Hannu Fritze

MICROBIAL COMMUNITY STRUCTURE AND pH RESPONSE IN RELATION TO SOIL ORGANIC MATTER QUALITY IN WOOD-ASH FERTILIZED, CLEAR-CUT OR BURNED CONIFEROUS FOREST SOILS

Humus phospholipid fatty acid (PLFA) analysis was used in clear-cut, wood-ash fertilized (amounts applied: 1000, 2500, and 5000 kg ha−1), or prescribed burned (both in standing and clear-cut) coniferous forests to study the effects of treatments on microbial biomass and community structure. The microbial biomass (total PLFAs) decreased significantly due to the highest rate of wood-ash fertilization, clear-cutting, and the two different fire treatments when compared to control amounts. Fungi appeared more seriously reduced by these treatments than bacteria, as revealed by a decreased index of fungal:bacterial PLFAs when compared to the controls. The community structure was evaluated using the PLFA pattern. The largest treatment effect was due to burning in both areas studied, which resulted in increases in 16:1ω5 and proportional decreases in 18:2ω6. Clear-cutting and the different amounts of ash application resulted in similar changes in the PLFA pattern to the burning treatments, but these were less pronounced. Attempts to correlate the changes in the PLFA pattern to soil pH, bacterial pH response patterns (measured using thymidine incorporation), or substrate quality (measured using IR spectroscopy) were only partly successful. Instead, we hypothesize that the changes in the PLFA pattern of the soil organisms were related to an altered substrate quantity, that is the availability of substrates after the treatments.

Clear-cutting and prescribed burning in coniferous forest : comparison of effects on soil fungal and total microbial biomass, respiration activity and nitrification

Abstract The effects of clear-cutting (CC) and clear-cutting followed by prescribed burning (CC-B) on humus chemical and microbiological variables and quality were compared in a Norway spruce dominated stand in North-Eastern Finland. The pattern of chemical changes in humus was similar after both treatments but CC-B caused greater changes than CC. Treatments raised the pH, cation exchange capacity and base saturation compared to an untreated standing forest control (Ctr). Total microbial carbon (C mic ) measured by substrate-induced respiration (SIR) and fumigation-extraction (FE) methods decreased following treatments. CC caused a 21% reduction of C mic compared to Ctr (10,890 μg g −1 dry wt), as measured by SIR, and a 27% reduction compared to Ctr (7281 μg g −1 dry wt) as measured by FE. CC-B resulted in 53 and 67% lower C mic than Ctr as measured by SIR and FE, respectively. Reasons for this decline in C mic are proposed. Fungal biomass determined as humus ergosterol concentration fell even more steeply than total C mic . Humus quality was analysed by near infrared reflectance spectroscopy (NIR) which revealed differences in humus structure between treatments. The NIR data could be interpreted to explain 75–82% of the variation in C mic -FE, C mic -SIR and ergosterol concentration. CC and CC-B lowered soil basal respiration, but not proportionally with the reduction in C mic since the specific respiration rate (CO 2 -C evolved per unit C mic ) was clearly higher with CC-B than CC or Ctr. CC and CC-B both resulted in a higher concentration of NH 4 + but only the humus from CC-B showed nitrification during a 6 week laboratory incubation.

Structure of the Microbial Communities in Coniferous Forest Soils in Relation to Site Fertility and Stand Development Stage.

A bstractThe structure, biomass, and activity of the microbial community in the humus layer of boreal coniferous forest stands of different fertility were studied. The Scots pine dominated CT (Calluna vulgaris type) represented the lowest fertility, while VT (Vaccinium vitis-idaéa type), MT (Vaccinium myrtillus type), and OMT (Oxalis acetocella–Vaccinium myrtillus type) following this order, were more fertile types. The microbial community was studied more closely by sampling a succession gradient (from a treeless area to a 180-years-old Norway spruce stand) at the MT type site. The phospholipid fatty acid (PLFA) analysis revealed a gradual shift in the structure of the microbial community along the fertility gradient even though the total microbial biomass and respiration rate remained unchanged. The relative abundance of fungi decreased and that of bacteria increased with increasing fertility. The structure of the bacterial community also changed along the fertility gradient. Irrespective of a decrease in fungal biomass and change in bacterial community structure after clear-cutting, the PLFA analysis did not show strong differences in the microbial communities in the stands of different age growing on the MT type site. The spatial variation in the structure of the microbial community was studied at a MT type site. Semivariograms indicated that the bacterial biomass, the ratio between the fungal and bacterial biomasses, and the relative amount of PLFA 16:1ω5 were spatially autocorrelated within distances around 3 to 4 m. The total microbial and fungal biomasses were autocorrelated only up to 1 m. The spatial distribution of the humus microbial community was correlated mainly with the location of the trees, and consequently, with the forest floor vegetation.

Ecosystem properties and microbial community changes in primary succession on a glacier forefront

Abstract We studied microbial community composition in a primary successional chronosequence on the forefront of Lyman Glacier, Washington, United States. We sampled microbial communities in soil from nonvegetated areas and under the canopies of mycorrhizal and nonmycorrhizal plants from 20- to 80-year-old zones along the successional gradient. Three independent measures of microbial biomass were used: substrate-induced respiration (SIR), phospholipid fatty acid (PLFA) analysis, and direct microscopic counts. All methods indicated that biomass increased over successional time in the nonvegetated soil. PLFA analysis indicated that the microbial biomass was greater under the plant canopies than in the nonvegetated soils; the microbial community composition was clearly different between these two types of soils. Over the successional gradient, the microbial community shifted from bacterial-dominated to fungal-dominated. Microbial respiration increased while specific activity (respiration per unit biomass) decreased in nonvegetated soils over the successional gradient. We proposed and evaluated new parameters for estimating the C use efficiency of the soil microbial community: “Max” indicates the maximal respiration rate and “Acc” the total C released from the sample after a standard amount of substrate is added. These, as well as the corresponding specific activities (calculated as Max and Acc per unit biomass), decreased sharply over the successional gradient. Our study suggests that during the early stages of succession the microbial community cannot incorporate all the added substrate into its biomass, but rapidly increases its respiration. The later-stage microbial community cannot reach as high a rate of respiration per unit biomass but remains in an “energy-saving state,” accumulating C to its biomass.

Wood-ash fertilization and fire treatments in a Scots pine forest stand: Effects on the organic layer, microbial biomass, and microbial activity

We studied the reactions of humus layer (F/H) microbial respiratory activity, microbial biomass C, and the fungal biomass, measured as the soil ergosterol content, to the application of three levels of wood ash (1000, 2500, and 5000 kg ha-1) and to fire treatment in a Scots pine (Pinus sylvestris L.) stand. Physicochemical measurements (pH, organic matter content, extractable and total C content, NH4+and total N content, cation-exchange capacity, base saturation) showed similarity between the fire-treated plots and those treated with the lowest dose of wood ash (1000 kg ha-1). The ash application did not change the level of microbial biomass C or fungal ergosterol when compared to the control, being around 7500 and 350 μg g-1 organic matter for the biomass C and ergosterol, respectively. The fire treatment lowered the values of both biomass measurements to about half that of the control values. The fire treatment caused a sevenfold fall in the respiration rate of fieldmoist soil to 1.8 μl h-1 g-1 organic matter compared to the values of the control or ash treatments. However, in the same soils adjusted to a water-holding capacity of 60%, the differences between the fire treatment and the control were diminished, and the ash-fertilized plots were characterized by a higher respiration rate compared to the control plots. The glucose-induced respiration reacted in the same way as the water-adjusted soil respiration. The metabolic quotient, qCO2, gradually increased from the control level with increasing applications of ash, reaching a maximum in the fire treatment. Nitrification was not observed in the treatment plots.

Pathways for Methanogenesis and Diversity of Methanogenic Archaea in Three Boreal Peatland Ecosystems

ABSTRACT The main objectives of this study were to uncover the pathways used for methanogenesis in three different boreal peatland ecosystems and to describe the methanogenic populations involved. The mesotrophic fen had the lowest proportion of CH4 produced from H2-CO2. The oligotrophic fen was the most hydrogenotrophic, followed by the ombrotrophic bog. Each site was characterized by a specific group of methanogenic sequences belonging to Methanosaeta spp. (mesotrophic fen), rice cluster-I (oligotrophic fen), and fen cluster (ombrotrophic bog).

Does short-term heating of forest humus change its properties as a substrate for microbes?

Abstract Prescribed burning is known to reduce the size of the microbial biomass in soil, which is not explained by preceding clear-cutting or the effects of ash deposition. Instead, burning induces an instant heat shock in the soil, which may either directly kill soil microbes or indirectly alter the soil organic matter. We heated dry forest humus at temperatures from 45 to 230°C, inoculated them to ensure equal opportunities for microbial proliferation and incubated the heated humus samples at 14°C. After 1, 2, 4 and 6 months we studied the microbial community structure of the samples by determining the phospholipid fatty acid pattern (PLFA), microbial substrate utilization pattern using Biolog Ecoplates and total microbial biomass ( C mic ) by substrate-induced respiration (SIR). The chemical structure of humus was scanned by Fourier-transform infrared (FTIR) and 13 C NMR spectroscopy. Heating at 230°C caused changes in the chemical structure of the humus as indicated by FTIR spectroscopy, increased the pH of the humus by 1.1 units, reduced C mic by 70% compared with the control and caused changes in substrate utilization patterns and proportions of PLFAs. More interestingly, the heat treatments from 45 to 160°C, which did not increase humus pH, resulted in differences in both microbial community structure and substrate utilization patterns. The severely heated samples (120–160°C) were relatively richer in 16:1 ω 7 t , cy19:0 and 18:1 ω 7, while the mildly heated samples (45–100°C) showed higher proportions of 16:1 ω 5, 16:1 ω 9, 10me16:0 and a15:0. The t / c ratio calculated from trans and cis configurations of 16:1 ω 7 increased from 1 to 6 months in the severely heated humus, possibly indicating nutrient deprivation. The control showed a decreasing t / c ratio and a stable amount of C mic indicating sufficient amount of decomposable organic matter. After incubation for 1 month, similar amounts of C mic had reestablished in 160°C-treated and control samples. However, the C mic in 160°C-treated samples decreased over 5 months. This might have been caused by a heat-induced flush of easily decomposable carbon, which was later exhausted. We conclude that changes in chemical properties of humus during dry heating at 230°C were capable of causing changes in microbial community structure of the humus.

Quantification of ectomycorrhizal mycelium in soil by real-time PCR compared to conventional quantification techniques

Mycelial biomass estimates in soils are usually obtained by measuring total hyphal length or by measuring the amount of fungal-specific biomarkers such as ergosterol and phospholipid fatty acids (PLFAs). These methods determine the biomass of the fungal community as a whole and do not allow species-specific identification. Molecular methods based on the extraction of total soil DNA and the use of genes as biomarkers enable identification of mycelia directly from the environment. Three molecular techniques were compared to determine the most reliable method for determining the biomass of individual fungal species in soil. The growth of extramatrical mycelium of two ectomycorrhizal (EM) fungal species (Suillus bovinus and Paxillus involutus) in soil was monitored by denaturing gradient gel electrophoresis, a cloning technique and real-time quantitative polymerase chain reaction, and the results were compared with those obtained with hyphal length determination and PLFA analysis. The molecular methods enabled identification and relative quantification of both species separately in an environment with several fungal species present and showed consistent results. Amounts of target DNA per gram soil were used to quantitatively compare soil samples. Increasing amounts of S. bovinus DNA and decreasing amounts of P. involutus DNA were detected over time in an environment containing a more complex community. This work demonstrates that molecular methods provide tools to determine the biomass of individual fungal species in soil.

The role of Sphagnum mosses in the methane cycling of a boreal mire.

Peatlands are a major natural source of atmospheric methane (CH4). Emissions from Sphagnum-dominated mires are lower than those measured from other mire types. This observation may partly be due to methanotrophic (i.e., methane-consuming) bacteria associated with Sphagnum. Twenty-three of the 41 Sphagnum species in Finland can be found in the peatland at Lakkasuo. To better understand the Sphagnum-methanotroph system, we tested the following hypotheses: (1) all these Sphagnum species support methanotrophic bacteria; (2) water level is the key environmental determinant for differences in methanotrophy across habitats; (3) under dry conditions, Sphagnum species will not host methanotrophic bacteria; and (4) methanotrophs can move from one Sphagnum shoot to another in an aquatic environment. To address hypotheses 1 and 2, we measured the water table and CH4 oxidation for all Sphagnum species at Lakkasuo in 1-5 replicates for each species. Using this systematic approach, we included Sphagnum spp. with narrow and broad ecological tolerances. To estimate the potential contribution of CH4 to moss carbon, we measured the uptake of delta13C supplied as CH4 or as carbon dioxide dissolved in water. To test hypotheses 2-4, we transplanted inactive moss patches to active sites and measured their methanotroph communities before and after transplantation. All 23 Sphagnum species showed methanotrophic activity, confirming hypothesis 1. We found that water level was the key environmental factor regulating methanotrophy in Sphagnum (hypothesis 2). Mosses that previously exhibited no CH4 oxidation became active when transplanted to an environment in which the microbes in the control mosses were actively oxidizing CH4 (hypothesis 4). Newly active transplants possessed a Methylocystis signature also found in the control Sphagnum spp. Inactive transplants also supported a Methylocystis signature in common with active transplants and control mosses, which rejects hypothesis 3. Our results imply a loose symbiosis between Sphagnum spp. and methanotrophic bacteria that accounts for potentially 10-30% of Sphagnum carbon.

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.