Pollen as nutrient source in Holocene ombrotrophic bogs

Several laboratory experiments and field observations demonstrate that saprotrophic and ectomycorrhizal fungi effectively use pollen cytoplasm and suggest pollen produced by wind-pollinated trees as a crucial nutrient source for fungi and their plant hosts in nutrient-limited environments. However, the role of such interactions is still underestimated or neglected in ecology and paleoecology. Here, we consider pollen attacked by fungi in palynological records from Holocene raised peat bogs as a nutrient source for ecosystems in the past. The attacks occurred through the pollen germination areas by a variety of saprotrophic, ericoid mycorrhizal, ectomycorrhizal or dark septate endophyte fungi. Large amounts of attacked pollen in phases rich in Calluna vulgaris highlight the importance of Ericaceae shrubs, hosting ericoid mycorrhizal fungi and forming hotspots of decomposition in nutrient-deficit bogs. Applying estimations of pollen rain from literature, and based on own observed pollen infection rates we estimate the annual release of nitrogen, phosphate and potassium from pollen, and highlight their significance in pushing the ecosystem nutrient cycle in early spring time, when several species release their pollen. We highlight the significant role of anthropogenic changes in pollen deposition for pre-industrial bogs and hypothesize about the consequences of the pollen-based interrelation between wind-pollinated plants and their mycorrhizal fungi in paleoecology and evolution.