Jonna Perkiömäki

Short and long-term effects of wood ash on the boreal forest humus microbial community

The short-term effects of loose and hardened wood ash on the coniferous forest humus layer microbes were studied 1– 3 years after fertilization. The experiment was performed using two fertilization levels (3 and 9 t ash ha 21 ) and repeated in two coniferous forest stands of different site fertility. It was hypothesized that the effects of hardened wood ash on soil microbes are of less magnitude when compared to loose ash due to the slower dissolution rates. The long-term effects of loose ash (3 t ash ha 21 ) were studied in four forest stands of different site fertility 18 years after ash application. In order to study ash effects, the microbial activity (basal respiration- and thymidine incorporation rates) and microbial community structure (PLFA pattern) were determined. The results showed that irrespective of the forest site fertility, ash fertilization induced the same responses in the humus layer. It raised the microbial activity and changed the community structure. The changes were related to the dose and form of ash applied. Applying the same fertilization rate induced comparatively more changes to the loose wood ash sites than hardened wood ash sites, due to the detected slower dissolution of hardened ash into the humus. The effects of wood ash were long-term. Changes in the humus microbial activity and PLFA pattern were still detectable after 18 years. q 2002 Elsevier Science Ltd. All rights reserved.

Organic material as a copper immobilising agent: a microcosm study on remediation

Remediation of heavy metal polluted forest soil was studied using nine different organic immobilising agents in a laboratory microcosm study. Composted sewage sludge, compost of organic household waste, a mixture of compost and woodchips, a mixture of compost and barkchips, garden soil, birch leaves, barkchips, humus or peat was applied on the surface of a polluted soil. Changes in the exchangeable Cu concentration, microbial respiration activity, microbial biomass and structure of the microbial community were assessed at four points during a 16-month period. Cu fractions, Cu 2+ and complexed Cu, and toxicity of the soil solution to bacteria, bacterial growth rate, number of bacterial cells, and bacterial copper tolerance were determined on samples taken after 16 months. Sewage sludge, compost, the compost mixtures, and garden soil decreased the exchangeable Cu concentration in the polluted soil, but had no effect on microbial activities, bacterial tolerance to copper or on the structure of the microbial community directly attributable to remediation. Zur Remediation von Schwermetall belasteten Waldboden wurden in einem Mikrokosmosversuch neun verschiedene Schwermetall immobilisierende organische Substanzen getestet. Klarschlamm, Haushaltskompost, eine Mixtur von Haushaltskompost und Holzspanen, eine Mixtur von Haushaltskompost und Rindenspanen, Gartenerde, Birkenblatter, Rindenspane, Humus oder Torf wurde einem belasteten Waldboden als neue organische Schicht aufgetragen. Uber den 16 Monate lang andauernden Laborversuch haben vier Beprobungen stattgefunden und die Konzentration von austauschbaren Cu, die Mikrobielle Respiration, die Mikrobielle Biomasse, und die Zusammensetzung der Bodenmikroflora wurden jeweils bestimmt. Zusatzlich wurden bei der letzten Beprobung (16 Monate) auch zwei verschiedene Cu Fraktionen, Cu ++ und komplekziertes Cu, die Toksizitat des Bodenwassers gegenuber Bakterien, die Bakterielle Wachstumsrate, die Bakterienanzahl und die Tolreranz der Bakterien gegen Cu bestimmt. Die Auftragung von Klarschlamm, Kompost, der beiden Kompostmixturen oder Gartenerde auf die Bodenoberflache erniedrigte die Konzentration von austauschbaren Cu des Bodens aber hatte keine lang anhaltenden Remedierungsefekte auf die Bodenbiologie des Schwermetal belasteten Waldbodens.

A microcosmos study on the effects of cd-containing wood ash on the coniferous humus fungal community and the cd bioavailability

Background and AimsThe use of wood ash in forestry has been questioned because the cadmium (Cd) concentration of ash, which varies between 1 and 20 mg kg-1 ash, exceeds the level allowed for fertilizers (3 mg kg-1) used in agriculture. To investigate the effects of Cd and ash on the fungal community composition and Cd bioavailability of the humus layer of boreal, coniferous forests, pumice or wood ash, spiked with a water soluble (CdCl2) or insoluble (CdO) form of Cd at three levels (0, 400 and 1000 mg kg-1), were applied at a fertilization level of 5000 kg ha-1 in a laboratory microcosm study.MethodsAfter 2 months, the humus in the microcosms was sampled and extracted for total DNA to detect changes in the fungal community by using polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) techniques. PCR was performed using the fungal 18S rDNA primers FR1 + FF390 and FR1 + NS1. The bioavailability of Cd was measured with a bacterial biosensor(Bacillus subtilis BR 151/pT0024) emitting light in the presence of Cd.ResultsUsing the primer pairs FR1 + FF390 and FR1 + NS1, resulted in over 35 and 15 DGGE bands, respectively. Both primer pairs detected an ash, but no Cd effect. When using FR1 + FF390, a higher fluorescence was observed in one DGGE band of all ashed samples compared to the pumiced samples. With the primer pair FR1 + NS1, the ashed samples had a DGGE band which was not visible or only faintly visible in the pumiced samples. In addition, one DGGE band disappeared from the ashed samples. Humus layer water extracts showed that the Cd added with the pumice was in a bioavailable form. The luminescence intensity of the biosensor was dependent on the form and level of the Cd added. No luminescence was detected when the Cd was added with the ash.ConclusionsAsh fertilization altered the humus layer fungal community, whereas the level and form of additional Cd in the ash had no influence because it was not bioavailable.

Does simulated acid rain increase the leaching of cadmium from wood ash to toxic levels to coniferous forest humus microbes

Abstract Wood ash contains Cd in concentrations not permitted for fertilization use in agriculture (>3 mg kg(-1)). It has been shown that spiking ash with Cd to concentrations of 1000 mg kg(-1) induced no further changes in humus microbial activity and community structure as ash alone. To accelerate the weathering process and thus to liberate the spiked Cd from the ash, three treatments - wood ash (A), Cd spiked wood ash (ACd, 1000 mg Cd kg(-1) ash), both applied at a fertilization rate of 5000 kg ha(-1), together with a control (C) - were performed in microcosms and incubated in field condition under two types of irrigation - water and simulated acid rain. During the incubation period of one growing season the simulated acid rain plots received a sulfur load of 3.64 g S m(-2), which was 15 times more than the S deposition on the water irrigated plots. The treatments resulted in a mean Cd increase of the humus from 0.23 mg kg(-1) of the C treatment to 0.52 and 39.5 mg kg(-1) of the A and ACd treatments, respectively. The irrigation had no further effect on the result. The microbial activity, measured as soil basal respiration, and the microbial community structure, measured as humus phospholipid fatty acid and 16S and 18S polymerase chain reaction/denaturing gradient gel electrophoresis patterns, changed only due to the ash (A and ACd treatments) fertilization irrespective of the irrigation. The bacterial biosensor, emitting light in the presence of bioavailable Cd, did not react to any of the treatments. This result shows that Cd in ash was not leached into the humus due to increased deposition of acidified rain.