Stomatal length correlates with elevation of growth in four temperate species

Stomatal size and density are considered two key ecophysiological parameters, because they jointly influence stomatal conductance. In the present study, we examine trends in these anatomical traits along a 660-m elevational gradient on Mt. Moosilauke, in the White Mountains of New Hampshire. Samples were collected from two broadleaf tree species (Betula papayrifera var. cordifolia and Sorbus americana) and two herbaceous understory species (Cornus canadensis and Dryopteris carthusiana). Guard cell length increased with elevation in all four species (all p ≤.10), but there were no clear elevational trends in stomatal density in any of the four species (all p ≥ .10). A "potential conductance index" [= (guard cell length)² × stomatal density × 10-⁴] was positively correlated with elevation for all species, but this trend was significant only for the two understory species (both p ≤ .10). Results are discussed in the context of prevailing theories to explain changes in stomatal traits with elevation.