Breaking down the invader of mesic meadows: fungi accelerate Solidago canadensis leaf litter decay more than protists at the first six months of decomposition

Solidago canadensis (L.) is an invasive plant species in Eurasia, native to North America. It is known as an environmental engineer modifying biogeochemical processes probably due to the massive leaf litter production and its influence on decomposition. Nevertheless, we do not know what is the impact of different microorganisms on this process. We conducted a litterbag experiment aiming to determine the influence of protists and microfungi on the decomposition process along the S. canadensis invasion gradient established in unmown mesic meadows. We evaluated how fast the leaf litter of S. canadensis decomposes and how the mass loss can be modified by increasing the cover of this plant. The invasion gradient had a negligible effect on the mass loss. Higher taxonomic diversity of mycobiota and protists accelerated the decomposition of S. canadensis but the taxonomic diversity of fungi exerted a bigger positive impact. Trophophase of ascomycetes accelerated decomposition, whereas the presence of pycnidia and perithecia inhibited it. Additionally, the presence of Oomycota, Sordariales, Orbiliales, and Cladosporiales representatives were the factors that accelerated mass loss. The presence of flagellates and Pleosporales representatives inhibited it. We found that generalists (pathotrophic-saprotrophic and pathotrophic-saprotrophic-symbiotrophic fungi) contributed to the deceleration of S. canadensis leaf litter mineralization. Our results show the rate of decomposition does not depend on the density of the Solidago population and indicates that Oomycota and Orbiliales are the most efficient accelerators of S. canadensis decomposition while Pleosporales slow down this process.