Living particulate fluxes in throughfall and stemflow during a pollen event

Michele Guidone,D Alex Gordon,John T Van Stan

doi:10.1007/s10533-021-00787-7

Abstract

Pollen shedding can produce rapid, abundant exchanges of nutrient-rich biomass from plant canopies to the surface. When pollen deposits onto understory plants, it can be washed off during storms via throughfall (a drip flux) and stemflow (a flux down plant stems). Pollen deposition may also alter the organismal community on plant surfaces, changing other biological particulates transported by throughfall and stemflow. We report concentrations and fluxes of pollen and other biological particulates (flagellate cells, nematodes, rotifers, mites and hexapodans) in throughfall and stemflow from an understory forb, Eupatorium capillifolium (Lam. dogfennel), during a Pinus palustris (Mill. longleaf pine) pollen shedding event, then compare these results to observations collected when pollen was absent. Pollen flux was 95.6 × 106 grains ha−1 season−1 from dogfennel canopies (63% and 37% transported by throughfall and stemflow, respectively), representing 0.1–3.2 g ha−1. Median concentrations in flagellates, nematodes and rotifers for throughfall and stemflow were higher during pollen shedding; however, mites and hexapodan concentrations were similar regardless of pollen presence. This is the first report of flagellate and hexapodan concentrations in canopy drainage waters. Flagellate concentrations were higher than for other organisms—being similar to those reported for streams, 105–107 cells L−1—and hexapodan fluxes were ~ 50 individuals m−2 per 1 cm of rainfall. These results indicate that throughfall and stemflow can (i) transport ecologically relevant amounts of pollen and organisms from the phyllosphere to the surface, and (ii) that the composition and flux of biological particulates can change markedly during pollen shedding.

Highlights

IntroductionThis relatively rapid and abundant canopy-to-surface exchange of biomass can play important roles in the biogeochemistry of the canopy and receiving aquatic and terrestrial systems
Forest canopies can shed 101-103 kg ha-1 of pollen over a short period of time—days, weeks or months—depending on the plant species and meteorological conditions (e.g., Boyer, 1981; Doskey and Ugoagwu, 1989; Greenfield, 1996; Lee et al, 1996; Cho et al, 2003; Lee andBooth, 2003)
Throughfall and stemflow generally had concentrations of 1-6 x pollen grains L-1, but zero-to-negligible pollen concentrations were observed in October (Figure 1a)

Summary

Introduction

This relatively rapid and abundant canopy-to-surface exchange of biomass can play important roles in the biogeochemistry of the canopy and receiving aquatic and terrestrial systems. Pollen macronutrient concentration is relatively high, being 2-5 times greater than litterfall (Stark, 1973; Lee et al, 1996). The unique stoichiometry of pollen can result in the release of biolabile material after deposition to detrital and freshwater systems (Rösel et al., 2012; Masclaux et al, 2013; Filipiak, 2016). Pollen P concentrations can be three times those of desert dust aerosols (Bigio and Angert 2018) and pollen P may be rapidly released by microbial communities (Graham et al, 2006; Filipiak, 2016)

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Conclusion