Search

Climate change predictions suggest that arctic and subarctic ecosystems will be particularly affected by rising temperatures and extreme weather events, including severe heat waves. Temperature is one of the most important environmental factors controlling and regulating microbial decomposition in soils; therefore, it is critical to understand its impact on soil microorganisms and their feedback to climate warming. We conducted a warming experiment in a subarctic birch forest in North Sweden to test the effects of summer heat waves on the thermal trait distributions that define the temperature dependences for microbial growth and respiration. We also determined the microbial temperature dependences 10 and 12 months after the heat wave simulation had ended to investigate the persistence of the thermal trait shifts. As a result of warming, the bacterial growth temperature dependence shifted to become warm‐adapted, with a similar trend for fungal growth. For respiration, there was no shift in the temperature dependence. The shifts in thermal traits were not accompanied by changes in α‐ or β‐diversity of the microbial community. Warming increased the fungal‐to‐bacterial growth ratio by 33% and decreased the microbial carbon use efficiency by 35%, and both these effects were caused by the reduction in moisture the warming treatments caused, while there was no evidence that substrate depletion had altered microbial processes. The warm‐shifted bacterial thermal traits were partially restored within one winter but only fully recovered to match ambient conditions after 1 year. To conclude, a summer heat wave in the Subarctic resulted in (i) shifts in microbial thermal trait distributions; (ii) lower microbial process rates caused by decreased moisture, not substrate depletion; and (iii) no detectable link between the microbial thermal trait shifts and community composition changes. [ABSTRACT FROM AUTHOR]

Climate change is predicted to cause milder winters and thus exacerbate soil freeze–thaw perturbations in the subarctic, recasting the environmental challenges that soil microorganisms need to endure. Historical exposure to environmental stressors can facilitate the microbial resilience to new cycles of that same stress. However, whether and how such microbial memory or stress legacy can modulate microbial responses to cycles of frost remains untested. Here, we conducted an in situ field experiment in a subarctic birch forest, where winter warming resulted in a substantial increase in the number and intensity of freeze–thaw events. After one season of winter warming, which raised mean surface and soil (−8 cm) temperatures by 2.9 and 1.4°C, respectively, we investigated whether the in situ warming‐induced increase in frost cycles improved soil microbial resilience to an experimental freeze–thaw perturbation. We found that the resilience of microbial growth was enhanced in the winter warmed soil, which was associated with community differences across treatments. We also found that winter warming enhanced the resilience of bacteria more than fungi. In contrast, the respiration response to freeze–thaw was not affected by a legacy of winter warming. This translated into an enhanced microbial carbon‐use efficiency in the winter warming treatments, which could promote the stabilization of soil carbon during such perturbations. Together, these findings highlight the importance of climate history in shaping current and future dynamics of soil microbial functioning to perturbations associated with climate change, with important implications for understanding the potential consequences on microbial‐mediated biogeochemical cycles. [ABSTRACT FROM AUTHOR]

Harvesting whole-tree biomass for biofuel combustion intensifies removal of nutrients from the ecosystem. This can be partly abated by applying ash from the combustion back to the system, as the ash is rich in nutrients. Ash is very alkaline and ash application raises soil pH, which in turn can stimulate microbial activity and thus decomposition and mineralization. Our aim was to test if ash induced decomposition activity was associated with enhanced turnover of recalcitrant, i.e. relatively old, organic pools. Two experiments were conducted in the same coniferous plantation after the application of 0, 3, 4.5 and 6 t ash ha−1, and 0, 3, 9, 15 and 30 t ash ha−1, respectively. We used natural abundance of 15N in mosses, mites and ectomycorrhizal fungi 26 months after ash application, as well as temporal variation in δ15N values of ectomycorrhizal fungi, as an indicator of decomposition of recalcitrant organic matter in the first experiment. Furthermore, in the second experiment we used measurements of extracellular manganese peroxidase activity almost 4 years after ash application as an indication of potential decomposition of lignin, an important component of recalcitrant organic matter. The δ15N signature increased significantly for ectomycorrhizal fungi, dead moss, Nothroid and Gamasida mites, and manganese peroxidase activity tended to increase, with increasing ash doses. This suggests that ash application stimulates turnover of recalcitrant organic matter, which can increase the available pool of nitrogen in the system. This will potentially enhance the fertilizer value of ash. However, the δ15N in ectomycorrhizal fungi tended to peak at 18 months after ash application, before decreasing, suggesting that the turnover of recalcitrant organic matter is reduced again with time. Image 1 • We investigated if ash addition increases turnover of recalcitrant organic matter. • In a field experiment we measured δ15N in soil organisms and MnP activity in soil. • Soil organisms were δ15N enriched with increasing ash doses. • MnP activity tended to increase with increasing ash doses. • δ15N in ectomycorrhizal fungi tended to peak at 18 months after ash application. [ABSTRACT FROM AUTHOR]

Ectomycorrhizal (ECM) fungi are key players in N cycling in coniferous forests, and forest management such as application of wood ash can affect their functionality. The aim of this study was to determine the effects of wood ash application on ECM fungal mycelial production, capacity to retain N, diversity and community composition. In-growth mesh bags were installed in control and treated plots. After 6 months, 15N labeled ammonium and nitrate were applied into the mesh bags, and 24 h later extramatrical mycelium (EMM) was extracted and analyzed. Wood ash had no effects on EMM in-growth, N retention capacity, diversity or community composition. In contrast, there were significant seasonal differences in the amount of EMM produced. These results demonstrate that applying up to 6 t ha−1 of wood ash in this type of plantation forest is a safe management practice that does not increase N leaching or negatively affect ECM fungi. [ABSTRACT FROM AUTHOR]

Abstract: Ash from combustion of biofuels, for example wood chips, is often deposited as waste, but due to its high content of essential plant nutrients and alkalinity, it has been proposed to recycle ash as a fertilizer and liming agent in biofuel production forest. However, current legislation sets rather strict limitations for wood‐ash application in biofuel production systems. The soil microfood web, that is microorganisms and their microfaunal grazers, protozoa and nematodes, is pivotal for essential ecosystem processes such as decomposition and plant nutrient release. Therefore, a thorough assessment of the impacts on microfood web structure and functioning must precede actions towards raising the currently allowed application rates. In a Danish Norway spruce plantation, we evaluate the impact of wood ash applied at dosages from 0 to the extreme case of 90 t ash ha−1 on the microfood web, the bacterial community structure, soil content of inorganic nitrogen, organic matter, dissolved organic carbon and nitrogen. Using structural equation modelling (SEM), we disentangled the direct effect of the disturbance imposed by ash per se, the associated pH increase and changes in prey abundance on individual organism groups in the microfood web. The SEM showed that the pH rise was the main driver of increasing abundances of culturable heterotrophic bacteria with increasing ash doses, and via trophical transfer, this also manifested as higher abundances of bacterial grazers. Fungal‐feeding nematodes were unaffected by ash, whereas carnivorous/omnivorous nematodes decreased due to the direct effect of ash. Increasing ash doses enhanced the difference between bacterial communities of control plots and ash‐amended plots. The ash‐induced stimulation of culturable heterotrophic bacteria and bacterial grazers increased inorganic nitrogen availability at ash doses of 9 t ha−1 and above. Hence, raised limits for ash application may potentially benefit tree growth via enhanced N mineralization activity of the soil food web. [ABSTRACT FROM AUTHOR]

The identification of causal links between microbial community structure and ecosystem functions are required for a mechanistic understanding of ecosystem responses to environmental change. One of the most influential factors affecting plants and microbial communities in soil in managed ecosystems is the current land-use. In forestry, wood ash has been proposed as a liming agent and a fertilizer, but has been questioned due to the risk associated with its Cd content. The aim of this study was to determine the effects of wood ash on the structure and function of decomposer microbial communities in forest soils and to assign them to causal mechanisms. To do this, we assessed the responses to wood ash application of (i) the microbial community size and structure, (ii) microbial community trait-distributions, including bacterial pH relationships and Cd-tolerance, to assign the microbial responses to pH and Cd, and (iii) consequences for proxies of the function soil organic matter (SOM) turnover including respiration and microbial growth rates. Two sets of field-experiments in temperate conifer forest plantations were combined with laboratory microcosm experiments where wood ash additions were compared to additions of lime and Cd. Wood ash induced structural changes in the microbial community in both field experiments, and striking similarities were observed between the application of ash and that of lime in the microcosm experiments. Wood ash increased pH, and led to a shift toward faster SOM decomposition and a reduced importance of fungi. This coincided with shifts in bacterial community trait distributions for pH, with pH optima closely tracking the new soil pH. A Cd solution could induce Cd-tolerance in the microcosm experiments, but the ash did not affect the microbial tolerance to Cd in field or microcosm experiments. We demonstrate that the microbial community responded strongly to the application of wood ash to forest soils with consequences for its functional capabilities in terms of respiration and growth rates. The bacterial community's trait distributions revealed that the increased pH directly caused the microbial responses, while the wood ash associated Cd has no detectable effects on the microbial community. The study demonstrates the power of community trait distributions to (i) causally link microbial structural responses to environmental change and (ii) potential to predict the ecosystem functional consequences. [ABSTRACT FROM AUTHOR]

Reutilizing biomass ashes in agriculture can substitute inputs of P from finite primary sources. However, recycling of ashes is disputed due to their content of toxic substances such as heavy metals. This study evaluates the potential risk of replacing easily soluble inorganic P fertilizer with P in biomass ashes in a barley crop grown on soil with adequate P status. Two contrasting doses of three different types of ashes were applied to an agricultural field with spring barley and compared to similar doses of triple-superphosphate fertilizer. In the second growing season after biomass ash application, grain, straw and root dry matter yield, and P and Cd uptake were determined. Resin-extractable P was measured in soil and the symbiotic arbuscular mycorrhizal fungal activity, colonization, and community composition were assessed. Crop yield was not affected by ash application, while P-uptake and mycorrhizal status were slightly enhanced with high ash applications. Changes to the mycorrhizal community composition were evident with high ash doses. Cadmium uptake in aboveground plant tissue was unaffected by ash treatments, but increased in roots with increasing doses. Consequently, we conclude that fertilization with biomass ashes can replace conventional fertilizers without risk to barley crops in the short term. [ABSTRACT FROM AUTHOR]

Abstract: Ethnopharmacological relevance: To study the potential benefit of the traditional Mexican medicinal plant Galium mexicanum Kunth (Rubiaceae). Hexane, chloroform, and methanol extracts as well as various fractions from these extracts were tested to determine antibacterial, antifungal, antiparasitic or anti-inflammatory activities in vitro. Materials and methods: Aerial parts of the plant were extracted with various solvents and fractionated accordingly. Their antibacterial and antifungal activities were assessed on nine bacterial and four fungal strains. Leishmania donovani was used as a protozoan strain for antiparasitic activity. The anti-inflammatory activity of the compounds was investigated by measuring the secretion of interleukin-6 when macrophages were exposed to lipopolysaccharide. Results: Various extracts and fractions obtained from this plant exhibit antibacterial, antifungal, antiparasitic, and anti-inflammatory activities. Of special interest was the hexane fraction HE 14b, which show antibacterial (ranging between 67 and 666μg/ml) and antifungal (at concentrations of 333μg/ml) activities. Also the hexane fraction HE 5 exhibited antiparasitic activity (at concentrations of 260μg/ml), whereas the methanol fraction ME 13–15 showed a potent anti-inflammatory activity when compared to dexamethasone. Chemical analyses of the chloroform extract show the presence of triterpenes, saponins, flavonoids, sesquiterpene lactones, and glucosides, but no tannins were detected in the assayed extract. Conclusions: The benefit of Galium mexicanum as a traditional medicinal plant was confirmed using antibacterial and antifungal assays in vitro. We also report for the first time, and to the best of our knowledge, antiparasitic and anti-inflammatory activities of this plant. [Copyright &y& Elsevier]

Arbuscular mycorrhizal fungi (AMF) are important in plant nutrient uptake, but their function is prone to environmental constraints including soil factors that may suppress AMF transfer of phosphorus (P) from the soil to the plant. The objective of this study was to disentangle the biotic and abiotic components of AMF-suppressive soils. Suppression was measured in terms of AMF-mediated plant uptake of 33P mixed into a patch of soil and treatments included soil sterilization, soil mixing, pH manipulation and inoculation with isolated soil fungi. The degree of suppression was compared to volatile organic compound (VOC) production by isolated fungi and to multi-element analysis of soils. For a selected suppressive soil, sterilization and soil mixing experiments confirmed a biotic component of suppression. A Fusarium isolate from that soil suppressed the AMF activity and produced greater amounts than other fungal isolates of the antimicrobial VOC trichodiene (a trichothecene toxin precursor), beta-chamigrene, alpha-cuprenene and p-xylene. These metabolites deserve further attention when unravelling the chemical background behind the suppression of AMF activity by soil microorganisms. For the abiotic component of suppression, soil liming and acidification experiments confirmed that suppression was strongest at low pH. The pH effect might be associated with changed availability of specific suppressive elements. Indeed 33P uptake from the soil patches correlated negatively to Al levels and Al toxicity seems to play a major role in the AMF suppressiveness at pH below 5.0–5.2. However, the documentation of a biotic component of suppression for both low and high pH soils leads to the conclusion that biotic and abiotic components of suppression may act in parallel in some soils. The current insight into the components of soil suppressiveness of the AMF activity aids to develop management practices that allow for optimization of AMF functionality. • In some soils, suppression of AMF activity had a biotic component. • A Fusarium isolate from a suppressive soil inhibited the AMF activity. • This isolate produced greater amounts of antimicrobial VOCs than other isolates. • AMF suppression increased at low pH across several soils. • For these soils, Al toxicity played a major role in suppressiveness at pH ≤ 5.0 [ABSTRACT FROM AUTHOR]

It is of great importance to understand how terrestrial ecosystems will respond to global changes. However, most experimental approaches have focused on single factors. In natural systems, moisture and temperature often change simultaneously, and they can interact and shape microbial responses. Even though soil moisture and temperature are very important factors controlling microbial activity, there is disagreement on the dependence of microbial rates on temperature and moisture as well as their sensitivity when both variables change simultaneously. Here we created a moisture gradient and determined high resolution intrinsic temperature dependences for bacterial and fungal growth rates as well as respiration rates. We found that microbial rates decreased with lower moisture and increased with higher temperatures until optimum values. Additionally, we found independence between temperature and moisture as rate modifiers. We also found that temperature sensitivities (Q 10) for microbial growth and respiration were not affected by changes in moisture. This provided an experimental framework to validate assumptions of temperature and moisture rate modifiers used in ecosystem and global cycling models (GCMs). • Microbial carbon-use efficiency (CUE) is not affected by changes in moisture. • CUE does not change with temperature up to T opt , over which it decreases. • Temperature dependences for microbial rates are independent from moisture. • Results validate independence for temperature and moisture assumed in soil C models. [ABSTRACT FROM AUTHOR]

Suppression of the activity of arbuscular mycorrhizal fungi (AMF) in unsterile soils, as determined by transfer of 33P from soils to plants, has been recently demonstrated, and soils differ in their degree of suppressiveness. The previous experiments included only one R. irregularis isolate, BEG87. The aim of this study was to analyze the sensitivity to suppression of different cultivated AMF isolates as well of native AMF communities using shoot 33P content as a proxy of AMF activity in mesh-enclosed patches of unsterile soil. We found that the suppression of a panel of Rhizophagus isolates differed from the suppression of R. irregularis BEG87. Suppression overall correlated with low soil pH and high soil phosphorus, but there were large differences between the isolates. Some Rhizophagus isolates were less sensitive to soil suppression than BEG87, and tolerance to suppression may be a relevant property to consider when choosing future AMF inoculants. For native AMF communities showing high root colonization, we found one example of a community that was not suppressed by its 'home' soil, while BEG87 activity in that soil was completely suppressed. Hence, some AMF communities appear to be reservoirs for inoculants with high tolerance towards suppression. • AMF-mediated plant 33P uptake varied within and between Rhizophagus species • Suppression of AMF-mediated plant 33P uptake was in general seen at low soil pH and high soil P • Tolerance to suppression may be a relevant property when choosing future AMF inoculants. • Some AMF communities appear to be reservoirs for inoculants with high tolerance towards suppression. [ABSTRACT FROM AUTHOR]

In the face of global climate change there is an increasing demand for biofuel, which exerts pressure on production and thus management of biofuel plantations. The intensification of whole-tree harvest from biofuel plantations increases export of nutrients. Returning ash from biofuel combustion to the forest plantations can amend the soil nutrient status and thus facilitate sustainable forest management. However, ash affects the forest floor decomposer food web, potentially changing organic matter turnover, carbon sequestration and nitrogen availability. Our aim was to examine the response of decomposer organisms, food web structure and nitrogen mineralization function after ash application. In a coniferous forest plantation amended with 0, 3, 4.5 or 6 t ash ha−1, we sampled in several depths of the forest floor for key organisms of the decomposer food web (fungal biomass, 0–12 cm; bacteria, protozoa, nematodes and enchytraeids, 0–3 cm and 3–6 cm; microarthropods and earthworms, 0–5 cm), 2, 14 and 26 months after ash application. We used structural equation modelling (SEM) to detangle the direct and indirect effects of ash application on organisms in the decomposer food web and on nitrogen availability. We found that ash increased the abundance of bacteria and protozoa, as well as the inorganic nitrogen pool at 0–3 cm depth, whereas the effect of ash was negligible at 3–6 cm depth. Earthworm abundance increased, whereas enchytraeid abundance decreased 2 years after ash application. The structural equation modelling showed that ash application stimulated the bacterial feeding pathway and increased nitrogen mineralization. Contrary, ash had a negative effect on fungal biomass at the first sampling, however, this effect subdued over time. Our results suggest that as the soil decomposer food web is resilient to ash application, this is a viable option for sustainable management of biofuel plantations. Unlabelled Image • Wood ash affects decomposer organisms and thus N mineralization, when used as fertilizer. • We measured physicochemical factors and enumerated organisms in the forest floor. • Using SEM we detangled the effects of ash application on the decomposer food web. • Ash stimulated the basal decomposer food web which increased the inorganic N pool. • Enchytraeid abundance decreased and earthworms increased 2 years after ash addition. [ABSTRACT FROM AUTHOR]

Most plants form symbiotic associations with arbuscular mycorrhizal fungi (AMF). AMF increase the uptake of plant nutrients by extending their extra-radical mycelium (ERM) in the soil where other groups of microorganisms may suppress the activity of the ERM. However, little is known about such suppression in natural soils. This work aimed to investigate the incidence of AMF suppression among soils sampled from highly variable natural ecosystems, and used 33P uptake by the ERM to evaluate AMF activity. A second aim was to identify factors behind the observed AMF-suppression. We found that AMF-suppressiveness varied markedly among natural soils and occurred more frequently in low pH than in high pH soils. A previous study for cultivated soils revealed a strong biological component of suppressiveness against AMF, and in accordance we found that the composition of both fungal and bacterial communities differed significantly between AMF-suppressive and non-suppressive natural soils. Acidobacteria, Acidothermus, Xanthomonadaceae, Archaeorhizomyces sp. Mortierella humilis and some Mycena spp. were significantly more abundant in AMF-suppressive soils and may therefore be direct antagonists of AMF. This implies that the functioning of AMF in natural ecosystems is strongly modulated by specific soil microbes. [ABSTRACT FROM AUTHOR]

• Wood ash fertilization increased pH and nutrient concentrations of the soil. • Wood ash supported plant growth better than CaO and K + P treatments. • Wood ash and CaO (pH) increase increased N mineralization. • Cd concentration in plant tissue increased only at very high amendment of wood ash. Wood ash is a by-product from energy production that can be recycled to forests to regain nutrients and prevent acidification. However, low concentrations of nitrogen (N) in wood ash may reduce its potential positive effect on plant growth. In addition, wood ash can have a high content of toxic heavy metals such as Cd, thus there are concerns that it may increase Cd accumulation in plants. We grew Deschampsia flexuosa (Wavy hair-grass) in pots in acidic nutrient poor forest soil fertilized with different concentrations of wood ash (corresponding to field application of 0, 1.1, 3.3, 11 and 33 t ha−1). Additionally, to disentangle the pH and nutrient effects of wood ash application, we included treatments with either CaO, to simulate pH effects of wood ash, or potassium (K) + phosphorus (P) fertilizer to mimic the nutrient effects. After 4.5 months of growth, we measured soil pH, plant biomass, Cd accumulation in shoots and N concentration in the various compartments of the system. Wood ash addition stimulated plant growth, whereas CaO and K + P addition resulted in more moderate increases in biomass. Despite the low concentration of N in the wood ash, plant uptake of N increased in wood ash amendments, probably because wood ash stimulated mineralization of soil organic N. Plant Cd content significantly increased at the highest dose of wood ash. Our results suggest that addition of wood ash significantly stimulates plant growth due to the combined effect of increased pH, elevated nutrient levels and increased N mineralization. Furthermore, despite the rather high Cd content in used wood ash (16.3 mg kg−1), wood ash amendments up to 11 t ha−1 did not result in significantly increased plant uptake of Cd. [ABSTRACT FROM AUTHOR]

Temperature is a major determinant of biological process rates, and microorganisms are key regulators of ecosystem carbon (C) dynamics. Temperature controls microbial rates of decomposition, and thus warming can stimulate C loss, creating positive feedback to climate change. If trait distributions that define temperature relationships of microbial communities can adapt to altered temperatures, they could modulate the strength of this feedback, but if this occurs remains unclear. In this study, we sampled soils from a latitudinal climate gradient across Europe. We established the temperature relationships of microbial growth and respiration rates and used these to investigate if and with what strength the community trait distributions for temperature were adapted to their local environment. Additionally, we sequenced bacterial and fungal amplicons to link the variance in community composition to changes in temperature traits. We found that microbial temperature trait distributions varied systematically with climate, suggesting that an increase in mean annual temperature (MAT) of 1°C will result in warm-shifted microbial temperature trait distributions equivalent to an increase in temperature minimum ( T min ) of 0.20°C for bacterial growth, 0.07°C for fungal growth, and 0.10°C for respiration. The temperature traits for bacterial growth were thus more responsive to warming than those for respiration and fungal growth. The microbial community composition also varied with temperature, enabling the interlinkage of taxonomic information with microbial temperature traits. Our work shows that the adaptation of microbial temperature trait distributions to a warming climate will affect the C-climate feedback, emphasizing the need to represent this to capture the microbial feedback to climate change. IMPORTANCE One of the largest uncertainties of global warming is if the microbial decomposer feedback will strengthen or weaken soil C-climate feedback. Despite decades of research effort, the strength of this feedback to warming remains unknown. We here present evidence that microbial temperature relationships vary systematically with environmental temperatures along a climate gradient and use this information to forecast how microbial temperature traits will create feedback between the soil C cycle and climate warming. We show that the current use of a universal temperature sensitivity is insufficient to represent the microbial feedback to climate change and provide new estimates to replace this flawed assumption in Earth system models. We also demonstrate that temperature relationships for rates of microbial growth and respiration are differentially affected by warming, with stronger responses to warming for microbial growth (soil C formation) than for respiration (C loss from soil to atmosphere), which will affect the atmosphere-land C balance., Competing Interests: The authors declare no conflict of interest.

Isotope labeling enables the detection and quantification of nutrient fluxes between soil and plants through arbuscular mycorrhizal (AM) fungi. Here we describe the use of radioactive isotopes, 33 P and 32 P, to study the uptake of P from soil by AM fungal mycelium and its transfer to the host plant through the mycorrhizal pathway.

The present study investigates the potential benefits of the Mexican medicinal plant Lopezia racemosa (Onagraceae). Extracts and fractions from aerial parts of this plant were assessed to determine their antibacterial, antifungal, antiparasitic, anti-inflammatory and cytotoxic activities in vitro. Aerial parts of the plant were extracted with various solvents and fractionated accordingly. Extracts and fractions were tested against a panel of nine bacterial and four fungal species. The antiparasitic activity was tested against Leishmania donovani, whereas the anti-inflammatory activity of the compounds was determined by measuring the secretion of interleukin-6 from human-derived macrophages. The same macrophage cell line was used to investigate the cytotoxicity of the compounds. Various extracts and fractions showed antibacterial, antifungal, antiparasitic, and anti-inflammatory activities. The hexanic fraction HF 11-14b was the most interesting fraction with antimicrobial, and anti-inflammatory activities. The benefit of L. racemosa as a traditional medicinal plant was confirmed as shown by its antibacterial, antifungal and anti-inflammatory activities. To the best of our knowledge, this is the first study reporting the biological activities of L. racemosa, including antiparasitic and anti-inflammatory activities.