厩肥の施用効果について

Grazers can have a large impact on ecosystem processes and are known to changevegetation composition. However, knowledge of how the long-term presence of grazers affectssoil carbon sequestration is limited. In this study, we estimated total accumulated organic carbonin soils of a back-barrier salt marsh and determined how this is affected by long-term grazing byboth small and large grazers in relation to age of the ecosystem. In young marshes, where smallgrazers predominate, hare and geese have a limited effect on total accumulated organic carbon.In older, mature marshes, where large grazers predominate, cattle substantially enhanced carboncontent in the marsh soil. We ascribe this to a shift in biomass distribution in the local vegetationtowards the roots in combination with trampling effects on the soil chemistry. These large grazersthus act as ecosystem engineers: their known effect on soil compaction (based on a previous study)enhances anoxic conditions in the marsh soil, thereby reducing the oxygen available for organiccarbon decomposition by the local microbial community. This study showed that the indirecteffects of grazing can significantly enhance soil carbon storage through changing soil abiotic conditions.This process should be taken into account when estimating the role of ecosystems inreducing carbon dioxide concentration in the atmosphere. Ultimately, we propose a testableconceptual framework that includes 3 pathways by which grazers can alter carbon storage:(1) through above-ground biomass removal, (2) through alteration of biomass distribution towardsthe roots and/or (3) by changing soil abiotic conditions that affect decomposition