Global climate change is expected to initiate species distribution shift (e.g., the warming climate causes upslope shift of plant communities). However, downscaling this general shifting pattern to species level could lead to contrasting shifting directions (upslope and downslope shifts) and the underlying mechanisms that drive these contrasting directions are not well understood. We hypothesized that the shifting directions were determined by species-specific responses to nutrient and water stress with elevation. Here, the plant water and nutrient stress were estimated by foliar carbon and nitrogen isotope ratios in conjunction with measurements of leaf and soil parameters, and we sampled eight dominant woody species with different shifting directions along an elevational gradient (200m ~ 1300m).
Results/Conclusions
Our results showed that: (1) Both the up- and downslope shifting species had higher foliar δ13C values at lower elevations, indicating their higher water stress which was also supported by the reduced soil water content of lowland; (2) In contrast, only upslope shifting species had reduced foliar δ15N values at lower elevations, indicating their higher nutrient stress which corresponded to the reduced soil fertility of lowland; (3) Non-shifting species did not show any significant patterns of these two isotope ratios with elevation; (4) The nutrient sensitivity of the upslope shifting species was associated with their functional traits, especially their faster growth and larger tree height. This study, for the first time, highlights the primary role of nutrient stress on driving species elevational shifts. Notably, under the warming climate, the potentially enhanced drought would exacerbate the upslope shift of nutrient sensitive species. Another implication of our results is that current modeling practice, lacking consideration of the species-specific responses to nutrient stress, could lead to significant bias on prediction of species distribution.