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Effects of long-term fungicide applications on microbial properties in tallgrass prairie soil
Abstract
Several studies investigating the role of arbuscular mycorrhizal (AM) fungi in plant communities have included manipulations of AM fungal symbiosis using the fungicide benomyl. The objectives of this study were to evaluate the potential non-target effects of benomyl on soil biota and nutrient cycling in tallgrass prairie and to determine how mycorrhizae may influence these belowground properties. To accomplish these objectives, soil samples were collected during the 1996–1997 growing seasons from long-term benomyl-treated plots established on tallgrass prairie (Manhattan, KS) in 1991, and the following measurements were made: total bacterial and fungal biomass; abundance of nematodes; microbial biomass carbon and nitrogen; substrate-induced respiration; and potentially mineralizable C and N. Long-term benomyl applications resulted in an 80% reduction in mycorrhizal root colonization. By reducing root colonization, benomyl applications resulted in significant decreases in total bacterial biomass and abundance of fungal-feeding and predatory nematodes (20, 12 and 33% reductions compared to control, respectively). Total microbial potential activity (i.e., substrate-induced respiration) increased by 10% with benomyl treatment, whereas the relative contribution of fungi to total microbial activity decreased significantly with benomyl applications. In addition, microbial biomass C increased from 1364 (± 51.2 SE) to 1485 (± 51.2 SE) with benomyl treatment, and total carbon increased significantly (∼8%) only in annually burned soils treated with benomyl. The magnitude of benomyl effects on soil components and processes were small (<33% change with benomyl) relative to effects on mycorrhizal root colonization (80% decrease with benomyl). These results indicate that rather than having large non-target effects, benomyl applications principally affect mycorrhizal root colonization, thereby indirectly influencing soil biota and nutrient availability. Results also indicate that mycorrhizal fungi play an important role in altering the availability and flow of carbon in prairie soil and may influence the composition and abundance of groups of some soil biota. Changes in soil organisms and nutrient availability associated with altered mycorrhizal symbiosis may influence aboveground plant species responses to mycorrhizal suppression, but further research is needed to understand these potential effects.
... Заразом, за даними Всесвітньої організації охорони здоров'я (ВООЗ) у країнах, що розвиваються, щорічно фіксується до трьох мільйонів випадків отруєння агрохімікатами, що накопичуються у продуктах рослинництва [17]. Крім того, лише близько 0,1 % від загальної кількості застосовуваних засобів захисту досягає цільових організмів [21]. Інша частина чинить негативний вплив на нецільові об'єкти, знищуючи видову різноманітність мікрофлори та мікрофауни у ґрунтових екосистемах [10]. ...
... Критично важливим є дотримання рекомендованих норм, адже більшість негативних наслідків спричинено їх перевищенням [17]. У ряді досліджень було продемонстровано шкідливий вплив фунгіцидів на ріст, виживання та активність ґрунтових мікроорганізмів [18,12,15,21]. Наприклад, Бавістин токсичний для ряду ґрунтових мікробних популяцій, хоча його вплив короткотривалий [15]. ...
... Наприклад, Бавістин токсичний для ряду ґрунтових мікробних популяцій, хоча його вплив короткотривалий [15]. Бензоїл спричиняє довготривалий пригнічуючий ефект на розвиток мікоризних асоціацій [21], а Емісан та Карбендазим (беноміл) мають згубний вплив на арбускулярну мікоризу. ...
... Among the mycorrhizal types, arbuscular mycorrhizal fungi (AMF) are associated with almost 80% of the roots of vascular plants (Wang & Qiu 2006). AMF facilitate plant mineral nutrition, mostly of phosphorus and other macro-and micronutrients, nitrogen, zinc, copper, and magnesium (Clark & Zeto 2000;Smith et al. 2000), protect ...
... plants from root pathogens (Sikes 2010), and help plants tolerate drought (Augé 2001). In degraded soils, fertility is usually low and plant growth is limited compared to less degraded soils, while the presence of AMF could enhance growth and development of their host plants (Smith & Read 2008;Fajardo et al. 2011). ...
... Thus, our results agree with those of Menoyo et al. (2009) and Soteras et al. (2015) who observed that AMC in P. australis forests, where vegetation cover had not been lost, did not differ between different disturbance types such as high livestock density and reduced forest structural complexity, respectively. Mycorrhizal associations are complex systems (Smith & Read 2008) and soil disturbance can alter mycorrhizal colonization through dilution of, or damage to, infective propagules (Jasper et al. 1991;Mickan et al. 2017). In our work, although microsite degradation was heterogeneous, they did not affect AMC in P. australis, except for a higher number of hyphal entry points at the low degradation microsites. ...
Soil erosion affects extensive areas worldwide and must be urgently reduced promoting plant cover and beneficial microorganisms associated with plants, including arbuscular mycorrhizal fungi (AMF). In mountain environments plant cover is difficult to enhance due to harsh conditions during the dry season and steep slopes. Our objective was to evaluate the percentage of the soil surface covered by plants and the AMF community associated with trees planted 12.5 years of forest restoration efforts in microsites at different levels of soil degradation. The study was performed in the first montane forest restoration initiative of Central Argentina, where one of the trials consisted of planting Polylepis australis saplings at microsites with different levels of soil degradation: high, intermediate and low. After 12.5 years, percentage of bare soil cover was significantly reduced by 36 and 37% in the high and intermediate degradation microsites, respectively. Low degradation microsites were initially very low in bare soil and did not significantly change. Mycorrhizal colonization, hyphae, vesicles, arbuscules, AMF diversity and community structure were similar among microsite types. Percentage of hyphal entry points was higher at microsites with low degradation; number of spores was higher in high and intermediate degradation, and species richness was higher in high degradation. Acaulospora and Glomus were the most abundant genera in all microsites. We conclude that even in the most degraded microsites around 2.8% of the bare soil is covered by vegetation each year and that the arbuscular mycorrhizal community is highly tolerant and adapted to soils with different disturbance types.
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... Pesticides can also be harmful to beneficial soil organisms, such as earthworms and microorganisms (Riah et al., 2014), which lead to reduced soil fertility and decreased crop growth. Pesticides can also contaminate soil and water, leading to environmental damage (Smith et al., 2000;Pal et al., 2006;Riah et al., 2014). The negative economic impacts of pesticides can outweigh the benefits, if the use of pesticides leads to long-term damage to the environment. ...
... Virus resistance (Kang et al., 2005) Plum Resistance to plum pox virus conferred by insertion of a coat protein (CP) gene from the virus Vitamin enrichment (Wang et al., 2018;Rice Three genes for the manufacture of beta-carotene, a precursor to Dubocket al., 2017) vitamin A, in the endosperm of the rice prevent its removal (from husks) during milling ...
Pests are the major threat to agricultural crops. According to a recent survey up to 40% of the agricultural crops in the world are lost to pests every year. There are many different groups that can affect crops, including weeds, diseases, and insects. These pests can cause damage to crops through feeding, reproduction, and other activities, which can reduce crop yields and quality. Pest management strategies are used to control or eliminate pests in order to protect crops and maintain optimum level of productivity. These strategies can include the use of chemicals, such as pesticides, as well as cultural, biological, and physical methods. Plant protection techniques can either cease or significantly reduce crop losses caused by these destructive organisms. Synthetic pesticides can be effective in controlling pest populations, but can persist in soil and water, and have the potential to accumulate in the food chain system for long which can be toxic to non-target organisms, including pollinators and other beneficial insects. In recent years, there has been an increased focus on the development and use of more sustainable pest management practices, such as integrated pest management (IPM) and organic pest control methods to reduce the use of pesticides to a level that is economically and environmentally acceptable. One of the key tools in IPM is the use of genetically modified organisms (GMOs) or transgenic plants, which have been genetically engineered to be resistant to pests. In order to work toward a more sustainable and environment friendly approach to agriculture, this article aims to increase our understanding of GMOs as a potential tool for pest management.
... Additionally, neonicotinoids are often applied with fungicides, which can have synergistic effects that can have important implications for insects (Krupke et al., 2012;Main et al., 2020;Sgolastra et al., 2018). For example, microbial communities disrupted by fungicides can affect plant nutrition and shape plant communities (Koricheva et al., 2009;Smith et al., 2000;Yang et al., 2018). Such changes can influence the susceptibility of arthropods to pesticides (Gordon, 1961;Tosi et al., 2017). ...
... In terms of herbivore morphospecies richness, there was a synergistic interaction between clothianidin and captan, which resulted in 12% fewer herbivore morphospecies (Z = 1.828, p = 0.068) and this was stable across the growing season ( Figure 1, Table 1). By disrupting microbial communities, the fungicide may have lowered the nutritional quality of plant foods (Smith & Rice, 2000), which can compound the negative effects of neonicotinoids for some species (Tosi et al., 2017). ...
The non‐target effects of pesticides, particularly those that are long‐lasting and move easily through the environment, could have community‐level impacts on beneficial arthropods and hinder conservation efforts in agrolandscapes
We assessed the impacts of a neonicotinoid insecticide, clothianidin, and possible synergisms with a fungicide by quantifying predator, herbivore, and pollinator biomass and morphospecies richness in simulated prairie restorations.
Predator biomass was 66% lower in plots treated with clothianidin compared to controls and this effect persisted across the growing season.
Herbivore biomass was 51% lower in clothianidin‐treated plots in June, but the effect waned over the growing season, and no difference was detected in July or August. There was a synergistic effect of clothianidin and fungicide in lowering herbivore morphospecies richness by 12%.
Pollinators appeared unaffected by clothianidin. Instead, pollinator biomass increased by 71% with added fungicide in the absence of clothianidin.
The results of this study underscore the complexity of pesticide effects in field settings. Additional studies are necessary to understand how pesticide dissipation and predator release may interactively affect late‐season herbivore populations.
... phaseoli, pues durante la de selección una parte de esta población susceptible al diazinón murió, por el ello el número de UFC de R. phaseoli tolerante al diazinón fue menor [14][15][16] . Al igual que se ha reportado para otros géneros especies de la familia Rhizobiaceae como Bradyrhizobium spp, que también coometabolizan y/o mineralizan otros plaguicidas aplicados, en la agricultura convencional en el control de insectos-plaga que atacan las raíces de leguminosas 15,16 . ...
... Tabla 4 se muestra la tolerancia de R. phaseoli al diazinón fue el resultado de la capacidad de adaptación fisiológica de este género y especie, que además tiene en el genoma codificada la utilización de compuestos de carbono similares al diazinón, por lo que si existe otra fuente de carbono sencilla que al oxidarse facilite la degradación del plaguicida, una acción bioquímica conocida como coometabolismo. Lo que se demostró cuando R. phaseoli tolerante al diazinón creció en el AELM y el diazinón, en comparación con la inhibición del crecimiento de R. phaseoli en AEL sin manitol ni diazinón 4,8,11,14 . La selección de cepas de R. phaseoli resistentes a plaguicidas útiles en la agricultura convencional, se reporta en cepas Bradyrhizobium japonicum para el cultivo de Glycine max para evitar el ataque de insectos plaga 15,22,23 . ...
The genus and species of Rhizobium phaseoli are useful as an inoculant for the production of Phaseolus vulgaris
(beans) in the root nodules symbiotic stage fixes molecular nitrogen (FN) for supplying nitrogen (N) for healthy
growth. In P. vulgaris cropping, pesticides are used to control root insects, which could reduce the beneficial effect
of R. phaseoli. The purpose of this work was to isolate and select R. phaseoli diazinon´s tolerance. In that sense,
R. phaseoli were cultivated in a medium mixed with diazinon in order to select R. phaseoli tolerant to the pesticide.
This mutant of R. phaseoli tolerant to diazinon was inoculated in P. vulgaris the effect was evaluated 45 days later. The response of P. vulgaris was
The genus and species of Rhizobium phaseoli are useful as an inoculant for the production of Phaseolus vulgaris
(beans) in the root nodules symbiotic stage fixes molecular nitrogen (FN) for supplying nitrogen (N) for healthy
growth. In P. vulgaris cropping, pesticides are used to control root insects, which could reduce the beneficial effect
of R. phaseoli. The purpose of this work was to isolate and select R. phaseoli diazinon´s tolerance. In that sense,
R. phaseoli were cultivated in a medium mixed with diazinon in order to select R. phaseoli tolerant to the pesticide.
This mutant of R. phaseoli tolerant to diazinon was inoculated in P. vulgaris the effect was evaluated 45 days later. The response of P. vulgaris was measured by the number of effective nodules at the roots, fresh and dry weight,
and the height of the plant. Results showed that R. phaseoli tolerant to diazinon kept its beneficial activity for the
healthy growth of P. vulgaris. It was concluded that R. phaseoli tolerant to diazinon were infective and effective
for the health growth of P. vulgaris.
Key word. Soil R. phasoli, P.vulgaris, smbiotic, Biological N2 fixation, insectide pest contol
... Several studies have reported that long-term benomyl application does not alter the nonmycorrhizal plant community (Daleo et al., 2008) or the total fungal or microbial C or N (Hartnett and Wilson, 1999). However, some studies have shown that benomyl application has indirect effects on other fungi, especially pathogenic fungi (Newsham et al., 1995;Smith et al., 2000;Hodge and Fitter, 2013). In the present study, we found no evidence of negative benomyl effects on pathogen activity consistent with our other field studies (Zhang Zhang et al., 2016b;Zhao et al., 2019). ...
... The changes of soil processes and components caused by benomyl application (b33%) were small relative to the reported 80% decreases in mycorrhizal root colonization in other studies (Smith et al., 2000;Chen et al., 2001). This observation indicates that benomyl exhibited its effects mainly throughout decreased mycorrhizal root colonization. ...
... Several studies have reported that long-term benomyl application does not alter the nonmycorrhizal plant community (Daleo et al., 2008) or the total fungal or microbial C or N (Hartnett and Wilson, 1999). However, some studies have shown that benomyl application has indirect effects on other fungi, especially pathogenic fungi (Newsham et al., 1995;Smith et al., 2000;Hodge and Fitter, 2013). In the present study, we found no evidence of negative benomyl effects on pathogen activity consistent with our other field studies (Zhang Zhang et al., 2016b;Zhao et al., 2019). ...
... The changes of soil processes and components caused by benomyl application (b33%) were small relative to the reported 80% decreases in mycorrhizal root colonization in other studies (Smith et al., 2000;Chen et al., 2001). This observation indicates that benomyl exhibited its effects mainly throughout decreased mycorrhizal root colonization. ...
... While certain molecules in fungicides may affect Arbuscular Mycorrhizal Fungi (AMF), not all fungicides have uniform impacts on these fungi [69]. Benzoyl, found in some fungicides, can lead to long-term reductions in mycorrhizal associations [70], with many fungicides proving toxic to hyphal growth and root colonization by AMF [67]. Additionally, fungicides like emission and carbendazim can harm AMF populations [71]. ...
Soil amendment” refers to the alteration of soil properties driven by human activities. This includes actions such as spreading, compaction, erosion and fertility loss, which reshape the land and necessitate qualitative and quantitative risk assessment methods to address associated risks. Soil pollution, resulting from the excessive use of agrochemicals, waste materials, and toxic elements, disrupts soil organisms and fertility. Agrochemicals can contaminate soils through agricultural practices, impacting soil health. Irrigation water quality, indicated by salinity and soluble sodium percentage, also plays a crucial role in soil contamination. Additionally, emerging concerns arise from microplastics due to their persistence and potential ecological impacts. Remediation strategies for heavy metal-contaminated soils involve. Physical methods like soil replacement and thermal desorption address contamination by removing or treating soil on-site or off-site. Chemical fixation immobilizes contaminants using specific chemicals, while biological remediation, such as phytoremediation and bioremediation. Risk assessment, crucial for understanding the extent and severity of soil contamination, aids in effective remediation by considering factors such as contaminant concentrations, exposure pathways, and potential ecological and human health impacts. Overall, safeguarding soil health against pollution, erosion, and urbanization is essential for maintaining food and grazing resources.
... In this same study, bacterial α-diversity was reduced, and the community was restructured by azoxystrobin. Repeated fungicide applications can also reduce the colonization of arbuscular mycorrhizal fungi (AMF) [15] and decrease activity of root nodule forming bacteria [95]. In contrast, one study found that foliar application of the QoI fungicide pyraclostrobin enhanced the root nodulation and nitrogen xation in soybean. ...
Background
Understanding the factors that facilitate disease suppressive soils will contribute to more sustainable plant protection practices. Disease suppressive soils have been documented in many economically important crops, but not in turfgrass, one of the most intensively managed plant systems in the United States. Dollar spot, caused by the fungus Clarireedia jacksonii, is the most economically important disease of managed turfgrass and has historically been controlled through intensive use of fungicides. However, previous anecdotal observations of lower dollar spot severity on golf courses with less intensive fungicide histories suggests that intensive fungicide usage may suppress microbial antagonism of pathogen activity. This study explored the suppressive activity of transplanted microbiomes against dollar spot from seven locations in the Midwestern U.S. and seven locations in the Northeastern U.S. with varying fungicide use histories. Creeping bentgrass was established in pots containing homogenized sterile potting mix and field soil and inoculated with C. jacksonii upon maturity. Bacterial and fungal communities of root-associated soil and phyllosphere were profiled with short-amplicon sequencing to investigate the microbial community associated with disease suppression.
Results
The results clearly showed that plants grown in the transplanted soil microbiome collected from sites with lower fungicide intensities exhibited reduced disease severity. Plant growth promoting and pathogen antagonistic microbes may be responsible for disease suppression, but further validation is required. Additional least squares regression analysis of the fungicides used at each location suggested that contact fungicides such as chlorothalonil and fluazinam had greater influence on the microbiome disease suppressiveness than penetrant fungicides. Potential organisms antagonistic to Clarireedia were identified in the subsequent amplicon sequencing analysis but further characterization and validation is required.
Conclusion
Given the current reliance on fungicides for plant disease control, this research provides new insights into potential non-target effects of repeated fungicide usage on disease suppressive soils. It also indicates that intensive fungicide usage can decrease the activity of beneficial soil microbes. The results from this study can be used to identify more sustainable disease management strategies for a variety of economically important and intensively managed pathosystems.
... The process reduces the population of certain fungal feeders (Tylenchidae) by 13% and predatory nematodes (Dorylamidae) by 33%. Soil nematodes, earthworms and protozoa are affected by field application rates of the fungicide fenpropimorph and other herbicides [SMITH et al. 2000]. Tests of Bavistin and Dithane M-45 fungicides for the effect on soil mycoflora with special reference to mycorrhizal fungi of the sunflower crop showed that both fungicides had deleterious effect on the mycorrhizal spore number and percentage mycorrhizal root colonization [AGGARWAL et al. 2005]. ...
The paper discusses the impact of pesticides on the biological activity of soils, as well as an environmental assessment of the state of light chestnut soils by the Kazakh Research Institute of Agriculture and Crop Production with the aim to establish diagnostic indicators that reduce biological activity. The study covers physical, chemical and biological properties of soils under crops of winter wheat in the light chestnut soil in the SouthEast of the Republic of Kazakhstan. The content of pesticides in soil samples was determined using the gas chromatography mass-spectrometric method. The paper shows results of the chromatographic analysis of soil samples regarding the content of pesticides. The study of changes of light chestnut soil biological activity was conducted to determine their relative resistance to pesticide contamination. Data obtained revealed the degree of light chestnut soil resistance to pesticide contamination. The study also identified species of soil invertebrates, as well as soil enzymes that should be used as bioindicators for the monitoring of the contamination with pesticides. Results obtained expand knowledge about changes in the biological activity of light chestnut soils due to pesticide contamination in the ecosystems of SouthEast Kazakhstan. In contrast to abundance indicators, the results suggest that the species composition of soil organisms can be used as a criterion for a qualitative assessment of the soil exposure to pesticides.
... Pesticides can reduce the effectiveness of the natural enemies of arthropods by causing mortality and by influencing their movement, foraging and over reproductive rate (Jepson et al., 1989 iii. Fungicide usage: Fungicides can disrupt natural control of some insect and mite pest species as many are toxic to entomopathogenic fungi, e.g. Smith et al., 2000 reported an 80% reduced arbuscular mycorrhizal root colonization due to a benomyl fungicide application. ...
... AMF uninoculated treatments were realized by applying benomyl. Benomyl has been shown to effectively reduce AM colonization with minimal direct effects on plants (Hetrick et al., 1990;Smith et al., 2000) and widely used in the investigation related to AM fungi Li et al., 2019;Chen et al., 2020;Kang et al., 2020). Maize plants were grown at 28°C/25°C under a 16-h-day/8-h-night cycle for 8 weeks at a greenhouse of Yunnan University in China. ...
Arbuscular mycorrhizal fungi (AMF) can symbiose with many plants and improve nutrient uptake for their host plant. Rhizosphere microorganisms have been pointed to play important roles in helping AMF to mobilize soil insoluble nutrients, especially phosphorus. Whether the change in phosphate transport under AMF colonization will affect rhizosphere microorganisms is still unknown. Here, we evaluated the links of interactions among AMF and the rhizosphere bacterial community of maize (Zea mays L.) by using a maize mycorrhizal defective mutant. Loss of mycorrhizal symbiosis function reduced the phosphorus concentration, biomass, and shoot length of maize colonized by AMF. Using 16S rRNA gene amplicon high-throughput sequencing, we found that the mutant material shifted the bacterial community in the rhizosphere under AMF colonization. Further functional prediction based on amplicon sequencing indicated that rhizosphere bacteria involved in sulfur reduction were recruited by the AMF colonized mutant but reduced in the AMF- colonized wild type. These bacteria harbored much abundance of sulfur metabolism-related genes and negatively correlated with biomass and phosphorus concentrations of maize. Collectively, this study shows that AMF symbiosis recruited rhizosphere bacterial communities to improve soil phosphate mobilization, which may also play a potential role in regulating sulfur uptake. This study provides a theoretical basis for improving crop adaptation to nutrient deficiency through soil microbial management practices.
... The presence of pesticide residues in soil had short term inhibitory effects on soil microbial as well as toxicity effects to the soil microflora and microfauna (Hua et al. 2009;Babendreier et al. 2015;Singh et al. 2015;Sahoo et al. 2016). However, information on long-term effect of pesticides on non-target soil microflora and fauna is scanty (Smith et al. 2000). ...
A pot experiment was conducted to study the effects of insecticides on soil micro-biota
under laboratory condition. Soil was collected from control plot (0-15 cm depth) where no
insecticides were applied and filled in plastic pots. Three insecticides viz. indoxacarb 14.5
SC, chlorfenapyr 10SC and chlorpyrifos 20EC with two doses were applied twice at 15 days
of interval on the pot soil surface. Sampling of soil from pot was done by using PVC core (1
inch diameter) after 72 hours of each spray. Inoculation of serially diluted soil solution was
done on culture media for microbial count. The number of colonies of bacteria and fungi on
the plates were counted directly or with the help of a colony counter. The results revealed
that the higher mean log CFU/g population of soil bacteria was recorded in the normal dose
indoxacarb (5.77-5.99 cfu/g of soil) and chlorfenapyr (5.79-5.83cfu/g of soil) whereas soil
fungi was higher in normal dose of indoxacarb (5.49-6.10 cfu/g of soil) and chlorpyrifos
(5.54-5.99 cfu/g of soil).
... Benzoyl, emisan, and carbendazim have a damaging effect on mycorrhizal fungi. Benomyl, captan, mancozeb, tridemorph, and thiram fungicides adversely affect soil enzymatic activity (Kyei-Boahen et al., 2001;Shukla, 2000;Smith et al., 2000;Virág et al., 2007). ...
... AMFs are symbiotic associations between fungi and roots of higher plants, which enhance nutrient uptake, particularly P, nitrate (NO 3 ), and ammonium (NH 4 ), as well as improve soil aggregate stability [39]. It has been shown that mycorrhizal fungi and bacterial counts are affected by benzoyl application [40,41]. Monkiedje [42], found that metalaxyl is effective at promoting the colonization of AMFs in the roots of soybeans and maize. ...
Agricultural production is largely based on the use of agrochemicals in order to minimize pests, pathogens, and undesirable weeds toward increase production. In the current situation, however, several threats are emerging that threaten food security, human and environmental health, ecological balance, and soil biodiversity. Agrochemicals may shift beneficial microorganisms in the community over time, with potentially dangerous consequences, such as the development of antibiotic resistance. Farming systems utilizing agrochemicals might adversely affect soil microorganisms responsible for nutrient cycling processes, such as: nitrogen fixation, phosphorus solubilizing, and others. Some agrochemicals reduce soil enzyme activity and biochemical reactions, which are key indicators of soil microbiology. In this review, we explore how applied agrochemicals affect soil microbes and biochemical health attributes under different cropping systems, as well as ways to overcome the negative impacts of agrochemicals.
... These GCFs were chosen because they differ in their nature (i.e., physical, chemical), are likely to differ in their mode of action and effect direction 21 , and can be easily implemented. Each of the six GCFs have been shown to impact plants and their environment when applied on their own 10,13,17,19,20,[55][56][57][58][59][60] . Furthermore, all of the chosen GCFs are likely to continue to increase in magnitude or extent in the near future [61][62][63][64][65] . ...
Plant communities experience impacts of increasing numbers of global change factors (e.g., warming, eutrophication, pollution). Consequently, unpredictable global change effects could arise. However, information about multi-factor effects on plant communities is scarce. To test plant-community responses to multiple global change factors (GCFs), we subjected sown and transplanted-seedling communities to increasing numbers (0, 1, 2, 4, 6) of co-acting GCFs, and assessed effects of individual factors and increasing numbers of GCFs on community composition and productivity. GCF number reduced species diversity and evenness of both community types, whereas none of the individual factors alone affected these measures. In contrast, GCF number positively affected the productivity of the transplanted-seedling community. Our findings show that simultaneously acting GCFs can affect plant communities in ways differing from those expected from single factor effects, which may be due to biological effects, sampling effects, or both. Consequently, exploring the multifactorial nature of global change is crucial to better understand ecological impacts of global change. Multiple co-acting environmental pressures could affect ecosystems in ways not predictable based on single factors or pairwise combinations. Here, the authors show that the number of global change factors affects productivity, species composition and diversity of grassland plant communities.
... insecticides, fungicides, and herbicides, and found that they have a positive or negative effect on soil microbial biomass (Chowdhury et al., 2008;Saha et al., 2015;Kumar et al., 2020). Repeated application of pesticides has been reported to significantly lower the soil microbial biomass, mainly the fungal populations, and has been reported to increase certain bacterial populations (Smith et al., 2000;Pal et al., 2006;Singh et al., 2015). Molecular techniques like DGGE were also to determine the effect of specific pesticides on the soil microbial community (Lo, 2010). ...
Preventing degradation, facilitating restoration, and maintaining soil health is fundamental for achieving ecosystem stability and resilience. A healthy soil ecosystem is supported by favorable components in the soil that promote biological productivity and provide ecosystem services. Bio-indicators of soil health are measurable properties that define the biotic components in soil and could potentially be used as a metric in determining soil functionality over a wide range of ecological conditions. However, it has been a challenge to determine effective bio-indicators of soil health due to its temporal and spatial resolutions at ecosystem levels. The objective of this review is to compile a set of effective bio-indicators for developing a better understanding of ecosystem restoration capabilities. It addresses a set of potential bio-indicators including microbial biomass, respiration, enzymatic activity, molecular gene markers, microbial metabolic substances, and microbial community analysis that have been responsive to a wide range of ecosystem functions in agricultural soils, mine deposited soil, heavy metal contaminated soil, desert soil, radioactive polluted soil, pesticide polluted soil, and wetland soils. The importance of ecosystem restoration in the United Nations Sustainable Development Goals was also discussed. This review identifies key management strategies that can help in ecosystem restoration and maintain ecosystem stability.
... While during the 7 th week, the reduction was 58%, 64% and 65% respectively. Similarly, studies have shown that the presence of malathion insecticide decreased fungal population ( Walia et al., 2018;Smith, et al., 2000) . Our results show that the most adverse effect was seen in soil treated with malathion specially at 200ppm. ...
... Benomyl application has been proved to be an effective and direct method for suppressing AM fungal activity in natural conditions (O'Connor et al. 2002;Yang et al. 2014;Kang et al. 2020;Tang et al. 2020), while several earlier studies indicate that benomyl application has risks to affect pathogenic fungi and other soil organisms (Smith et al. 2000;Pech and Heneberg 2015). For example, benomyl application may reduce the fecundity of ants, and subsequently alter the composition of ant assemblages (Pech and Heneberg 2015). ...
Background and aims
Plant community stability is threatened by anthropogenic climate changes such as increased precipitation. Arbuscular mycorrhizal (AM) fungi have been shown to drive the resistance of ecosystems against climate changes to provide stable ecosystem functions. However, how AMF affects plant community stability under climate change is still not sufficiently clear in Central Asia.
Methods
A comprehensive study was conducted with increased precipitation and suppression of AMF in mycorrhizal and non-mycorrhizal plant communities, respectively. Changes in plant community composition and aboveground biomass were measured, and the temporal stability of plant community was calculated.
Results
Mycorrhizal plant community responded more sensitively to the increased precipitation and suppression of AMF than non-mycorrhizal plant community. Species synchrony and population variability were only significantly changed by increased precipitation in the mycorrhizal plant community. The stability of dominant and mycorrhizal plants were positively related to community temporal stability of both plant communities. While contrasted with the positive effects of increased precipitation on community temporal stability, increased precipitation reduced community temporal stability by increasing temporal variations of plant biomass in the mycorrhizal plant community, and by decreasing plant diversity in the non-mycorrhizal plant community. However, AMF buffer the decreases in community stability by increasing plant community biomass under increasing precipitation.
Conclusion
Our findings highlight ongoing increases in precipitation potentially weaken the temporal stability of ephemeral plant communities in the desert ecosystem stability; however, AMF can alleviate these negative effects through increasing community biomass, especially in the plant community dominated by mycorrhizal species.
... extent of 383 4%-20%, while plant species richness was decreased with benomyl addition to an extent of 384 21%-31%, the degree of reduction is less than that for AMF functions, indicating the primary effect 385 of benomyl in semi-arid grassland soils is suppression of mycorrhizal fungi and thus indirectly affect 386 soil biota and nutrient cycling.Smith et al., (2000) also found that the magnitude of benomyl effects 387 on soil biota and processes was small (e.g., 12-33% reduction) relative to the intended target effects 388 of benomyl on mycorrhizal fungi (e.g., an average of 80% reduction in mycorrhizal root colonization) 389 (57). ...
We examined the impacts of warming, nitrogen (N) addition, and suppression of arbuscular mycorrhizal fungi (AMF) on soil bacterial and fungal richness and community composition in a field experiment. AMF root colonization and the concentration of an AMFspecific phospholipid fatty acid (PLFA) were significantly reduced after the application of the fungicide benomyl as a soil drench. Warming and N addition had no independent effects but interactively decreased soil fungal richness, while warming, N addition, and AMF suppression together reduced soil bacterial richness. Soil bacterial and fungal species diversity was lower with AMF suppression, indicating that AMF suppression has a negative effect on microbial diversity. Warming and N addition decreased the net loss of plant species and the plant species richness, respectively. AMF suppression reduced plant species richness and the net gain of plant species but enhanced the net loss of plant species. Structural equation modeling (SEM) demonstrated that the soil bacterial community responded to the increased soil temperature (ST) induced by warming and the increased soil available N (AN) induced by N addition through changes in AMF colonization and plant species richness; ST directly affected the bacterial community, but AN affected both the soil bacterial and fungal communities via AMF colonization. In addition, higher mycorrhizal colonization increased the plant species richness by increasing the net gains in plant species under warming and N addition.
... Pesticides can affect these processes by altering the microbial composition of the soil. For instance, applications of the systemic fungicide benomyl during many years reduced mycorrhizal root colonization by 80%, thereby indirectly reducing the abundance of fungal-feeding and predatory nematodes by 33% while increasing microbial substrateinduced respiration by 10% [40]. Generally, fungicides eliminate fungal species, thus fostering the growth of competing bacteria while surviving and resistant strains of fungi become dominant (Fig. 1). ...
Pesticides are toxic chemicals used to control pests, weeds and pathogens. Three quarters of all pesticides are employed in agricultural production, particularly in developed countries, in an effort to mitigate crop damage endured by intensive agriculture. However, after more than 60 years of worldwide usage, their side-effects on terrestrial ecosystems – even when applied as recommended – are obvious. This chapter examines the ecological problems caused by specific chemicals/groups, so that this awareness may help improve agricultural practices through appropriate risk management. Fungicides alter the microbial-fungi communities responsible for the recycling of nutrients in the soil, and copper fungicides are toxic to earthworms and other animals. The routine application of herbicides has produced a net loss of plant biomass and biodiversity in many landscapes, which indirectly reduces the associated arthropod communities and leads to population declines in many species of birds, and possibly amphibians too, due to lack of food. Insecticides are very toxic to most invertebrates in the soil, birds and small mammals, causing significant reductions in their populations and disturbing the trophic structure of their communities. Persistent pesticides accumulate in soil and concentrate through the trophic chain, causing a plethora of sublethal effects which are negative for the survival of individuals as well as the viability of their populations; the long term effects of DDT and cyclodiene poisoning in birds is still an ecological issue despite more than 30 years of not being applied in most developed countries. While pesticides have increased our agricultural productivity and helped feed the current human population, the price of this productivity is being paid by the Earth's ecosystems at large.
... 3.2 Chemical pollutionpesticides (Fig. 2b) Pesticides are commonly used for the control of pests and diseases in agricultural systems but also in forests. However, the repeated and long-term use of these compounds, combined with their often high persistence in soils (for months or even years for some) may raise serious concerns about their side effects on non-target macro and micro-fauna and flora (Smith et al. 2000). One of the first review addressing the impact of pesticides on forest ecosystems has been conducted by Trappe et al. (1984) and was long time later updated by Marin (2011). ...
The association between ectomycorrhizal (ECM) fungi and trees is at the heart of forest ecosystems. Nowadays, this association is increasingly facing pressures resulting from anthropogenic activities, impacting the structure, biodiversity and functions of ECM fungal communities and their hosts. Here, we review some of the most common anthropogenic activities (i.e. enrichment of atmospheric carbon dioxide, increase of global temperature, atmospheric pollution, nitrogen deposition, use of pesticides, land use management, introduction of invasive species and biodiversity loss) affecting ECM fungi (i.e. species richness, abundance, taxonomy, production of spores and carpophores, and enzymatic activities) and their tree hosts. The review was conducted at different scales, from species to populations and ecosystems and whenever possible, example including boreal, temperate and tropical forests were reported. To conclude, we discussed about the present challenges hindering a better holistic understanding of our future forest ecosystems hosting ECM fungi. Overall, climate change is expected to affect ECM fungi through an alteration of plant metabolism and spatial distribution of trees. Although industrial pollutants and pesticides effects remains less clear at large scale, N-deposition and/or fertilization could induce ECM shifts and alter nutrient cycling. Regarding other anthropogenic parameters (e.g. land use, invasive species), they may affect ECM fungal communities by impacting their diversity, abundance and richness.
... AMF can be sensitive to some molecules of fungicides but not to all (Datta et al. 2017a). Benzoyl is responsible for the longterm reduction in mycorrhizal associations (Smith et al. 2000) with many fungicides being toxic to hyphal growth and thus root colonization of AMF associations of pea (Cycoń et al. 2006). The fungicides of dithiocarbamates group (e.g., thiran, ziram, and mancozeb) are harmful to AMF as tested in groundnut (Sugavanam et al. 1994). ...
... The resultant changes in the soil microbial activity due to repeated application depending on the intensity and spectrum of the activity and persistence of the original pesticide or their metabolites product (Margni et al., 2002). Culturable diversity, biochemical activities, and microbial community structure may also be affected by pesticide (Martinez-Toledo et al., 1998;Smith et al., 2000;Chen et al., 2001;Cycoń and Kaczyńska, 2004;Cycon and Piotrowska-Seget, 2007). Pesticides that interrupt the activities of soil microorganisms involved in the nutritional cycling of soils result in adverse consequences on the soil ecosystem. ...
Modern agriculture fundamentally relies on an extensive use of agrochemicals to enhance crop productivity by controlling harmful pests, pathogens, and undesirable weeds. However, currently, we have reached a stage where several threats are emerging on food security, human and environmental health, maintenance of ecological balance, and conservation of the soil biodiversity. Long-term unbalanced use of agrochemicals may lead to community shift of beneficial microorganisms with dangerous consequences such as the development of antimicrobial resistance. Agrochemicals usage in farming systems may adversely influence soil microorganisms that are mainly involved in nutrient cycling processes, such as nitrogen fixation, phosphorus solubilization, and other essential nutrient biotransformation. The recent report established that some agrochemicals reduce biochemical reaction and activities of soil enzymes that are key indicators of soil microbiological health. This chapter focuses on the effects of applied agropesticides on soil microbiological and biochemical health attributes under different cropping systems.
... AMF can be sensitive to some molecules of fungicides but not to all [73]. Benzoyl is responsible for the long-term reduction in mycorrhizal associations [74] with many fungicides being toxic to hyphal growth and thus root colonization of AMF associations of pea [72]. Emisan (holding 6% 2-methoxyethylmercury chloride) and carbendazim (benzimidazole fungicide and a metabolite of benomyl) both have a damaging effect on AMF in groundnut. ...
The World Health Organization (WHO) states that in developing nations, there are three million cases of agrochemical poisoning. The prolonged intensive and indiscriminate use of agrochemicals adversely affected the soil biodiversity, agricultural sustainability, and food safety, bringing in long-term harmful effects on nutritional security, human and animal health. Most of the agrochemicals negatively affect soil microbial functions and biochemical processes. The alteration in diversity and composition of the beneficial microbial community can be unfavorable to plant growth and development either by reducing nutrient availability or by increasing disease incidence. Currently, there is a need for qualitative, innovative, and demand-driven research in soil science, especially in developing countries for facilitating of high-quality eco-friendly research by creating a conducive and trustworthy work atmosphere, thereby rewarding productivity and merits. Hence, we reviewed (1) the impact of various agrochemicals on the soil microbial diversity and environment; (2) the importance of smallholder farmers for sustainable crop protection and enhancement solutions, and (3) management strategies that serve the scientific community, policymakers, and land managers in integrating soil enhancement and sustainability practices in smallholder farming households. The current review provides an improved understanding of agricultural soil management for food and nutritional security.
... AM removal treatments were realized by applying or not applying fungicide, benomyl (C 14 H 18 N 4 O 3 , 50 mg kg À1 soil per month) (Marler et al., 1999). Benomyl has been shown to effectively reduce AM colonization in glasshouse soils with minimal direct effects on plants (Hetrick et al., 1990;Smith et al., 2000), and widely used to investigate the effects of AM fungi on the interactions between native and invasive plants (Callaway et al., 2003;Grilli et al., 2014). For the competition treatment, a plant individual was either grown alone or in competition with its counterpart of the same species pair. ...
The invasion success of some exotic plants depends on associations
with arbuscular mycorrhizal (AM) fungi, which range along a
continuum from strong mutualism to parasitism frequently
affected by soil phosphorus (P) availability. It is unclear how P
availability shifts AM associations on native and invasive plants,
which in turn influence their competition. In this work, we
conducted a three-factor common garden experiment, including
manipulations of P availability, AM fungi occurrence and interspecific competition to evaluate how AM fungi influence competition between two pairs of invasive and native plants under
different P availabilities. Our results showed that P enrichment
reduced positive AM effects on the growth of both native and
invasive plants. Competition had no effect on AM colonization on
the invasive plants, but reduced AM colonization on the native
plants, which led invasive plants to receive greater AM benefits
under low-P treatment, but to be exposed to stronger AM
detriments under high-P treatment compared to the native
competitors. Therefore, the competitive advantage of invasive vs
native plants was enhanced by AM fungi under low-P treatment,
but weakened under high-P treatment. Our work highlights the
necessity to incorporate the interaction between soil microbes and
nutrient availability on plant invasion in future studies.
... While during the 7 th week, the reduction was 58%, 64% and 65% respectively. Similarly, studies have shown that the presence of malathion insecticide decreased fungal population ( Walia et al., 2018;Smith, et al., 2000) . Our results show that the most adverse effect was seen in soil treated with malathion specially at 200ppm. ...
In light of the rapidly growing human population, extensive pesticides have been utilized to maximize crop production. This has become a major environmental concern. To assess the influence of commonly used pesticides on soil microorganisms counts and microbial activities in the form of CO 2 production, a factorial experiment was conducted. Herbicide (Glyset I.P.A, Glyphosate 48%) and insecticides Miraj (Alphacypermethrin 10%) and Malathion (50% WP) were separately added to the soil at 0, 50, 100 and 200 ppm and incubated in the laboratory at 30 °C. The counts of bacteria, fungi, actinomycetes and CO 2 production were examined weekly for 7 consecutive weeks. The results demonstrated that the addition of the three mentioned pesticides significantly decreased the microbial activities and counts of soil bacteria, fungi and actinomycetes. The observed effect was depended upon the type and amount of pesticide as well as the length of incubation period. The microbial activities and the number of bacteria, fungi, and actinomycetes were inversely proportional to the concentration of pesticides added to the soil. In most treatments, soil samples treated with 200ppm of Malathion demonstrated the lowest microbial activities and counts of bacteria, fungi and actinomycetes. This study suggests that the investigated pesticides negatively affect microbial counts and activity in soil, which confirms and reinforces previously reported environmental concerns.
... The indiscriminate and excessive258 applications of these compounds could have harmful effects for the development of 259 plants, animals and human being(Benbrook 2016; Donham 2016; Igbedioh 1991; 260 Park et al. 2015). These toxic compounds even modify the microbial diversity and 261 microbial activity(Chen et al. 2001; Johnsen et al. 2001;Smith et al. 2000); which 262 ...
Plant growth-promoting bacteria (PGPB) have been extensively studied, because of different mechanisms to perform phytostimulation, as well as the abilities to colonize plants. The number of crop types and hectares of agricultural land, where PGPR are applied is low compared with the total crops or farming area. However, the PGPB application in crop fields is increasingly becoming more accepted due to the advantages to crops and environment such as the increment in productivity, the diminution in the use of chemical fertilizers and toxic compounds such as pesticides and herbicides. These traits make beneficial bacteria formulations the ‘right choice’ in healthy agriculture since they are highly compatible with sustainable crop production. The co-inoculation of plants with two or more beneficial bacteria apparently provides greater phytostimulation than mono-inoculation, perhaps because of the synergistic and multifarious effects occurring when two or more microorganisms are co-interacting. There is a consensus that bacterial mixtures provide greater benefits to the plants, the number of formulations containing more than three species of microorganisms in consortium is still limited. Therefore, we believe that more research and investment is needed to design and formulate multi-species inoculants containing compatible bacteria and other beneficial microorganisms in order to be capable of coexisting both in the designed formulation and associated with plants for sustainable benefits.
... As for the second possibility, it seems reasonable that it was not the bacteria biomass that drove N dynamic given nonsignificant effect of benomyl application on bacteria PLFA concentrations. However, we could not exclude the possibility that there was an increase in bacterial activity following the application of benomyl, particularly in relation to nitrogen mineralization (Wainwright and Pugh 1974;Smith et al. 2000). ...
Invasive plant species are often able to alter soils in a way that benefits their own fitness over that of native species. While interspecific competitions may drive species to acquire different forms of nitrogen (N) to avoid intensive competition, plant-mycorrhizal interactions can also influence plant nutrient acquisition. Yet, it is unclear whether a variation in N acquisition by an invasive species is driven by interspecific resource partitioning due to competition with native species or by its symbiosis with arbuscular mycorrhizal (AM) fungi. We conducted a pot experiment to examine the effects of competition and fungicide on the uptake of different N forms by Flaveria bidentis, an invasive plant having symbiotic relationships with AM fungi, and two coexisting native species, mycotrophic Bidens maximowicziana and non-mycotrophic Amaranthus retroflexus (referred to by genus hereafter), by growing them either in two-species mixtures or in monocultures. We found that the growth of Flaveria was suppressed by its association with AM fungi regardless of the presence of competing native species, but the degree of suppression was related to the native species with which Flaveria competed. When growing in monocultures, all three species showed a strong preference for NO3⁻-N over NH4⁺-N and glycine-N regardless of mycorrhizal status. However, under competition conditions, Flaveria increased ¹⁵N recovery in any form of N available (in particular NH4⁺-¹⁵N), depending on neighboring plant identity and AM fungi association, whereas Amaranthus specially tended to decrease NH4⁺-¹⁵N uptake when competing with Flaveria, suggesting a niche complementarity in the utilization of N between two species. Our findings suggested that AM fungi may have the potential to limit the invasion of Flaveria, in the short term, and that interspecific competition plays an important role in partitioning soil N acquisition between plant species.
... In the particular case of this work, the complex mixtures of pesticides employed represent an ecotoxicological scenario in which several synergistic effects might take place (Cedergreen, 2014;Munkegaard et al., 2008), thus translating into the disturbance of microbial communities. This aspect may be critical in the case of fungicides and their deleterious effect on fungal degrading populations (Sigler and Turco, 2002;Smith et al., 2000). Moreover, different DT 50 values have been obtained for some pesticides in biomixtures of the same composition, but in different chemical and biochemical environments due to the presence of different pesticide mixtures. ...
Biopurification systems (BPS) have been barely explored for removing complex mixtures of pesticides. In this study, the potential of a biomixture to remove simultaneously a mixture of herbicides (triazines), fungicides (triazoles) and insecticides (organophosphates) is presented. Also, a BPS using the same biomixture was used for treating a pesticide testing laboratory wastewater containing a mixture of 38 compounds. Ecotoxicological assays were conducted on the BPS elutriates to investigate the mixture detoxification. A mixture (concentrations of 4-8 mg kg-1) run in small-scale biomixture systems (SSB) for 128 d showed 59.3% removal of triazines, 68.5% of organophosphates and no elimination of triazoles. The treatment of the laboratory wastewater (individual concentrations range: 0.0036-0.25 mg kg-1) in the pilot-scale BPS for 281 d resulted in the elimination pattern of organophosphates (90.0%) > triazoles (73.4%) > carbamates (71.3%) > triazines (54.3%). Complete detoxification towards Daphnia magna and partial detoxification in Lactuca sativa seeds germination occurred in the BPS. Although the pesticide mixture complexity is higher in the BPS, the lower concentrations found in this matrix, could explain removal differences between SSB and BPS and the apparent inhibition in the elimination of carbamates and some triazines observed in the latter. These findings suggest that disposal of pesticide-containing laboratory-wastewater should be done in separate containers, according to chemical groups before their treatment in separate BPS, in order to reduce treatment periods. Monitoring the treatment process in the BPS with a battery of ecotoxicological tests is strongly recommended.
... It is routinely accepted that broad-spectrum antibiotic supplement (30 μg/mL chloramphenicol and 100 μg/mL streptomycin sulfate in this study) can effectively kill or inhibit the majority of prokaryotes 21 , making fungi the most abundant microorganism in the microcosms. This method has been applied in fungal incubation studies 22,23 . We have now rephrased the related discussion section. ...
... Soil is an important system for the biological interactions of various microorganisms, hence the applications of pesticides in the agriculture leads to pessimistic side effects on soil micro flora leading to soil pollution and soil contamination [1]. Pesticides may perturb microorganisms by reducing their numbers, biochemical activity, diversity and change the structure of microbial populations [2,3,4,5,6]. According to Dubey and Singh [7], pesticides application starts from pre sowing and post sowing stages of seeds, such as treatment of pesticides includes soil treatment, seed treatment and spraying treatment. ...
Aim: To study the impact of selected pesticides on Azospirillum sp. population and its nitrification in groundnut (Arachis hypogaea L.) soils. Study Design: Black clay and red sandy loam soils with known pesticide history were collected from groundnut (Arachis hypogaea L.) cultivated fields and were investigated to elucidate the impact of pesticides on Azospirillum sp. population and its nitrification in both the soils. Place and Duration of Study: The soil samples were collected from groundnut cultivated fields of Anantapur District, Andhra Pradesh (A.P) and the study was carried out for 3 months. Methodology: Ten gram portions of each soil sample were placed in (25 × 150 mm) test tubes and treated with different concentrations of pesticides, (10, 25, 50, 75 and 100 µg g-1 soil) which were equivalent - 1.0, 2.5, 5.0, 7.5 and 10 kg ha-1. Soil samples without pesticides served as controls. The soils with and without pesticides were incubated at room temperature (28 ± 4°C) in the laboratory and moisture content was maintained at 60% water holding capacity (WHC) throughout the experimental period. After 7 and 14 days of incubation, triplicate soil samples were used to estimate the population size of Azospirillum sp. using the MPN method. Five ml aliquots of semi – solid malate medium were added to five MPN tubes and inoculated with 0.5 ml of a soil suspension from 10-1 to 10-5 soil dilutions, and incubated at 37°C. Results: The population of Azospirillum sp. in both soils increased when pesticides were applied @ 2.5 - 5.0 kg ha-1 and incongruity, when the pesticides concentration increased from 7.5 - 10.0 kg ha-1, the Azospirillum sp. population gradually decreased in both soils. Conclusion: The present study aimed at determining the influence of selected pesticides such as oxydemeton methyl, emamectin benzoate, dithane Z-78 and benomyl on the population of Azospirillum sp. and nitrogen fixation in black clay soil and red sandy loam soils in groundnut cultivated fields of Anantapur District, Andhra Pradesh, India. Insecticides and fungicides applied up to 5.0 kg ha-1, enhanced the population of Azospirillum sp. and its nitrogen fixation also increased significantly after 7 and 14 days of incubation in both soils. However, the population of Azospirillum sp., decreased with increasing period of soil incubation in both treated and untreated soils.
... 30 NaClO has been shown to be effective in inhibiting the decomposing activity of bacteria, 31 and has been used in place of fungicides. 32 Electrolysis of sodium chloride (NaCl) was shown to negatively impact the denitrification process. Luo found that cytoplasmic membrane hydrophobicity and enzymatic activity was inhibited at a direct current of 20 mA. ...
BACKGROUND
A biofilm‐electrode reactor (BER) was developed on the basis of hydrogenotrophic denitrification. The BER can be strengthened by adding organic matter, and the nitrate removal will be enhanced by a combination of heterotrophic and autotrophic denitrification. Denitrification in a biological system can be affected by operating parameters, and the microbial community and functional genes can be changed at the same time. In this study, the effect of hydraulic retention time (HRT) and current on the denitrification of a low chemical oxygen demand to nitrogen ratio (COD/N), saline wastewater in a continuous‐flow BER was evaluated and compared to a conventional biofilm reactor (BR).
RESULTS
The highest extent of nitrate removal was obtained at the optimum HRT (8 h) and current (10 mA). Low levels of ammonia (0.5–4 mg L⁻¹), produced through dissimilatory nitrate reduction to ammonia (DNRA), were observed. Quantitative real‐time polymerase chain reaction analysis revealed that the proportion of nirS‐type denitrifiers (3.75–8.30%) exceeded nirK‐type denitrifiers (0.24–0.90%) in both BR and BER. The genera of T78, Paracoccus and Azoarcus were identified as the dominant denitrifying bacteria in the BER. The cooperative activity of nitrate, nitrite and nitrous oxide reductase is necessary to reduce nitrate to dinitrogen in the denitrification process. The highest ratio of nosZ/nir genes in the bacterial community was 0.25 when the applied current was 10 mA.
CONCLUSION
Compared to other denitrification reactors, the BER is more effective to treat low‐COD/N, saline wastewater with short HRT and low current. © 2018 Society of Chemical Industry
... 30 NaClO has been shown to be effective in inhibiting the decomposing activity of bacteria, 31 and has been used in place of fungicides. 32 Electrolysis of sodium chloride (NaCl) was shown to negatively impact the denitrification process. Luo found that cytoplasmic membrane hydrophobicity and enzymatic activity was inhibited at a direct current of 20 mA. ...
A dicyclic-type electrode-based biofilm-electrode reactor (BER) was investigated for simultaneous removal of nitrate and Cr(VI). In the absence of Cr(VI), almost complete denitrification of 50 mg/L NO3⁻–N was achieved at a very low C/N ratio of 0.8 with the optimal current of 50 mA. Cr(VI) was removed by biological reduction and co-precipitation when Cr(VI) was taken as the only electron acceptor, and the removal efficiencies of Cr(VI) were 99.8%. In the coexistent system of nitrate and Cr(VI), nitrate removal was the result of the cooperation of hydrogenotrophic denitrification and heterotrophic denitrification. The methanol and H2 were also used as electron donors for biological reduction Cr(VI). The denitrification process was slightly inhibited by 1.00 mg/L Cr(VI) and 94.15% removal efficiency was achieved at current = 50 mA and HRT = 8 h. The present results show that the biofilm-electrode reactor is an effective way to simultaneous remove co-contaminants.
Graphical abstract
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... Fungicides may however have direct effects on the non-target organisms particularly the saprobic and symbiotic soil-borne fungi. Benomyl for instance is particularly toxicto mycorrhizal fungi (Smith et al., 2000). Which could have implications for the nutrition of the plants. ...
T h e objectives of the present work were to determine the diversity of microorganisms in a heavily
contaminated soils with heavy metals or pesticides and to identify their most resistant species . Three soil types
were selected to represent clay alluvial (FFS), calcareous (WNS) and sewage farm (ARS) soils and subjected to
two incubation experiments, one to study the effect of heavy metals (Cd, Zn, Pb and Ni) and the other to study
the effect of two pesticides (Harness and Rugby) on the diversity of their microorganisms (bacteria, fungi and
actinomycetes). The data of the first experiment showed that Alluvial (FFS) and Wadi-Natrun (WNS) had the
highest values of maximum adsorption and fixation capacity of Cd, Zn, Pb and Ni metals. Abu Rawash soil
(ARS) recorded the highest numbers of culturable bacterial even with the presence of increasing concentrations
of cadmium, lead and zinc followed by alluvial soil (FFS) and calcareous soil (WNS). The bacterial population
present in Abu-Rawash (ARS) was relatively more tolerant to Cd toxicity than that for alluvial (FFS) one while
Ni toxicity order was: (FFS) >(ARS) > (WNS). A significant positive correlation coefficients were recorded
between viable bacterial numbers and activity of microbial enzyme dehydrogenase in all heavy metal
contaminated soils. The morphological examination showed that heavy metal resistant bacterial isolates for were
Bacillus sp .mostly isolated from Abu-Rawash with one Isolate No. BM+64 was Cocci sp. Isolate BM+48 was
the most resistant to heavy metals and was identified as Bacillus cereus/ or B.thuringiensis which was obtained
from Abu-Rawash soil (ARS). The highest counts of fungi were noticed in the calcareous soil (MNS) and
alluvial one (FFS) treated with Ni. Isolates No. FM01 and FM14 were the most tolerant for the highest
concentrations of the applied Zn, Pb and Cd. Three isolates (FM01, FM10 and FM15) were classified as
Aspergillus nidulans, while three isolates ( FM04, FM08 and FM28) were recognized as Aspergillus fumigates,
two isolates (FM09 and FM14) were recognized as Aspergillus flavus. Fungi isolate FM04 (Aspergillus
fumigates) was the most resistant to Pb, while isolates FM10 and FM15 both (Aspergillus nidulans ) were the
most tolerant to Zn. Abu-Rawash (ARS) soils (sewage farm) showed the highest population of actinomycetes at
all the highest levels of Cd, Zn and Pb followed by the calcareous (WNS) and normal alluvial (FFS) soils.
AM10 was the only one that tolerated the stresses of Zn, Ni, Pb, and Cd at concentrations of 75, 75, 100 and 12
mg/L.
T he second incubation experiment showed that The initial concentration of soluble carbon for Harness
treatment was higher than that for Rugby. Abu-Rawash sewage farm soil (ARS) had the highest bacterial counts
under the stresses of both Rugby and Harness with relatively lower numbers in Harness. The bacterial isolates
dominated by Bacillus spp. with 60% of short rods bacteria. isolates BP01, BP07 and BP15 tolerated upto 2mg/l
of Harness while isolates BP01, BP15 and BP18 tolerated the same level as Rugby. Isolate BP01 was the most
tolerant one to both harness and Rugby and it was identified as Bacillus subtilis. Abu-Rawash soil (ARS) had the
highest fungal counts under the stresses of both Rugby and Harness pesticides. Harness was more toxic to fungi
than Rugby in all the investigated isolates. The pesticides resistant fungi isolates were identified as Aspergillus
spp., and Cladosporium spp. which were found in Abu-Rawash (ARS). The FP03 isolate was identified
morphologically as Aspergillus flavus which showed the highest tolerance to both Rugby herbicide and Harness
nematocide. The counts of actinomycetes in Harness treatment were, generally, lower than that in Rugby in both
alluvial (FFS) while the reverse was true in the sewage farm soil (ARS). Harness was more toxic to
actinomycetes than Rugby in all the investigated isolates. Actinomycetes isolate AP07 was the most tolerant
one to 2.0 mg/l of both Rugby and Harness while AP06 had tolerance to 2 mg/l of Harness and it was identified
as Nocardia spp.
Aggravated use of pesticides to intensify production and their transmigration to the aquatic environments jeopardises mother earth's ecological balance. To overcome this menace, the search for better and more efficient technologies for pesticides removal is still rambling on. In this regard, metal-organic frameworks (MOFs) have been found promising owing to their hybrid property, tunable size, greater surface area, multidimensional porosity, and functional effectiveness. With a steadily growing interest in the application of MOFs in the plethora of environmental and biomedical fields, this article takes the lead by providing a detailed depiction of the synthesis and structural variation of the frameworks, potential application of pristine, surface functionalized and composite MOFs for sensing, monitoring and removal of pesticides from water using combination of Grand Canonical Monte Carlo and Molecular Dynamics (GCMC & MD) simulation models. It also highlights the recent advances in the field, mechanistic insights of adsorption, followed by the directions for future research.
Aggravated use of pesticides to intensify production and their transmigration to the aquatic environments jeopardises mother earth’s ecological balance. To overcome this menace, the search for better and more efficient technologies for pesticides removal is still rambling on. In this regard, metal–organic frameworks (MOFs) have been found promising owing to their hybrid property, tunable size, greater surface area, multidimensional porosity, and functional effectiveness. With a steadily growing interest in the application of MOFs in the plethora of environmental and biomedical fields, this article takes the lead by providing a detailed depiction of the synthesis and structural variation of the frameworks, potential application of pristine, surface functionalized and composite MOFs for sensing, monitoring and removal of pesticides from water using combination of Grand Canonical Monte Carlo and Molecular Dynamics (GCMC & MD) simulation models. It also highlights the recent advances in the field, mechanistic insights of adsorption, followed by the directions for future research.
Aggravated use of pesticides to intensify production and their transmigration to the aquatic environments jeopardises mother earth's ecological balance. To overcome this menace, the search for better and more efficient technologies for pesticides removal is still rambling on. In this regard, metal-organic frameworks (MOFs) have been found promising owing to their hybrid property, tunable size, greater surface area, multidimensional porosity, and functional effectiveness. With a steadily growing interest in the application of MOFs in the plethora of environmental and biomedical fields, this article takes the lead by providing a detailed depiction of the synthesis and structural variation of the frameworks, potential application of pristine, surface functionalized and composite MOFs for sensing, monitoring and removal of pesticides from water using combination of Grand Canonical Monte Carlo and Molecular Dynamics (GCMC & MD) simulation models. It also highlights the recent advances in the field, mechanistic insights of adsorption, followed by the directions for future research.
Aggravated use of pesticides to intensify production and their transmigration to the aquatic environments jeopardises mother earth’s ecological balance. To overcome this menace, the search for better and more efficient technologies for pesticides removal is still rambling on. In this regard, metal–organic frameworks (MOFs) have been found promising owing to their hybrid property, tunable size, greater surface area, multidimensional porosity, and functional effectiveness. With a steadily growing interest in the application of MOFs in the plethora of environmental and biomedical fields, this article takes the lead by providing a detailed depiction of the synthesis and structural variation of the frameworks, potential application of pristine, surface functionalized and composite MOFs for sensing, monitoring and removal of pesticides from water using combination of Grand Canonical Monte Carlo and Molecular Dynamics (GCMC & MD) simulation models. It also highlights the recent advances in the field, mechanistic insights of adsorption, followed by the directions for future research
The purpose of this work was to study the persistence of pesticides in different soil conditions (fallow, cultivated, and microbial inoculation) and their impact on the soil microbial diversity. The experiment was set up in pots under net house conditions. Using Biolog, substrate utilization patterns for community-level physiological profiling (CLPP) were carried out. The persistence of carbendazim in different treatments of fallow soil, maize rhizosphere, and plant parts with and without Trichoderma was studied using HPLC. The HPLC analysis of soil and maize tissue reveals increased persistence of carbendazim and its degraded products in fallow treatment compared to maize with or without Trichoderma. The application of Trichoderma enhanced the carbendazim removal and alleviated its effect on the microbial populations. The present study concludes that fallow conditions prolong the presence of residual pesticides in soil and affect the soil microbial community, whereas bio-fungicides such as Trichoderma facilitate its degradation.
Arbuscular mycorrhizal fungi (AMF) can form symbiotic relationships with most crops, but their impact on the environmental migration of cadmium (Cd) in farmland is limited. A field experiment was performed in the rainy season (May–October) for two years in Cd-polluted farmland used for maize cultivation. A fungicide (benomyl) was used to specifically inhibit native AMF growth in the farmland. The growth and Cd uptake of maize and the Cd concentration and loss in runoff and interflow were investigated. Benomyl strongly and significantly inhibited AMF colonization rate in maize roots, reduced the contents of total and easily extractable glomalin-related soil protein (GRSP) in soil and the Cd uptake in maize roots, and increased the Cd uptake in shoots. Particulate Cd was the main form of Cd loss in runoff, while dissolved Cd was the main form of Cd leaching loss at depths of 20 cm and 40 cm. Inhibiting AMF increased the Cd concentration in runoff and interflow and promoted dissolved Cd loss in runoff and interflow at 20 cm depth by 34.7% and 68.0% and particulate Cd loss by 46.4% and 19.7%, respectively. Furthermore, the AMF colonization rate in maize roots and the GRSP content in soil were significantly positively correlated with Cd uptake in roots and negatively correlated with the concentration and loss of Cd in runoff and interflow. These results indicated that the benomyl-induced inhibition of native AMF promoted Cd transfer to maize shoots and increased Cd loss via runoff and interflow from polluted farmland.
Alternaria blight of oilseed Brassica crop is most widespread disease caused by necrotrophic ascomycetes fungus such as Alternaria brassicae and Alternaria brassicicola which cause huge economic loss. Among large reasons, the key reason for Alternaria blight infection is due to nutrients deficiency such as copper (Cu), zinc (Zn), sulfur (S) and potassium (K). Thus, B. juncea requires different nutrients for improving its health and capability to resist the disease. Since the use of agrochemicals and fungicides is not much efficient, fungal pathogens develop resistance and fungicides have large side effects on human and soil health, there is a need to screen biocidal agents developed through newly advanced and innovative technology known as nanotechnology. Enormous reports have recommended the use of metal oxide nanoparticles (NPs) for disease management such as titanium dioxide NPs (TiO2), iron oxide NPs (Fe3O4), zinc oxide NPs (ZnO NPs), cerium oxide (CeO2) and copper oxide NPs (CuO NPs). Among these, biogenic CuO NPs synthesized from different species of Trichoderma can be considered as promising and most efficient antifungal agent against Alternaria blight. Due to some specific properties, nanoparticles have been used for agricultural needs, among which CuO NPs have special feature as they activate defense system of plants and inhibit spore germination of phytopathogens. The cost effective synthesis and novel properties of CuO NPs makes them an alternative to copper fungicides. Therefore, the following review summarizes an insight into the proposed mechanism of CuO NPs as a protective and curative agent for Alternaria blight disease management. The biogenic CuO NPs monitor the disease development and its control by two methods. One is preventive method in which CuO NPs retard the growth of Alternaria brassicae on susceptible leaf tissues, thus preventing the Alternaria blight, while in another method, CuO NPs act as a curative medicine which kills the pathogen by releasing Alternaria inhibiting compounds and helps in transportation of these compounds at the site of infection. Hence, the current review focused on the properties of CuO NPs for their biocontrol efficacy against Alternaria blight through in vivo studies.
Arbuscular mycorrhizal fungi (AMF) are vital for nutrient cycling and aboveground ecosystem stability. To understand soil microbe resource limitations and AMF feedback regulation of the soil microbial biomass and litter stoichiometry under warming and nitrogen (N) application conditions, a 3-year experiment involving AMF suppression by benomyl under warming and N application conditions was conducted in the Songnen meadow, in which soil microbial nutrient limitation was measured by ecoenzymatic stoichiometry. We assessed the soil microbes and stoichiometric variables of Leymus chinensis and Phragmites australis litter under various treatment conditions. Carbon (C) and phosphorus (P) are commonly limited nutrients in soil microbial communities in the Songnen meadow ecosystem. AMF alleviated soil microbe C and P limitations by decreasing the microbial C:P ratio under warming and N application conditions and by accelerating litter decomposition, which occurred independently of warming and N application. AMF play a critical role in balancing nutrient stoichiometry and are key to maintaining microbial metabolism and nutrient cycle homeostasis. AMF can shorten the litter nutrient cycle, which is of great significance for the absorption, utilization and storage of plant nutrients in the Songnen grassland ecosystem.
Root-associating arbuscular mycorrhizal (AM) fungi foster vegetation recovery in degraded habitats. AM fungi increase nutrient availability for host plants; therefore, their importance is expected to be higher when nutrient availability is low. However, little is known about how small-scale variation in nutrient availability influences plant and AM fungal communities in a stable ecosystem. We conducted a 2-year field study in the understorey of a boreonemoral forest where we examined plant and AM fungal communities at microsites (15 cm diameter) with intact vegetation cover and at disturbed microsites where vegetation was cleared away and soil was sterilized to remove soil biota. We manipulated soil nutrient content (increased with fertilizer, unchanged, or decreased with sucrose addition) and fungal activity (natural or suppressed by fungicide addition) at these microsites. After two vegetation seasons, manipulations with nutrient content resulted in significant, although moderate, differences in the content of soil nutrients (e.g. in soil phosphorus). Suppression of fungal activity resulted in lower richness, abundance and phylogenetic diversity of AM fungal community, independently of microsite type and soil fertility level. Plant species richness and diversity decreased when fungal activity was suppressed at disturbed but not in intact microsites. The correlation between plant and AM fungal communities was not influenced by microsite type or soil fertility. We conclude that small-scale variation in soil fertility and habitat integrity does not influence the interactions between plants and AM fungi. The richness, but not composition, of AM fungal communities recovered fast after small-scale disturbance and supported the recovery of species-rich vegetation.
Herbivores experience an unprecedented variously impacts of climate warming. Besides, arbuscular mycorrhiza fungi (AMF) also is influence on herbivores through their common host plants. Surprisingly, there are no reports about how AMF affect the responses of herbivores to warming. To close this gap, we conducted a two factors experiment to research the effects of warming, fungicide (AMF suppression), and their interaction on the development of Gynaephora menyuanensis larvae, an endemic generalist herbivore species in northeastern Tibetan Plateau, and nitrogen content of Elymus nutans, which was the main food of G. menyuanensis. Warming significantly advanced the pupation time (PT), expanded the phenomena of protandry and increased the growth rate (GR) of G. menyuanensis larvae. Fungicide not affected the development of G. menyuanensis larvae, despite their negative effects on the content of E. nutans. Warming with fungicide decreased the GR of G. menyuanensis compared with warming treatment. In other words, AMF strengthen the beneficial effects of warming to G. menyuanensis. This study provides the first evidence of the impacts of AMF on the response of herbivore to warming.
The effects of 19 years of cumulative annual field application of five pesticides (benomyl, chlorfenvinphos, aldicarb, triadimefon and glyphosate), applied at, or slightly above, the recommended rates in 25 combinations, on soil microbial biomass and the mineralization of soil organic matter were investigated. Soil samples were taken 1 month after the application of benomyl, chlorfenvinphos and aldicarb in April 1992, and again in October 1992, 1 month after the application of triadimefon and glyphosate. The addition of aldicarb caused a significant increase of 7–16% in soil microbial biomass carbon (biomass C), an effect which appeared to be persistent. This effect of aldicarb was not reflected in the mineralization rate of soil organic C, possibly because the measurements of CO2 evolution showed a greater variation than those of biomass C. Measurement of microbial biomass activyty by the substrate-induced respiration method also gave much less precise results than measurements of biomass C by fumigation-extraction. The mineralization of soil organic N to ammonium and then nitrate was mostly unaffected by the pesticide treatments. In the autumn-sampled soil, there was significantly less NH4-N in the aldicarb-treated soil. It is possible that this was due to immobilization by the increased microbial biomass in these treatments, and did not represent a loss to the soil system. The continuous use of these pesticides, either singly or in combination, therefore had no measurable long-term harmful effects on the soil microbial biomass or its activity, as assessed by C or N mineralization.
In grassland ecosystems, symbiotic associations between plants and mycor- rhizal fungi are widespread and have important influences on the life histories, demography, and species interactions of plants, and on belowground ecosystem processes. To assess the consequences of the symbiosis at the plant community level, we conducted a 5-yr field experiment in tallgrass prairie to investigate the influence of arbuscular mycorrhizal fungi on plant species composition, relative abundances, and diversity. Replicate plots in which mycorrhizal fungi were suppressed with benomyl application every two weeks during each growing season, were compared to nontreated mycorrhizal control plots on six watershed units at the Konza Prairie in northeastern Kansas. Benomyl successfully reduced mycor- rhizal colonization to
Mycorrhizal fungi form a symbiotic association with the roots of most plants, and significantly alter the morphology and physiology of the plant. Among other physiological changes, root exudation is qualitatively and quantitatively altered, and thus the microbial composition of the rhizosphere changes. The kinds of microbial interactions that occur in the ‘mycorrhizosphere’ are often reflected in plant responses as a result of the combination of mycorrhizae and their microbial associates. Mycorrhiza-microbial interactions may be direct between organisms, or indirect as mediated by the host plant. For example, plant growth and health may be influenced when mycorrhizal fungi interact with the general microflora, or with specific microbes such symbiotic and free-living nitrogen-fixing bacteria, nutrient solubilizing bacteria, fungal and bacterial biocontrol agents, and other fungi. These associations and interactions occur naturally but to varying degrees in most soils. Those with positive effects on crop plants can be managed by inoculation with microbial combinations selected for their compatibility and combined effects.
Maize (Zea mays L. cv. Alize) plants were grown in a calcareous soil in pots divided by 30-m nylon nets into three compartments, the central one for root growth and the outer ones for hyphal growth. Sterle soil was inoculated with either (1) rhizosphere microorganisms other than vesicular-arbuscular mycorrhizal (VAM) fungi, (2) rhizosphere microorganisms together with a VAM fungus [Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappel], or (3) with a gamma-irradiated inoculum as control. Plants were grown under controlled-climate conditions and harvested after 3 or 6 weeks. VAM plants had higher shootroot ratios than non-VAM plants. After 6 weeks, the concentrations of P, Zn and Cu in roots and shoots had significantly increased with VAM colonization, whereas Mn concentrations had significantly decreased. Root exudates were collected on agar sheets placed on the interface between root and hyphal compartments. Six-week-old VAM and non-VAM plants had similar root exudate compositions of 72–73% reducing sugars, 17–18% phenolics, 7% organic acids and 3% amino acids. In another experiment in which root exudates were collected on agar sheets with or without antibiotics, the amounts of amino acids and carbohydrates recovered were similar in VAM and non-VAM plants. However, threeto sixfold higher amounts of carbohydrates, amino acids and phenolics were recovered when antibiotics were added to the agar sheets. Thus, the high microbial activity in the rhizosphere and on the rhizoplane limits the exudates recovered from roots.
External hyphae of vesicular-arbuscular mycorrhizal (VAM) fungi were quantified over a growing season in a reconstructed tallgrass prairie and an ungrazed cool-season pasture. In both sites, hyphal lengths increased throughout the growing season. Peak external hyphal lengths were 111 m cm–3 of soil in the prairie and 81 m cm–3 of soil in the pasture. These hyphal lengths calculate to external hyphal dry weights of 457 g cm–3 and 339 g cm–3 of soil for prairie and pasture communities, respectively. The relationships among external hyphal length, root characteristics, soil P and soil moisture were also determined. Measures of gross root morphology [e.g., specific root length (SRL) and root mass] have a strong association with external hyphal length. Over the course of the study, both grassland communities experienced a major drought event in late spring. During this period a reduction in SRL occurred in both the pasture and prairie without a measured reduction in external hyphal length. Recovery for both the pasture and prairie occurred not by increasing SRL, but rather by increasing external hyphal length. This study suggests that growth is coordinated between VAM hyphae and root morphology, which in turn, are constrained by plant community composition and soil nutrient and moisture conditions.
Experimental microcosms (40 X 52 X 32 cm) containing an assemblage of eight tallgrass prairie grass and forb species in native prairie soil were maintained under mycorrhizal (untreated control) or mycorrhizal-suppressed (fungicide-treated) conditions to examine plant growth, demographic, and community responses to mycorrhizal symbiosis. The fungicide benomyl successfully reduced mycorrhizal root colonization in the fungicide-treated microcosms to only 6.4% (an 83% reduction relative to mycorrhizal controls). Suppression of mycorrhizas resulted in a 31% reduction in total net aboveground plant production and changes in the relative production of C4 and C3 plants. The C4 tallgrasses Andropogon gerardi and Sorghastrum nutans produced less plant biomass in the fungicide-treated microcosms, and had a greater ratio of reproductive to vegetative biomass. Cool-season C3 grasses, Koeleria pyramidata and Poa pratensis accumulated more biomass and were a significantly greater proportion of total community biomass in mycorrhizal-suppressed microcosms. Forbs showed variable responses to mycorrhizal suppression. The two legumes Amorpha canescens and Dalea purpurea had significantly lower survivorship in the fungicide-treated microcosms, relative to the controls. The results confirm the high mycorrhizal dependency and growth responsiveness of dominant prairie grasses, and indicate that differential growth and demographic responses to mycorrhizal colonization among species may significantly affect plant productivity and species relative abundances in tallgrass prairie.
Symbiotic associations between plants and arbuscular mycorrhizal fungi are ubiquitous and ecologically important in many grasslands. Differences in species responses to mycorrhizal colonization can have a significant influence on plant community structure. The growth responses of 36 species of warm- and cool-season tallgrass prairie grasses and 59 tallgrass prairie forbs to arbuscular mycorrhizal (AM) fungal colonization were assessed in greenhouse studies to examine the extent of interspecific variation in host-plant benefit from the symbiosis and patterns of mycorrhizal dependence among host plant life history (e.g., annual, perennial) and taxonomic (e.g., grass, forb, legume, nonlegume) groups and phenological guilds. There was a strong and significant relationship between phenology of prairie grasses and mycorrhizal responsiveness, however this relationship was less apparent in forbs. Perennial warm-season C(4) grasses and forbs generally benefited significantly from the mycorrhizal symbiosis, whereas biomass production of the cool-season C(3) grasses was not affected. The root systems of the cool-season grasses were also less highly colonized by the AM fungi, as compared to the warm-season grasses or forbs. Unlike the native perennials, annuals were generally not responsive to mycorrhizal colonization and were lower in percentage root colonization than the perennial species. Plant growth responsiveness and AM root colonization were positively correlated for the nonleguminous species, with this relationship being strongest for the cool-season grasses. In contrast, root colonization of prairie legumes showed a significant, but negative, relationship to mycorrhizal growth responsiveness.
Because research on nematode involvement in trophic interactions, foodweb structure, and biodiversity is constrained by lack of an overview of nematode feeding habits, this outline presents a consensus of current thought on nematode feeding habits. The source of food is fundamental to trophic interactions and provides the basis for our definitions of the essential feeding types: 1) plant feeder, 2) hyphal feeder, 3) bacterial feeder, 4) substrate ingester, 5) predator of animals, 6) unicellular eucaryote feeder, 7) dispersal or infective stage of parasites, and 8) omnivore. Lists of families and genera with their presumed feeding types are given. Major gaps in knowledge of feeding in the smaller tylenchids and many dorylaims are noted.
This is the first volume in the Long-Term Ecological Research (LTER) Network Series. Established in 1980, the LTER program is exploring a wide variety of biomes characteristic of the United States and developing a baseline for ecosystem dynamics over long time periods and broad spatial scales. The volumes in this series will include both comprehensive reviews of research from particular sites and topical overviews which use data from many sites to examine important questions in ecology. This volume, which focuses on the Konza Prairie in northeastern Kansas, is a synthesis of over 15 years of research in pristine tallgrass prairie. It gives a comprehensive site description and summarizes the key long-term studies that form the basis for the Konza Prairie Long-Term Ecological Research Program. It then presents a synthesis of the many research areas involved and develops a foundation for future ecological studies in tallgrass prairie. With over 150 figures and tables, chapters that encompass microbial through landscape scales, and an emphasis on lessons learned from long-term studies, this volume provides a unique and comprehensive perspective on the structural and functional ecology of the grassland ecosystem that once covered most of central North America.
Warm-seaon tallgrass prairie grasses rely heavily on vesicular-arbuscular mycorrhizal symbiosis, while cool-season grasses are less dependent on the symbiosis. Mycorrhizal activity was greater in cool-season grasses than in warm-season grasses early (April and May) late (December) in the growing season, while mycorrhizal activity in roots of the warm-season grasses was greater in midseason (July and August). Active mycorrhizal colonization was relatively high in both groups of grasses late in the growing season, suggesting that mycorrhizal fungi may proliferate internally or may be parasitic at this time. Total Glomales sporulation was generally greater in the rhisozphere of cool-season grasses in June and in the rhizosphere of the warm-season grasses in October. For both groups of grasses, mycorrhizal dependence was greatest at the temperature that favoured growth of the host. Results suggest that mycorrhizal fungi are active in roots when cool-season grasses are growing and that cool-season grasses may receive benefit from the symbiosis under relatively cool temperature regimes. -from Authors
Chemical exclusion of fungi, using fungicides is probably the only practical method of studying the overall role of these organisms in natural vegetation. No currently available systemic fungicide is active against both lower and higher fungi and only one compound shows significant basipetal translocation. On the one hand, these restrictions may allow the effects of different fungal groups to be isolated. On the other, the chemical exclusion of a broad range of fungi will require the use of at least 2 compounds and both root and shoot applications. -from Authors
Synopsis
The likely consequences of disturbance of the mycorrhizal mycelial network in soil are considered, emphasis being placed on the impact of small-scale events upon infection in vesicular-arbuscular and ectomycorrhizal systems. The importance of the intact network is stressed and the effects of its disruption upon infection processes and upon the nutrition of natural plant communities and of crops is analysed. It is considered that the most serious effect of disturbance will be to reduce the inoculum potential of the fungi and hence to decrease the vigour of infections that occur. The impact of these effects is likely to be felt most seriously at the stage of seedling establishment, and the interactions between disturbance events, mycorrhizal infection and plant successional processes are discussed.
1. The fungicide benomyl was applied to a lichen-rich plant community growing on a sandy soil in Suffolk, UK, once a month from November to May for 3 years. Benomyl application eliminated the lichen Cladonia rangiformis from the community and resulted in a large increase in the cover of the moss Ceratodon purpureus. There were also changes in the frequencies of several higher plant species in response to benomyl application. 2. There were significant reductions in mycorrhizal colonization following fungicide application in Crepis capillaris and Erodium cicutarium, which were reduced in abundance by benomyl application, whereas the non-mycorrhizal Arenaria serpyllifolia and Rumex acetosella increased in abundance in fungicide-treated plots. Changes in the frequencies of mycorrhizal higher plant species were negatively correlated with reductions in mycorrhizal colonization of their root systems. There was also a 22% increase in plant species density m-2 in plots treated with benomyl. 3. Ordination analyses showed that 60% of the variation in the vegetation data set could be accounted for by Carex arenaria, Cladonia rangiformis and R. acetosella on the first component axis, and by Ceratodon purpureus, Hypnum cupressiforme var. lacunosum and Cerastium fontanum on the second axis, and demonstrated that the two sets of plots were vegetationally distinct. 4. The results show that two groups of symbiotic fungi are important regulators of plant community structure: the lichen C. rangiformis was a keystone organism in the community studied and appeared to be able to suppress the moss C. purpureus, and arbuscular mycorrhizal fungi appeared to play a significant role in determining the interspecific competitive abilities of higher plant species.
1 We applied the fungicides benomyl and prochloraz to natural populations of the winter annual grass Vulpia ciliata ssp. ambigua at three sites in East Anglia, UK, in an attempt to assess the relative losses and benefits to the plant caused by root pathogenic and arbuscular mycorrhizal fungi in the field, and to explore the possibility that the two groups of fungi interact to determine plant fitness.
2 Prochloraz did not affect fungal colonization of roots or plant performance, but benomyl reduced arbuscular mycorrhizal colonization in the roots of V. ciliata. However, total plant biomass, shoot and root biomass and phosphorus inflows were unaffected in benomyl treated plants. The only direct effect of benomyl on the plants was to increase fecundity (seed number) at one site.
3 These null or positive effects of benomyl on plant performance may be explained by the deleterious effects of the fungicide on the abundance of other root-inhabiting fungi such as Fusarium oxysporum or Embellisia chlamydospora isolated from the roots of V. ciliata.
4 Whilst direct comparisons of plant performance with the abundance of root-inhabiting fungi showed that arbuscular mycorrhizal fungi appeared to play a relatively insignificant role in the ecology of the plant, the abundance of root pathogenic fungi such as F. oxysporum E. chlamydospora and a species of Phoma was found to be negatively correlated with plant fecundity, even though these fungi produced asymptomatic infections.
5 The poor relationship between plant fecundity and benomyl application contrasted markedly with the clear effects of benomyl on root pathogenic and arbuscular mycorrhizal fungi, and with the clear impact of the root pathogenic fungi on plant fecundity. The most likely explanation for this apparent paradox was that the two groups of fungi were in some way interactive, and that when both groups were reduced in abundance, the resultant effects on the plants were neutral.
6 A generalized linear model applied to the fecundity data appeared to indicate that the arbuscular mycorrhizal fungi interacted directly with the root pathogenic fungi, and improved fecundity by interfering with the negative effects of the pathogens. We concluded that asymptomatic root pathogenic fungi were important determinants of fitness in V. ciliata and that the main benefit supplied by arbuscular mycorrhizal fungi to the plant was apparently in protection from pathogenic attack, not in phosphorus uptake. The implications of the results for plant population dynamics are discussed.
Methods to estimate the amount of N mineralized from soil organic matter are needed for accurate fertilizer recommendations. The authors conducted laboratory and field studies to evaluate the method of Stanford and Smith for predicting N mineralized under field conditions. Soil samples were incubated to determine their N mineralization potentials and first-order rate constants of mineralization. To predict N mineralized in the field, the rate constants of mineralized predicted with the N mineralization potentials and adjusted rate constants were further adjusted by soil water content. Nitrogen mineralized in the field was measured in sorghum (Sorghum bicolor (L.) Moench) plots established on Haynie, Kahola, and Richfield soils in 1983 and 1984. Nitrogen mineralized was also measured in fallow plots on Haynie and Wymore soils in 1984. The method only accurately predicted the amount of N mineralized in 104 d in a fallow plots on Haynie soil. In all other cases, the method significantly overpredicted by 67 to 343% the amounts of N mineralized in the field. Among possible causes for the overpredictions may be an improper soil water content factor and the drying and sieving of the samples before incubation.
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Using the most probable number method, differences in inoculum potential between six vesicular‐arbuscular (VA) mycorrhizal fungal isolates were demonstrated. Inoculum of Glomus mosseae had the highest inoculum potential while G. constrictus , and G. fasciculatus isolate 92 , and isolate 0–1 were approximately 1/5, 1/6 and 1/12 as effective. G. fasciculatus isolate 185 and G. epigaeus were approximately 1 /50 as effective. These differences were not correlated with differences in spore viability or germinability since approximately 75 % germination occurred in all species after 3 weeks. While G. mosseae has the largest spore size and had the highest inoculum potential, no further correlation between spore size and inoculum potential was observed. The rate of increase of infection by these six VA mycorrhizal fungi differed more when equal spore numbers were used as inoculum than when equalized inoculum potentials were used. The percentage root infection, subjected to the multiple infection correction, was regressed against log of inoculum density and yielded slopes of 063 to 070 for all VA mycorrhizal fungi tested. The inoculum density‐infection relationships of mycorrhizal fungi are discussed with respect to Baker's epidemiological models.
Microbial biomass estimated by CO2 evolution following fumigation was 2.5–14.7 times greater than that estimated by direct microscopy in prairie soil. Bacteria, fungi and protozoa were counted by direct microscopy before, during and periodically for 10 days following chloroform fumigation and compared with microbial biomass as estimated by CO2 evolution and N mineralization following chloroform fumigation. Protozoan populations were reduced to below detection levels immediately after fumigation and remained below detection levels during incubation following fumigation. Bacterial and fungal populations were reduced by fumigation to 37–79% of their original populations but usually recovered to their initial numbers by the second day following fumigation. In one case protozoa contributed up to 74 μg C, or about half of the total microbial biomass, to CO2 evolution following fumigation.Microbial biomass was estimated in soil wetted to 60% of water-holding capacity (WHC) 1 wk or 1 day before fumigation. Microbial activity changed during the 1 wk incubation before fumigation but not total microbial biomass determined by microscopy.The ratio of CO2 evolved-to-N mineralized followed fumigation changed in direct proportion to the ratio of fungal-to-bacterial biomass present in the soil before fumigation. Although more experiments with different soils should be performed, these results indicate that CO2 evolved or N mineralized varies with the ratio of fungal-to-bacterial biomass initially present.
An incubation experiment was performed with two soils and five pesticide treatments (benomyl, isoproturon, simazine, dinoterb and chloroform). Microbial biomass C and N was estimated by fumigation-extraction (FE). Two modifications of the substrate-induced respiration (SIR) method were used: (1) a continuous flushing system and (2) a static system with soil slurry. In addition, CO2 production was measured. Estimates of biomass C by the two SIR methods were generally higher than those obtained by the FE method. The two SIR measurements and the two biomass estimates were closely correlated, indicating a similar response to pesticide treatments. Pesticide application almost always reduced the size of the microbial biomass. Of the different ways of measuring biomass, the FE method revealed the largest number of significant differences from the nil treatment. The biomass C-to-N ratio was only slightly influenced by soil or pesticide treatments. Apart from the benomyl treatment, pesticide application always increased soil respiration during the 0-10 day incubation.
PLANTS and soils are a critically important element in the global carbon–energy equation. It is estimated that in forest ecosystems over two-thirds of the carbon is contained in soils and peat deposits1. Despite the importance of forest soils in the global car-bon cycle, fluxes of carbon associated with fundamental processes and soil functional groups are inadequately quantified, limiting our understanding of carbon movement and sequestration in soils. We report here the direct measurement of carbon in and through all major pools of a mycorrhizal (fungus-root) coniferous seedling (a complete carbon budget). The mycorrhizal symbiont reduces over-all retention of carbon in the plant–fungus symbiosis by increasing carbon in roots and below-ground respiration and reducing its retention and release above ground. Below ground, mycorrhizal plants shifted allocation of carbon to pools that are rapidly turned over, primarily to fine roots and fungal hyphae, and host root and fungal respiration. Mycorrhizae alter the size of below-ground carbon pools, the quality and, therefore, the retention time of carbon below ground. Our data indicate that if elevated atmos-pheric CO2 and altered climate stressors alter mycorrhizal colonization in forests, the role of forests in sequestering carbon could be altered.
Organophosphate (isofenphos) and carbamate (carbaryl) insecticides were used. Modest changes in nematode and arthropod densities did not result in any changes in plant standing crops. A small but statistically significant increase in detritus standing crops occurred during the 1st year in treatments that reduced nematode and arthropod densities, but this effect disappeared in the 2nd year when densities of native earthworm species (Diplocardia spp.) became more abundant in these plots. A European earthworm, Aporrectodea turgida, also became more abundant in plots treated with carbaryl (which reduced densities of canopy arthropods), but not in plots treated with isofenphos. The earthworm response is probably the result of release from negative interaction(s) with the arthropods. -from Authors
A new method for the determination of biomass in soil is described. Soil is fumigated with CHCl3 vapour, the CHCl3 removed and the soil then incubated. The biomass is calculated from the difference between the amounts of CO2 evolved during incubation by fumigated and unfumigated soil. The method was tested on a set of nine soils from long-term field experiments. The amounts of biomass C ha−1 in the top 23 cm of soil from plots on the Broadbalk continuous wheat experiment were 530 kg (unmanured plot), 590 (plot receiving inorganic fertilizers) and 1160 (plot receiving farmyard manure). Soils that had been fallowed for 1 year contained less biomass than soils carrying a crop. A calcareous woodland soil contained 1960 kg biomass C ha−1, and an unmanured soil under permanent grass 2020. The arable soils contained about 2% of their organic C in the biomass; uncultivated soils a little more—about 3%.
S ummary
A mixture of bacteria and a vesicular‐arbuscular mycorrhizal fungus isolated from field‐collected sods of blue grama ( Bouteloua gracilis (H.B.K.) Griffiths) were tested for their interaction in the rhizosphere of pot‐grown blue grama plants. Populations of the inoculated bacterial species and actinomycete populations, as influenced by the presence or absence of Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe, were enumerated by dilution plate counts from rhizosphere and non‐rhizosphere soil samples. Total bacterial counts and the population of one bacterial species in the non‐rhizosphere soil of pots containing plants were significantly greater than in soil of pots without plants. The population of two bacterial species and actinomycetes were not significantly different in the non‐rhizosphere soil of both mycorrhizal and non‐mycorrhizal plant treatments when compared to the soil of pots without plants. In the rhizosphere of mycorrhizal plants, the total bacterial population and colony counts of one of the four bacterial isolates, when expressed as colony‐forming units (CFU) per gram of root dry weight, were significantly reduced compared with controls. The numbers of CFU per gram of rhizosphere soil of one bacterial species were significantly increased by the presence of the mycorrhizal fungus. Although no significant negative correlation was observed between populations of bacterial species in the rhizosphere soils, significant positive correlations between specific bacterial populations depended on whether or not the roots were mycorrhizal.
Potted soybean (Glycine max (L.) Merr.) plants were grown in P-fertilized (+P) or low-P soil (-P), or colonized in -P soil by one of the arbuscular mycorrhizal (AM) fungi Glomus etunicatum (Ge), Glomus mosseae (Gm), or Gigaspora rosea (Gr). Treatment effects on plant development, on the soil microflora, and on the status of water-stable soil aggregates (WSA) were evaluated for all 5 treatments or for the 3 AM treatments alone. Dry weights of the AM plants, as a group, were half-way between the dry weights of the +P and -P plants, but within the AM group, Gm plants had the highest pod dry weights and pod/stem and root/stem ratios and the lowest specific root lengths, while Ge plants had high stem dry weights and were highly nodulated. High reproductive development and coarse roots in the Gm plants were associated with the most extensive growth of AM soil hyphae (km pot-1: Gm, 20; Gr, 12; Ge, 8), while nodulation was inversely related with AM-colonized root length. The soils colonized by AM fungi had significantly higher levels of WSA (size classes 1 to 2 and 2 to 4 mm), and within the larger size class, Gm soils had the highest percentage of WSA. Proliferation (plate counts) of Gram positive (G+) and Gram negative (G-) bacteria, Arthrobacter sp. (G+), and Pseudomonas sp. (G-) was greatest in the -P soils, but the bacterial populations of the +P and the AM soils were generally not significantly different. There were, however, differences among the AM treatments, where Gm soils had the lowest G- bacterial populations, while Ge soils had the highest populations of both G+ and G- bacteria. Correlations between plant and soil traits indicated that interactions within the plant-soil system were mediated by the AM fungi.
The effects of biocide use on nontarget organisms, such as arbuscular mycorrhizal (AM) fungi, are of interest to agriculture, since inhibition of beneficial organisms may counteract benefits derived from pest and disease control. Benomyl, pentachloronitrobenzene (PCNB) and captan were tested for their effects on the germination and early hyphal growth of the AM fungiGlomus etunicatum (Becker & Gerd.),Glomus mosseae (Nicol. & Gerd.). Gerd. and Trappe andGigaspora rosea (Nicol & Schenck) in a silty-clay loam soil placed in petri plates. Application of fungicides at 20 mg active ingredient (a.i) kg–1 soil inhibited spore germination by all three AM-fungal isolates incubated on unsterilized soil for 2 weeks. However, fungicides applied at 10 mg a.i. kg–1 soil had variable effects on AM-fungal isolates. Fungicide effects on germination and hyphal growth of G.etunicatum were modified by soil pasteurization and CO2 concentration in petri plates and also by placing spores below the soil surface followed by fungicide drenches. Effects of fungicides on mycorrhiza formation and sporulation of AM fungi, and the resulting host-plant response, were evaluated in the same soil in associated pea (Pisum sativum L.) plants. Fungicides applied at 20 mg a.i. kg–1 soil did not affect the root length colonized byG. etunicatum, but both benomyl and PCNB reduced sporulation by this fungus. Benomyl and PCNB reduced the root length colonized byG. rosea at 48 and 82 days after transplanting. PCNB also reducedG. mosseae-colonized root length at 48 and 82 days, but benomyl only affected root length colonized byG. mosseae at the earlier time point. Only PCNB reduced sporulation byG. mosseae, consistent with its effect on root length colonized by this fungus. captan reduced the root length colonized by G. rosea at 48 days, but not at 82 days, and reduced colonization byG. mosseae at 82 days, but not at 48 days. Captan did not affect sporulation by any of the fungi.G. rosea spore production was highly variable, but benomyl appeared to reduce sporulation by this fungus. Overall,G. etunicatum was the most tolerant to fungicides in association with pea plants in this soil, andG. rosea the most sensitive. Benomyl and PCNB were overall more toxic to these fungi than captan. Interactions of AM fungi and fungicides were highly variable and biological responses depended on fungus-fungicide combinations and on environmental conditions.
The major source of substrates for microbial activity in the ectorhizosphere and on the rhizoplane are rhizodeposition products. They are composed of exudates, lysates, mucilage, secretions and dead cell material, as well as gases including respiratory CO2. Depending on plant species, age and environmental conditions, these can account for up to 40% (or more) of the dry matter produced by plants. The microbial populations colonizing the endorhizosphere, including mycorrhizae, pathogens and symbiotic N2-fixers have greater access to the total pool of carbon including that recently derived from photosynthesis. Utilization of rhizodeposition products induces at least a transient increase in soil biomass but a sustained increase depends on the state of the native soil biomass, the flow of other metabolites from the soil to the rhizosphere and the water relations of the soil. In addition, the phenomena of oligotrophy, cryptic growth, plasmolysis, dormancy and arrested metabolism can all influence the longevity of rhizosphere organisms. With this background, microbial growth in the rhizosphere will be discussed.
Approaches suitable for the study on the functioning of vesicular-arbuscular mycorrhizas (VAM) in the field are discussed,
with emphasis on those VAM-specific processes which may influence P nutrition of crops. These processes are related to hyphal
P transport in particular, and conventional techniques based on comparisons between VAM-colonized plants and uncolonized controls
are therefore of limited value in such studies. Novel methods are described, which make use of a two-compartment principle
and isotopes to directly measure the P transport by the VAM mycelium under controlled conditions and in the field. The principle
of isotopic equilibrium may be used for indirectly quantifying the relative amounts of P supplied by hyphae and by roots of
VAM plants. The hyphal contribution to P uptake may also be assessed by comparing hyphal uptake of 32P from a hyphal compartment with uptake of 33P from a corresponding compartment containing both roots and hyphae. These methods are suitable for a functional characterization
of VAM fungi and for identifying constraints to the functioning of VAM.
A method is described for the rapid and objective estimation of the amount of carbon in the living, non-resting microbial biomass of soils. The method, which is based on the initial respiratory response of microbial populations to amendment with an excess of a carbon and energy source, was quantified using an expanded version of Jenkinson's technique.The simultaneous application of the two methods to 50 soil samples showed a highly significant correlation (r = 0.96) between both. From this correlation it could be deduced that at 22°C, a substrate-induced maximal respiratory rate of 1 ml CO2· h−1 corresponds to c. 40 mg microbial biomass C. Evidence supporting these results was obtained from pure culture studies. The various soil types investigated were collected from agricultural as well as forest sites and they contained between 15 and 240 mg microbial C·100g dry soil−1. The respiratory method provides reproducible estimates of biomass size within 1–3 h after soil amendment. It can be combined without difficulty with a selective inhibition method for determination of bacterial and fungal contributions to soil metabolism.
Improvements to the selective inhibition technique of Anderson and Domsch (Arch. Mikrobiol. 93, 113–127, 1973) are described. Microbial anabolic metabolism in soil was stimulated by glucose addition. Simultaneous addition of eukaryote and/or prokaryote-specific antibiotics, which inhibit anabolic metabolism, fractionated the microbial biomass on the basis of selective respiratory inhibition. The improvements proposed here are that: (1) the glucose and antibiotic(s) are dissolved in water prior to addition to soil (the ratio of glucose and antibiotic(s) solution to dry weight of soil being 2 ml:l g); (2) maximal respiratory inhibition is required for each antibiotic; and (3) soil + glucose and antibiotic(s) solution are incubated for 3.5 h prior to the assay. The improved selective respiratory inhibition technique gave eukaryote:prokaryote (fungal:(discrete bacteria + actinomycete)) respiratory ratios of 1 for two soils under pasture, but failed to work on an arable soil. Mycelial (fungal + actinomycete):discrete bacterial biomass C ratios derived by the biovolume procedure were 1 and 2 for the soils under pasture and 3 for the arable soil.
Arbuscular mycorrhizal (AM) cucumber seedlings and uncolonized controls were grown in growth chambers which allowed separation of compartments with roots from compartments with the extraradical mycelium alone. Two fungi, Glomus invermaium Hall and G. caledonium (Nicol. and Gerd.) Trappe and Gerdemann, were used. Bacterial numbers (direct and viable count) and activities (thymidine incorporation) were highest in the root compartment, but were not affected by the AM mycelium after 30 days of plant growth. The soil was stored after harvest for 16 d at 13°C to study the effect of disconnected mycorrhizal hyphae on bacterial activity. This treatment increased bacterial activity in mycorrhizal treatments compared to non-mycorrhizal control soils. The highest increase was found in the root compartment. The bacterial community structure was studied by analyzing the phospholipid fatty acid (PLFA) pattern. The bacteria specific PLFAs cy17:0 and cy19:0 increased in both experiments in the root compartments. The PLFAs 15:0 and 17:0, which are usually considered to be bacteria specific, also increased due to the presence of roots, but it was shown that these fatty acids were present in aseptically grown cucumber roots, and thus not bacteria specific. No bacterial PLFAs were affected by the presence of mycorrhiza.
14C-labelled glucose and 15N-labelled KNO3 were added to soil and the microbial biomass during 42 days' incubation was estimated using the chloroform fumigation-incubation method (CFIM). By day 1, most of the glucose (1577 μgCg−1 soil) was metabolized and 110 μg NO−3-Ng−1 soil were immobilized. In situ values for the proportions of biomass C (kC) and biomass N (kN) mineralized during the 10 days after CHCl3 fumigation were determined on the basis that the immobilized labelled C and N remaining in the soil at this time were present as living microbial cells and their associated metabolites. The tracer data indicated that biomass C could be calculated by applying a kc value of 0.41 to the CO2-C evolved from the fumigated sample without subtraction of an unfumigated “control”. Biomass N was estimated from the net NH4−-N accumulation during the fumigation-incubation. The problem of reimmobilization of NH+4-N where organisms of wide C:N ratio occur was overcome by adjusting the value of kN according to the ratio of CO2-C evolved: net NH4+-N accumulated during the fumigation-incubation (CF:NF).A CF:NF ratio of 6:1 resulted in a kN of 0.30 whereas a ratio of 13:1 indicated a kN of 0.20.
Nematodes and vesicular-arbuscular mycorrhizal (VAM) fungi often occur in the rhizosphere and roots of plants and therefore frequently encounter each other. Mycorrhizal fungi benefit the plant by increasing the absorption of nutrients and water and by protecting the root from soil-borne diseases. Nematodes can interfere with any of these functions. Vesicular-arbuscular fungi do not colonize regions infected by endoparasitic nematodes, and nematodes rarely infect regions colonized by VA fungi. Nematode-mycorrhizal interactions appear to be very specific and highly dependent on the particular association of plant cultivar, fungal and nematode species, the order of colonization by the symbionts and the soil nutrient level. Plant-parasitic nematodes generally reduce the amount of benefit gained by the association with the fungus. However, VA mycorrhizae usually more than compensate for the amount of nematode damage sustained by non-mycorrhizal plants, since their function is generally not affected except in close proximity to the nematode feeding site. Mycorrhizal fungi and endoparasitic nematodes are often mutually inhibitory, each reducing the population of the other. In other cases, the stimulation of root growth by the fungus provides greater habitat and nematode populations increase. Some studies have also observed increased spore production and higher percent root colonization by the fungus when nematodes were present. Fungal-feeding nematodes may feed on the fungal symbiont to such an extent that in vitro cultures may be killed and in vivo infections significantly reduced. In some studies, plants were severely disadvantaged by this grazing pressure on the fungus, while in others plant growth was not affected. Under heavy grazing pressure by fungal-feeding nematodes, sufficient hyphae may be destroyed to limit phosphorus uptake to a level inadequate for nodulation in legumes.
Barley plants were grown for up to 16 days in solution culture either under axenic conditions or in the presence of a mixed population of microorganisms. The quantities of soluble carbohydrate released by the roots grown in the absence of microorganisms and the numbers of bacteria which developed in the inoculated solutions were determined. Except for the first 4 days after germination, a greater biomass was produced than could be accounted for by the utilization of the carbohydrates released by the roots grown in the absence of microorganisms; this supports the view that the microorganisms stimulate the loss of soluble organic materials. These results are considered in relation to microbial activity in the soil and in particular to the significance of N2 fixation by free-living rhizosphere bacteria in the nitrogen economy of plants.
Oxytetracycline-penicillin (combined), captan, fumigillan and dimethoate-carbofuran (combined) were applied to forest soils to test their effects on soil populations of active and total bacteria, active and total fungi, protozoa, nematodes and microarthropods. All biocides significantly reduced the populations of target organisms, except dimethoate-carbofuran, which failed to reduce the number of microarthropods. All biocides also affected populations of non-target organisms. Oxytetracycline-penicillin reduced lengths of active hyphae. Captan reduced nematode and bacterial numbers. Fumagillin reduced active hyphal lengths and the number of nematodes and total bacteria. Dimethoate-carbofuran reduced active hyphal lengths and the number of active bacteria.