Fungal community assembly during Solidago canadensis shoot decomposition is driven by the plant’s invasion gradient
Solidago canadensis (L.) is an invasive plant species native to North America, but it is also widespread in Eurasia, Australia and New Zealand. Numerous authors suggest that the leaf litter of this plant decomposes rapidly. However, knowledge about the decomposition of its strongly lignified shoots, which remain in the environment for longer than one season, is limited. A comprehensive understanding of how fungal community assembly during Solidago canadensis shoot decomposition varies along the plant’s invasion gradient and which ecological factors drive these patterns, is still lacking. We conducted a one-year litterbag study to assess the mass loss of S. canadensis shoot litter within the gradient of its invasion, expressed as the percentage cover of this plant on the study plots. We also identified fungi participating in this process using a morphological approach and assessed their functional diversity. Predictions, based on generalised linear mixed models, revealed that the importance of different ecological mechanisms in fungal community assembly changed over the course of the decomposition, as mass loss of S. canadensis shoots progressed: from the prevalence of habitat filtering and niche differentiation to interspecific competition and, subsequently, habitat filtering again. We conclude that the decomposition starts with the high activity of endophytes, which are highly adapted to particular conditions within S. canadensis tissues and ends with saprotrophs that are highly specialised in the decomposition of plant litter. Moreover, our results suggest that the most abundant fungi, which we identified as weak degraders, appear to be unaffected by S. canadensis cover. This indicates their potential to decompose the type of plant litter recently introduced to the ecosystem. Based on this finding, we wish to place the emphasis on the invasiveness of S. canadensis, whose litter can be degraded by native fungi already present in the ecosystem, thereby allowing large amounts of newly-introduced biomass to enter the carbon cycle. This suggests that the invasibility of Natura 2000-protected mesic meadows may increase, as native fungi readily establish novel interactions with non-native plant species. Moreover, other areas similar to them within the secondary range of S. canadensis may be habitats more susceptible to changes than expected before.
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