Plant hosts reported to form ectomycorrhizal association.
Abstract
Deforestation is among the greatest challenges the Earth is facing. The annual deforestation rate is more than 3%. To uplift the economic growth of any country, the forest cover should be at least 25%. To overcome this problem, rapid afforestation and reforestation strategies are required. Inoculation of ectomycorrhizal fungi growing efficiently in the biodiversity-rich regions could be a leading approach in this regard. Several ectomycorrhizal fungi have been reported in association with many coniferous and deciduous tree species growing in these regions. The success of this association is mainly based on the mutual exchange of nutrients between the symbionts. These ectomycorrhizal fungi can mitigate the stress conditions and enhance the seedling survival. Inoculation of these fungi with indigenous tree species of the region can greatly improve plant growth and survival. This symbiosis may play a major role in the function, maintenance, and evolution of biodiversity and ecosystem stability and productivity.
Keywords
- Ascomycota
- Basidiomycota
- Mucoromycota
- mutualistic symbiotic
- temperate
- tropical
1. Introduction
Deforestation is indeed one of the greatest challenges that the Earth is facing, and has several detrimental impacts. The removal of forests results in the destruction of diverse habitats that support a wide range of plant and animal species. Many species, including those unique to specific ecosystems, may face extinction as their habitats disappear. Even if some areas remain untouched, the fragmentation of forests into smaller patches can isolate populations, limit genetic diversity, and make it difficult for species to survive and reproduce.
Deforestation releases stored carbon into the atmosphere, contributing to global warming. It disrupts climate patterns, impacting agriculture, water resources, and settlements. Forests play a crucial role in water cycle regulation, and deforestation leads to altered river flow and increased flooding. The removal of trees weakens soil structure, making areas prone to erosion and landslides, especially in hilly regions. Preserving forests is vital to mitigate these environmental challenges. Many indigenous communities rely on forests for their livelihoods, obtaining food, medicine, and materials for shelter and cultural practices. Deforestation can displace these communities, disrupt their traditional way of life, and lead to the loss of cultural and ecological knowledge. While deforestation may provide short-term economic benefits through activities like logging and conversion of land for agriculture, the long-term consequences can be severe.
Loss of ecosystem services, including clean water, pollination, and climate regulation, can have significant economic impacts. Planting new trees to replace those that have been cut down helps restore ecosystems and mitigate the impacts of deforestation. Reforestation projects are essential for combating climate change and preserving biodiversity. Implementing practices that ensure the responsible use of forest resources, such as selective logging and regeneration plans, can help maintain the ecological integrity of forests while meeting human needs for wood and other products. Supporting and promoting alternative livelihoods for communities dependent on forest resources can reduce pressure on forests. This may involve the development of sustainable agroforestry, ecotourism, or non-extractive economic activities.
An annual deforestation rate exceeds 3%. To uplift the economic growth of any country, the forest cover should be at least 25%. Addressing deforestation requires a holistic approach that considers environmental, social, and economic factors. International collaboration and policies that promote sustainable land use practices are crucial in mitigating the negative impacts of deforestation and promoting a more harmonious relationship between humans and the environment. Rapid afforestation and reforestation strategies are essential and effective remedies to address deforestation and increase forest cover.
Ectomycorrhiza is a type of mutualistic symbiotic association between certain groups of fungi and the roots of higher plants. In this association, the fungi do not penetrate the root cells; instead, they form a mycelium between the cortical cells. This mycelium is known as Hartig’s net. This relationship is beneficial for both partners. The fungus enhances the plant’s nutrient absorption capabilities, especially for minerals like phosphorus and nitrogen, which can be less accessible to the plant in the soil. In return, the plant provides the fungus with carbohydrates produced through photosynthesis. The fungal hyphae form a sheath around the outer surface of the plant root tips, creating a structure known as a “mantle”. The mantle layer offers protection against certain soil-borne pathogens, helping to enhance the plant’s resistance to diseases and helps plants in coping with stress. The hyphae which originate from the mantle layer extend into the soil, forming a dense network around the plant roots to play a role in improving water uptake by the host plant, especially in conditions of water stress [1, 2, 3].
2. Evolution of ectomycorrhiza
Numerous studies propose that diverse ectomycorrhizal associations evolved independently, occurring at least once in the
3. Plants forming ectomycorrhizal association
Approximately 8000 species of seed plants, which represent about 3% of all seed plant species, engage in this type of symbiosis [8, 9]. Even though being a minority among seed plants, these ectomycorrhizal (ECM) species are incredibly significant ecologically and economically. This is because they play a dominant role in forest and woodland ecosystems across much of the Earth’s surface. Their presence shapes these ecosystems and influences the diversity and abundance of other organisms living within them [4]. Despite the prevalence of woody perennials, some non-woody plants also form ectomycorrhizal associations. For example, certain sedges (plants resembling grasses with triangular stems) e.g.,
It is believed that ectomycorrhizal associations are primarily found in temperate and boreal forests, with their presence elsewhere being sporadic and of lesser ecological significance. It is certainly true that dominant tree species in these regions, such as those from the
However, contrary to this belief, extensive portions of land beyond temperate and boreal zones also host vegetation with a significant ectomycorrhizal component. For instance, Arctic and alpine habitats in the northern hemisphere are characterized by dwarf shrub communities dominated by species such as Dryas and Salix, which form ectomycorrhizal associations supporting diverse communities of fungal partners. Similarly, regions with winter-wet ecosystems, such as those found in the Mediterranean region, exhibit a pronounced presence of ectomycorrhizal associations among species like
However, it is in the tropics that the occurrence and importance of ECM host species have been most consistently underestimated. Consider the
Ectomycorrhizas are prevalent in certain members of
Two temperate ectomycorrhizal plant taxa;
Endemic ectomycorrhizal tropical pines like
Family | Genus |
---|---|
Table 1.
4. Fungi forming ectomycorrhizal association
Approximately 5000–6000 fungal species form ectomyorrhizal association with the roots of trees. In recent years, more intensive mycological investigations in tropical forests and studies on hypogeous fungi associated with
The contributing fungi are not evenly distributed over the kingdom
Weiss et al. [23] revealed that the significance of heterobasidiomycetes within the
Certain ectomycorrhizal fungal genera are restricted to particular vegetation types. Members of
With the exception of some Tuber spp. [32], the knowledge of the ecology of ascomycete ECM fungi is very limited. Recent work [33, 34] suggests that the occurrence and importance of the
Division | Family | Genus | Species |
---|---|---|---|
Table 2.
Fungal partners known to form ectomycorrhizal association.
5. Ectomycorrhiza in forestry
Since ectomycorrhizal fungi are known as integral to the ecosystem, and a huge diversity of these fungi form associations with a number of economically important tree species cultivated for timber, their potential importance in tree nutrition has been acknowledged since the earliest experiments [40]. Plantation forestry is on the rise globally due to the growing demand for timber and pulp, as well as efforts to boost carbon sequestration by expanding forested areas. Although seedlings that are outplanted or naturally regenerate can form ectomycorrhizal associations from any naturally present mycorrhizal inoculum, the evident benefits of nursery stock being mycorrhizal prior to outplanting are apparent.
Many commercial practices, especially those aimed at enhancing hygiene in tree nurseries, are detrimental to the growth of most ectomycorrhizal fungi species, except for a few ruderal ones. As a result, specific techniques have been devised to facilitate the colonization of plants by selected fungi before outplanting. The application of these techniques has facilitated superior performance in tree crops in many parts of the world, particularly those which lack natural local sources of inoculum [41]. Grove and Le Tacon [42] provide a comprehensive outline of the imperatives for developing successful strategies to maximize the benefits of ectomycorrhizas in forestry. Meanwhile, there has been an increasing interest in the potential of harvesting edible fruiting bodies of ECM fungi, which have been utilized as commercial inoculants to enhance both diet and revenue. Inoculation can provide benefits at two key stages of timber production systems: in the nursery phase and post-outplanting in the field.
A significant portion of experimental research has concentrated on the benefits associated with producing well-developed seedlings that, along with their fungal symbionts, can thrive once transplanted into the field. While this focus primarily aims to ensure successful establishment, there are also direct cost savings realized through the accelerated throughput resulting from rapid growth in nurseries.
Furthermore, the utilization of inoculated seedlings has provided valuable insights. It has been observed that the responses to ectomycorrhizal colonization are particularly pronounced under challenging conditions, such as drought, metal contamination, and pathogen exposure. These observations have prompted an in-depth analysis of the functional mechanisms underlying the beneficial effects of ectomycorrhizal fungi, shedding light on their role in ameliorating adverse environmental factors.
Beyond the extensively studied effects on plant nutrition and growth, significant progress has been achieved in comprehending the roles of symbiotic relationships in imparting resistance to various stresses. These stresses, while occurring naturally in ecosystems, are often exacerbated locally due to prior land-use practices or the afforestation process itself. Discrepancies in performance between nursery and field conditions following inoculation may indeed arise from differential impacts of soil and environmental conditions on the specific mycorrhizal partnerships established through inoculation.
Forest productivity faces threats from global change factors such as increased inputs of nitrogen and sulfur directly into soils, leading to simultaneous decreases in pH, which can negatively affect both symbiotic partners. These effects are believed to contribute to forest decline syndromes witnessed in various parts of the world. Additionally, there are indications that the availability of base cations may eventually constrain forest productivity, emphasizing the potential benefits of ectomycorrhizal associations in enhancing nutrient uptake under such circumstances.
Acknowledgments
Sincere thanks to my students; Memoona Azeem, Wasiqa Arshad, and Mehboobullah Khan who helped me in formatting the text.
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