Abstract
The production of tree seedlings in forest nurseries and their use in the replanting of clear-cut forest sites is a common practice in the temperate and boreal forests of Europe. Although conifers dominate on replanted sites, in recent years, deciduous tree species have received more attention due to their often-higher resilience to abiotic and biotic stress factors. The aim of the present study was to assess the belowground fungal communities of bare-root cultivated seedlings of Alnus glutinosa, Betula pendula, Pinus sylvestris, Picea abies and Quercus robur in order to gain a better understanding of the associated fungi and oomycetes, and their potential effects on the seedling performance in forest nurseries and after outplanting. The study sites were at the seven largest bare-root forest nurseries in Lithuania. The sampling included the roots and adjacent soil of 2–3 year old healthy-looking seedlings. Following the isolation of the DNA from the individual root and soil samples, these were amplified using ITS rRNA as a marker, and subjected to high-throughput PacBio sequencing. The results showed the presence of 161,302 high-quality sequences, representing 2003 fungal and oomycete taxa. The most common fungi were Malassezia restricta (6.7% of all of the high-quality sequences), Wilcoxina mikolae (5.0%), Pustularia sp. 3993_4 (4.6%), and Fusarium oxysporum (3.5%). The most common oomycetes were Pythium ultimum var. ultimum (0.6%), Pythium heterothallicum (0.3%), Pythium spiculum (0.3%), and Pythium sylvaticum (0.2%). The coniferous tree species (P. abies and P. sylvestris) generally showed a higher richness of fungal taxa and a rather distinct fungal community composition compared to the deciduous tree species (A. glutinosa, B. pendula, and Q. robur). The results demonstrated that the seedling roots and the rhizosphere soil in forest nurseries support a high richness of fungal taxa. The seedling roots were primarily inhabited by saprotrophic and mycorrhizal fungi, while fungal pathogens and oomycetes were less abundant, showing that the cultivation practices used in forest nurseries secured both the production of high-quality planting stock and disease control.
Highlights
IntroductionIn Europe, forest tree planting has increased considerably in recent decades [1,2], thereby increasing the demand for planting stock
The clustering of the high-quality sequences showed the presence of 3564 non-singleton contigs representing different operational taxonomic units (OTUs)
The results demonstrated that the seedling roots and the rhizosphere soil were inhabited by a high diversity of fungal and oomycete OTUs (Figures 1 and 2, Table 2), thereby corroborating previous observations that the belowground habitat in forest nurseries supports species-rich communities of fungi [66]
Summary
In Europe, forest tree planting has increased considerably in recent decades [1,2], thereby increasing the demand for planting stock. The increased planting is primarily due to the commitment in many countries to increase the forest area and/or to rehabilitate degraded forest ecosystems, and to reclaim disturbed sites for forestry. This allows us to maintain and increase biodiversity, and to mitigate the negative effects of global climate change [2,3]. Most of the planting stock, which is used in forestry, is produced in forest nurseries [4]. The quality of the seedlings produced is one of the critical factors that contributes to successful
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