Changes in leaf vein traits among vein types of alpine grassland plants on the Tibetan Plateau

Vein traits influence photosynthesis and drought resistance and are sensitive to climate change.It is unclear whether vein traits, similar to other leaf traits, have obvious regional characteristics and covariance with other leaf traits, especially in Tibetan Plateau grasslands. We collected 66 species from 37 sites in late July of 2012 and early August of 2013 to investigate leaf vein traits and their relationships with other leaf traits in comparison with the available global database data and to elucidate vein investment of plants with different vein types. The average vein length per area(VLA) of plants in the Tibetan Plateau was within the range of the global dataset, and the relationships among vein traits and other leaf traits of alpine plants were consistent with the global models.The VLAs of parallel-veined grasses and pinnateveined forbs were significantly lower and higher than the global mean value, respectively. The leaf mass perarea and total nitrogen content of parallel-veined grasses were significantly lower and higher,respectively, than the global mean values; the opposite was observed in pinnate-veined forbs. The parallel-veined grasses exhibited almost a four-fold higher vein biomass investment(i.e., vein mass per leaf mass) than pinnate-veined forbs in the same region. The average VLA and its relationships with other leaf traits of the alpine grassland plants on the Tibetan Plateau had no regional characteristics,suggesting a convergence in plant leaf functioning.Plants with different leaf types differ in their adaptation strategies to plateau environments, and this may relate to biomass investment into leaf veins.Our study fills the gap with regard to vein density in alpine grassland species and provides a new perspective for understanding plant physiology and ecology by calculating and comparing the proportion of vein investment among different vein types.