Isoprene fluxes from warm temperate and tropical seagrass communities

Abstract

Isoprene is an important biogenic volatile organic compound (BVOC), with a contribution to annual greenhouse gas emissions similar to that of methane in terms of carbon equivalent. Isoprene is mostly produced by terrestrial vegetation, although marine ecosystems also play an important role in isoprene production. Here, we report isoprene fluxes from warm temperate seagrass communities dominated by specific seagrass species (Posidonia australis, Zostera muelleri and Halophila ovalis) in Wallis Lake, NSW, Australia, and from tropical seagrass communities (H. ovalis/Halodule uninervis mixed patches) on Lizard Island, QLD, Australia. P. australis and Z. muelleri were net isoprene sinks (-0.6 ± 0.1 and -3.4 ± 2.0 nmol m-2 h-1, respectively), whereas H. ovalis (2.4 ± 0.2 nmol m-2 h-1) and mixed patches of H. ovalis/H. uninervis (13.2 ± 3.2 nmol m-2 h-1) were a net source of isoprene, indicating that seagrass communities can be both a source of and a sink for isoprene on a local scale depending on species. Overall, isoprene effluxes were more than 5 times higher on Lizard Island than in Wallis Lake, likely due to higher temperatures and prolonged sunlight on Lizard Island during the time of measurement. Wallis Lake and Lizard Island seagrass communities emit isoprene to the water column at an average rate of -0.3 and 8 mg m-2 yr-1, respectively. Seagrass communities are a benthic source of isoprene in coastal waters, but only make a small contribution (2.3 Gg C yr-1) to the global marine isoprene flux (11.6 Tg C yr-1).

The climate benefit of seagrass blue carbon is reduced by methane fluxes and enhanced by nitrous oxide fluxes

“…16,35,36 ). Seagrasses also emit other climate warming greenhouse gases like isoprene 37 , which we have not considered. In addition, we have not compared the net climate benefit of seagrass communities to the net climate benefit of adjacent unvegetated sediments.…”

Mangrove Creeks Are a Sink for Isoprene—A Functional Link Between Ecosystems

“…Isoprene concentrations were highest at high tide and lowest at low tide, suggesting that isoprene was carried into the creeks from the Broadwater, southern Moreton Bay. The source of isoprene was most likely from production by phytoplankton (Shaw et al., 2003), MPB (Acuña Alvarez et al., 2009; Exton et al., 2012), and seagrass communities (Hrebien et al., 2021) in the Broadwater (Eyre et al., 2011b). Isoprene and dissolved oxygen followed the same tidal trend, suggesting the most likely producer of O 2 and isoprene was in the Broadwater.…”

“…Although species specific, benthic bacteria from estuarine systems have been identified as a sink for isoprene in marine systems, with a rapid degradation of isoprene occurring during the highest isoprene production rates in sediments (Acuña Alvarez et al., 2009; Broadgate et al., 2004; Shaw et al., 2003). Seagrass has also been identified as a source and a sink for isoprene, which is also species specific (Hrebien et al., 2021). Isoprene production has been found in mangrove leaves and flowers in Key Largo, Florida (up to 92 ± 109 µg (g dry weight) −1 h −1 ) but is a low emitter of isoprene compared to terrestrial forest ecosystems (Barr et al., 2003).…”