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 a nd bacteria is proposed, in which information on biovolume and biovolu me contents is directly integrated. This AC method was developed to pr ovide information on limited cytoplasm occurrence in an extended hypha l network which is characteristic of the non-discrete filamentous soil fungi. In this procedure, fumigation extraction (FE) derived carbon i s allocated proportionally to the cytoplasm-containing biovolumes (fun gal, inactive and active bacteria) followed by identification of the p roportion of FE-derived carbon allocated to hyphal lengths and the act ive 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 microscopi c analyses indicated that fungal hyphal lengths increased significantl y from the early successional to the uncultivated site at both samplin gs. while the functional (cytoplasm-tilled) hyphal volume decreased. I n comparison, the bacterial total and active numbers did not show dist inct changes related to succession. Using this AC approach, the active fungal-bacterial cytoplasm was found to become more bacterial with su ccession in this shortgrass steppe ecosystem. By estimating active cyt oplasm occurrence in fungal and bacteria in relation to succession, th is approach provided unique information on fungal-bacterial community changes, particularly related to hyphal development and cytoplasm main tenance, which is not given by the independent use of biovolume or FE carbon-based analyses. (C) 1998 Elsevier Science Ltd. All rights reser ved.