the time of introduction to the soil columns needs to be taken into account. The baseline data obtained from this experiment concerned the potential effects of roots and abiotic factors on collembolan distribution. The results led to the conclusion that root systems may facilitate collembolan migration, but soil moisture was the primary reason for the migration of collembolan populations.