Effects of fenpropimorph on bacteria and fungi during decomposition of barley roots

The study examined the effects of the fungicide fenpropimorph (in the formu lation Corbel) on primary decomposer organisms in soil. Bacterial and funga l succession was followed on dead young barley roots buried in fungicide-tr eated or untreated soil, Fenpropimorph was added to the soil in a concentra tion realistically achieved in field topsoil when using the recommended dos e. Over a 56-day period we measured the length of active fungal hyphae, the abundance of total culturable bacteria, the abundance of two culturable su bgroups relevant to the soil environment (hyphae-forming actinomycetes and Pseudomonas), and the diversity of bacterial DNA. The soil fenpropimorph content followed first order disappearance concomita nt with the first order formation of fenpropimorphic acid. Fenpropimorph in hibited the growth of active fungi during the first 10 days, when fungal ac tivity peaked in both the treated and non-treated root samples. The number of total culturable bacteria was significantly lowered by fenpropimorph at day 17 and stimulated at day 56, indicating a possible indirect effect of t he fungicide on the culturable bacteria as a whole. Nevertheless, culturabl e Pseudomonas and actinomycetes were not affected. The succession of the tw o bacterial subgroups differed considerably, so, whereas Pseudomonas peaked in the early decomposition stages, actinomycetes were most abundant after 2 months, and on the very first sampling day. Thus, the present findings su ggest a possible effect of fenpropimorph on soil fertility. The diversity o f total bacterial DNA measured by denaturing gradient gel electrophoresis ( DGGE) was unaffected by fenpropimorph treatment, there being a clear and hi ghly reproducible succession in bacterial diversity during decomposition of the barley roots. The diversity in the hotspot on the last sampling occasi on at two months was similar to the diversity of the bulk soil, thus indica ting a return to the level prior to addition of the roots. (C) 2001 Elsevie r Science Ltd. All rights reserved.