Subnivean and Emergent Microclimate, Photosynthesis, and Growth in Erythronium grandiflorum Pursh, a Snowbank Geophyte

Abstract

In alpine/subalpine zones of the central Rocky Mountains, U.S.A., snowbank geophytes commonly sprout and even flower while still buried beneath late-lying snowbanks that can persist well into summer. Photosynthesis and growth in the snowbank geophyte Erythronium grandiflorum Pursh (glacier lily) was investigated before and after emergence from snowbanks at locations with early or late snowmelt. Although subnivean plant heights were not related to snowbank depth, heights at emergence were significantly greater in snowbanks with early melt dates. Also, there were no plants emerging from snowbanks that persisted until late June. Net photosynthesis in the subnivean and on the initial day of emergence was negative and photochemical development negligible (indicated by low chlorophyll fluorescence), despite pre-emergent light levels of over 500 μmol m^–2 s^–1 at snow depths of <5 cm. Increases in photosynthetic capabilities after emergence were rapid, as indicated by substantial shifts in photosynthetic light response curves over the subsequent 5 d. Photochemical development appeared to reach a steady state first (2 d), considerably ahead of stomatal conductance (6 d). Despite this lack of synchrony between stomatal and nonstomatal limitations to photosynthesis, steady states in the internal CO₂ concentration and the ratio of photosynthesis to stomatal conductance occurred within 2 to 3 d following emergence. Thus, the ecophysiology of this snowbank species appears to be most strongly influenced by the total time of emergence during summer, not its photosynthetic capabilities in the subnivean environment. These characteristics of subnivean growth and rapid photosynthetic acclimation following emergence probably minimize interspecific competition and maximize annual carbon gain in an extremely short, cold-limited growth season.