Strukturelle und funktionelle Charakterisierung von mikrobiellen Gemeinschaften in ökologisch und konventionell bewirtschafteten Ackerböden

Strukturelle und funktionelle Charakterisierung von mikrobiellen Gemeinschaften in ökologisch und konventionell bewirtschafteten Ackerböden

Response of soil microbial biomass and community structures to conventional and organic farming systems under identical crop rotations

In this study the influence of different farming systems on microbial community structure was analyzed using soil samples from the DOK long-term field experiment in Switzerland, which comprises organic (BIODYN and BIOORG) and conventional (CONFYM and CONMIN) farming systems as well as an unfertilized control (NOFERT). We examined microbial communities in winter wheat plots at two different points in the crop rotation (after potatoes and after maize). Employing extended polar lipid analysis up to 244 different phospholipid fatty acids (PLFA) and phospholipid ether lipids (PLEL) were detected. Higher concentrations of PLFA and PLEL in BIODYN and BIOORG indicated a significant influence of organic agriculture on microbial biomass. Farmyard manure (FYM) application consistently revealed the strongest, and the preceding crop the weakest, influence on domain-specific biomass, diversity indices and microbial community structures. Esterlinked PLFA from slowly growing bacteria (k-strategists) showed the strongest responses to long-term organic fertilization. Although the highest fungal biomass was found in the two organic systems of the DOK field trial, their contribution to the differentiation of community structures according to the management regime was relatively low. Prokaryotic communities responded most strongly to either conventional or organic farming management

Soil microbial community structure and organic matter transformation processes in organic and integrated farming systems

The DOK long-term field trial in Switzerland started in 1978 (Mäder et al., 2002). Biodynamic (BIODYN), bioorganic (BIOORG) and integrated (CONFYM) farming systems with manure fertilization, an integrated system based on mineral fertilizer only (CONMIN) and an unfertilized control (NOFERT) were investigated for changes in soil organic matter and on the structure of the soil microbial communities. Soil organic matter (SOM) in the Ap-horizon (0-20 cm) was analysed from the beginning of the DOK field trial in 1978. Roughly 20% of the initial SOM was lost when no manure was applied for 21 years as in the CONMIN and the NOFERT system, whereas SOM increased slightly by 4% in the BIODYN system that makes use of composted farmyard manure, corresponding to 1.4 livestock units per hectare (LSU). The BIOORG and the CONFYM system lost about 7%. Soil microbial biomass analysed from 2000 and 2003 samplings revealed higher values in organically fertilised plots. Bacterial and eukaryotic biomasses followed the order: CONMIN < CONFYM ≤ BIOORG ≤ BIODYN. Phospholipid etherlipids, indicative for micro-organisms of the domain Archaea occurred in abundance compared to other organically fertilised soils and followed the order: CONMIN < BIODYN = BIOORG = CONFYM. Clear differences in PLFA based microbial community structure among the four farming systems were observed. Organic fertilization compared to no manure had the strongest effect, followed by organic farming compared to integrated, and finally the kind of organic farming management (BIODYN with composted manure vs. BIOORG with rotted manure). The incorporation of maize-derived carbon – with higher 13C content – to some of the PLFA was detected and highlights the functional role of the corresponding microbial groups in carbon transformation processes. Contrasting 13C values in the PLFA-biomarkers for Archaea in organic and conventional soils support the assumption that carbon transformation processes are affected by the farming systems. Our results suggest that changes in SOM are indicated by changes in soil microbial biomass. The functional role of microbial groups will be further investigated. The enhanced chemical and biological soil quality found in the field plots fertilized with manure and manure compost maintains key soil functions, on which low input farming systems rely

Microbial food web dynamics along a soil chronosequence of a glacier forefield

Microbial food webs are critical for efficient nutrient turnover providing the basis for functional and stable ecosystems. However, the successional development of such microbial food webs and their role in "young" ecosystems is unclear. Due to a continuous glacier retreat since the middle of the 19th century, glacier forefields have expanded offering an excellent opportunity to study food web dynamics in soils at different developmental stages. In the present study, litter degradation and the corresponding C fluxes into microbial communities were investigated along the forefield of the Damma glacier (Switzerland). 13C-enriched litter of the pioneering plant Leucanthemopsis alpina (L.) Heywood was incorporated into the soil at sites that have been free from ice for approximately 10, 60, 100 and more than 700 years. The structure and function of microbial communities were identified by 13C analysis of phospholipid fatty acids (PLFA) and phospholipid ether lipids (PLEL). Results showed increasing microbial diversity and biomass, and enhanced proliferation of bacterial groups as ecosystem development progressed. Initially, litter decomposition proceeded faster at the more developed sites, but at the end of the experiment loss of litter mass was similar at all sites, once the more easily-degradable litter fraction was processed. As a result incorporation of 13C into microbial biomass was more evident during the first weeks of litter decomposition. 13C enrichments of both PLEL and PLFA biomarkers following litter incorporation were observed at all sites, suggesting similar microbial foodwebs at all stages of soil development. Nonetheless, the contribution of bacteria, especially actinomycetes to litter turnover became more pronounced as soil age increased in detriment of archaea, fungi and protozoa, more prominent in recently deglaciated terrain.ISSN:1726-4170ISSN:1726-417