Grasslandification has significant impacts on soil carbon, nitrogen and phosphorus of alpine wetlands on the Tibetan Plateau

Changes in land use will alter soil profiles of wetlands under climatic change and human disturbance, especially through grasslandification. Grasslandification is the process where a wetland is drained and converted to pasture. Grasslandificationon on the Tibetan plateau has been intensive over the last 40 years, mostly from drainage by humans. However, many previous studies have generally analysed only wetland ecological processes, despite the fact that grasslandificaiton, the biggest change process on the Tibetan plateau, has resulted from social and economic stresses. The assessment of changes to the soil C, N and P by grasslandification is the key to understanding the contribution to carbon management from alpine wetlands and variation of soil nutrition. We experimentally investigated the effect of grasslandification on soil physical (water, pH and EC) and chemical profiles (C, N and P) in grasslandification-pasture plots and reference wetland plots based on previous remote sensing results of the Maqu alpine wetland on the Tibetan plateau. The grasslandification process of alpine wetlands reduced vegetation quality and increased degree of drought, especially relevant with heavy grazing of the pasture. In general, grasslandification reduced the C, N and P content of soils and increased pH and EC, all significantly associated with variation to the vegetation and soil water. Soil C has changed more than N, P with grasslandification, but the soil C:N:P ratio has been relatively stable, and grasslandification has lead the wetland to the habitat with nitrogen limited. Thus, the grasslandification process of alpine wetlands on the Tibetan plateau over the last 40 years has increased net carbon emissions from alpine wetland soil contributions to atmospheric CO2. The grasslandification of alpine wetland is a drying process and observed changes were mainly influenced by variations of soil water and nutrients. Maintaining vegetation and soil water is an important approach to mitigating soil degradation and carbon emissions from alpine wetlands. In consideration of the current social and economic status of the study site, it is difficult to return or restore the grasslandification area to the original wetland, so the better strategy is to protect the existing wetland and reduce the human disturbance.