Assessment of fungal–bacterial development in a successional shortgrass steppe by direct integration of chloroform-fumigation extraction (FE) and microscopically derived data

An active cytoplasm (AC) approach for characterization of soil fungi and bacteria is proposed, in which information on biovolume and biovolume contents is directly integrated. This AC method was developed to provide information on limited cytoplasm occurrence in an extended hyphal network which is characteristic of the non-discrete filamentous soil fungi. In this procedure, fumigation extraction (FE) derived carbon is allocated proportionally to the cytoplasm-containing biovolumes (fungal, inactive and active bacteria) followed by identification of the proportion of FE-derived carbon allocated to hyphal lengths and the active bacteria, considered to be the active cytoplasm. This approach was used during 1995 (summer and autumn samplings) to characterize three northeastern Colorado shortgrass steppe sites of different ages since cultivation, in comparison with an uncultivated site. Based on FE, the sites had similar extractable C contents. In contrast, the microscopic analyses indicated that fungal hyphal lengths increased significantly from the early successional to the uncultivated site at both samplings, while the functional (cytoplasm-filled) hyphal volume decreased. In comparison, the bacterial total and active numbers did not show distinct changes related to succession. Using this AC approach, the active fungal–bacterial cytoplasm was found to become more bacterial with succession in this shortgrass steppe ecosystem. By estimating active cytoplasm occurrence in fungal and bacteria in relation to succession, this approach provided unique information on fungal–bacterial community changes, particularly related to hyphal development and cytoplasm maintenance, which is not given by the independent use of biovolume or FE carbon-based analyses.