Mutants and isolates of Metarhizium anisopliae are diverse in their relationships between conidial pigmentation and stress tolerance

Conidial pigmentation is involved in protection against heat and UV radiation in several fungal species. In this study, we compare the tolerance of 17 color mutants of wild-type ARSEF 23 plus 13 color mutants of wild-type ARSEF 2575 of Metarhizium anisopliae var. anisopliae to wet-heat and UV-B or simulated-solar radiation. The stress tolerance of each mutant was compared with that of its wild-type parent, and with the most thermo- and UV-tolerant wild-type Metarhizium we have tested to date, M. anisopliae var. acridum (ARSEF 324). The color of each isolate or mutant was identified with the PANTONE Color Standard book [Eiseman, L., Herbert, L., 1990. The PANTONE((R)) Book of Color: over 1000 color standards: color basics and guidelines for design, fashion, furnishing... and more. Harry N. Abrams, Inc., Publishers, New York]. In addition, the pigments of each mutant or wild-type were extracted and the UV absorbances of the extracts compared to the stress tolerance of those isolates; but no relationships were detected. Color mutants of ARSEF 23, in general, were less UV tolerant than their parent wild-type. With ARSEF 23 and its mutants, conidial pigmentation was important to conidial tolerance to UV-B and simulated-solar radiation; but color had less impact on ARSEF 2575 and its mutants. The ARSEF 2575 color mutants were less variable in UV tolerance than those of ARSEF 23, even though very similar colors occurred in the two groups of mutants. When color mutants of ARSEF 23 reverted to wild-type color they recovered wild-type levels of UV tolerance. Results of UV-B and UV-A exposures of wild-types ARSEF 23 and ARSEF 2575 conidia indicated that they are equally tolerant of UV-A, but differ in UV-B-response. For thermotolerance, several mutants were more heat tolerant than their wild-type parents. Accordingly, darker pigmentation of wild-type isolates was not important to protection against heat.     

Differential susceptibility of blastospores and aerial conidia of entomopathogenic fungi to heat and UV-B stresses

We investigated the comparative susceptibility to heat and UV-B radiation of blastospores and aerial conidia of Metarhizium spp. (Metarhizium robertsii IP 146, Metarhizium anisopliae s.l. IP 363 and Metarhizium acridum ARSEF 324) and Beauveria bassiana s.l. (IP 361 and CG 307). Conidia and blastospores were produced in solid or liquid Adámek-modified medium, respectively, and then exposed to heat (45 ± 0.2 °C) in a range of 0 (control) to 360 min; the susceptibility of fungal propagules to heat exposures was assessed to express relative viability. Similarly, both propagules of each isolate were also exposed to a range of 0 (control) to 8.1 kJ m⁻² under artificial UV-B radiation. Our results showed that fungal isolates, propagule types and exposure time or dose of the stressor source play critical roles in fungal survival challenged with UV-B and heat. Conidia of ARSEF 324, IP 363, IP 146 and IP 361 exposed to heat survived significantly longer than their blastospores, except for blastospores of CG 307. Conidia and blastospores of IP 146 and IP 363 were equally tolerant to UV-B radiation. We claim that blastospores of certain isolates may be promising candidates to control arthropod pests in regions where heat and UV-B are limiting environmental factors.     

Characterization of fungal soil communities by F-RISA and arbuscular mycorrhizal fungi fromAraucaria angustifolia forest soils after replanting and wildfire disturbances

The Fungal Ribosomallntergenic Spacer Analysis (F-RlSA) was used to characterize soil fungal communities from three Cecosystems ofAraucaria angustifolia from Brazil: a native forest and two replanted forest ecosystems, one of them with a past history of wildfire. The arbuscular mycorrhizal fungi (AMF) infection was evaluated inAraucaria roots of 18-monthold axenic plants previously inoculated with soils collected from those areas in a greenhouse experiment. The principal componentanalysis of F-RISA profiles showed different soil fungal community betweenthe three studied areas. Sixty three percent of F-RISA fragments amplified in the soil and the substrate samples presented lengths between 500 and 700 bp. The number of Operational Taxonomic Units (OTUs) was 34 for soil and 38 for substrate, however, more fragments were detected in soil (214) than in substrate (163). Anin silico F-RISA analysis to compare our data with ITSI-5.8S-ITS2 sequences from NCBI database showed the presence of Ascomycota, Basidiomycota and Glomeromycota among the soil and substrate fungal communities. AMF infection was higher in plants inoculated with soil from the native forest and the replanted forest with wildfire, both presenting similar chemical characteristics but with different disturbance levels. These results indicate that soil chemical composition may influence the soil fungal community structures rather than the anthropogenicor fire disturbances.     

Effects of an introduced mustard,Thlaspi arvense,on soil fungal communities in subalpine meadows

The subalpine meadows of the Rocky Mountains, USA, are at the advancing front of global change; however, little is known about the sensitivities of high-elevation soil fungal communities to ongoing ecological changes. Soil fungi are sensitive to abiotic and biotic environmental stressors, including climate change, soil disturbance, and the presence of introduced, non-native plants. Invasive plants in the Brassicaceae (mustard family) are known to alter fungal community structure, suppress arbuscular mycorrhizal fungi, and change their relationship with native plant hosts in forest ecosystems, but these phenomena have not been studied in the subalpine zone where non-native mustard plants are becoming established. Here, we investigated whether the presence of the introduced mustard plant, Thlaspi arvense, is associated with distinct properties of the whole fungal and arbuscular mycorrhizal fungal communities in subalpine meadow ecosystems. We observed clear differences in the composition, relative abundance of core taxa, and mean taxon relatedness of soil fungal communities in plots with T. arvense relative to those with only native vegetation. A suite of novel fungi were associated with T. arvense, and overall patterns of AMF phylogenetic diversity were drastically reduced in association with its presence. Our results suggest that T. arvense introduction impacts the soil fungal community, with potential implications for native plant communities and soil nutrient cycling in high elevation meadows of the Rocky Mountains.     

Superoxide dismutase production by Isaria fumosorosea on metals and its role in stress tolerance and fungal virulence

Superoxide dismutase (SOD) is an anti-oxidant enzyme which also plays a role in fungal virulence. The present study was conducted to elucidate its role in fungal infection and stress tolerance of entomopathogenic fungi, Isaria fumosorosea. SOD activity of I. fumosorosea conidia differed significantly on the growth medium supplemented with different metal compounds. The use of Cu + Zn proved to be the most active inducer of SOD activity. Cu + Zn treatment enhanced the fungal tolerance to oxidative stress generated by menadione in the medium (0–3 mM) as evaluated by colony growth. The conidial tolerance to UV-B radiation and heat was evaluated by assays of spore germination. Conidia produced on cultures with Cu + Zn were more tolerant to UV-B and thermal stress as well as exhibiting a higher rate of virulence against P. xylostella larvae. Our study highlights that SOD contributes significantly to the virulence and stress tolerance of I. fumosorosea and reveals possible means to improving field persistence and efficacy of a fungal formulation by manipulating the antioxidant enzymes of fungal pathogens.     

增强的UV-B辐射对春小麦植株化学成分、真菌定殖和分解的影响

在UVB辐射下,叶可溶性糖含量显著降低,叶可溶性蛋白含量和粗纤维含量以及茎粗纤维含量显著增加,而根粗纤维含量没有显著变化.在生长期接受UVB辐射的叶和茎上,赭绿青霉和黑曲霉的定殖率显著增加,康宁木霉和出芽短梗霉的定殖率明显降低,而土曲霉的定殖率未受明显影响.这些叶和茎经过60d和100d的分解,分解率均显著增加.叶分解率与粗纤维含量和可溶性蛋白含量呈显著正相关,而与可溶性糖含量呈显著负相关.茎分解率与粗纤维含量呈显著正相关.在增强的UVB辐射下,春小麦植株化学成分的变化,真菌定殖率的改变,分解率的增加,可能会导致麦田生态系统营养周转加快,土壤库中营养贮量增加.     

Influence of Shrub Encroachment on the Soil Microbial Community Composition of Remnant Hill Prairies

Hill prairies are remnant grasslands perched on the bluffs of major river valleys, and because their steep slopes make them unsuitable for traditional row crop agriculture, they have some of the lowest levels of anthropogenic disturbance of any prairie ecosystems in the Midwestern USA. However, many decades of fire suppression have allowed for shrub encroachment from the surrounding forests. While shrub encroachment of grasslands can modify soil respiration rates and nutrient storage, it is not known whether shrubs also alter the community composition of soil microorganisms. We conducted transect sampling of nine different hill prairie remnants showing varying degrees of shrub encroachment, and we used DNA-based community profiling (automated ribosomal intergenic spacer analysis) to characterize the composition of bacterial and fungal communities in the open prairie habitat, the shrub-encroached border, and the surrounding forest. While both bacterial and fungal communities showed statistically significant variation across these habitats, their predominant patterns were different. Bacterial communities of forest soils were distinct from those of the open prairie and the shrub-encroached areas, while fungal communities of the open prairie were distinct from those of the forest and the shrub-encroached border. Shrub encroachment significantly altered the community composition of soil fungal communities. Furthermore, fungal communities of heavily encroached prairie remnants more closely resembled those of the surrounding forest than those of lightly encroached prairies. Thus, shrub encroachment can cause soil fungi to shift from a “grassland” community to a “woody” community, with potential consequences for soil processes and plant-microbe interactions.     

Diversity of soil fungal communities of Cerrado and its closely surrounding agriculture fields

Cerrado is a savanna-like region that covers a large area of Brazil. Despite its biological importance, the Cerrado has been the focus of few microbial diversity studies. A molecular approach was chosen to characterize the soil fungal communities in four areas of the Cerrado biome: a native Cerrado, a riverbank forest, an area converted to a soybean plantation, and an area converted to pasture. Global diversity of fungal communities in each area was assessed through Ribosomal intergenic spacer analysis which revealed remarkable differences among the areas studied. Sequencing of approximately 200 clones containing 18S rDNA sequences from each library was performed and, according to the genetic distance between sequences, these were assigned to operational taxonomic units (OTUs). A total of 75, 85, 85, and 70 OTUs were identified for the native Cerrado, riverbank forest, pasture, and soybean plantation, respectively. Analysis of sequences using a similarity cutoff value of 1% showed that the number of OTUs for the native Cerrado area was reduced by 35%; for the soybean plantation, a reduction by more than 50% was observed, indicating a reduction in fungal biodiversity associated with anthropogenic activity. This is the first study demonstrating the anthropogenic impact on Cerrado soil fungal diversity.     

Differential stimulation of an arid-environment winter ephemeral Dimorphotheca pluvialis (L.) Moench by ultraviolet-B radiation under nutrient limitation

A South African winter ephemeral D. pluvialis was exposed, under low and high nutrient conditions, to four different daily doses of biologically effective UV-B radiation. These simulated different depletions (range 0–30%) in the ozone layer at the southerly distribution limit (33° 56′S) of this species, and included daily UV-B doses received at the northerly distribution limit (26° 38′S) without ozone depletion. Growth inhibition by increased UV-B radiation was observed during early vegetative stages, but only under low nutrient conditions. Thereafter, net CO₂ assimilation rate, growth and reproduction were stimulated by an increase in UV-B radiation, though doses above those approximating a 20% ozone depletion appeared to be inhibitory. Differential stimulation occurred in the two nutrient treatments. Under high nutrient conditions, photosynthesis (specifically carboxylation efficiency), and numbers of leaves, inflorescences and diaspores per plant, and leaf areas increased, but leaf thickness decreased with increased UV-B radiation. Under low nutrient conditions, dry masses of leaves, stems, inflorescences and diaspores, and total above-ground dry masses increased with increased UV-B radiation. Foliar organic carbon and nitrogen concentrations and foliar concentrations of UV-B absorbing compounds were unaffected by increased UV-B radiation, but foliar P concentrations declined. Diaspore viability declined with increased UV-B radiation. The net effect was a 35 to 43% reduction in viable diaspore production under high nutrient conditions at UV-B doses equivalent to those currently received at the northerly distribution limit during the reproductive phase. It is concluded that anticipated increases in UV-B radiation could reduce regeneration success, and seedling survival in areas of low soil fertility, particularly at lower latitudes, and consequently increase the risk of localized population extinctions from stochastic causes.     

The effect of solar UV-B radiation on terpenes and biomass production in Grindelia chiloensis (Asteraceae), a woody perennial of Patagonia,Argentina

UV-B radiation is absorbed effectively by nucleic acids and other sensitive targets, potentially causing harmful photochemical effects. Protection against UV-B radiation may be afforded by flavonoids and other phenolics, which absorb strongly in the UV region, but little is known about the role played by other compounds, such as terpenes. Grindelia chiloensis, native of Patagonia (Argentina), can accumulate as much as 25% resin (terpenes) in its leaves. The present investigation was carried out to test the effect of solar UV-B radiation on the allocation of photoassimilates to biomass and terpenes. Exposure to UV-B radiation reduced whole plant biomass, plant height and leaf area, and increased leaf thickness and resin accumulation in Grindelia chiloensis. Higher absorbance was found for refined resin in the UV-B waveband from plants grown under solar UV-B radiation than plants without UV-B radiation. These chemical and structural changes could protect the plant from UV radiation, and may help elucidate the importance of epicuticular resins for a species as G. chiloensis native to an environment with maximum daily integrated values of solar UV-B irradiance.     

UV-B辐射对马尾松凋落叶分解和养分释放的影响

由大气臭氧层减薄导致的UV-B辐射变化将直接影响到凋落物的分解。目前,有关UV-B辐射影响木本植物凋落物分解的研究还很少,在国内还没有开展。采用分解袋法开展了马尾松凋落叶在自然环境和UV-B辐射滤减两种辐射环境下的分解试验。结果表明：在UV-B辐射滤减环境下的马尾松凋落叶年分解速率比对照环境减慢了47.74%。UV-B辐射极显著(p<0.01)地加快了马尾松凋落叶的分解速率,促进了凋落叶中碳、磷、钾的释放和木质素的降解,对氮的释放无明显影响。研究结果意味着UV-B辐射将加快马尾松林的营养循环速度,降低马尾松林凋落物层的碳储量。     

Effects of enhanced UV-B radiation and nitrogen deposition on the growth of invasive plant Triadica sebifera

Aims Exotic plant invasions are important components of global change, threatening both the stability and function of invaded ecosystems. Shifts in competitive ability of invasive plants versus their native congeners have been documented. Enhanced UV-B radiation and nitrogen (N) deposition might interact with soil biota communities impacting the invasion process of exotic plant species. To understand the potential effects by UV-B and N with soil biota on plant growth would enhance our understanding of the mechanisms in plant invasions in the context of global change.
Methods We conducted a full-factorial pot experiment in the native range (China) of Triadica sebifera invading US to investigate how UV-B radiation, N and soil biota together determined their seedling growth.
Important findings The results showed that UV-B radiation, N and soil sterilization together impacted the growth of T. sebifera seedlings. UV-B radiation induced changes in biomass allocation with larger leaf biomass observed in response to UV-B radiation. In addition, N increased aboveground biomass and decreased root biomass simultaneously. Soil biota imposed positive effects on growth of T. sebifera, and the addition of N amplified these positive effects. The negative effects by UV-B radiation on growth of T. sebifera showed no response to N addition. Plant height, leaf biomass and total biomass of the invasive T. sebifera populations out- performed those of the native ones. In addition, invasive T. sebifera populations weakened the dependence of root/shoot ratio and root biomass on local soil microorganisms than native populations, but enhanced that of leaf area ratio.     

Cold activity and tolerance of the entomopathogenic fungus Tolypocladium spp. to UV-B irradiation and heat

Studies on the stress resistance of insect-pathogenic fungi are very important to better understand the survival of these organisms in the environment. In this study, we examined the cold activity (8 ± 1 °C for 7 days), UV-B tolerance (Quaite-weighted UV-B irradiance at 847.90 mW m⁻² for 1, 2, 3, and 4 h), and wet-heat tolerance (45 °C for 1, 2, 3, and 4 h) of two isolates of Tolypocladiumcylindrosporum (ARSEF 3392 and 5558), one isolate of Tolypocladium geodes (ARSEF 3275), and two isolates of Tolypocladium inflatum (ARSEF 4772 and 4877) based on their germination, compared with Metarhizium robertsii (ARSEF 2575). After 3 h of UV-B exposure, T. cylindrosporum germinated at a greater rate than the other Tolypocladium species and had similar viability to that of the M. robertsii. Most Tolypocladium isolates, however, were less UV-B tolerant than M. robertsii. The T.cylindrosporum isolates were also the most thermotolerant, with similar tolerance to the M. robertsii. The isolates of T. inflatum and T. geodes, which had similar heat tolerance, were the least heat tolerant compared with the isolates of T. cylindrosporum and M. robertsii. After 4 h of heat exposure, the germination of T. inflatum and T. geodes isolates was not significantly different. For cold activity, both T.cylindrosporum isolates germinated to ca. 100% in only 3 days. Approximately 50% of the two T. inflatum isolates germinated, and less than 5% of T. geodes germinated after 3 days. All fungal isolates, however, completely germinated by the seventh day, except M.robertsii. The isolates of T. cylindrosporum, therefore, were the most heat and UV-B tolerant, and had the highest cold activity compared to the other species. The tolerance of M. robertsii to UV-B radiation and heat was similar to that of T.cylindrosporum.     

The Impact of Selective-Logging and Forest Clearance for Oil Palm on Fungal Communities in Borneo

Tropical forests are being rapidly altered by logging, and cleared for agriculture. Understanding the effects of these land use changes on soil fungi, which play vital roles in the soil ecosystem functioning and services, is a major conservation frontier. Using 454-pyrosequencing of the ITS1 region of extracted soil DNA, we compared communities of soil fungi between unlogged, once-logged, and twice-logged rainforest, and areas cleared for oil palm, in Sabah, Malaysia. Overall fungal community composition differed significantly between forest and oil palm plantation. The OTU richness and Chao 1 were higher in forest, compared to oil palm plantation. As a proportion of total reads, Basidiomycota were more abundant in forest soil, compared to oil palm plantation soil. The turnover of fungal OTUs across space, true β-diversity, was also higher in forest than oil palm plantation. Ectomycorrhizal (EcM) fungal abundance was significantly different between land uses, with highest relative abundance (out of total fungal reads) observed in unlogged forest soil, lower abundance in logged forest, and lowest in oil palm. In their entirety, these results indicate a pervasive effect of conversion to oil palm on fungal community structure. Such wholesale changes in fungal communities might impact the long-term sustainability of oil palm agriculture. Logging also has more subtle long term effects, on relative abundance of EcM fungi, which might affect tree recruitment and nutrient cycling. However, in general the logged forest retains most of the diversity and community composition of unlogged forest.     

UV-B resistance as a criterion for the selection of desert microalgae to be utilized for inoculating desert soils

The adaption capability of microalgae species to intense UV-B radiation is an important feature for their survival under the harsh growth conditions they have to face when used for inoculating unconsolidated sand soils in desert areas. In this study, the responses of photosynthetic activity, reactive oxygen species (ROS) generation, and DNA strand breaks to UV-B radiation in four microalgae isolated from artificially induced biological soil crusts were investigated. It was found that low UV-B doses easily inhibited the photosynthetic activity and induced serious DNA damage in Chlorella vulgaris. Microcoleus vaginatus showed the capability to withstand only moderate doses of UV-B, while Nostoc was capable of facing high doses of UV-B due to its lower generation of ROS and higher capability to repair photosystem II (PSII) and DNA damages. On the other hand, Scytonema javanicum showed additional strategies to survive UV-B irradiance, namely the closure of PSII when ROS generation increased rapidly, in addition to a high repair ability of PSII and DNA damage. The results obtained point out different resistance and defense mechanisms of the four microalgae in response to UV-B irradiance and suggest that the strain of Nostoc sp. tested is the most suitable for surviving under the high UV irradiation levels typical of desertified areas.     

增强的UV—B辐射对春小麦植株化学成分、真菌定殖和分解的影响

在UV－B辐射下,叶可溶性糖含量显著降低,叶可溶性蛋白含量和粗纤维含量以及茎粗纤维含量显著增加,而根粗纤维含量没有显著变化,在生长期接受UV－B辐射的叶和茎上,赭绿青霉和黑曲霉的定殖率显著增加,康宁木霉和出芽短梗霉的定殖率明显降低,而土曲霉的定殖率未受明显影响,这些叶和茎经过60d和100d的分解,分解率均显著增加,叶分解率与粗纤维含量和可溶性蛋白含量呈显著正相关,而与可溶性糖含量呈显著负相关,茎分解率与粗纤维含量呈显著正相关,在增强的UV－B辐射下,春小麦植株化学成分的变化,真菌定殖率的改变,分解率的增加,可能会导致麦田生态系统营养周转加快,土壤库中营养贮量增加。     

Trophic interactions between viruses, bacteria and nanoflagellates under various nutrient conditions and simulated climate change

Population dynamics in the microbial food web are influenced by resource availability and predator/parasitism activities. Climatic changes, such as an increase in temperature and/or UV radiation, can also modify ecological systems in many ways. A series of enclosure experiments was conducted using natural microbial communities from a Mediterranean lagoon to assess the response of microbial communities to top-down control [grazing by heterotrophic nanoflagellates (HNF), viral lysis] and bottom-up control (nutrients) under various simulated climatic conditions (temperature and UV-B radiations). Different biological assemblages were obtained by separating bacteria and viruses from HNF by size fractionation which were then incubated in whirl-Pak bags exposed to an increase of 3°C and 20% UV-B above the control conditions for 96 h. The assemblages were also provided with an inorganic and organic nutrient supply. The data show (i) a clear nutrient limitation of bacterial growth under all simulated climatic conditions in the absence of HNF, (ii) a great impact of HNF grazing on bacteria irrespective of the nutrient conditions and the simulated climatic conditions, (iii) a significant decrease in burst size (BS) (number of intracellular lytic viruses per bacterium) and a significant increase of VBR (virus to bacterium ratio) in the presence of HNF, and (iv) a much larger temperature effect than UV-B radiation effect on the bacterial dynamics. These results show that top-down factors, essentially HNF grazing, control the dynamics of the lagoon bacterioplankton assemblage and that short-term simulated climate changes are only a secondary effect controlling microbial processes.     

Sexual differences in defensive and protective mechanisms of Populus cathayana exposed to high UV‐B radiation and low soil nutrient status

Previous studies have indicated that Populus cathayana Rehder females are more sensitive and less tolerant to stressful environments than males, but it is still unknown whether there are sexual differences in defensive and protective traits under high UV‐B (HUVB) radiation and low soil nutrient status. In this study, P. cathayana was employed as a model species to investigate sex‐related physiological and biochemical responses to UV‐B radiation under different soil nutrient conditions. Cuttings were exposed to two UV‐B radiation regimes (ambient UV‐B radiation and decreased UV‐B radiation) under two soil nutrient status (topsoil and deep soil) for 100 days over one growing season. Both HUVB radiation and low soil nutrient status induced greater decreases in plant growth, dry mass accumulation, gas exchange and leaf nitrogen use efficiency in females than in males, and greater increases in lipid peroxide and antioxidant enzyme activities, and secondary defense capacities in males than in females. Moreover, sexually different responses happened also in organelle ultrastructure. Our results showed that: (1) females suffered greater negative effects and exhibited lower defense capacities than did males under HUVB radiation, low soil nutrient status and their combination; (2) low soil nutrient status reduced plant's sensitivity to HUVB radiation by increasing allocation to defense and decreasing allocation to growth compared with high soil nutrient status. These results provide evidence that sexually different tradeoffs happen between growth and defense in P. cathayana under HUVB radiation and low soil nutrient status.     

Proportion of mycorrhiza-associated trees mediates community assemblages of soil fungi but not of bacteria

Recent studies have shown that mycorrhizal trees can greatly influence soil microbial communities, which in turn play important roles in the function offorest ecosystems. However, there is lack of understanding how the composition of trees with different mycorrhizal types affects soil microbial communities. Here, we collected 1606 soil samples from a 25-ha subtropical forest plot to investigate how the proportion of arbuscular mycorrhizal (AM) versus ectomycorrhizal (EcM) trees mediated soil microbial assemblages. Results showed the alpha diversities of both soil fungal and bacterial communities were significantly positively correlated with the ratio of AM/EcM trees. The AM/EcM tree ratio was important to the fungal community assembly, whereas soil pH was key to the bacterial communities. The increase in the AM/EcM tree ratio decreased the importance of stochastic forces in assembling fungal communities, while it had no significant effect on the bacterial communities. The differential importance of the AM/EcM tree ratio to fungal and bacterial communities highlights the role of mycorrhiza-associated tree composition in regulating soil microbial communities. This finding suggests that forests with different AM/EcM tree ratios would have different soil microbial communities, potentially leading to differences in soil nutrient cycling and in return different tree diversity and forest productivity.