Contrasting altitudinal patterns of leaf UV reflectance and absorbance in four herbaceous species on the Qinghai-Tibetan Plateau

Aims Alpine plants have to cope with intense ultraviolet(UV)radiation and its altitudinal changes.It has been argued that leaf UV reflec-tance and absorbance should play a central role in acclimation and adaptation to changes in UV radiation,but evidence is lim-ited from high altitudinal ecosystems.In this study,we assessed whether leaf UV reflectance and leaf pigments jointly vary with altitude in alpine broadleaved herbaceous species.The primary hypothesis is that leaves with higher UV reflectance should have lower UV absorbance and/or lower contents of photosynthetic pigments.Methods Leaf UV reflectance,leaf UV absorbance and photosynthetic pig-ments(chlorophyll a and b,carotenoids)were examined in four broadleaved herbaceous species in relation to their habitat alti-tudes.The leaf surface reflectance and leaf extract absorbance at wavelengths of 305 and 360 nm were measured to examine the leaf optical and photochemical characteristics in the UV-B and UV-A bands,respectively.The species included Saussurea katochaete Maxim.,Saussurea pulchra Lipsch.,Anaphalis lactea Maxim.and Rheum pumilum Maxim.,which are distributed along the same slope from 3200 to 4200 m in the Qilian Mountains,Qinghai-Tibetan Plateau.Important Findings The leaf UV absorbance was approximately twice as high at 305 nm(UV-B)than at 360 nm(UV-A)for all species except R.pumilum.Among the four species,the leaf UV absorbance was the highest and almost all values were within 2-6 Abs cm^(−2)(absorbance cm^(−2))in S.pulchra,but the lowest(frequently<1 Abs cm^(−2))were observed in R.pumilum.Only R.pumilum showed significantly higher values at higher elevations.Leaf UV reflectance was generally higher at higher elevations for all species except for A.lactea,and exhibited much larger altitudinal variations compared to leaf UV absorbance.Anaphalis lactea showed a very high UV reflectance even at low altitudes.Among the four species,photosynthetic pigments tended to decrease with an increase in leaf UV reflectance but increased with leaf UV absorbance.The study suggests that leaf UV reflec-tance,rather than leaf UV absorbance,plays a more active role in acclimation to altitudinal changes in UV radiation,and a high investment in leaf UV reflectance may limit the accumulation of photosynthetic pigments in alpine plants.