Comparison of Mycorrhizal Colonization between Urban and Rural Environments

Human populations continue to grow and with it the urbanization of natural environments. There are numerous implications associated with this transformation, the greatest being the destruction of the ecosystem. It affects the air, the land, and all the organisms residing in the area. Characteristics of urban<!–[if supportFields]> XE “urban” <![endif]–><!–[if supportFields]><![endif]–> areas are buildings, square miles of concrete, and artificial mixes of vegetation<!–[if supportFields]> XE “vegetation” <![endif]–><!–[if supportFields]><![endif]–>. Usually, the introduction of exotic species takes over the remaining patches of habitat for native species. The exposed soil also undergoes drastic changes including lack of aeration, higher pH, and appearance of pollutants. Bainard and Klironomos (2010) focus on one of the effects urbanization produces on the mycorrhizal colonization of 26 tree species It compares the colonization of the tree species between urban and rural forests in Ontario, Canada<!–[if supportFields]> XE “Canada” <![endif]–><!–[if supportFields]><![endif]–>; and it seeks to expand the literature on the effect of urbanization on mycorrhizal fungi. —Daniella Barraza
Bainard, L., Klironomos, J., 2010. The mycorrhizal status and colonization of 26 tree species growing in urban<!–[if supportFields]> XE “urban” <![endif]–><!–[if supportFields]><![endif]–> and rural environments. Mycorrhiza 21, 91–96.

Bainard & Klironomos identified 26 tree species, found in both urban<!–[if supportFields]> XE “urban” <![endif]–><!–[if supportFields]><![endif]–> and rural environments, as their focus for mycorrhizal colonization. The rural area consisted of forests in southern Ontario and the urban area consisted of parks, streetscapes, and residential areas in southern Ontario. The species belonged to the genera Acer, Aesculus, Betula, Cercis, Fraxinus, Gleditsia, Juglans, Juniperus, Populus, Prunus, Quercus, Robinia, and Thuja. In urban and rural environments, five different locations were chosen for each of the tree species. The locations were chosen at 5 km intervals. Besides their location, another difference between tree species is that most trees found in the urban environment were grown in nurseries before being transplanted into their current location. At each location, three trees were chosen to represent their species, and all the chosen trees were mature at 20–25 years of age. For analysis, a soil core was obtained from beneath the trees. The soil cores were collected between May 26 and June 21 to keep seasonal changes at a minimum. From the soil cores, tree roots were examined for ectomycorrhizal (EM) and arbuscular mycorrhizal (AM) fungi colonization. To determine EM fungi colonization, root tips with mycorrhizal structures and a hartig net were counted and percent EM colonization was calculated. A hartig net is the hyphal network for nutrient exchange and its presence is to ensure that the symbiotic relationship between tree and fungi is active. To determine AM fungi colonization, roots were observed under a microscope since they are smaller than EM fungi. Percent AM fungi colonization was also calculated. Statistical analyses were computed to find out the insignificant and significant difference between colonization in urban and rural areas.
In both areas, all of the tree species were colonized by AM fungi and only seven were colonized by EM fungi. These seven species were also colonized by AM fungi and this relationship is called the tripartite association. Across the board, the species showed lower AM and tripartite association colonization in urban<!–[if supportFields]> XE “urban” <![endif]–><!–[if supportFields]><![endif]–> areas. For AM fungi, the range for percent colonization was broad from 2.4 % to 53.5 %. For EM fungi, the range for percent colonization was from 14.4 % to 50.8 %. In tripartite associations, the colonization of AM fungi was the lowest. This result accords with the trees’ stages of growth and fungal colonization.  During the early stages of growth, the tree is colonized by AM fungi, but as it matures, the EM fungi become more prominent. As mentioned, the studied trees were all mature trees.
However, there is one exception to lower fungal colonization in urban<!–[if supportFields]> XE “urban” <![endif]–><!–[if supportFields]><![endif]–> areas. Populus deltoides<!–[if supportFields]> XE “Populus deltoides” <![endif]–><!–[if supportFields]><![endif]–> with a tripartite association had a significantly higher AM fungi colonization in urban areas. When the data collected from each tree were averaged, AM colonization was significantly lower in urban areas; in tripartite association, AM colonization was not significantly different in urban areas.
The reasons for lower colonization could be discovered in the composition of urban<!–[if supportFields]> XE “urban” <![endif]–><!–[if supportFields]><![endif]–> soils, they’re pH, presence of pollutants and nutrients, and lack of aeration. Another reason can be attributed to the density of tree species in urban areas. There are fewer hosts for fungi to colonize since the trees are relegated to certain areas in the city. Finally, in disturbed soils, such as urban soils, fungi have more competition from other plant species, thereby reducing the fungal infectivity of the soil. However, not all disturbed soils result in lower fungal infectivity; some disturbances like clear-cutting have no effect on fungi colonization.
It is not known what the causes are for lower fungal colonization in urban<!–[if supportFields]> XE “urban” <![endif]–><!–[if supportFields]><![endif]–> areas, and it is not known what negative effects can occur. A suggestion for possible negative effects is inoculating the trees with mycorrhizal fungi. Although definitely more research needs to be done since trees in urban areas seem to be doing fine, and there is enough mycorrhizal fungi colonization to form structures for symbiosis.

Effect of Global Warming on the Aymbi-otic Relationship between Fungi and Plants

The ecosystems of mycorrhizal fungi take place below ground in symbiosis with plants. These ecosystems are not well researched despite their significant contribution to their surroundings. The fungi under study are ericoid mycorrhizal (ErM) fungi, fine endophytic (FE) fungi, and dark septate endophytic (DSE) fungi. ErM fungi can decompose a broad range of organic compounds such as protein, chitin, cellulose<!–[if supportFields]> XE “cellulose” <![endif]–><!–[if supportFields]><![endif]–>, hemicellulose, and starch. This decomposition<!–[if supportFields]> XE “decomposition” <![endif]–><!–[if supportFields]><![endif]–> releases amino acids<!–[if supportFields]> XE “amino acids” <![endif]–><!–[if supportFields]><![endif]–> and amino sugars which are then received by the symbiotic plant. FE fungi can improve host nutrient uptake. DSE fungi are ascomycetous but perform as mycorrhizal fungi in harsh environments. Plants in symbiosis with DSE fungi can resist droughts and infections better. In return, fungal symbionts receive approximately 20% of their plants’ net primary production<!–[if supportFields]> XE “net primary production (NPP)” <![endif]–><!–[if supportFields]><![endif]–>. Olsrud et al. (2010) present research of the effect on these symbiotic relationships due to global warming factors, elevated atmospheric CO2, and temperature. The area under study is a subarctic birch forest<!–[if supportFields]> XE “forest” <![endif]–><!–[if supportFields]><![endif]–> understory in Sweden<!–[if supportFields]> XE “Sweden” <![endif]–><!–[if supportFields]><![endif]–> at latitude 68°21’N<!–[if supportFields]> XE “nitrogen, N” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–>. Compared to regions of low latitude, global warming will have an appreciable effect on regions of high latitude. —Daniella Barraza
Olsrud, M., Carlsson, B., Svensson, B., Michelsen, A., Melillo, J., 2010. Responses of fungal root colonization, plant cover and leaf nutrients to long-term exposure to elevated atmospheric CO2 and warming in a subartic birch forest<!–[if supportFields]> XE “forest” <![endif]–><!–[if supportFields]><![endif]–> understory. Global Change Biology 16, 1820–1829.

Olsrud et al. conducted a six-year long study (2000–2006) on the responses of the three fungi to global warming. How plant cover and C, N<!–[if supportFields]> XE “nitrogen, N” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–>, and P concentrations in leaves responded to global warming was also examined. Six 0.45 m by 0.75 m experimental plots were established and surrounded by an open-top chamber (OTC). Each plot was divided into fifteen 0.15 by 0.15 m subplots. Four out of the six chambers were randomly selected for treatment. One of the chambers was heated so that soil and air temperatures were 5 °C above ambient temperatures. Another chamber was CO2enriched to double the ambient concentrations. The third chamber was both heated and CO2 enriched. Finally, the last chamber was a control so there was no change in CO2 or temperature from the ambient. For the heated chambers, resistance cables were run through the upper layer of the soil to warm the soil. These were controlled by a data logger which was programmed to switch on and off every two minutes to maintain the temperature difference. To heat the air, infrared lamps were suspended above the soil surface. For the CO2 enriched chambers, CO2 concentration was increased to 730 ± 25 ppm. Two tanks were placed on opposite sides of the chamber to blow CO2enriched air into the chamber. Their position was to maintain an even concentration of CO2, to maintain an even blowing effect, and to reduce convective heating.
In each of the four experimental plots, one subplot was randomly chosen for analysis. The presence of symbiotic plants was recorded using point-frequency analysis. This involved recorded the species present at 5 cm intervals using a sheet of Plexiglass with 97 holes of 5 mm diameters. The plant cover, roots and leaves, was then harvested to calculate for biomass. Plant cover and biomass increased throughout the study. The three dominant plants found were Vaccinium myrtillus<!–[if supportFields]> XE “Vaccinium myrtillus” <![endif]–><!–[if supportFields]><![endif]–>, Vaccinium vitis-idaea<!–[if supportFields]>XE “Vaccinium vitis-idaea” <![endif]–><!–[if supportFields]><![endif]–>, and Deschampisa flexuosa<!–[if supportFields]> XE “Deschampisa flexuosa” <![endif]–><!–[if supportFields]><![endif]–>. The leaves and roots of these plants were then analyzed for C, N<!–[if supportFields]>XE “nitrogen, N” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–>, and P concentrations.
To examine the fungi, soil samples were taken. Three soil samples of 2.1 cm in diameter and 7 cm in depth were obtained from the center of each of the randomly selected subplots. The soil samples were placed on ice and transported to a cooling room at 2 °C in the laboratory. There, the soil samples were sorted for hair roots and grass roots. Hair roots belong to V. myrtillus and V. vitis-idaea whose symbiotic fungi is ErM. Further analysis of ErM Fungi involved a staining method and a visual examination. Grass roots belong to D. flexuosa whose main symbiotic fungi are FE and DSE fungi. Colonization of these fungi also involved visual examination. Visual examination refers to the process where 81 cm roots are examined under X400 magnification and 0.5 cm intervals.
Warming, CO2, and fungi root colonization were analyzed using two-way ANOVA<!–[if supportFields]> XE “ANOVA” <![endif]–><!–[if supportFields]><![endif]–>. There was a significant increase in plant cover under elevated temperatures, but not under elevated CO2. Under elevated CO2, V. myrtillus and V. vitis-idaea had a lower N<!–[if supportFields]> XE “nitrogen, N” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–> concentration in leaves, and the C to N ratio was higher. Nitrogen deficiency prevents plants from growing, but not root density. ErM colonization in these plants increased under elevated CO2 since plants will transfer more carbon to the fungi to obtain more N. Future global warming will allow ErM fungi to dominate the ecosystem. In D. flexuosa, FE fungi colonization was lower in CO2 treated and in higher temperature plots. DSE fungi colonization increased in warmer temperature plots, but there was no significant change in CO2 enriched plots. A reason FE fungi are affected by temperature is because they are not adapted to dry conditions. Higher temperatures can lead to dryer conditions. The response of FE fungi to CO2 can be explained by their slow growth compared to the fast growth of the roots. For DSE fungi, the main explanation for their response is competition with FE fungi. Under lower FE fungi density, they were able to flourish. However, further investigation needs to be done on their functional capabilities. There were no significant changes in P concentration for none of the plants.

Carbon Dioxide Levels have a Significant Effect on Allergenic Fungal Spores

Airborne allergens commonly include pollen<!–[if supportFields]> XE “pollen” <![endif]–><!–[if supportFields]><![endif]–> and fungal spores. These allergens aggravate allergy and asthma symptoms. In light of global warming, pollen has increased because CO2 levels have increased. However, the effect of CO2concentrations on fungal spore production has not been significantly investigated. Wolf et al. (2010) investigate whether there is a clear relationship between CO2 levels and fungal spore production. The fungi under study are Alternaria alternata<!–[if supportFields]> XE “Alternaria alternata” <![endif]–><!–[if supportFields]><![endif]–> and Cladosporum phlei<!–[if supportFields]> XE “Cladosporum phlei” <![endif]–><!–[if supportFields]><![endif]–>. A. alternata spores are sensitized by 11.9% of the asthmatic global population. On a more local scale, they are sensitized by 28.2% of asthmatic people residing in Portland, Oregon. People diagnosed with severe asthma are more likely to be sensitized to A. alternata. C. pheli does not produce allergenic spores. However, other Cladosporumspecies do produce them. These fungi, of course, do not grow alone. They grow on plants, either on live or dead tissue. The plant for this experiment was the perennial C3<!–[if supportFields]>XE “C3plants”<![endif]–><!–[if supportFields]><![endif]–> monocot timothy grass (Phleum pratense<!–[if supportFields]> XE “Phleum pratense” <![endif]–><!–[if supportFields]><![endif]–>).—Daniella Barraza
 Wolf, J., O’Neill, N<!–[if supportFields]> XE “nitrogen, N” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–>., Rogers, C., Muilenberg, M., Lewis, Z., Halvorsen, 2010. Elevated Atmospheric Carbon Dioxide Concentrations Amplify Alternaria alternata<!–[if supportFields]> XE “Alternaria alternata” <![endif]–><!–[if supportFields]><![endif]–> Sporulation and Total Antigen Production. Environmental Health Perspectives 118, 1223–1228.

Wolf et al. grew the fungi and timothy grass separately. The authors’ main focus was to study the indirect effect CO2 has on production of fungal spores through the host species, timothy grass. Timothy grass was grown in two chambers at different CO2 concentrations: 300, 400, 500, and 600 µmol/mol. These concentrations correspond to preindustrial levels at the beginning of the 19th century, current ambient levels, and projected levels in 2025 and 2040, respectively. Each chamber maintained two different CO2concentration levels at different times. These levels were replicated four times. Each chamber contained ten pots with a single timothy plant. The controlled variables in the chamber were temperature and photosynthetically active radiation (PAR) supplied by high-pressure sodium and metal halide lamps. Temperature was changed gradually from the lowest at night, 20 °C, to the highest in the afternoon, 30 °C. PAR was also changed gradually in conjunction with temperature and lasted 14 hours. After 60 days, the timothy grass was stripped of the leaves. Ten leaves from each plant were analyzed for total area, mass, and nitrogen<!–[if supportFields]>XE “nitrogen”<![endif]–><!–[if supportFields]><![endif]–> and carbon concentrations. The rest were then inoculated by recently prepared fungal inocula and then placed in a sterilized media bottle. After one week, the spores were dislodged from the leaves and counted. For A. alternata spores, the antigen protein was extracted.
The ratio of C to N<!–[if supportFields]> XE “nitrogen, N” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–> in the ten leaves was significantly higher in timothy grass grown at the highest CO2 concentrations, 500 and 600 µmol/mol. Leaf mass was significantly higher at 600 µmol/mol. There was no significant change in area. A. alternata spores produced per gram of leaf showed a positive and significant relationship with C to N ratio. However, the antigen produced per spore was negatively correlated with C to N ratio. In other words, in the two highest CO2 concentrations, the number of spores produced tripled, and as a result, the antigen produced was doubled. This doubling occurred because there more spores were produced rather than an increase of production of antigen per spore. The decrease in antigens can be attributed to the decreasing nitrogen in the timothy grass. There was no relationship between the size of the spores and the C to N ratio. For C. phlei, the production of spores also increased with the C to N ratio, but the C. phlei spore production did not reach the quantity that A. alternata produced.
There are still lots of unknowns but the relationship between global warming and allergenic fungal spores such as the effects of increasing temperatures and the more significant role that nitrogen<!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–> has in spore production. This study showed that increased levels of CO2 will increase allergenic fungal spores through their relationship with a host plant. This will decidedly have an effect on allergy and asthma symptoms.

The Possibility of using Fungi as a Treatment for Wastewater

If effluents are released without treatment, the industrial chemicals in the surroundings will lead to environmental pollution. To prevent this, wastewater treatment has become common practice and numerous systems have arisen. Specifically, in the fruit packaging industry the chemicals found in wastewater are typically from fungicides and pesticides. To combat the high concentration of a certain fungicide, a depuration system based on pesticide<!–[if supportFields]> XE “pesticide” <![endif]–><!–[if supportFields]><![endif]–> adsorption was patented and the result was a reduction of that fungicide by 7000 times. However, the costs for implementing this system on a large scale basis are too great to be efficient. Similarly, a filter system to treat this wastewater removed more than 98% of certain fungicides; however, its implementation was also impractical in terms of cost and volume capacity. Panagiotis et al. (2011) recognize the need for a viable option; therefore, they suggest the bioremediation of these chemicals by fungi. Irreversible chemical degradation by microbes has already been studied. It is known that white rot fungi (WRF) can degrade various organic pollutants. Aspergilus niger<!–[if supportFields]> XE “Aspergilus niger” <![endif]–><!–[if supportFields]><![endif]–> has also been shown to degrade several pesticides. This study focuses on the bioremediation by these two types of fungi on fungicides and pesticides in the wastewater of the fruit packaging industry. Another aim is to increase the understanding of the enzyme’s role in this degradation process.—Daniella Barraza
Panagiotis, K., Perruchan, C., Exarhou, K., Ehaliotis, C., Karpouzas, D., 2011. Potential for bioremediation of agro-industrial effluents with high loads of pesticides by selected fungi. Biodegradation 22, 215–228.

Panagiotis et al. used A. niger and three different types of WRF: Phanerochaete chyrsosporium<!–[if supportFields]> XE “Phanerochaete chyrsosporium” <![endif]–><!–[if supportFields]><![endif]–>, Trametes versicolor<!–[if supportFields]> XE “Trametes versicolor” <![endif]–><!–[if supportFields]><![endif]–>, and Pleurotus ostreatus<!–[if supportFields]> XE “Pleurotus ostreatus” <![endif]–><!–[if supportFields]><![endif]–>. From the WRF, the enzymes lignin<!–[if supportFields]> XE “lignin” <![endif]–><!–[if supportFields]><![endif]–> peroxidase (LiP), Mn dependent peroxidas (Mn), and laccase (Lac) can be studied since WRF has an extracellular enzymatic system called lignin mineralizing enzyme (LME) system that produces these three enzymes. The pesticides used were CHL, TBZ, OPP, IMZ, DPA, and TM. The evaporated residues of these pesticides were place in two different media selected to mimic the natural environment of the fungi. The first is a soil extract medium (SEM) and the second is straw extract medium (StEM). The soil in SEM is sandy loam with a pH of 6.5. StEM is composed of the supernatant of chopped and sterilized wheat straw and has a pH of 5.5. For the experiment, flasks were divided into two categories: non-inoculated and inoculated. The non-inoculated flasks contained either medium and evaporated residues of one pesticide<!–[if supportFields]> XE “pesticide” <![endif]–><!–[if supportFields]><![endif]–>. The inoculated flasks allowed a strain of fungi to grow before adding pesticides on the third day. After this addition, samples were taken in set intervals until 30 days had passed. Another part to this experiment was to investigate the ability of T. versicolor to degrade really high concentrations of the fungicides TBZ, OPP, IMZ, and DPA; and its ability to degrade mixtures of these pesticides as would be expected from the fruit packaging industry such as the post-harvest treatment of citrus fruits which would contain TBZ, OPP, and IMZ. For the enzymatic portion of the experiment, pesticide-free flasks were made for comparison to determine if pesticides have an effect on the enzymes.
In StEM, WRF degraded most of the pesticides. T. versicolor and P. ostreatus almost completely degraded DPA and TM within the first two days. P. chyrsosporium had a slower rate of degradation for the same pesticides and was not able to degrade OPP. In non-inoculated flasks, the rate of degradation for all of the pesticides was much slower around 50% and 80% slower for DPA and TM, respectively. In SEM, the results were slightly different. Within the first two hours, T. versicolor and P. ostreatus were able to completely degrade DPA, TM, and OPP. However, WRF did not degrade IMZ in SEM whereas it had completely degraded it in StEM. The reason is because WRF are adapted to ligninocellulosic material like straw and not soil. P. chrysosporium and A. niger rapidly degraded DPA. A. niger, however, despite being in a medium similar to its natural environment had the slowest degradation rate for OPP comparable to the degradation rate in the controlled flask. In both SEM and StEM, activity for the enzyme LiP was not detected. Activity for the enzymes MnP and Lac were detected in flasks containing T. versicolor and P. ostreatus. There was a positive trend between the rapid degradation of DPA and OPP by T. versicolor and P. ostreatus and the activity of MnP and Lac which suggests that the enzymes play a strong role in degradation. A reason for this is because MnP and Lac are known to oxidize phenol rings of lignin<!–[if supportFields]> XE “lignin” <![endif]–><!–[if supportFields]><![endif]–> and these two pesticides contain phenol rings in their molecules. This result further suggests that other enzymes are responsible for the rapid degradation of other pesticides. Finally, T. versicolor was able to degrade high concentrations of pesticides and mixtures of pesticides except with a few discrepancies the reasons which remain unknown. WRF, especially T. versicolor and P. ostreatus, had the best records for degradation of pesticides and can serve as depuration systems for the fruit packaging industrial wastewater. 

Mycotoxin production and growth changes due to predicted climage change

A constant concern in agriculture is the productivity and health of the crops. Diseases, droughts, and a growing human population are contributors to this concern. This paper focuses on the damage mycotoxins can cause to crops, both pre- and post-harvest, in light of climate change (Magan et al. 2010). Mycotoxins are the toxic secondary metabolites of certain fungi, with varying harmful effects. This paper concentrates especially on three mycotoxins: aflatoxin B, ochratoxin A, and deoxynivalenol (DON). Aflatoxin B is produced by Aspergilius flavus; ochratoxin A is produced by Aspergilius carbonarius; and DON is produced by Fusarium graminearum. Besides crops, mycotoxins can also be harmful to consumers. They are often carcinogenic and highly heat-tolerant which allows them to survive the processing after harvest. The European Union has the strictest laws setting limits on how much mycotoxins crops and their products can contain. In African countries, export crops are regulated; therefore, for residents, the risk to health is high. In Kenya, in 2004, there was an outbreak of aflatoxicosis with 125 deaths Lewis et al. (2005). Climate change is predicted to affect the relationship between mycotoxins and crops by stimulating growth of the mycotoxigenic fungi and changing the physiology of plants so that they are more susceptible to pests and pathogens. Due to climate change, CO2 concentrations are prognosticated to rise 1.5 µmol per year, global temperature is expected to increase 0.03°C per year, and water activity (aw) will decrease significantly in certain areas. Water activity is similar to water availability, however, aw has more to do with the chemical interaction between water and other solutes. The more solutes interact with water molecules, the less water there is available for hydration leading to values lower than 1.0 (pure water).    —Daniella Barraza
Magan, N., Medina, A., Aldred, D., 2011. Possible climate-change effects on mycotoxin contamination of food crops pre- and post-harvest. Plant Pathology 60, 150–163.

Magan et al. reviewed the scientific literature to examine influence of climate change on pre-harvest and post-harvest mycotoxin contamination, the relationship between increased CO2, increased temperature, and decreased aw, and whether models based on molecular and ecological data can be used to reliably predict mycotoxin levels of risk. Under each topic, they include studies utilizing different models and systems for analysis.
For pre-harvest contamination, an historical occurrence the impact climate change might have. In the years 2003 and 2004, northern Italy experienced very hot and dry spells. A. flavus and Fusarium verticilloides are two competing fungi pathogens in maize grown in this area, but because of the arid conditions, the more xerotolerant A. flavus was able to gain an advantage. Maize contamination was high and, as a result, cow’s milk became heavily infected with aflatoxins since maize was used as animal feed. This contamination resulted in great economic losses. Other crops that are easily contaminated by aflatoxins because of dry conditions are peanuts and cottonseed. One way to determinate which crops will be at high risk of contamination because of dry conditions is through geostatistics. A three year study used goetstatistics to find the relationship between meteorological data and contamination, indicating that contamination was highest just before harvest. This method can be useful for understanding the spatial (latitude and longitude) and temporal variations in mycotoxin contamination and can be useful in determining the timing of fungicide application and pest control. An agricultural production systems simulator which relates seasonal temperature and soil moisture can also be useful in determining the aflatoxin risk index (ARI). For the mycotxin DON, the DONCAST takes into account weather conditions including number of rain days before anthesis and after ripening, and temperature variations. A systems approach can also be taken for DON prediction which takes a look at the life cycle of F. graminearum. However, these models are very simple and don’t demonstrate complex interactions. They have yet to include many important factors such as levels of CO2 and ongoing changes to the physiology of host species and mycotoxigenic fungi.
Post-harvest storage of crops and processing that occurs to turn them into marketable products can also incur risk of mycotoxin contamination. Crops stored at high temperatures and in damp conditions are at risk and any infection with aflatoxins or ochratoxin A can result in the loss of the entire crop. Fungistatic preservatives are used, but they are likely not completely effective, even applied at the most appropriate concentration. Higher temperatures and damp conditions increase the volatility of these fungistatic preservatives thus cutting their job short.
Atmospheric CO2 concentrations of 800–1000 ppm, triple the current levels, may not have a much effect on fungi. Although they can withstand extremely high levels, atmospheric CO2 will not be the only variable to change. In combination with temperature and aw , CO2 does have an effect. With higher aw, aflatoxin growth is restricted under atmospheres containing 25% and 50% CO2. Atmospheres with 75% CO2 resulted in greater growth restrictions despite changes in aw levels. Elevated CO2 mixed with N2 have a different effect on aflatoxin B. A 70% CO2 concentration with 0.80 aw prevented spoilage of bakery products. Focusing only on temperature and aw, contour maps have been used to predict mycotoxin production at +3°C and +5°C with varying aw. One discovery was that exactly 0.90 aw and temperature +5°C will cause no mycotoxin production.
To relate the genetics of mycotoxins and ecological data, a microarray was developed. A key marker gene under study is aflD which produces aflatoxin B. The microarray established that there are two peaks for mycotoxic production. The first is the exact intersection between temperature and aw which is most conducive to production, and the second peak is when the mycotoxic fungi is under stress and overreaching the demonstrated extremes. Changes in CO2, temperature, and aw can be modeled based on understood gene expressions.
There are still many questions left to answer especially since models need improvement and more studies need to be made. Future questions that need to be addressed should be more specifically determining the impact of climate change on the physiology of host species, on the life cycle of mycotoxigenic fungi, and how to improve storage for post-harvest crops.
Additional sources:

Lewis, L., Onsongo, M., Njapau, H., Schurz-Rogers, H., Luber, G., et al., 2005. Aflatoxin Contamination of Commercial Maize Products during an Outbreak of Acute Aflatoxicosis in Eastern and Central Kenya. Environmental Health Perspective 113, 1763–1767.

Determination of Silver Accumulation in Ectomycorrhizal and Saprobic Macrofungi

Silver (Ag) has an average concentration below 1 mg kgˉ1 in soil and presence in the rhizosphere makes it susceptible to uptake by plants, bacteria, and other organisms in the soil. However, little is known about its biogeochemical cycle. This paper considers macrofungi because they are vital in the biogeochemical cycles of many elements and have the ability to accumulate Ag (Borovička et al. 2010). Silver in its non-charged state is not considered a toxin, but there are locations that have acquired an excess of silver where it might be. It is known that Ag-polluted areas have a positive correlation with Ag concentration in ectomycorrhizal and saprobic macrofungi. The research presented here combines a review of related published literature with a summary of the data on accumulation and distribution of Ag, and original research on Ag concentration in fungi in pristine and Ag-polluted areas. —Daniella Barraza
Borovička, J., Kotrba, P., Gryndler, M., Mihaljevič, M., Řanda, Z., Rohovec, J., Cajthaml, T., Stijve, T., Dunn, C., 2010. Bioaccumulation of silver in ectomycorrhizal and saprobic macrofungi from pristine and polluted areas. Science of the Total Environment 408, 2733–2744.

Borovička et al. collected samples of soil and fungi from various regions throughout the Czech Republic. For Ag-polluted areas, macrofungal samples were gathered from a forest in Lhota. The macrofungi were a mixture of ectomycorrhizal and saprobic fungi and consisted of 30 different species encompassing 22 genera. Lhota is polluted by a nearby lead smelter and mining activities. The topsoils in this area were reported to have values of up to 78 mg kg–1. The soil samples for verification were also collected from this area near a Norway spruce. The sample was a soil profile with five organic soil horizons: O1 (needles), Of (decomposing matter), Oh (well-decomposed matter), and mineral soil horizons, Ah and Bw. A representative part of each soil horizon was used for analysis. For the case study, a fungus Agaricus bernardii was chosen and was collected from the center of Prague. The soil profile from Prague was a technosol which is soil whose composition is altered by urban and industrial activity. To detect Ag concentration in the fungi, the fruit-bodies of a specific species were cleaned, cut, and dried to a constant weight. These samples were then ground and analyzed by instrumental neutron activation analysis (INAA). This method involves exposing the sample to a neutron flux so it will produce characteristic gamma rays. Silver concentration in soil was determined with the same method. For A. bernardii, Ag concentration in the caps and stipes of 19 fruit-bodies was also measured using the same technique. The authors also did a meta-analysis of related literature. They included only papers stating Ag concentration values for ectomycorrhizal and saprobic fungi from pristine places. The data were separated into eight classes based on concentration ranges and compared to the original data the authors had collected from pristine places in another, unpublished, study.
In pristine areas, the median Ag concentration was 0.79 and 2.94 mg kg–1 in ectomycorrhizal and saprobic fungi, respectively. The macrofungi have higher Ag concentrations than soil suggesting that they are very potent in absorbing Ag from the soil. The effectiveness of absorption can sometimes be intense and leads to the term hyperaccumulation. A hyperaccumulator is a species with 100 times higher concentration than the surroundings. A few fungi from the Amanita genus, an ectomycorrhizal fungi hyperaccumulators. In Ag-polluted areas with Ag concentration in the soil around 26.9 mg kg–1, the median concentration for both types of macrofungi was 24.7 mg kg–1 unlike the differences between the two types of macrofungi in pristine areas. The highest Ag concentrations were found in the ectomycorrhizal fungi. The hyperaccumulators had concentration values of 287–692 mg kg–1and Boletus edulis had a Ag concentration of 206 and 242 mg kg–1. In saprobic fungi, the highest Ag concentrations were found in Lepista nuda with a value of 84–123 mg kg–1. This is the opposite case in pristine areas where ectomycorhizzal fungi, of the genus Amanita, have the highest Ag concentrations . The reason saprobic fungi have lower values is because they absorb other metals besides Ag. The best competitors for silver for uptake by saprobic fungi are probably cadmium and mercury. In soils containing these two metals, an increase in Ag concentration does not result in an Ag concentration increase in the fungi. Ecotmycorrhizal fungi, however, do differentiate between metals. As another study showed, these fungi near a gold deposit absorbed the Ag but not the gold. The results of the case study show that caps accumulate twice as much Ag as the stipes. The caps had a range between 81–544 mg kg–1 and the stipes has values between 31–303 mg kg–1. For both parts, there was positive correlation between Ag concentration and biomass.
Other results show that there is no current risk of metal poisoning associated with consuming fungi. The most common fungi on the market are Agaricus bisporus and their Ag concentration does not surpass 1 mg kg–1. There is even less risk of bioaccumulation in humans since mushrooms comprise a small part of the consumer’s diet.
There are many unknowns still remaining about macrofungi. A few unknowns are which tissues favor Ag accumulation, how age of the fungi plays a role in the Ag accumulation, or the purpose of hyperaccumulation. It appears that the reason why fungi are able to accumulate high concentrations of Ag is because they can store excess metal safely so that it does not intervene in cellular processes.

Effects of Increasing Water Temperature and Nutrient Concentration on Fungi Activity and Subsequent Litter Decomposition.

Woodland streams are characterized as small forest streams located in moderate to high latitude and altitude magnitudes. The ecosystem of these streams is dependent on the decomposition of organic matter which is primarily decomposed by aquatic hyphomycetes. The streams do not obtain energy through photosynthesis because riparian vegetation, aside from supplying organic matter, provides a lot of shade to the streams. This shade, in addition to the streams’ location, causes the streams to have low water temperatures, and be, therefore, more susceptible to temperature increases from global warming. Two factors associated with global warming and which are expected to have a great impact on litter decomposition in streams are water temperature and nutrient concentrations (Ferreira and Chauvet 2010). These two factors are expected to increase and to affect litter decomposition, specifically alder leaves; aquatic hyphomycetes will also be affected as they are the primary decomposers. The hypothesis states that increases in water temperature and nutrient concentration will increase hyphomycete activity and decomposition rates.  —Daniella Barraza

Ferreira, V., Chauvet, E., 2010. Synergistic effects of water temperature and dissolved nutrients on litter decomposition and associated fungi. Global Change Biology 17, 551–564.

Ferreira and Chauvet simulated stream-like conditions at the lab by creating fungal microcosms.  A microcosm consisted of a glass chamber with an opening at the bottom for air to enter and create turbulence for the leaf discs.  The leaf discs represent the organic matter to be decomposed. Inside the discs are samples of Alnus glutinosa (alder leaves). Also, at the bottom, was a valve to allow the glass chamber to drain and to obtain the conidial suspension for analysis. A conidium is an asexual spore of the hyphomycete. The strains were acquired from a conidium found in three streams of different biomes. A total of six species were collected to form an assemblage for experimentation to represent the fungal diversity of a decomposing leaf in a stream. This number was indicated as adequate by another study. Articulospora tetracladia was gotten from a lowland stream in Portugal. Clavariopsis aquatica, Flagellospora curvula, and Tetracladium marchalianum were gotten from a Mediterranean stream in the French Pyrenees. Heliscus lugdunensis and Tumularia aquatica were gotten from a temperate mountain stream in the southwest of France. These strains were grown in petri dishes until they produced conidia. These conidia were then placed in a solution to be used in the microcosm. There were six microcosms and they were replicated twelve times. The treatment each microcosm received was a variation of the pair of factors being studied: water temperature and nutrient concentration. Water temperature was three levels: 5°C, 10°C, and 15°C. Nutrient concentration (NP) was two levels: low and high. The information procured from the microcosms was rate of oxygen consumption of the leaf discs, biomass of hyphomycetes by converting from the mass loss of the leaves, and fungal carbon budget which is the percentage of carbon dioxide the hyphomycetes produced. The data was statistically analyzed through three-way ANOVA and Tukey HSD.

The results were consistent across the whole spectrum and fell in line with the stated hypothesis. High NP levels and high water temperatures (10°C and 15°C) resulted in higher hyphomycete activity and higher decomposition rates. This means that if global warming does not occur and temperatures stay low, despite high NP levels, hyphomycete activity will remain low. Placing these results into the scenarios of eutrophic waters versus oligotrophic waters yields different interpretations of the results. In eutrophic waters, carbon mineralization might occur due to stimulation of decomposition rates and oxygen consumption rates but this might not occur in oligotrophic waters. It might not occur in oligotrophic waters because the maximum predicted global temperature increase is 6.4°C for this century. Oligotrophic waters need at least a 10°C increase in temperature to stimulate decomposition and oxygen consumption rates before carbon mineralization can take place. Carbon mineralization is the process by which fungi (and other organisms) obtain carbon from the decomposing litter which they then respire and release into the atmosphere as carbon dioxide. Therefore, litter decomposition rates in oligotrophic waters will remain relatively the same in spite of the global warming.