Ectomycorrhizal fungi promote higher allocation of freshly added organic nitrogen to POM than arbuscular mycorrhizal fungi in a temperate common garden experiment

Mycorrhizal fungi mediate organic matter allocation and transformation in forest soils worldwide. Ectomycorrhizal (ECM) and arbuscular (AM) fungi differently influence the formation of distinct soil organic matter (SOM) pools, such as particulate (POM) and mineral-associated organic matter (MaOM), which differ in composition and stability. In AM-dominated systems, organic matter cycling is characterized by the rapid decomposition of fresh plant litter. This is largely driven by high-quality litter inputs of AM-associated tree species and the stimulation of microbial activity, including saprotrophic fungi and bacteria. In contrast, ECM-dominated systems exhibit slower decomposition rates and nutrient cycling that are more tightly regulated by fungi. ECM fungi efficiently access complex organic forms of nitrogen and phosphorus through enzymatic degradation of organic matter, shaping nutrient availability in these ecosystems. Research was conducted at the MyDiv tree diversity experiment, located at the Bad Lauchstadt Experimental Research Station of the Helmholtz Centreer for Environmental Research - UFZ, (51.3918 N, 11.8858 E), Germany. The experiment was established in October 2023. To assess the incorporation of different organic resources to different pools of soil organic matter and assimilation of those by mycorrhizal fungi, soil samples were collected from each experimental enclosure. DNA was extracted from the mycelium using the Qiagen DNEasy PowerSoil kit. The concentration of isolated DNA was measured using a QuBit fluorometer. PCR was conducted on the ITS2 marker region with the use of primer pair fITS7:fITS7o/ITS4, that allowed both ECM and AM fungali identification. Illumina NextSeq sequencing (2 x 250 bp) of the ITS2 marker region was performed.