John Wiley & Sons, Ltd.

Microbial community structure and functioning along metal pollution gradients

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Toxic effects of heavy metals on soil microorganisms have been confirmed in a number of laboratory studies. However, most real‐field studies do not allow for strong general conclusions due to a range of problems, such as pseudoreplication and confounding factors, which are almost impossible to control for with the most commonly used polluted‐vs.‐unpolluted or random sampling designs. Effects of metal contamination on soil microbial community traits were measured along two pollution gradients in Southern Poland. Employing an experimental regression design, using two separate gradients, we aimed to control for effects of soil properties and beta‐diversity of microbial communities. General microbial activity was measured as soil basal respiration rate (BAS) and substrate‐induced respiration (SIR), while microbial functional and structural diversity were analyzed with Community‐Level Physiological Profiles (CLPP) and Phospholipid Fatty Acid (PLFA) patterns, respectively. Metal concentrations were normalized to their toxicity and integrated in a Toxicity Index (TI). Microbial activity (BAS and SIR) decreased in both gradients with increasing TI. CLPPs for fungi correlated positively with TI, but no impact of TI on the CLPPs of bacteria was observed. The PLFAs a:15 and i:17 were positively correlated, while 16:1ω9 and 18:2ω9 were negatively correlated with TI. The use of two gradients (Olkusz and Miasteczko Śląskie) allowed us to reveal a clear effect of pollution on general microbial structure and activities, even though we were not able to control completely for all confounding factors. Soil pH, organic matter content and nutrient level appeared to be at least as important as TI in determining microbial community structure and activities. Environ Toxicol Chem © 2013 SETAC

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