Variation in foliar δ15N among oriental oak (Quercus variabilis) stands over eastern China: Patterns and interactions

The patterns of variation in natural abundance of foliar and soil (15N) (expressed as δ15N) related to geographical and climatic variables frequently vary over plant species or plant function groups. It is essential to identify the pattern of foliar δ15N for specific plant species which has a widespread distribution and to explore the underlying mechanisms in the context of environmental change such as global warming and anthropogenic nitrogen deposition. Oriental oak (Quercus variabilis Bl.), characterized by cork bark, is a widely distributing deciduous broadleaf tree species that can be found in temperate and subtropical areas of East Asia. In this study, the variations in foliar and soil 15N were investigated based on the data of leaf and soil samples collected in 22 stands over eastern China (from 24 to 41° N in latitude and 102 to 123° E in longitude), and the mechanisms were discussed. The results showed that for oriental oak stands, mean foliar and soil δ15N were − 4.8‰ and 2.0‰, respectively, indicating an evident 15N enrichment in the soils. The average foliar δ15N value of oriental oak in warm temperate forest was significantly lower (p < 0.01), while a higher enrichment factor was also observed in temperate forests, than that in the subtropical areas. Over the eastern China, the foliar δ15N increased linearly and significantly with increasing mean annual precipitation (MAP) (R2 = 0.481 and p < 0.001) and mean annual temperature (MAT) (R2 = 0.285 and p = 0.01) and decreasing pH value of rain water (R2 = 0.333 and p = 0.005). With these results in eastern China, there are great implications in understanding how nitrogen dynamics of ecosystems responds to warming, drought and acid rain.