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The current opinion and position paper highlights (1) correct assignation of indicator phospholipid fatty acids (PLFA), (2) specificity and recycling of PLFA in microorganisms, and (3) complete extraction and detection of PLFA. The straight-chain PLFA 14:0, 15:0, 16:0, and 17:0 occur in all microorganisms, i.e., also in fungi and not only in bacteria. If the phylum Actinobacteria is excluded from the group of Gram-positive bacteria, all remaining bacteria belong to the bacterial phylum Firmicutes, which should be considered. The PLFA 16:1ω5 should be used as an indicator for the biomass of arbuscular mycorrhizal fungi (AMF) as there is no experimental evidence that they occur in marked amounts in Gram-negative bacteria. Fungal PLFA should embrace the AMF-specific 16:1ω5. In the presence of plants, ergosterol should be used instead of the PLFA 18:2ω6,9 and 18:1ω9 as fungal indicators for Mucoromycotina, Ascomycota, and Basidiomycota. The majority of indicator PLFA are not fully specific for a certain microbial group. This problem might be intensified by recycling processes during decomposition to an unknown extent. Soil handling and extraction conditions should be further optimized. The reliability and accuracy of gas chromatographic separation need to be regularly checked against unintentional variations. PLFA analysis will still be of interest over the next decades as an important independent control of DNA-based methods. [ABSTRACT FROM AUTHOR]

We studied the effect of liming and P fertilization of extremely acid soil (accidently acidified by sulfidic mining waste) on P availability and the subsequent adaptive responses of wheat roots. The wheat plants were grown in rhizoboxes allowing precise sampling of rhizosphere and bulk soil for sequential extraction of P fractions and determination of exchangeable Al. Root exudates were collected by pieces of paper for electrophoresis and subjected to HPLC analysis. Expression of organic anions and P transporter genes was analyzed by a real-time quantitative PCR. The concomitant application of lime with P fertilization increased the concentrations of plant-available P fractions in both rhizosphere and bulk compartments. The applied soil amendments strongly affected plant growth, biomass partitioning and shoot P accumulation. Liming enhanced root exudation of citrate in P unfertilized plants, while the high malate efflux was maintained until both P deficiency and Al toxicity were eliminated by the amendments. We showed the importance of liming for recovering of P acquisition potential of wheat roots, which can be strongly impaired in acid soils. Our results clearly demonstrated that P-deficient roots not subjected to Al stress in the limed soil can maintain high efflux of malate and even increase efflux of citrate along with the enhanced expression of related anion transporters (TaMATE1 and TaALMT1). [ABSTRACT FROM AUTHOR]

Abstract  In this paper we report on the influence of clay content and acidity of soil on growth and reproduction of the epigeic earthworm species Lumbricus rubellus (Hoffm.), which is common in most temperate soils and abundant in grasslands. Growth, cocoon production and survival of L. rubellus were tested in 12 Dutch soils which differed in soil properties. A matrix model was used to assess the population-level consequences of changes in growth and reproduction. Soil acidity had a strong negative effect on earthworm survival, and the maturation weight decreased with clay content. Individual weight gain in L. rubellus decreased with both acidity and clay content. The acidity of soils had a larger influence on population growth rate than the clay content. The acidity of the soil also changed the population composition towards younger age classes, whereas in soils rich in clay, the population composition did not change. The average individual weight of L. rubellus in clayey soils, however, was lower compared with that in soils low in clay, a result that agrees with literature data. [ABSTRACT FROM AUTHOR]