DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 5-6/2021 str. 78 <-- 78 --> PDF |
can lead not only to migrations (change of xeric distributional limits) of different forest tree species, but also to mortality of forest trees and decline of entire forests (Stojanović et al., 2013). Moreover, climate change can disturb the soil carbon balance by reducing carbon storage and by inducing a large positive feedback to atmospheric CO2 levels. Not only that disturbances could affect soil carbon storage and do harm to the trees, they could also accelerate nutrient cycling, alter microbial community structure, and change dynamics of soil food web. Carbon storage in soils involves complex interactions between plants and soil organisms and depends on the balance between carbon inputs through photosynthesis and outputs through respiration, which are both affected by climate change (Simard and Austin, 2010). Under climate change the stability of the entire forest ecosystems and the carbon balance depend to a large degree on the interactions between trees and soil microorganisms, especially mycorrhizal fungi. Mycorrhizal fungi make mutualistic association with more than 90% of plant species and represent the key players in carbon dynamics and carbon fluxes among plants, soil and the atmosphere, due to their well branched system of hyphae which is used to obtain water and nutrients from the soil and deliver them to the host plant in exchange for photosynthetically produced carbohydrates (Smith and Read, 2008; Simard and Austin, 2010). In temperate regions there are two dominant types of mycorrhizas. Ectomycorrhiza is formed mainly by ectomycorrhizal (ECM) fungi from phyla Basidiomycota and Ascomycota with trees and shrubs. Sporocarps of many ECM fungal species are edible, some even delicious and expensive (Katanić et al., 2017). An ECM root is characterized by three structural components: a mantle (or sheath), a Hartig net and an extraradical (extramatrical or external) mycelium. The mantle is a structure formed by fungal hyphae that enclose the rootlet. Function of Hartig net, a labyrinthine intercellular network, is exchange of nutrients between partners in ECM. Extraradical mycelium is an outwardly growing system of hyphal elements (hyphae, rhizomorphs and cystidia) which connect ECM fungus with both the soil and the sporocarps. This is an extensive system which increase the surface area of colonized root in the contact with soil, and it is active in absorption of nutrients and water (Smith and Read, 2008). Arbuscular mycorrhiza is formed by arbuscular mycorrhizal (AM) fungi from phylum Glomeromycota with 80-90% of all plants but primarily with grasses and herbs. The name “arbuscular” is derived from characteristic three like structures, arbuscules which occur within cortical cells of plant and increase the contact area between symbionts. These structures are together with storage vesicles considered diagnostic for AM symbiosis (Smith and Read, 2008). The main difference between these two types of mycorrhizae is that in ECM hyphae never enter plant cells while in AM fungal structures are mainly formed within cells of their host. AM fungi never produce mantle and their extraradical mycelium is not so complexly developed as in ECM fungi (Smith and Read, 2008). However, in both ECM and AM fungi extensive external mycelial networks can function in the colonization of new seedlings and transfer of carbon, nutrients or water between plants of the same or different species thus affecting plant and fungal community dynamics (Simard et al., 2002; Selosse et al., 2006; Smith and Read, 2008). Considering the fact that the small and profuse hyphae have about 60 times more absorptive area than fine roots, during drought stress plants invest their photosynthetic carbon (4-20 %) in the development of hyphae, due to the higher efficacy of hyphae in provision of inaccessible water. Generally, as nutrient and water limitations increase, plants allocate more photosynthate to mycorrhizal hyphae to increase soil resource uptake (Simard et al., 2002; Smith and Read, 2008). Although mycorrhizal fungi are not saprotrophic, in cases when amounts of plant photosynthates are low, some ECM fungi are prone to enzymatically decompose large organic molecules (e.g. proteins, chitin, pectin, hemicellulose, cellulose) as an alternative carbon and energy source, which is not specific for AM fungi (Talbot et al., 2008). On the other hand, arbuscular mycorrhizal fungi play important roles in promoting soil aggregation and soil carbon storage. Although AM hyphae turnover is short (lasts from days to a few months), AM fungi are able to deposit significant amounts of relatively recalcitrant carbon compounds such as chitin and glomalin. Glomalin binds small soil particles, promoting in that way aggregation and soil stability (Simard and Austin, 2010). The ongoing climate change have multi-faceted effects not only on metabolism of plants, but also on the soil properties and all microorganisms including mycorrhizal fungal communities (Simard and Austin, 2010). Beside pivotal role of mycorrhizal fungi in linking aboveground and belowground components of forest ecosystems through common mycelial network, mycorrhizal fungi can improve plant tolerance to unfavorable abiotic stress factors such as heat, drought, salinity or presence of heavy metals, as well as boost plant immunity and increase resistance to pathogens and provide other ecosystem services (Smith and Read, 2008; Smith et al, 2010; French, 2017). There are a lot of unfavorable factors and processes connected with climate change which influence forest ecosystems stability. According to Bellgard and Williams (2011) they are called the drivers of climate change and include: increasing CO2 concentration in the atmosphere, temperature rise, altered precipitation, increased N deposition, soil |