Soil Ergosterol Research Articles

Soil aggregation, glomalin and enzyme activities under conservation tilled rice-wheat system in the Indo-Gangetic Plains

Although many farmers in the Indo-Gangetic Plains (IGP) are currently adopting zero tilled wheat (ZTW), limited information is available on the impacts of conservation tillage and conservation agriculture (CA) practices on soil aggregation, glomalin content, soil enzymatic activities and their inter-relationships. Hence, this study investigated the effects of direct seeded rice (DSR)-ZTW, DSR-ZTW with brown manuring (BM) or mungbean (Vigna radiata) residue retention (MBR) with rice residue retention on soil aggregation, glomalin content and soil enzymatic activities after four years under an irrigated rice (Oryza sativa L.)–wheat (Triticum aestivum L.) system. Eight treatments, involving transplanted rice (TPR)-conventional tilled wheat (CTW), TPR-ZTW, DSR-ZTW and combinations of residue management in DSR-ZTW were evaluated for soil aggregation and microbial activities in the 0–5 and 5–15 cm layers. Plots under mungbean residue + DSR – ZTW + rice residue retention (RR) – ZT summer mungbean + wheat residue retention (DSR + MBR-ZTW + RR-ZTMB+WR) had better microbial indices (except soil ergosterol content) than TPR-CTW in the topsoil and higher MBC and dehydrogenase activity in the 5–15 cm layer than TPR-CTW plots. Plots under DSR + brown manuring (BM)-ZTW + RR (CA module 1) had ~53%, 26% and 32% higher ergosterol, glomalin and MBC contents, respectively, in the topsoil (0–5 cm layer) than DSR + BM-ZTW plots. Similarly, plots under CA module 2 had ~23% and 29% higher ergosterol and glomalin contents, respectively, than DSR + MBR-ZTW plots. Plots under CA module 2 also had ~47% more alkaline phosphatase activity than farmers’ practice in the topsoil. These plots also had ~247% and 100% more large macroaggregates in the 0–5 and 5–15 cm soil layers than TPR-CTW. However, there were less small macroaggregates in plots under CA module 2 than TPR-CTW in the topsoil. There were significant positive relationships between glomalin, carboxy-methyl cellulase activity and MBC with large macroaggregates in the topsoil and between glomalin and MBC in the 5–15 cm soil layer, indicating the role of glomalin in soil aggregation. Thus, DSR + MBR-ZTW + RR-ZTMB treatment resulted in an improved soil microbial environment after four years of rice–wheat cropping in the IGP, and this practice may be adopted. The enhanced soil properties was mainly due to residue retention of crop residues, zero tillage (ZT) in two crops (in the first three years) and triple ZT (in the fourth year), and growing of a legume crop in the conventional rice-wheat system in the IGP.

The advancing mycelial frontier of ectomycorrhizal fungi.

This article is a Commentary on Hagenbo et al. (2021), 230: 1609–1622.

Temperature modifies the magnitude of a plant response to Collembola presence

Soil properties and the growth and maturation of herbaceous plants are known to be influenced by the soil fauna (Collembola) and by the temperature. But little is known about how these two factors interact. We hypothesised that the vegetative and reproductive responses of Poa annua L. to the presence of soil Collembola density will change according to temperature. P. annua was grown in microcosms with or without Collembola at two different air temperature conditions, 16 °C as a Low T° vs. 19 °C as a High T°. Both factors “Collembola” and “Temperature” significantly influenced several plant and soil variables. The number of flowers, the root biomass of P. annua were higher either in presence of Collembola or under elevated temperature. The same applied for soil ergosterol or K content for example. Soil nitrate content was exclusively affected by the presence/absence of Collembola and not by the temperature. Finally, significantly interactive effects between temperature and Collembola upon several plant or soil variables (root biomass, number of flowers, soil K and Mg content) were shown. Our study suggests that biotic factors (here soil fauna) may strongly interact with climatic variables in regulating plant growth through changes in soil nutrient availability. We provide experimental evidence that climate warming modifies the effect of soil Collembola on the reproduction strategy of the plant.

Application of a Stir Bar Sorptive Extraction sample preparation method with HPLC for soil fungal biomass determination in soils from a detrital manipulation study

Ergosterol is a sterol found ubiquitously in cell membranes of filamentous fungi. Although concentrations in different fungal species span the range of 2.6 to 42μg/mL of dry mass, many studies have shown a strong correlation between soil ergosterol content and fungal biomass. The analysis of ergosterol in soil therefore could be an effective tool for monitoring changes in fungal biomass under different environmental conditions. Stir Bar Sorptive Extraction (SBSE) is a new sample preparation method to extract and concentrate organic analytes from liquid samples. SBSE was here demonstrated to be a simple, fast, and cost effective method for the quantitative analysis of ergosterol from field-collected soils. Using this method we observed that soil ergosterol as a measure of fungal biomass proved to be a sensitive indicator of soil microbial dynamics that were altered by changes in plant detrital inputs to soils in a long-term field experiment.

Enzymatic activities and microbial biomass in peanut field soil as affected by the foliar application of tebuconazole

Field experiments in peanut (Arachis hypogaea L.) soil ecosystem were conducted during the summer seasons (February–June) of the year 2013 and 2014 in black clay soil treated with tebuconazole at field rate (FR), 2-times FR (2FR) and 10-times FR (10FR) as foliar spray to determine the impact of tebuconazole on soil microbial properties and enzymatic activities. Tebuconazole application at FR and 2FR resulted in a short-lived and transitory toxic effect on soil microbial properties and enzymatic activities. The duration of this disturbance was slightly longer at 10FR. Incorporation of tebuconazole in soil resulted in stimulating the soil microbial activity as evidenced by increased ammonification and nitrification rates and increased soil microbial biomass at later stage. However, it was more toxic to soil ergosterol which is the indicator of the presence of viable fungi. Soil enzymatic activities like fluorescein diacetate-hydrolyzing activity, urease, phosphatase and aryl sulfatase are either unaffected or shortly inhibited and then recovered. However, dehydrogenase and nitrate reductase activity decreased more drastically and can be used as valuable indicator to assess the impact of tebuconazole application on soil health. The results indicated that instead of single assays, a broad spectrum analysis of soil microbial and enzymatic activities gives a better insight about the impacts of pesticide on soil health. From this study, it is also concluded that the application of tebuconazole at 10FR had adverse effects on the microbial variables and the effect on long-term application should be studied further.

Effects of biogas and raw slurries on grass growth and soil microbial indices

AbstractBiogas slurry is increasingly used as fertilizer. Earlier research was focused on plant growth and soil chemical properties, with only little information available regarding the effects of biogas slurry on soil and root microbial indices. For this reason, a 70 d pot experiment was conducted in which biogas and raw slurries obtained from six biodynamic farms were added to a soil. Italian ryegrass (Lolium multiflorum Lam.) was cultivated to investigate the effects on plant yield, N uptake (two harvests), soil microbial biomass, soil fungi, and root‐colonizing microorganisms. Biogas slurries increased the mean total above‐ground plant biomass by 66% and raw slurries by 35% in comparison to the control. The mean plant N‐uptake increased under biogas and raw slurry application by 166% and 65%, respectively, compared with the unfertilized pots. The effects of biogas and raw slurry application on soil microbial indices were similar except for the lower fungal biomass after biogas slurry amendment. In contrast to biogas slurries, the raw slurries significantly increased microbial biomass C and N by roughly 25% in comparison to the control. The application of biogas slurries significantly decreased the soil ergosterol content in comparison with raw slurry and control treatment, leading to a significantly lower ergosterol : microbial biomass C ratio. In the roots, biogas and raw slurry application significantly decreased the concentrations of the amino sugars galactosamine and glucosamine by 39 and 27%, respectively, but not that of ergosterol in comparison with the control. This was most likely due to a reduced colonization with arbuscular mycorrhizal fungi in the presence of highly available plant nutrients.

Ectomycorrhizal fungal mycelia turnover in a longleaf pine forest.

Elucidation of the patterns and controls of carbon (C) flow and nitrogen (N) cycling in forests has been hindered by a poor understanding of ectomycorrhizal fungal mycelia (EFM) dynamics. In this study, EFM standing biomass (based on soil ergosterol concentrations), production (based on ergosterol accrual in ingrowth cores), and turnover rate (the quotient of annual production and average standing biomass estimates) were assessed in a 25-yr-old longleaf pine (Pinus palustris) plantation where C flow was manipulated by foliar scorching and N fertilization for 5yr before study initiation. In the controls, EFM standing biomass was 30±7gm(-2) , production was 279±63gm(-2) yr(-1) , and turnover rate was 10±3 times yr(-1) . The scorched×fertilized treatment had significantly higher EFM standing biomass (38±8gm(-2) ), significantly lower production (205±28gm(-2) yr(-1) ), and a trend of decreased turnover rate (6±1 times yr(-1) ). The EFM turnover estimates, which are among the first reported for natural systems, indicate that EFM are a dynamic component of ecosystems, and that conventional assessments have probably underestimated the role of EFM in C flow and nutrient cycling.

Effects of mefenoxam fungicide on soil biochemical properties.

We studied the effect of mefenoxam on soil biochemical properties. Soil was mixed with three rates of mefenoxam (0.5, 1 and 2 L ha(-1)) and incubated for 83 days. Fungicide was applied to the soil four times during the experiment, according to the manufacturer's instructions. Soil ergosterol, dehydrogenase, urease, β-glucosidase, and phosphatase activities were measured during the experiment. Compared to controls, soils with the highest doses of mefenoxam demonstrated decreased ergosterol and dehydrogenase activities by 81 and 27 %, respectively; whereas, urease, β-glucosidase, and phosphatase activities increased. These results suggest that mefenoxam may possibly have consequences for agronomic crop production due to the negative effect on soil fungal populations and stimulation of the growth of soil bacterial activity.

Temporal variations of the distribution of water-stable aggregates, microbial biomass and ergosterol in temperate grassland soils with different cultivation histories

In grassland soils, the temporal dynamics in different fractions of soil organic carbon (SOC) is not completely understood. We investigated the temporal variations of water-stable aggregates, microbial biomass C (Cmic) and ergosterol concentrations (as a proxy for fungal biomass) in loamy sandy soils under grassland (north of Kiel, Germany). Samples were taken six times between October 2010 and October 2011 from i) a permanent grassland, ii) an arable plot converted to grassland and iii) a grassland with a one-time tillage operation (both in September 2010). Water-stable aggregate concentrations were determined by a wet-sieving procedure, Cmic concentrations by chloroform-fumigation-extraction and ergosterol concentrations by ethanol extraction. Temporal variation in aggregate distribution of soil samples from the permanent grassland was considerable: the large macroaggregate (>2000μm) concentrations (mean±standard error, n=3) in the surface soil (0–10cm) were highest in October 2011 (666±12gkg−1) and lowest in May (206±49gkg−1). The tillage operation in grassland led to lower concentrations of large macroaggregates, ergosterol and Cmic in the surface soil than in the permanent grassland. The conversion of arable land into grassland did not affect macroaggregate concentrations, despite an increase in Cmic (1.4-fold) and ergosterol concentration (3.3-fold) in the surface soil. Multiple linear regression analysis described the variations in the large macroaggregate concentration satisfactorily (R2=0.60) and indicated that the gravimetric moisture content and the Cmic concentration had positive effects and the pH a negative effect. While ergosterol concentrations (mean±standard error) showed some temporal variations (values for the surface soil in the grassland ranged from 0.5±0.1 to 1.5±0.1mgkg−1), Cmic concentrations varied much less, indicating a higher sensitivity of ergosterol to soil cultivation or changing environmental conditions.

Changes in Soil Ergosterol Content, Glomalin-Related Soil Protein, and Phospholipid Fatty Acid Profile as Affected by Long-Term Organic and Chemical Fertilization Practices in Mediterranean Turkey

The present study examines the effects of different fertilization treatments (chemical fertilization, farmyard manure, plant compost, and mycorrhiza-inoculated compost) on the soil fungi under a crop rotation of wheat (Triticum aestivum L.) and corn (Zea mays L.) in a long-term field experiment established in Mediterranean Turkey in 1996. Soil samples were collected in May, August, and October 2009. Soil pH, organic carbon, plant-available nitrogen and phosphorus, mycorrhizal colonization, and a series of biochemical markers (phospholipid and neutral lipid fatty acid [PLFA and NLFA] profiles, soil ergosterol content, and glomalin related soil protein [GRSP] as indicators of abundance of bacteria, saprotrophic, and arbuscular mycorrhizal [AM] fungi) were assessed. No significant difference was observed in soil organic C and plant available N in relation to long-term fertilization treatments, but plant available P in soil changed significantly in relation to the fertilization treatment used and the sampling season (between 11.5–33.8 mg · kg−1 in spring, 10.4–28.6 mg · kg−1 in summer, and 10.5–33.2 mg · kg−1 in autumn). Mycorrhizal colonization patterns were similar for both plants. However, mycorrhiza-inoculated compost treatment exhibited higher root colonization (77.3%) over control (16.3%), chemical fertilization (10.0%), farmyard manure (19.3%), and plant compost (20.0%). No statistically significant change was observed in ergosterol content. The effect of long-term organic treatments on soil PLFA structure was statistically prominent; whereas seasonality only affected bacterial PLFAs. Organic fertilization increased GRSP (mean annual ranging from 0.91 to 2.46 mg · g−1 total GRSP) but long-term annual mycorrhizal inoculation had no significant effect on the soil GRSP pool.

Short-Term Changes in Humus Fungal Biomass, Mesofauna and CO2 Efflux Following Liming in a Microcosm Experiment

Our objective was to test how liming influence fungal biomass, abundance and diversity of organisms belonging to mesofauna and soil respiration associated to soil during a microcosms experiment. Soil was collected in the Vosges Mountains (North-eastern France) on acidified forested catchments lying on sandstone and granite of Vosges Mountain. After liming, we followed CO2 by using LiCor 6400, fungal biomass by quantifying soil ergosterol content during 8 weeks. At the end of the experiment, we extracted mesofauna by using Berlese method. Soil pH, rain, temperature and rate of liming were similar to natural conditions. Liming decreased the abundance of mesofauna including collembola on sansdstone substrate, while on granite, collembola abundance decreased but total mesofauna did not show any significant differences between acid control and limed samples. The ergosterol soil content showed immediate increasing tendencies on both geological substrates and followed by decreasing tendencies on both geological substrates. The CO2 efflux was significantly increased by liming on sandstone and granite substrates, indicating an increase of soil respiration in limed samples. However, this result is depending on the geological substrate.

Carbon and nitrogen mineralization at different salinity levels in Omani low organic matter soils

A 56-d incubation experiment at 30 °C was carried out to study how salinity affects C and N mineralization of composted dairy manure and date palm straw. A low- and a high-saline soil were amended with (1) manure, (2) manure + low straw, (3) manure + straw, and (4) sole straw. The microbial and fungal biomass contents are very low in Omani soil abandoned for at least 6 years. Straw application revealed a highly significant increase in microbial biomass C, but especially in ergosterol in the low-saline soil. In contrast, straw led only to an increase in ergosterol in the high-saline soil, where only the combined application of manure with straw had significant positive effects on microbial biomass C. In the high-saline soil, the sum of C mineralized reached only 55% of SOC-derived CO2–C, 65% of manure-derived CO2–C, and 75% of straw-derived CO2–C in comparison with the respective treatments of the low-saline soil. The application of straw led always to a net N immobilization, which was markedly stronger in the high- than in the low-saline soil. The increase in salinity by composted cattle manure should be considered if this fertilizer is applied to soils sensitive to changes in salinity.

Organic fertilizer effects on growth, crop yield, and soil microbial biomass indices in sole and intercropped peas and oats under organic farming conditions

In a field experiment, peas (Pisum sativum L.) and oats (Avena sativa L.) were grown as sole crops and intercrops, fertilized with horse manure and yard-waste compost derived from shrub and garden cuttings at 10tCha−1 each. The objectives were to compare the effects of these organic fertilizer and cropping system in organic farming on (a) yield of peas and oats, grown as the sole crop or intercropped, as well as N2 fixation and photosynthetic rates, (b) the yield of wheat as a succeeding crop, (c) microbial biomass indices in soil and roots, and (d) microbial activity estimated by the CO2 evolution rate in the field and the amount of organic fertilizers, recovered as particulate organic matter (POM). In general, organic fertilizer application improved nodule dry weight (DW), photosynthetic rates, N2 fixation, and N accumulation of peas as well as N concentration in oat grain. Averaged across fertilizer treatments, pea/oat intercropping significantly decreased nodule DW, N2 fixation and photosynthetic rate of peas by 14, 17, and 12%, respectively, and significantly increased the photosynthetic rate of oats by 20%. However, the land equivalent ratio (LER) of intercropped peas and oats exceeded 1.0, indicating a yield advantage over sole cropping. Soil microbial biomass was positively correlated with pea dry matter yields both in sole and intercropped systems. Organic fertilizers increased the contents of microbial biomass C, N, P, and fungal ergosterol in soil and CO2 production, whereas the cropping system had no effects on these microbial indices. According to the organic fertilizer recovered as POM, 70% (manure) and 64% (compost) of added C were decomposed, but only 39% (manure) and 13% (compost) could be attributed to CO2–C during a 101-day period. This indicated that horse manure was more readily available to soil microorganisms than compost, leading to increased grain yields of the succeeding winter wheat.

Effects of Prochloraz fungicide on soil enzymatic activities and bacterial communities

We studied in the laboratory the effect of Prochloraz fungicide on the biological properties (soil enzymatic activities and soil bacterial communities) of a Plaggic Anthrosol. Five hundred grams of soil (<2 mm) was mixed with three dosages of Prochloraz (1, 2, and 4 l ha −1) for 83 days. A non-Prochloraz polluted soil was used as control. Following commercial recommendations, fungicide was applied four times during the incubation experiment. For all treatments, the soil ergosterol and levels of dehydrogenase, urease, β-glucosidase, and phosphatase activity were measured at nine different times (0, 1, 21, 22, 41, 42, 62, 63, and 83 days). The 16S rDNA-DGGE profiles in all treatments were determined at the beginning and end of the incubation period. At the end of the experiment, a significant decrease in ergosterol by 72.3%, 80.8%, and 83.1%, compared with control soil, was observed when 1, 2, and 4 l ha −1, respectively, was added. Soil enzymatic activities increased when the Prochloraz applied to the soil increased, possibly because the fungicide is used by bacterial communities as a source of energy and nutrients. The 16S rDNA-DGGE profiles indicated that the fungicide did not negatively affect soil bacterial biodiversity. These results suggested that the fungicide Prochloraz has a very interesting agronomic effect, possibly due to the negative effect on soil fungal population stimulating the growth of soil bacterial activity.

Application of MCPA herbicide on soils amended with biostimulants: Short-time effects on soil biological properties

In this paper we studied in the laboratory the effect of MCPA herbicide at a rate of 1.5 l ha −1 (manufactures rate recommended) on biological properties of a Plagic Antrosol amended with four biostimulants (WCDS, wheat condensed distillers soluble; PA-HE, hydrolyzed poultry feathers; CGHE, carob germ enzymatic extract; and RB, rice bran extract). Seven hundred grams of soil were mixed with WCDS at a rate of 10%, CGHE at a rate of 4.7%, PA-HE at a rate of 4.3%, and RB at a rate of 4.4%, respectively, in order to applying the same amount of organic matter to the soil (16.38 g organic matter). An unamended polluted and amended non-polluted soil were used as control. For all treatments, the soil ergosterol, dehydrogenase, urease, and phosphatase activities were measured at two incubation times (0 and 60 d). The 16S rDNA-DGGE profiles in all treatments were determined at the beginning and end of the incubation period. The results indicated that at the end of the incubation period and compared with the control soil, the dehydrogenase, urease and phosphatase activities and ergosterol decreased 39.3%, 20%, 15.7% and 56.5%, respectively in the non-organic amended polluted soil. The application of organic matter to unpolluted soil increased the enzymatic activities and ergosterol. However, this stimulation was higher in the soil amended with RB, followed by PA-HE, WCDS and CGHE. The application of herbicide in organic-amended soils decreased the enzymatic activities and ergosterol content. However, this decrease was lower than for the non-amended herbicide polluted soil. Possibly the low molecular weight protein content easily assimilated by soil microorganisms and the adsorption capacity of humic substances are responsible for less inhibition of these enzyme activities and soil ergosterol. The 16S rDNA-DGGE profiles indicated that herbicide did not negatively affect soil bacterial biodiversity.

Impact of endochitinase-transformed white spruce on soil fungal biomass and ectendomycorrhizal symbiosis.

The impact of transgenic white spruce [Picea glauca (Moench) Voss] containing the endochitinase gene (ech42) on soil fungal biomass and on the ectendomycorrhizal fungi Wilcoxina spp. was tested using a greenhouse trial. The measured level of endochitinase in roots of transgenic white spruce was up to 10 times higher than that in roots of nontransformed white spruce. The level of endochitinase in root exudates of three of four ech42-transformed lines was significantly greater than that in controls. Analysis soil ergosterol showed that the amount of fungal biomass in soil samples from control white spruce was slightly larger than that in soil samples from ech42-transformed white spruce. Nevertheless, the difference was not statistically significant. The rates of mycorrhizal colonization of transformed lines and controls were similar. Sequencing the internal transcribed spacer rRNA region revealed that the root tips were colonized by the ectendomycorrhizal fungi Wilcoxina spp. and the dark septate endophyte Phialocephala fortinii. Colonization of root tips by Wilcoxina spp. was monitored by real-time PCR to quantify the fungus present during the development of ectendomycorrhizal symbiosis in ech42-transformed and control lines. The numbers of Wilcoxina molecules in the transformed lines and the controls were not significantly different (P > 0.05, as determined by analysis of covariance), indicating that in spite of higher levels of endochitinase expression, mycorrhization was not inhibited. Our results indicate that the higher levels of chitinolytic activity in root exudates and root tissues from ech42-transformed lines did not alter the soil fungal biomass or the development of ectendomycorrhizal symbiosis involving Wilcoxina spp.

Microbial community structure in a silty clay loam soil after fumigation with three broad spectrum fungicides

The short-term effect of three broad spectrum fungicides on microbial activity, microbial biomass, soil ergosterol content, and phospholipid fatty acid (PLFA) profiles was studied. A silty clay loam soil was treated separately with captan, chlorothalonil and carbendazim at three different dosages of each fungicide. Chlorothalonil and carbendazim significantly altered soil microbial activity. However, changes in soil microbial biomass were only observed in soil treated with higher dosages of these fungicides. All dosages of fungicides significantly decreased fungal biomass as estimated by soil ergosterol content. PLFA analysis indicated that there was a shift in PLFA pattern. Higher dosages of all three fungicides decreased a straight-chain PLFA 22:0. In addition, soil treated with carbendazim increased cyclopropyl fatty acids. Compared to untreated soil, higher dosages of both captan and chlorothalonil affected PLFA 10Me 16:0, indicating that these fungicides can reduce actinomycetes population. Finally, our results suggest that application of both captan and chlorothalonil decreased Gram-positive to Gram-negative ratio.

Effects of litter addition and warming on soil carbon, nutrient pools and microbial communities in a subarctic heath ecosystem

Climatic warming leads to the expansion of deciduous shrubs and trees in the Arctic. This leads to higher leaf litter inputs, which together with warming may alter the rate of carbon and nutrient cycling in the arctic ecosystems. We assessed effects of factorial warming and additional litter on the soil ecosystem of a subarctic heath in a 7-year-long field experiment. Fine root biomass, dissolved organic carbon (DOC) and total C concentration increased in response to warming, which probably was a result of the increased vegetation cover. Litter addition increased the concentration of inorganic P in the uppermost 5 cm soil, while decreasing the pool of total P per unit area of the organic profile and having no significant effects on N concentrations or pools. Microbial biomass C and N were unaffected by the treatments, while the microbial biomass P increased significantly with litter addition. Soil ergosterol concentration was also slightly increased by the added litter in the uppermost soil, although not statistically significantly. According to a principal component analysis of the phospholipid fatty acid profiles, litter addition differed from the other treatments by increasing the relative proportion of biomarkers for Gram-positive bacteria. The combined warming plus litter addition treatment decreased the soil water content in the uppermost 5 cm soil, which was a likely reason for many interactions between the effects of warming and litter addition. The soil organic matter quality of the combined treatment was also clearly different from the control based on a near-infrared reflectance (NIR) spectroscopic analysis, implying that the treatment altered the composition of soil organic matter. However, it appears that the biological processes and the microbial community composition responded more to the soil and litter moisture conditions than to the change in the quality of the organic matter.

Relationships between Fungal Biomass and Nitrous Oxide Emission in Upland Rice Soils under No Tillage and Cover Cropping Systems

The relationships between soil microbial properties and nitrous oxide emission were examined in upland soil under different tillage systems [no tillage (NT), rotary and plow tillage] and cover crop systems (fallow, cereal rye, and hairy vetch) in 2004 and 2005. Microbiological analyses included the determination of soil ergosterol as an indicator of fungal biomass, bacterial plate counting, and MPN estimations of ammonia oxidizers and denitrifiers. The combined practice of NT with rye-cover crop treatment increased fungal biomass but not bacterial populations in 0-10 cm deep soils. Such increase in fungal biomass was not found in 10-20 cm and 20-30 cm deep cover-cropped NT soil. The combined practice of NT with rye-cover cropping resulted in higher in situ N(2)O emission rates compared with rotary- and plow-till treatments. N(2)O flux was positively correlated with soil ergosterol content but not with denitrifier MPN and other soil chemical properties. These results suggested a significant contribution of fungi to N(2)O emission in cover-cropped NT soils.

Application of near infrared reflectance (NIR) and fluorescence spectroscopy to analysis of microbiological and chemical properties of arctic soil

Applicability of near infrared reflectance (NIR) and fluorescence spectroscopic techniques was tested on highly organic arctic soil. Soil samples were obtained at a long-term climate change manipulation experiment at a subarctic fell heath in Abisko, northern Sweden. The ecosystem had been exposed to treatments simulating increasing temperature (open-top greenhouses), higher nutrient availability (NPK fertilization) and increasing cloudiness (shading cloths) for 15 years prior to the sampling. For each of the 72 samples from the 0 to 5 cm soil depth and 36 samples from the 5 to 10 cm depth, the wavelength range of 400–2500 nm (visible and near infrared spectrum) was scanned with a NIR spectrophotometer and fluorescence excitation-emission matrices (EEMs) were recorded with a spectrofluorometer. Principal component analyses of the visible, NIR and fluorescence spectra clearly separated the treatments, which indicates that the chemical composition of the soil and its spectral properties had changed during the climate change simulation. Similarly to the results from the conventional analyses of soil chemical and microbiological properties, fertilization treatment posed strongest effects on the spectra. Partial least-squares (PLS) regression methods with cross-validation were used to analyse relationships between the spectroscopic data and the chemical and microbiological data derived from the conventional analyses. The fluorescence EEMs of the dried solid soil samples were moderately related to soil ergosterol content (correlation coefficient r=0.84), bacterial activity analysed by leucine incorporation technique ( r=0.78) and total phospholipid fatty acid (PLFA) content ( r=0.74), but in general fluorescence provided inferior predictions of the chemical and microbiological variables to NIR. NIR was highly related to soil organic matter content ( r>0.9) and showed promising predictions of soil ergosterol content ( r>0.9), microbial biomass C, microbial biomass P, and total PLFA contents ( r=0.78–0.79). These results suggest that especially NIR could be used to predict soil organic matter and fungal biomass. Since it is rapid and inexpensive, and requires little sample mass, it could be used as a ‘quick and dirty’ technique to estimate progression of the treatment responses in long-term ecosystem experiments, where extensive soil sampling is to be avoided.