High resistance to low-temperature photoinhibition in two alpine, snowbank species

Abstract

At high elevation, the combination of low temperature and high solar irradiance may be particularly conducive to the low-temperature photoinhibition of photosynthesis (LTP). Microclimate and photosynthesis were measured in situ in Caltha leptosepala and Erythronium grandiflorum, alpine perennials that may experience even lower temperatures and higher sunlight (PFD, photon flux density) than other alpine plants due to their proximity to snowbanks. Light-saturated CO2 assimilation (A(sat)) and chlorophyll a fluorescence were measured for naturally frosted and non-frosted plants that also experienced either natural or experimentally-lowered sunlight. Following several hours of full sunlight exposure, A(sat) in both species was not different in leaves that experienced either frostless nights, shading (ca. 1200 versus 2000 μmol m-2 s-1 PFD), or the combination of frostless nights and shade, compared to leaves that experienced frost followed by full sunlight. However, increases in the maximum efficiency of photosystem II photochemistry occurred following either frostless nights (change in F(v)/F(m) = 5.3%; P < 0.001), experimental shade (4.0%; P < 0.1), or the combination of frostless nights and shade (8.4%; P < 0.001) in C. leptosepala. Corresponding increases in F(v)/F(m) were less in E. grandiflorum (1.8% following frostless nights, P < 0.05; 3.7% with shade, P < 0.05; and 5.1% with both, P < 0.001). Plants of E. grandiflorum in the process of emerging through snowbanks had a 10% increase in F(v)/F(m) with experimental shading (P < 0.05). In both species, depressions in F(v)/F(m) that resulted from natural frost and high sunlight exposure recovered fully by sunset the same day, and depressed F(v)/F(m) was associated with greater non-photochemical quenching. Thus, only slight and reversible LTP was apparent, and both species appeared well-adapted for maintaining carbon gain on days following frost and high sunlight exposure.