A novel source of atmospheric H2: abiotic degradation of organic material

[摘要] Molecular hydrogen (H₂) plays an important role in atmosphericchemistry by competing for reactions with the hydroxyl radical (OH·) andcontributing to the production of H₂O in the stratosphere, indirectlyinfluencing stratospheric ozone concentrations. The dominant pathway forloss of H₂ from the atmosphere is via microbially-mediated soil uptake,although the magnitude of this loss is still regarded as highly uncertain.Recent studies have shown that abiotic processes such as photochemicallymediated degradation (photodegradation) of organic material result in directemissions of carbon (C) and nitrogen (N)-based trace gases as well asH₂. This H₂ production has important implications on source-sinkdynamics of H₂ at the soil-atmosphere interface and thus it isimportant to quantify its variability over a range of plant types andmaterials. Here, we show laboratory observations of H₂ production andits temperature dependence during abiotic degradation of four plant littertypes as well as pure cellulose and high lignin content woody material. Agreater amount of H₂ was produced in the absence of solar radiationthan from photodegradation alone, verifying that low temperature thermaldegradation of plant litter is a source of H₂. In addition, we measureda significant release of H₂ both in the presence and absence ofO₂. Our results suggest that abiotic release of H₂ during organicmatter degradation is ubiquitous in arid ecosystems and may also occur inother terrestrial ecosystems. We propose that because these processes occurat the soil-atmosphere interface, they provide a previously unrecognizedproximal source of H₂ for microbial uptake and confound interpretationof direct measurements of atmospheric uptake that are important forconstraining the global H₂ budget.

[学科分类] 地球化学与岩石