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Large Uptake of Atmospheric OCS Observed at a Moist Old Growth Forest: Controls and Implications for Carbon Cycle Applications
Author(s) -
Rastogi Bharat,
Berkelhammer Max,
Wharton Sonia,
Whelan Mary E.,
Itter Malcolm S.,
Leen J. Brian,
Gupta Manish X.,
Noone David,
Still Christopher J.
Publication year - 2018
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2018jg004430
Subject(s) - epiphyte , environmental science , daytime , atmospheric sciences , ecosystem , diurnal cycle , canopy , flux (metallurgy) , forest ecology , leaf area index , carbon sink , ecology , chemistry , biology , geology , organic chemistry
Diurnal and vertical patterns of carbonyl sulfide (OCS) and CO 2 mixing ratios above and within a 60‐m‐tall old‐growth temperate forest are presented. Canopy air from four different heights was sampled in situ using a continuous integrated cavity output spectroscopy analyzer during August–September 2014. Measurements revealed large vertical gradients in OCS, from which we inferred ecosystem fluxes. The diurnal cycle of OCS mixing ratios at all heights exhibited a typical pattern characterized by nighttime drawdown, an early morning minimum, and a maximum of OCS around midday. Daytime increase in the upper canopy is attributed to entrainment of planetary boundary layer air into the canopy. The ecosystem was found to be a large daytime sink of OCS (mean maximum daytime flux ~ −75 pmol · m −2 · s −1 ). Mean leaf relative uptake (concentration normalized uptake of OCS flux to CO 2 uptake) was found to be 6.9. We discuss this high leaf relative uptake in the context of the presence and distribution of epiphytes at the site. While epiphytic uptake of OCS has been studied before, we show for the first time that this may contribute significantly to ecosystem fluxes under humid or moist conditions. We test this theory using a chamber experiment measuring epiphytic fluxes for two species of lichen and one moss species (in situ and in a laboratory). We suggest that the role of epiphytes should be explicitly considered when using OCS as a tracer of ecosystem‐scale photosynthesis in forest ecosystems with abundant epiphytic cover and biomass.