Alpine species and drought: impacts of timing of dry events on leaf growth and senescence

Abstract

Drought effects on plants can depend on timing, especially in seasonal ecosystems. Using a mesocosm, we assessed impacts of zero-precipitation timing and duration on six species typical of one of the most widespread alpine grasslands in the Alps.

Four two-month treatments were applied: control (C), continuous irrigation; early-season drought (ED), no irrigation during month one; mid-season drought (MD), no irrigation during month two; and full-season drought (FD), no irrigation. Leaf growth and senescence onset and intensity (number of yellow leaves or length of yellow lamina) were measured for Carex curvula, Alchemilla pentaphyllea, Scorzoneroides helvetica, Mutellina adonidifolia, Phyteuma hemisphaericum, and Poa alpina. Species- and community-level responses were analyzed using t-tests, generalized least squares, generalized/mixed-effects models, and Kruskal-Wallis tests.

Leaf growth was reduced by ED and FD for most species and at community level (−30% and −51% compared to C); only C. curvula showed reduced growth under MD (−24%). Senescence began earlier in ED and FD (33 days earlier at community level and for all species except A. pentaphyllea and M. adonidifolia). After two months, senescence increased across species under ED, MD and FD compared to C (+88%, +316%, +627%, respectively, at community level) with forbs more impacted by MD than graminoids (+85% vs +32%).

Impacts on growth were strongest under early-season drought, while effects on senescence were greatest when drought occurred one month after snowmelt. These findings highlight the role of species-specific responses and drought timing in determining how, and to what extent, high-elevation grasslands may be affected by climate change.