Variation in the plant-mediated methane transport and its importance for methane emission from intact wetland peat mesocosms

Aims and Methods Vascular plants are known to influence the production,transport and oxidation of methane in wetland soils,but these processes are not well understood.using plants grown in intact peat cores,we compared the influence upon methane emissions of 20 forb and graminoid species from European wetlands.We measured plant-mediated transport of methane(conduit or chimney effect)using a novel agar-sealing technique that prevented methane exchange from the bare soil to the atmosphere.Important Findings the plant-mediated transport(chimney effect)represented between 30%and almost 100%of the total methane flux,with graminoids exhibiting greater internal transport than forbs.In general,plants with less dense root tissues and a relatively larger root volume exhibited a larger chimney effect.most species(12 out of 20)signif-icantly reduced methane emissions compared to bare soil and only one species,Succisa pratensis,increased them.We suggest that characterising vegetation in terms of plant functional traits and plant processes offers an effective method for estimating methane emis-sions from wetlands.However,we found no correlation between the magnitude of the chimney effect and the overall influence of different plant species on methane emissions.besides introducing a useful tool to study plant-mediated transport,this work suggests that characterising vegetation in terms of functional traits could improve estimates of methane emissions from wetlands,which in turn could help in designing mitigation strategies.

Testing experimentally the effect of soil resource mobility on plant competition

Aims The volume of soil beyond a plant’s roots from which that plant is able to acquire a particular nutrient depends upon the mobility of that nutrient in the soil.For this reason it has been hypothesized that the strength of competitive interactions between plants vary with soil nutrient mobility.We aimed to provide an experimental test of this hypothesis.Methods We devised two experimental systems to investigate specifically the effect of nutrient transport rates upon intraspecific competition.In the first,the exchange of rhizosphere water and dissolved nutrients between two connected pots,each containing one plant,was manipulated by alternately raising and lowering the pots.In the second experiment,the roots systems of two competing plants were separated by partitions of differing porosity,thereby varying the plants’access to water and nutrients in the other plant's rhizosphere.In this second experiment,we also applied varying amounts of nutrients to test whether higher nutrient input would reduce competition when competition for light is avoided,and applied different water levels to affect nutrient concentrations without changing nutrient supply.Important findings In both experiments,lower mobility reduced competitive effects on plant biomass and on relative growth rate(RGR),as hypothesized.In the second experiment,however,competition was more intense under high nutrient input,suggesting that low nutrient supply rates reduced the strength of the superior competitor.Competitive effects on RGR were only evident under the low water level,suggesting that under lower nutrient concentrations,competitive effects might be less pronounced.Taken together,our results provide the first direct experimental evidence that a reduction in nutrient mobility can reduce the intensity of competition between plants.