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ŠUMARSKI LIST 5-6/2021 str. 82     <-- 82 -->        PDF

Effects of invasion of non-native mycorrhizal fungi, plants, pests, and diseases on mycorrhizae – Učinci invazije alohtonih mikoriznih gljiva, biljaka i štetočina i bolesti na mikorize
The introduction and spread of non-native and invasive species represent a great risk to stability of forest ecosystems. Climate change, visible as change of climatic, atmospheric, and edaphic conditions, enables competitive and invasive non-native species to extend their present distribution ranges and reduce domestic biodiversity. Also, climate change causes shifts of plant species into previously marginal habitats which induce attendant shift in distribution and abundance of mycorrhizal fungi in association with these invading plant species. Many shifts in spatial distribution of plant species are accelerated by human mediation through trans-continental transport. Humans can also facilitate the introduction of non-native plant pests and non-native plant diseases into native forests and wildland ecosystems. Introduction of invasive mycorrhizal fungi, invasive non-native plants and non-native plant diseases is detrimental to native host plants (Bellgard and Williams, 2011).
Researches have shown that inoculation of higher plant species with mycorrhizal fungi might reduce infections of pathogenic fungi and nematode infestations. This protection results from passive and active stimulation/modulation of plant secondary metabolism by AM fungi. Passively, AM fungal colonization stimulate host plants to produce and store highly potent defensive compounds such as alkaloids and terpenoids which are stored in trichomes and vacuoles and that can be released when attacked (Champagne and Boutry, 2016; French, 2017). On the other hand, fungal hyphae may react on pathogen in the surrounding environment and ‘warn’ host cells by producing special compounds which will be transmitted as signals throughout the host plant from cell to cell through the plasmodesmata (Zipfel and Oldroyd, 2017).
Mycorrhizal colonization triggers both plant’s immune and defense systems, by triggering a primed state of plants resistance known as mycorrhiza-induced resistance (MIR). MIR improves holistic tolerance to attackers, either belowground by changing roots exudate metabolic composition in rhizosphere, or aboveground by alternation of volatile organic compounds (VOC) on shoot surface affecting allelopathic interaction by expressing repellent properties (López-Ráez et al., 2010). The phenomenon of priming could be defined as enhanced readiness of defense responses (Kim and Felton, 2013) and was described in plants with AM.
Different stimuli from pathogens, pests or chemicals can act as warning signals and trigger the establishment of priming. After perception of stimulus, changes may occur in the plant at the physiological, metabolic, transcriptional, and even epigenetic level (Avramidou, 2019). Upon subsequent pathogen attack primed plants display faster and/or stronger activation of various cellular defense responses to biotic or abiotic stress which leads to increased resistance and/or tolerance (Maunch-Mani et al., 2017). Best described and understood metabolic pathways induced by AM fungi priming signaling involve jasmonic acid (JA) and salicylic acid (SA) pathways that are in general mutually antagonistic (Jung et al., 2012). Furthermore, beneficial effects of AM fungi and increased resistance to pests could be broaden to transgenerational level, so it could be transferred to progeny, conferring better protection from pathogen attack and general fitness compared to descendants of unprimed plants by generating immunological memory (Pastor et al., 2012). Thus, priming of defense allows plants to boost their innate immune system and offers a long-term adaptation to disease-conducive conditions.
MIR can mitigate both abiotic and biotic stress factors and modulate and orchestrate entire plants response to environmental stresses to a certain extent. With regard to bioprotective, biofertilizer and priming properties of mycorrhizal symbiosis, Fester and Sawers (2011) consider that focus of the future research should be investigation of mycorrhization of the soil as an possible alternative to chemical fertilizers and pesticides in sustainable management and conservation of natural ecosystems.
Role of mycorrhizas in forest stability under climate change – Uloga mikoriza u stabilnosti šuma u uvjetima klimatskih promjena
Mycorrhizas are one of essential components of forest ecosystem stability. Their most important role in climate change conditions may be in stabilizing effects on forests trees that are under increasing environmental stress. The importance of mycorrhizal fungi in the ecosystem function is increasingly recognized, including the role of mycorrhizal networks in forest regeneration, succession, and resistance against different stress factors. Such networks which connect plants of the same or different species can affect the physiological and ecological processes of plants by facilitating interplant nutrient exchange, acting as inoculum reservoirs for seedlings and altering plant competitive abilities, but also play a pivotal role in orchestration of multitrophic above- and belowground interactions (Selosse et al., 2006).
The most of young trees in forests are linked to large one, old and highly connected trees, which are important for forest regeneration. Moreover, the extensive mycorrhizal networks of large trees facilitate survival and growth of younger trees helping them to resist and cope with the stressful environmental conditions. Access to the mycorrhizal network not only improves seedling survival and physiology, but seedlings are colonized by a more complex fungal community and receive carbon, nutrients and water transferred from the older trees (Selosse et al., 2006; Simard and