Effects Of Saltmarsh Vegetation On Spatial And Temporal Variations Of Soil Carbon Storage And Emissions

Soils of coastal vegetated ecosystems,one of the largest reservoir of C in terrestrial ecosystems,can effectively sequester and store CO2 in the form of organic carbon(C).Due to the long-term waterlogged environment,coastal wetlands are also an important methane source.However,it is still unclear the changes and the underlying mechanisms of soil organic carbon(SOC)and soil C processes when responding to changes in vegetation type(i.e.,C3 to C4)in saltmarsh.Here,we quantified the effects of plant ecophysiological traits and soil properties on the SOC in the native Phragmites australis(C3)and invasive Spartina alterniflora(C4)community in the Yangtze River Estuary of China.The main findings are as follows:1.Species-specific differences in ecophysiological traits between invasive and native species can cause differential changes in soil properties through plant-soil feedback.Compared to the P.australis community,the S.alterniflora community had superior photosynthetic characteristics(e.g.,higher specific leaf area and leaf photosynthetic rate)and higher plant biomass,with higher soil water content(+22%)and lower soil temperature(-1.53?)and soil redox potential(-73.33 mV).In addition,the S.alterniflora community was salt-secreting,and soil salinity was relatively low(-0.08 mS/cm).2.In this study,SOC,LOC and ROC in the S.alterniflora community was generally higher than that in the P.australis community(P<0.05).The two plant communities had similar spatial patterns of soil carbon pools.The highest concentrations of SOC,LOC and ROC were found in the surface soil of both communities and then decreased with soil depth.Our results showed that the horizontal distribution of SOC,LOC presented an increase and then slow-down from the mudflats to the vegetated tidal marshes.3.Soil carbon emissions were dominated by soil respiration(CO2 effluxes;P.australis,94%;S.alterniflora,99%)with no significant difference between the two communities(P.australis,3.43 ?mol m-2 s-1;S.alterniflora,4.74 ?mol m-2 s-1).However,soil methane emission rates from S.alterniflora communities were 22.2 times higher than those of P.australis(S.alterniflora,179.68 nmol m m-2 s-1).Furthermore,soil carbon emissions of S.alterniflora community showed obvious seasonal dynamics and higher rates near the middle tidal flats,while the P.australis community did not show obvious spatial and temporal patterns.The results indicated that exotic species can affect carbon input and output processes by altering plant ecophysiological traits and soil properties,and eventually significantly alter the spatial and temporal patterns of soil carbon stocks and emissions in native ecosystems.Plant invasion under global climate change and intensive human activities will significantly affect coastal wetland ecosystems,ultimately changing the ecosystem structure,function and C cycling processes.