Liming in a beech forest results in more mineral elements stored in the mantle of Lactarius subdulcis ectomycorrhizas

Liming is a forest practice used to counteract forest decline induced by soil acidification. It?consists of direct Ca and Mg input in forest soil and restores tree mineral nutrition, but also causes drastic changes in nutrient availability in soil. Ectomycorrhizal (ECM) fungi significantly contribute in nutrient uptake by trees, and can recover them through organic acid secretion or through enzymatic degradation of organic matter. The symbiotic fungi use their extraradical mycelium for nutrient uptake, and then store them into the ECM mantle. In this study we measured how liming influences element contents in the mantle of Lactarius subdulcis ECMs, an abundant and particularly active in oxalate and laccase secretion in beech stands. For this purpose we used SEM observation coupled with energy- (EDX) and wavelength-dispersive-X-ray microanalyses (WDX). Results showed that ECM mantles of this species presented significantly higher Ca, Mg, Mn, K, Si, Al and Fe contents in limed plots. The nutrient amounts of L. subdulcis ECMs were significantly different between individuals for all the elements, showing a differential storage ability between individuals. The storage role of the ECM mantle can be interpreted in two different ways: i) a detoxification role for Al or heavy metals and ii) an increased potential nutrient resource by the fungus, which can benefit the tree.     

Respiration activity of ectomycorrhizas from Cenococcum geophilum and Lactarius sp. in relation to soil water potential in five beech forests

Forest trees are involved in root symbioses with hundreds of species of ectomycorrhizal fungi which constitute functional guilds able to improve the water and mineral nutrition of host trees. In temperate ecosystems, water shortage is a main factor limiting tree vitality. To assess how soil water conditions affected the physiological state of beech (Fagus silvatica L.) ectomycorrhizal roots, we monitored glucose respiration of two ectomycorrhizal types (Lactarius sp. and Cenococcum geophilum) during two complete growing seasons. Five stands of contrasting soil conditions were chosen in north-eastern France. The top soil horizons were equipped with micropsychrometers for measuring water potential and temperature. Glucose respiration on individual ectomycorrhizas was measured in vitro by trapping [¹⁴C]-CO₂ from radiolabelled glucose. For soil water potential <-0.2 MPa, the potential respiration activity of C. geophilumectomycorrhizas was significantly less altered than that of Lactariussp. ectomycorrhizas, indicating that C. geophilumis more likely than Lactariussp. to maintain the physiological integrity of beech roots facing drought stress.     

Quantification of extraradical soil mycelium and ectomycorrhizas of Boletus edulis in a Scots pine forest with variable sporocarp productivity

The availability of most edible ectomycorrhizal mushrooms depends on their natural fructification. Sporocarp formation of these fungi is linked to habitat characteristics and climate conditions, but these data alone do not explain all the trends of fungal fruiting and dynamics. It could be hypothesized that the amount of soil mycelia could also be related to the production of carpophores. Soil samples (five cylinders of 250 cm³ per plot) were taken monthly, from September to November, in five fenced permanent plots (5 × 5 m) in Pinar Grande (Soria, Spain), a Pinus sylvestris stand situated in the north of the Sistema Ibérico mountain range. Plots were chosen to establish a gradient of Boletus edulis productivity from 0 to 38.5 kg/ha year, according to the mean fresh weight of sporocarps collected during the last 10 years. B. edulis ectomycorrhizal root tips were identified in each soil sample according to its morphology and counted. DNA extractions were performed with the PowerSoil^TM DNA Isolation Kit and quantification of extraradical soil mycelium by real-time polymerase chain reaction using specific primers and a TaqMan? probe. The concentration of soil mycelium of B. edulis (mg mycelium/g soil) did not differ significantly between plots (p = 0.1397), and sampling time (p = 0.7643) within the fructification period. The number of mycorrhizal short roots per soil volume showed significant differences between the plots (p = 0.0050) and the three sampling times (p < 0.0001). No significant correlation between the number of mycorrhizas and the productivity of the plot (kg of B. edulis/ha year) was detected (p = 0.615). A statistically significant positive correlation (p = 0.0481) was detected between the concentration of mycelia of B. edulis in the soil samples and the presence of short roots mycorrhizal with B. edulis in these samples. The productivity of the plots, in terms of sporocarps produced during the last 10 years, was not correlated either with the concentration of soil mycelium or with the presence or abundance of ectomycorrhizas.     

Acetate synthesis in soil from a bavarian beech forest

Soil obtained from a beech forest formed significant amounts of acetate when incubated in a bicarbonate-buffered, mineral salt solution under anaerobic conditions at both 5 and 20 degrees C (21 and 38 g of acetate per kg [dry weight] of soil, respectively). At 20 degrees C, following an 18-day lag period, rates of 0.07 mmol of acetate synthesized per g (dry weight) of soil per day were observed. Acetate was not subject to immediate turnover; methane and hydrogen were not formed during the time intervals (5 degrees C, 335 days; 20 degrees C, 95 days) evaluated. The synthesis of acetate from endogenous materials was coincident with acetogenic potentials, i.e., the capacity to catalyze the H(2)-dependent synthesis of acetate. Hydrogen consumption was not directed towards the synthesis of methane. Collectively, these results suggest that acetogenesis may be an underlying microbial activity of this forest soil.     

Patterns of ammonia volatilization from a forest soil

Summary Ammonia volatilization from urea-treated soils was estimated under field and laboratory conditions. Acid-washed filter papers were hung in the air in a spruce stand treated with N and P fertilizers in a factorial design. In the laboratory, moss sods were incubated to quantify ammonia volatilization.Ammonia volatilization increased with the level of N applied and more ammonia was absorbed by filter papers at 0.6 m above the ground than those at 1.2 m. Maximum rates of ammonia volatilization in urea-treated plots were observed between the third and fourth day after fertilizer application and similar absorption patterns were observed in areas not treated with urea. It is, therefore, suggested that ammonia volatilized from urea-treated plots can move to untreated areas. Addition of P along with urea significantly reduced ammonia volatilization under field conditions.Laboratory experiments showed that addition of urea to moss sods increased the pH of the organic layer from about 3.6 to 8.8. Sphagnum moss sods volatilized more ammonia (about 1.7 per cent of the added material) than feather moss sods (about 0.8 per cent). At higher incubation temperatures, however, the rate of ammonia volatilization decreased in sphagnum moss sods but increased in feather moss sods.     

Characterization of a novel asparaginase from soil metagenomic libraries generated from forest soil

Objectives

To screen soil metagenomic libraries for novel enzymes with enhanced activities.

Results

To screen soil metagenomic libraries for novel enzymes with enhanced activities. A novel l-asparaginase was identified from forest soil metagenome and its characteristics were studied. The purified protein had a specific activity of 696 IU mg^?1 and optimum activity at pH 7 and 35 °C. Enhanced enzyme activities were observed in the presence of Mg²⁺, Ca²⁺ and K⁺. The K_m value, 2 mM, and enzyme specificity constant 7.7 mM^?1s^?1 indicated that the recombinant enzyme has good substrate affinity to l-asparagine compared with commercially-available Escherichia coli asparaginase. The IC₅₀ value of 0.78 µg ml^?1 (0.47 IU ml^?1) was observed with HL60 cell line and 0.39 µg ml^?1(0.23 IU ml^?1) with MOLT-3 and MOLT-4 cell lines, which is better than that of commercially-available drugs.

Conclusion

The soil metagenome derived l-asparaginase with enhanced activities could be a potential candidate to develop as a drug in Acute Lymphoblastic Leukemia (ALL) therapy.

     

Gene flow and hybridisation in a mixed oak forest (Quercus pyrenaica Willd. and Quercus petraea (Matts.) Liebl.) in central Spain

Oaks are long-standing models for the study of gene flow and hybridisation. Temperate (Quercus petraea) and sub-Mediterranean (Quercus pyrenaica) oaks coexist in central Spain, showing remarkable differences in population size and structure. Q. petraea has a scattered distribution in central Spain, where it is at one of the southernmost limits of its range, and forms low-density stands; in contrast, Q. pyrenaica is widespread in the region. We selected a mixed population of the two species ( approximately 13 ha, 176 adults and 96 saplings) to compare the patterns of gene flow within each species and the extent of introgression between them. Using five nuclear microsatellite markers, we performed a parentage analysis and found considerable immigration from outside the stand ( approximately 38% for Q. petraea and approximately 34% for Q. pyrenaica), and estimated average seed-dispersal distances of 42 and 14 m for Q. petraea and Q. pyrenaica, respectively. Introgression between species was also estimated using our microsatellite battery. First, we developed a multivariate discriminant approach and, second, we compared our results with a widely used clustering method (STRUCTURE). Both analyses were consistent with a low level of introgression between Q. petraea and Q. pyrenaica. Indeed, only 15 adult trees, approximately 8.5%, were identified as putative hybrids when both methods of analysis were combined. Hybrids may be most common in contact zones due merely to physical proximity.     

Oligotrophic bacteria from rendzina forest soil

Oligotrophic bacteria were shown to exist abundantly in all layers of a rendzina forest soil throughout the year. Two-hundred-three oligotrophic bacteria were isolated from forest soil (Aoba, Sendai) at different layers (L, F, H and A layers) throughout the year, and their morphological and physiological characteristics were examined. A high proportion (95%) of the isolated oligotrophs were Gram-negative, non-spore forming bacteria. Based on the cell shape, the isolates were divided into four groups: regular rods, curved/spiral bacteria, irregular rods, and buddin and/or prosthecate bacteria. Each group of bacteria is discussed in relation to the physiological characteristics. Notably oligotrophic bacteria of different cell types showed a marked zonal distribution in respect to profile depth.     

Soil N and C trace gas fluxes and microbial soil N turnover in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary

During two intensive field campaigns in summer and autumn 2004 nitrogen (N₂O, NO/NO₂) and carbon (CO₂, CH₄) trace gas exchange between soil and the atmosphere was measured in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary. The climate can be described as continental temperate. Fluxes were measured with a fully automatic measuring system allowing for high temporal resolution. Mean N₂O emission rates were 1.5 μg N m⁻² h⁻¹ in summer and 3.4 μg N m⁻² h⁻¹ in autumn, respectively. Also mean NO emission rates were higher in autumn (8.4 μg N m⁻² h⁻¹) as compared to summer (6.0 μg N m⁻² h⁻¹). However, as NO₂ deposition rates continuously exceeded NO emission rates (−9.7 μg N m⁻² h⁻¹ in summer and −18.3 μg N m⁻² h⁻¹ in autumn), the forest soil always acted as a net NO _x sink. The mean value of CO₂ fluxes showed only little seasonal differences between summer (81.1 mg C m⁻² h⁻¹) and autumn (74.2 mg C m⁻² h⁻¹) measurements, likewise CH₄uptake (summer: −52.6 μg C m⁻² h⁻¹; autumn: −56.5 μg C m⁻² h⁻¹). In addition, the microbial soil processes net/gross N mineralization, net/gross nitrification and heterotrophic soil respiration as well as inorganic soil nitrogen concentrations and N₂O/CH₄ soil air concentrations in different soil depths were determined. The respiratory quotient (ΔCO_{2 resp} ΔO_{2 resp}⁻¹) for the uppermost mineral soil, which is needed for the calculation of gross nitrification via the Barometric Process Separation (BaPS) technique, was 0.8978 ± 0.008. The mean value of gross nitrification rates showed only little seasonal differences between summer (0.99 μg N kg⁻¹ SDW d⁻¹) and autumn measurements (0.89 μg N kg⁻¹ SDW d⁻¹). Gross rates of N mineralization were highest in the organic layer (20.1–137.9 μg N kg⁻¹ SDW d⁻¹) and significantly lower in the uppermost mineral layer (1.3–2.9 μg N kg⁻¹ SDW d⁻¹). Only for the organic layer seasonality in gross N mineralization rates could be demonstrated, with highest mean values in autumn, most likely caused by fresh litter decomposition. Gross mineralization rates of the organic layer were positively correlated with N₂O emissions and negatively correlated with CH₄ uptake, whereas soil CO₂ emissions were positively correlated with heterotrophic respiration in the uppermost mineral soil layer. The most important abiotic factor influencing C and N trace gas fluxes was soil moisture, while the influence of soil temperature on trace gas exchange rates was high only in autumn.     

Variations of soil enzyme activities in a temperate forest soil

Soil enzyme activities (dehydrogenase, urease, phosphatase, and arylsulfatase) in a temperate forest soil were determined in relation to landscape position and seasons. Overstory of the area is dominated by Quercus mongolica, Kalopanax pictus, Carpicus cordata, and Acer pseudo-sieboldianum. The activities were measured in three patches, namely a north-facing backslope, a ridge, and a south-facing backslope in autumn and spring over 2 years. In addition, spatially more detailed analysis for phosphatase was conducted before and after litterfall production in six patches. Dehydrogenase, urease, phosphatase, and arylsulfatase activities varied 1.8–18.5 μg INT-formazan g⁻¹ h⁻¹, 45.4–347.0 μg NH₄ ⁺ g⁻¹ h⁻¹, 0.9–4.5 mmol pNP g⁻¹ h⁻¹, and 0.7–2.6 mmol pNP g⁻¹ h⁻¹, respectively. In general, higher enzyme activities were found in the northern aspect than in the southern aspect. This variation appears to be related to differences in chemical properties (e.g., Fe, Al, and Mg) of soil as well as distribution of leaf litter. Two patterns were discernible in relation to seasonal variations. Dehydrogenase and urease exhibited a positive correlation with mean air temperature, suggesting that temperature would be a major controlling variable for those enzymes. In contrast, higher activities were detected in autumn for phosphatase and arylsulfatase activities, which appeared to be closely related to litter production and distribution. Overall results of this study indicate that soil enzyme activities in a forest floor are influenced by several variables such as temperature, nutrient availability, and input of leaf litter, which are closely related to landscape position.     

Temperature-independent diel variation in soil respiration observed from a temperate deciduous forest

The response of soil respiration (R_s) to temperature depends largely on the temporal and spatial scales of interest and how other environmental factors interact with this response. They are often represented by empirical exponential equations in many ecosystem analyses because of the difficulties in separating covarying environmental responses and in observing below ground processes. The objective of this study was to quantify a soil temperature‐independent component in R_s by examining the diel variation of an R_s time series measured in a temperate deciduous forest located at Oak Ridge, TN, USA between March and December 2003. By fitting 2 hourly, continuous automatic chamber measurements of CO₂ efflux at the soil surface to a Q₁₀ function to obtain the temperature‐dependent respiration (R_t) and plotting the diel cycles of R_t, R_s, and their difference (R_i), we found that an obvious temperature‐independent component exists in R_s during the growing season. The diel cycle of this component has a distinct day/night pattern and agrees well with diel variations in photosynthetically active radiation (PAR) and air temperature. Elevated canopy CO₂ concentration resulted in similar patterns in the diel cycle of the temperature‐independent component but with different daily average rates in different stages of growing season. We speculate that photosynthesis of the stand is one of the main contributors to this temperature‐independent respiration component although more experiments are needed to draw a firm conclusion. We also found that despite its relatively small magnitude compared with the temperature‐dependent component, the diel variation in the temperature‐independent component can lead to significantly different estimates of the temperature sensitivity of soil respiration in the study forest. As a result, the common practice of using fitted temperature‐dependent function from night‐time measurements to extrapolate soil respiration during the daytime may underestimate daytime soil respiration.     

Determinants of isotopic coupling of CO2 and water vapour within a Quercus petraea forest canopy

Concentration and isotopic composition (δ¹³C and δ¹⁸O) of ambient CO₂ and water vapour were determined within a Quercus petraea canopy, Northumberland, UK. From continuous measurements made across a 36-h period from three heights within the forest canopy, we generated mixing lines (Keeling plots) for δ_a ¹³CO₂, δ_a C¹⁸O¹⁶O and δ_a H₂ ¹⁸O, to derive the isotopic composition of the signal being released from forest to atmosphere. These were compared directly with measurements of different respective pools within the forest system, i.e. δ¹³C of organic matter input for δ_a ¹³CO₂, δ¹⁸O of exchangeable water for δ_a C¹⁸O¹⁶O and transpired water vapour for δ_a H₂ ¹⁸O. [CO₂] and δ_a ¹³CO₂ showed strong coupling, where the released CO₂ was, on average, 4 per mil enriched compared to the organic matter of plant material in the system, suggesting either fractionation of organic material before eventual release as soil-respired CO₂, or temporal differences in ecosystem discrimination. δ_a C¹⁸O¹⁶O was less well coupled to [CO₂], probably due to the heterogeneity and transient nature of water pools (soil, leaf and moss) within the forest. Similarly, δ_a H₂ ¹⁸O was less coupled to [H₂O], again reflecting the transient nature of water transpired to the forest, seen as uncoupling during times of large changes in vapour pressure deficit. The δ¹⁸O of transpired water vapour, inferred from both mixing lines at the canopy scale and direct measurement at the leaf level, approximated that of source water, confirming that an isotopic steady state held for the forest integrated over the daily cycle. This demonstrates that isotopic coupling of CO₂ and water vapour within a forest canopy will depend on absolute differences in the isotopic composition of the respective pools involved in exchange and on the stability of each of these pools with time. Received: 21 March 1998 / Accepted: 10 December 1998     

Nutrient loading of a forest soil

Summary During July 1988 rooted and non-rooted experimental chambers were established in a Norway spruce (Picea abies. Karst) stand in south Devon U.K. Replicates were supplemented with ammonium and nitrate. The leachates were analysed to monitor the release of mineral-N species and cations over the 17-week experimental period. Ammonium treatments leached 300% more calcium and magnesium than controls. The onset of nitrification resulted in a decrease in sodium losses from ammonium treatments reflecting a decrease in the exchanging capacity of the soil solution. These results are discussed in relation to mineral ion leaching in soils subjected to increesed N-loading, and the ability of soils to buffer these perturbations.     

Effects of experimental drought on soil respiration and radiocarbon efflux from a temperate forest soil

Soil moisture affects microbial decay of SOM and rhizosphere respiration (RR) in temperate forest soils, but isolating the response of soil respiration (SR) to summer drought and subsequent wetting is difficult because moisture changes are often confounded with temperature variation. We distinguished between temperature and moisture effects by simulation of prolonged soil droughts in a mixed deciduous forest at the Harvard Forest, Massachusetts. Roofs constructed over triplicate 5 × 5 m² plots excluded throughfall water during the summers of 2001 (168 mm) and 2002 (344 mm), while adjacent control plots received ambient throughfall and the same natural temperature regime. In 2003, throughfall was not excluded to assess the response of SR under natural weather conditions after two prolonged summer droughts. Throughfall exclusion significantly decreased mean SR rate by 53 mg C m^?2 h^?1 over 84 days in 2001, and by 68 mg C m^?2 h^?1 over 126 days in 2002, representing 10–30% of annual SR in this forest and 35–75% of annual net ecosystem exchange (NEE) of C. The differences in SR were best explained by differences in gravimetric water content in the Oi horizon (r²=0.69) and the Oe/Oa horizon (r²=0.60). Volumetric water content of the A horizon was not significantly affected by throughfall exclusion. The radiocarbon signature of soil CO₂ efflux and of CO₂ respired during incubations of O horizon, A horizon and living roots allowed partitioning of SR into contributions from young C substrate (including RR) and from decomposition of older SOM. RR (root respiration and microbial respiration of young substrates in the rhizosphere) made up 43–71% of the total C respired in the control plots and 41–80% in the exclusion plots, and tended to increase with drought. An exception to this trend was an interesting increase in CO₂ efflux of radiocarbon‐rich substrates during a period of abundant growth of mushrooms. Our results suggest that prolonged summer droughts decrease primarily heterotrophic respiration in the O horizon, which could cause increases in the storage of soil organic carbon in this forest. However, the C stored during two summers of simulated drought was only partly released as increased respiration during the following summer of natural throughfall. We do not know if this soil C sink during drought is transient or long lasting. In any case, differential decomposition of the O horizon caused by interannual variation of precipitation probably contributes significantly to observed interannual variation of NEE in temperate forests.     

Feedback from soil inorganic nitrogen on soil organic matter mineralisation and growth in a boreal forest ecosystem

Current nitrogen (N) deposition rates are considerably higher than during pre-industrial times and the growing interest in forest fertilisation requires better understanding of how the N and carbon (C) cycles interact. This study is based on experimental data showing how Scots pine (Pinus sylvestris L.) forests respond to single or consecutive pulse doses of N. The data were used to support the implementation of a dynamic feedback mechanism in the Q model, allowing for changes in soil N availability to regulate the rate of decomposer efficiency. Simulations of the long-term effects of slowly increasing N deposition with and without dynamic decomposer efficiency were then compared. Both versions of the model accurately predicted the response of tree growth to N fertilisation. Slowly increasing inputs of N over a century in the modified version acted on the inputs and outputs of soil C in opposing ways: (a) rate of litter input slowed down because more N was retained in the soil and thus not available for tree growth; (b) rate of C output, through soil heterotrophic respiration, was also gradually reduced due to increasing decomposer efficiency, although not enough to sufficiently balance the reduced litter input. Accurate prediction of the amount of added N retained in the ecosystem seems to be one of the key issues for estimating enhanced C sequestration.     

Volemolide,a Novel Norsterol from the Fungus Lactarius volemus

A novel sterol with a heptanorergostane skeleton was isolated from the neutral fraction of Lactarius volemus, together with two known sterols. The structures of these compounds were determined by chemical transformation of ergocalciferol and by spectroscopic methods.     

Denitrification studies in a temperate forest catena soil

Summary Formation of ammonium during the reduction of nitrate under moderate and strict anaerobic incubation of two topsoils of a temperate forest catena, an acid mull and an anmoor was studied. In mull, both conditions of incubation caused reduction of nitrate and release of ammonium. The accumulation of ammonium continued even when there was no nitrate left hence indicating the formation of ammonium apparently through desamination of organic matter. Whereas, in anmoor neither any such formation of ammonium nor any significant reduction of nitrate was observed in the case of moderate anaerobic incubation. But under strict anaerobic incubation, progressive disappearance of nitrate was encountered from the beginning up to 30 days and this was accompanied by an increasing accumulation of ammonium in this soil. Yet this accumulation stopped when there was no nitrate left. Thus, the formation of ammonium is caused by the reduction of nitrate in anmoor.