Abstract
BackgroundThe important greenhouse gas (GHG) methane is produced naturally in anaerobic wetland soils. By affecting the production, oxidation and transport of methane to the atmosphere, plants have a major influence upon the quantities emitted by wetlands. Different species and functional plant groups have been shown to affect these processes differently, but our knowledge about how these effects are influenced by abiotic factors such as water regime and temperature remains limited. Here we present a mesocosm experiment comparing eight plant species for their effects on internal transport and overall emissions of methane under contrasting hydrological conditions. To quantify how much methane was transported internally through plants (the chimney effect), we blocked diffusion from the soil surface with an agar seal.ResultsWe found that graminoids caused higher methane emissions than forbs, although the emissions from mesocosms with different species were either lower than or comparable to those from control mesocosms with no plant (i.e. bare soil). Species with a relatively greater root volume and a larger biomass exhibited a larger chimney effect, though overall methane emissions were negatively related to plant biomass. Emissions were also reduced by lowering the water table.ConclusionsWe conclude that plant species (and functional groups) vary in the degree to which they transport methane to the atmosphere. However, a plant with a high capacity to transport methane does not necessarily emit more methane, as it may also cause more rhizosphere oxidation of methane. A shift in plant species composition from graminoids to forbs and/or from low to high productive species may lead to reduction of methane emissions.
Highlights
The important greenhouse gas (GHG) methane is produced naturally in anaerobic wetland soils
There have been many studies showing that more than half of CH4 emitted from wetland soils, including rice paddies, was transported internally by plants [13,20,33,34,35,36]; and in a study of Alaskan tundra vegetation, 92–98% of CH4 was attributed to plantmediated transport [29]
Lowering the water table caused a significant reduction in CH4 emissions from almost all mesocosms, including the control (Table 1, Figure 1), but there was no significant interaction between water table and plant species (Table 1)
Summary
The important greenhouse gas (GHG) methane is produced naturally in anaerobic wetland soils. Different species and functional plant groups have been shown to affect these processes differently, but our knowledge about how these effects are influenced by abiotic factors such as water regime and temperature remains limited. Plants influence the amounts of CH4 emitted from wetlands in various ways They may enhance emissions, both by providing a carbon substrate for methanogenesis in the form of root exudates [10,11], and by transporting CH4 internally from the rhizosphere to Moisture conditions are known to have a large effect upon CH4 emissions from soils. To understand the importance of this mechanism for CH4 emissions from wetlands, it is necessary to measure the chimney effect for a range of wetland species under conditions of both high and low water table. To the best of our knowledge, no such studies have yet been carried out
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