Mushrooms for Soil Improvement: History
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The main fields in which mushroom cultivation could improve soil quality may include (1) soil erosion control, (2) improving soil aggregates, (3) increasing soil organic matter, (4) enhancing soil nutrition, (5) promoting C, and NPK cycling, and (6) the bioremediation of polluted soils.

  • Soil
  • mushroom

1. Controlling Soil Erosion

Soil erosion is considered an important key factor leading to poor soil health and the productivity loss of crops, particularly under heavy rainfall conditions. To control soil erosion, the biological approach may be a crucial route, which represents the promotion of the intensive growth of mushroom mycelium in agricultural soils [83,84]. Growing mushrooms in agricultural soils has direct and indirect benefits on eroded soil, which may include the binding of mushroom mycelia of soil particles, establishing strong cord-forming mycelial networks, and forming soil aggregates as a direct mechanism, whereas the indirect mechanism may include exudating the fungal hyphae with some extracellular compounds such as the hydro-phobin group (e.g., glomalin) and polysaccharides into soils, which boost soil organic matter [85]. Forming hydrophobicity and adhesion exopolymers of fungal mycelium is the proposed mechanism for enhancing soil erosion resistance by mushrooms [84]. Therefore, mushrooms can control and limit soil erosion through forming a net from soil aggregate clumps and fungal hyphae, which contain organic matter, lipids, protein, water, nutrients, and minerals [83,86]. This net may result from the interaction between plants and mushrooms or microbes (from one side) and the mineral particles and soil microbes (from the other side), which plays a major role in forming the soil. Soil fungi are well-known by their production of a non-water soluble called glomalin as a highly persistent glycol-protein (e.g., mushrooms or mycorrhizae), which can maintain the structure of soil and its fertility [86].

2. Improving Soil Aggregates

The life cycle of a mushroom starts with a spore (i.e., a diameter of a few microns). This spore swells, germinates, and elongates to form filamentous cells in humid and nutrient-rich environments, called a “hypha”. After growing the hypha, they elongate and form a network of interconnected hyphal threads called a “mycelium” [87]. The cultivation of mushroom species is useful for soil and its quality (e.g., the good soil aggregation), because mushrooms are considered saprobic fungi living on organic matter that exist in soil and/or the compost layers [83]. Forming the “cord-forming mycelial network” occurs during the cultivation process of mushrooms, when mushroom mycelium grows in compost, seeking nutrients. Mycelia grow in the soil layers after the complete forming of the fungal mycelial network and once it has fully colonized the compost layers. So, mushrooms have a very strong relationship with soil; mushrooms can obtain nutrients and carbon from the soil, and the soil can receive many release-fungal-based organic compounds from the mushrooms [87].
The fungal hyphae can penetrate the soil layers and support the formation of soil aggregates by their hyphal networks, which can chemically and/or physically bind soil particles [88,89]. Thus, mushrooms can improve the overall soil quality by forming networks of cored-forming mycelia, which enhance soil aggregations through the increasing abundance of mushroom-hyphae in soils [83]. Hence, forming soil aggregates not only reduces the erosion of soil, but also increases the movement of gases within the soil (mainly O2 and CO2), improving the ability of roots to penetrate different soil systems [90]. Moreover, several microbial dynamic processes in soil could be supported by aggregates, including microbial evolutionary [91], soil carbon sequestration [92], nutrient turnover [93], and gas emissions [83,94]. Regarding applied spent mushroom wastes to soils, they can increase larger stable aggregates (i.e., >2.0 mm), as reported by Udom et al. [95].

3. Increasing Soil Organic Matter Content

Soil organic matter content is a key mechanism for mitigating several soil processes and functions including soil fertility, biota biomass, soil aeration, soil structure, the formation of aggregation, soil erosion, water-storage capacity, and the biodiversity of soil ecosystems [83]. Soils with high organic matter can preserve excellent protection against erosion [96]. Soil organic matter binds their particles with increasing soil moisture content, which prevents soil particles drying out during strong winds or heavy rain events [97]. Mushroom cultivation in soils is an effective approach for promoting soil organic matter content in two main ways: (1) applying fungal-based organic materials (i.e., hyphal exudates and mycelium) and/or (2) applying compost and spent mushroom substrates to the soils [83]. Several studies on the application of the compost of the substrate of mushrooms to soil have confirmed many benefits of organic matter derived from mushrooms to soil and its quality (e.g., [98,99]). More details on the role of applied compost or substrate derived from mushrooms and their impact on soil and cultivated crops can be found in Table 1.
Table 1. List of some published articles concerning applied spent mushroom substrates (SMS) to cultivated or non-cultivated soil under different purposes.
Cultivated Plant or Used
Mushroom for SMS
Soil Properties or Used
Main Purpose of the Application Refs.
I. Applied SMS under cultivated soils    
Paddy rice (Oryza sativa L.) Silty loam, pH (5.58), SOM (1.2 g kg−1), and Cd (72.87 mg kg−1) SMS of both P. eryngii and A. bisporus decreased soil content of Cd by 99% and increased rice yield by 38.8% [100]
Roselle (Hibiscus sabdarifa L.) Loamy sand, pH (7.98), SOM (0.25%) Applied SMS to improve plant growth, soil fertility, and its quality as a biofertilizer [101]
Cucumber (Cucumis sativus L.) Silty, pH (6.12), TOC (11.1 g kg−1) SMS enhanced soil microbial diversity and the activity of enzymes for long-term cultivated cucumber in greenhouse [102]
Barely (Hordeum vulgare L.) Clayey, pH (5.40), initial soil 60 kg N ha−1 and fertilized up to 200 kg N ha−1 Applied SMS (50%) caused a strong shift in soil-rhizosphere microbiota due to release enzymes as root exudates, depending on the kind of applied organic fertilizers [103]
Pumpkin (Cucurbita pepo ssp.) Sandy loam, pH (8.0), N (6.0 mg kg−1) Applied SMS as organic fertilizer is promising under organic farming [104]
Tomato (Solanum lycopersicum L.) Modified paddy straw as substrate Paddy straw based-silica rich SMS of P. ostreatus is effective for plant disease and nutrient management [105]
Lettuce (Lactuca sativa L.) Composted SMS, vermiculite, coir, and perlite at (3:1:1:1) Microbial agents can inhibit potentially pathogenic microbes of plants and increase the efficient utilization of SMS [106]
Cherry tomato (Solanum lycopersicum Mill.) Soil (dystro-ferric red latosol) Co-cultivation at the same bucket tomato and A. bisporus reduced by 60 days and continuous producing mushroom prolonged by 120 days [107]
II. Applied SMS under non-cultivated soils    
SMS provided by Xiangfang edible fungi factory, Harbin, China Sandy, pH (6.83), SOM (38.64 g kg−1) SMS was compared to biochar and lime on reducing Cd-bioavailability by 66.47% and increased soil enzyme activities [108]
Organic amendment (SMS and its biochar) Soil pH (6.83), SOM (38.64 g kg−1), ava. N (115.7 mg kg−1) Applied amendment alleviated Cd and N damage on soil, by increasing microbial biomass and enzyme activities in the soil [109]
SMS-derived biochar Soil pH (4.62), TOC and TN (57.2 and 3.9 g kg−1, resp.) Spent mushroom substrate derived biochar was pyrolyzed at 450 °C can mitigate greenhouse gas emissions [110]
Applied SMS, bacteria of Paracoccus sp., and humic acid PAHs in soil was 1.97 mg kg−1, soil pH (6.71) Bio-degradation of PAHs by humic acid and SMS via soil laccase activity as bioremediation [111]
Abbreviations: soil organic matter (SOM), total organic carbon (TOC), polycyclic aromatic hydrocarbons (PAHs), cadmium (Cd), nitrogen (N), soil acidity (soil pH).

4. Enhancing Bioavailability of Soil Nutrients

A huge amount of wastes or spent mushroom substrates (SMS) result from mushroom cultivation; about 5–6 kg of SMS for production of every kg of fresh mushroom [83]. These substrates contain different nutrients (e.g., NPK) and various organic compounds such as crude protein, carbohydrate, cellulose, lignin, hemicelluloses, and neutral and acid detergent fibers [112]. Dumping or incineration is the current disposing of the majority of spent mushroom substrates [113]; however, many innovative techniques can be applied for the valorization of these wastes, including composting, the production of animal feeds and enzymes, energy production (bioethanol), the cultivation of new mushroom species, packing, and construction materials [112]. On the field scale of mushroom cultivation, SMS can be disposed through composting for biofertilizer, which uses and/or amends the degraded soil in situ [114].
The SMS could be utilized as a biofertilizer because it contains many essential nutrients, besides it being a resource for microbial biomass. Thus, the SMS can enhance the bioavailability of nutrients in the soil as a biofertilizer; consequently, SMS may promote the growth of seedlings and the growing of other mushroom varieties [115,116]. The aged compost of SMS has high macro-nutrient contents (if its age is more than 6 months) compared to a fresh one. This compost could be used as an alternative source of some components of growth media such as peat or perlite, and it is reported to be 30% mixable with SMS compost (and 70% for SMS). This mixture has led to an increase in the germination rate and the morphology of cultivated pepper seedlings [115]. The role of SMS compost was confirmed by many researchers in mitigating stress from Pb or Mn or Zn on Paulownia fortunei seedlings [117,118], Pb-Zn-stress on Macleaya cordata [119], or drought stress on Althaea rosea [120]. For obtaining a healthy SMS compost, biocontrol agents such as Bacillus subtilis and Trichoderma harzianum may need to be added during the compositing process [121].

5. Resorting of Damaged and Polluted Soils

The restoration of damaged soil or the environment through mushroom mycelium has been reported by some investigators due to its strong ability to decompose or degrade many pollutants and wastes. The mode of action of this biodegradation by mushroom mycelium may revert to the formation of complex extracellular enzyme groups [53]. The mycelia of mushroom also have a crucial role in restoring damaged environments in four different ways, including (1) myco-remediation [122] or bioremediation through the decontamination of a certain area by the mycelia, (2) myco-filtration, using mycelia to filter toxic wastes and microorganisms from soil or water medium [123], (3) myco-pesticides, using mycelia to control insect pests [124], and (4) myco-forestry, using mycelia to restore the forests [53]. The previous approaches represent different methods for a clean agroecosystem, which can remove damage in agro-environments after mushroom implementation. Regarding the mode of action of myco-pesticides, this mechanism could increase the biopesticide efficacy through reducing plant diseases by the mycoparasitism, direct antagonism, and induction of resistance [124]. The removal of pollutants using a network of fungal mycelium is called myco-filtration. It is an eco-friendly technology that treats contaminated water/wastewater by calculating the removal efficiency [125]. Myco-forestry is considered a crucial system, which could enhance plant communities and forest ecosystems through different species of mushrooms as an ecological forest management system. A myco-forestry system also can restore the environment through myco-remediation and myco-filtration activities, which clean up toxins in the environment.
Concerning myco-remediation, it is a sustainable approach for the bioremediation of polluted environments using the fungi of mushrooms to remove toxic pollutants through biosorption, bioaccumulation, and bioconversion [126]. This approach could be applied using live and dead mushrooms to myco-mediate the polluted soil [127,128], wastewater [129,130], and lignocellulosic biorefinery sludge [131]. It found that the fungal mycelia act as bio-sorbents to remove polluted metals from industrial wastewaters [130] or through the production of many lignocellulolytic enzymes, removing 90% of organic contaminants [131].

This entry is adapted from the peer-reviewed paper 10.3390/su14074328

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