Contrasting altitudinal trends in leaf anatomy between three dominant species in an alpine meadow

Variation in leaf anatomical traits underpins the adaptations and phenotypic responses of plant species to their different natural environments. Temperature is a primary driver of plant trait variation along altitudinal gradients. However, other environmental drivers may also play important roles, and the interactions between drivers may have different effects on leaf anatomy for different species of the same larger clade. Such interactions might be especially important along shorter altitudinal (i.e. temperature) gradients. We predicted, therefore, that different monocot species could show idiosyncratic responses of leaf anatomical traits to a short altitudinal gradient. Moreover, for a species in which vegetative growth and reproduction are separated in time, its anatomical responses to altitude may differ and trade-offs between leaf and flowering stem anatomy may occur. To test these hypotheses, we examined leaf anatomy and δ 13 C signature (a possible indicator of anatomy-related water use efficiency or indicator of response to a decrease in CO 2 concentration with altitude) of three dominant and widely distributed monocot species (Scirpus distigmaticus, Elymus nutans, Carex moorcroftii) from seven elevations in an alpine meadow on the Qinghai-Tibetan Plateau. In addition, we examined the flowering stem anatomy of S. distigmaticus, across a short altitudinal gradient (four elevations) in the same region. Leaf anatomical traits (e.g. epidermal cell area, epidermal cell thickness, cuticular layer thickness, xylem transect area, phloem transect area) varied with altitude, but the patterns varied substantially among species and among anatomical traits within species. Additionally, for S. distigmaticus, (allometric) coordination between leaves and flowering stems was apparent for xylem transect area and phloem transect area. Trade-offs between leaf and flowering stem traits were also found for epidermal cell area, epidermal cell thickness and mesophyll cell area. Leaves were more responsive to altitude in their anatomical traits than flowering stems in S. distigmaticus, perhaps reflecting their relatively short period of stem development during a climatically relatively favourable season compared with that for leaves, which already start growing earlier in the year. Further research is needed on the interactive effects of environmental variables, as well as vegetative versus reproductive phenology both across and within suites of species to better understand and upscale plant anatomical responses to climate warming in alpine environments.