Plants' eye view of temperature governs elevational distributions.

Explaining species geographic distributions by macroclimate variables is the most common approach for getting mechanistic insights into large scale diversity patterns and range shifts. However, species' traits influencing biophysical processes can produce a large decoupling from ambient air temperature, which can seriously undermine biogeographical inference. We combined stable oxygen isotope theory with a trait-based approach to assess leaf temperature during carbon assimilation (TL ) and its departure (DeltaT) from day-time free air temperature during the growing season (Tgs ) for 158 plant species occurring from 3400 to 6150 m a.s.l. in Western Himalayas. We uncovered a general extent of temperature decoupling in the region. Plant height and delta(13) C, and leaf dry matter content explained the interspecific variation in DeltaT and TL respectively. The combination of TL and DeltaT, with DeltaT contributing most, explained the interspecific difference in elevational distributions. Stable oxygen isotope theory appears promising for investigating how plants perceive temperatures, a pivotal information to species biogeographic distributions.