Climate and ecosystem N natural abundance along a transect of Inner Mongolian grasslands: Contrasting regional patterns and global patterns

[1] Nitrogen isotopes provide integrated information about nitrogen cycling in terrestrial ecosystems. This study explores the regional patterns of ecosystem N abundance along a 1200 km transect in Inner Mongolian grasslands and their relationships with climate. Results indicate that climatic variables control approximately 50% of the variation in ecosystem N abundance along the transect. Ecosystem N abundance decreases as both mean annual precipitation (MAP) and mean annual temperature (MAT) increase. Regional patterns obtained from our study differ from reported global patterns. Ecosystem N abundance is negatively correlated with MAT along the eastern part of the transect, while a positive correlation between MAT and ecosystem N is apparent at the global scale. MAP exerts stronger controls on ecosystem N abundance along the western part of the transect than what is shown in a global regression model. Ecosystem N abundance in the western part of the transect is substantially higher (ca. 3%) than the values projected by a global model. The DNsoil-plant (%) (difference in d N values between plant and soil) values in Inner Mongolian grasslands are not significantly correlated with either MAP or MAT; but DNsoil-plant values are positively correlated with MAT and negatively correlated with MAP at the global scale. These conflicting trends strongly indicate that climatic controls on ecosystem N abundance are scaledependent. Regional N deposition gradients, grazing-induced ammonia volatilization, and variation in plant-soil types are among the possible causes of these inconsistencies. Citation: Cheng, W., Q. Chen, Y. Xu, X. Han, and L. Li (2009), Climate and ecosystem N natural abundance along a transect of Inner Mongolian grasslands: Contrasting regional patterns and global patterns, Global Biogeochem. Cycles, 23, GB2005, doi:10.1029/ 2008GB003315.