How pollen organic matter enters freshwater food webs

Abstract

Huge amounts of pollen can accumulate at the air-water interface during the floral bloom of wind-pollinated trees. We hypothesized that such pollen rains act as subsidy pulses, promoting the development of a neustonic microbial food web and the transfer of pollen organic carbon to aquatic consumers. During a pine pollen rain event on an oxbow lake, microorganism concentrations were by far higher in the neuston, where pollen grains accumulated, than in the seston. Zooplankton species were also unevenly distributed in the two compartments. Bulk isotope and isotopes of fatty acid analyses revealed trophic partitioning among these zooplankton species, with some of the taxa foraging specifically on neuston, where they benefit from pollen-derived carbon. Microorganisms were identified as a key element in the trophic upgrading of pollen food quality and in the transfer of pollen carbon to metazoan consumers. Pollen rains may thus contribute, as an allochthonous food pulse, to aquatic production at specific seasons, but they may also act as a structuring factor in lake habitats.

Highly unsaturated fatty acids in nature: what we know and what we need to learn

“…They work best when the fatty acids of interest from different resources have distinct isotopic signatures (Bec et al ). For example, Masclaux et al () revealed that several freshwater zooplankton taxa relied largely on inputs of terrestrial pollen grains that were relatively enriched in δ 13 C as their principal source of ω‐3 HUFAs, while relying on freshwater phytoplankton that was relatively depleted in δ 13 C for their other fats. Thus far most compound‐specific stable isotope work has focused on characterizing food web links in soil communities and in freshwater and marine systems (Ruess and Chamberlain , Gladyshev et al ).…”

Comparison of sterol and fatty acid profiles of chytrids and their hosts reveals trophic upgrading of nutritionally inadequate phytoplankton by fungal parasites

“…This mechanism might enhance overall trophic transfer efficiency in the pelagic food web. Chytrids have been shown to upgrade allochthonous organic matter by increasing digestibility of pollen grains and facilitating the transfer of otherwise inaccessible PUFA from pollen to metazoans through chytrid zoospores (Masclaux et al, 2013;Kagami et al, 2017). However, it is unclear if a similar biochemical upgrading of autochthonous carbon sources, such as phytoplankton, occurs upon infection by chytrid parasites.…”

Pollen Stoichiometry May Influence Detrital Terrestrial and Aquatic Food Webs

“…Indeed, it was suggested that, in detrital food webs, litter-decomposing fungi are colimited by the scarcity of N, P, and S in litter, which they mitigate by foraging on pollen and which allows them to complete litter decomposition (Stark, 1972;Staaf and Berg, 1982;Hutchison and Barron, 1997). Forests may produce pollen in masses reaching 100 to 1000 kg/ha (Greenfield, 1996), and the bulk of this mass is deposited onto forest floors and in lakes (Richerson et al, 1970;Proctor et al, 1996;Shumilovskikh et al, 2015), thus increasing the productivity of the ecosystem (Graham et al, 2006;Masclaux et al, 2013). The present study considers the ecological stoichiometry framework to relate data on pollen nutritional quality to the role of pollen in nutrient cycling within and between terrestrial and aquatic ecosystems.…”