The dynamics of plant and arbuscular mycorrhizal fungal communities in grasslands under changing land use

Abstract

Enam kui kaks kolmandikku maismaaökosüsteemidest on inimtegevuse poolt tugevasti mõjutatud. Viimaste hulka kuuluvad ka Euroopa pool-looduslikud rohumaad, mis paistavad silma oma taimekoosluste suure mitmekesisusega. Need rohumaad on kujunenud kestva ja mõõduka niitmise ja/või karjatamise tulemusel ning nende säilitamiseks on vaja samasuguse maakasutuse jätkumist. Kuna pool-looduslike rohumaade pindala on drastiliselt vähenenud, on looduskaitseliste eesmärkide täitmiseks tihtipeale vajalik ka nende rohumaade taimekoosluste taastamine. See omakorda nõuab detailset arusaama rohumaade elurikkust mõjutavatest teguritest. Madalakasvulised väheviljakate rohumaade taimeliigid on valguslembesed ja neil on väiksed, tuule või kariloomade kaasabil levivad seemned. Kinnikasvanud rohumaadel ei ole selliste taimeliikide jaoks piisavalt valgust ning puuduvad sobilikud tingimused seemneleviks. Lisaks võib niiduliikide populatsioonide seisundit halvendada ning taastumist takistada sümbiontsete mullamikroobide puudumine. Viimaste hulka kuuluvad ka arbuskulaarmükoriissed (AM) seened. Antud doktoritöö tulemused kinnitasid, et lisaks seemnelevi soodustamisele ja valgustingimuste parandamisele on kinnikasvanud rohumaade taastamisel tähtis roll ka AM seentel. Tüüpilises avatud rohumaa taimekoosluses on tunduvalt rohkem mükoriisa olemasolust oluliselt sõltuvaid taimeliike kui kinnikasvanud rohumaa taimekoosluses. Seetõttu võib AM seente olemasolu või puudumine rohumaade taastamisprotsessi oluliselt mõjutada.

Human activities have modified about two thirds of all terrestrial ecosystems. European semi-natural grasslands are among the most diverse ecosystems globally; at the same time, they are among the ecosystems most affected by human activities. Such grasslands develop under extensive land use practices – notably grazing and mowing – and land use change can dramatically decrease the extent and quality of such habitats, posing a considerable threat to grassland biodiversity. Many restoration efforts have been undertaken to mitigate against habitat loss, but re-establishing grassland specialist plants often challenges restoration practitioners. This may be because many typical grassland plant species have small seeds adapted to dispersal by wind or grazing animals. As such, a lack of grazing animals or dense vegetation around restored grassland patches might hinder seed dispersal between grassland patches, and thus maintenance of vital meta-populations. It is also possible that restoration sites lack certain soil organisms found in intact habitats, and their absence impairs the establishment of plants that rely on them (e.g. symbiotic fungi, such as arbuscular mycorrhizal (AM) fungi). The aim of this doctoral thesis was to assess the relevance of these factors for successful grassland restoration. The results of the thesis confirm the importance of facilitating plant species dispersal between grassland patches by re-opening the vegetation to create dispersal corridors and by re-introducing continuous grazing management, with grazing animals able to move between grassland patches. Moreover, the results suggest that a lack of suitable AM fungi in the soil of severely altered and isolated grassland patches might hamper natural re-establishment of typical grassland vegetation. Coordinated re-introduction of target plant and AM fungal communities could increase restoration succession in such cases.