Seasonal changes in temperature and light drive acclimation of photosynthetic physiology and macromolecular content in Lobaria pulmonaria

Abstract

Lobaria pulmonaria (L.) Hoffm. is an epiphytic lichen common to temperate deciduous forests where it copes with large changes in temperature and light levels through repeated annual cycles. Samples of L. pulmonaria were taken from a deciduous forest in southeastern Canada at 35-day intervals from February 1999 to February 2000 and also from a rare population in an evergreen forest in March and August 1999. At field-ambient temperatures and light levels, the realised photosystem II (PSII) electron transport was low both in the summer and winter, with transient peaks in the spring and autumn. In contrast, the seasonal pattern of potential electron transport measured at a fixed 20 degrees C peaked in winter, showing the importance of temperature in driving photosynthesis to low levels in the winter despite an acclimation of electron-transport potential to exploit the high ambient light. Realised gross CO2 uptake was correlated with PSII electron transport at mechanistically plausible rates at all sampling sites in the summer but not in the winter, indicating electron diversion away from CO2 fixation in the winter. Chlorophyll content was highest in the dark summer months. The amount of ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) large subunit (LSU) was highest in spring. Changes in the level of this hyperabundant protein and in the activity of PSII maintained a relatively constant rate of maximum CO2 uptake per RuBisCO LSU from April through November, despite great changes in the seasonal light and temperature. L. pulmonaria acclimates between light and temperature stress in the winter months to light-limitation in the dark summer months. Transition intervals in the spring and autumn, with warm, bright and wet conditions, are likely the most amenable times for growth.

Growth and ecophysiological acclimation of the foliose lichen Lobaria pulmonaria in forests with contrasting light climates

“…Recent studies have shown seasonal shifts in the macromolecular complexes of the photosynthetic system of L. pulmonaria in forests (MacKenzie et al 2001(MacKenzie et al , 2002(MacKenzie et al , 2004. The photosynthetic acclimation in L. pulmonaria occurs within a non-dividing algal cell population that maintains its photosynthetic capacity over many years (Schofield et al 2003).…”

“…Clear changes in macromolecular allocation, chlorophyll fluorescence quenching and xanthophyll cycle driven by slow seasonal changes in temperature and light have been shown for L. pulmonaria (MacKenzie et al 2001(MacKenzie et al , 2002, but less is known about acclimation to sudden changes in light that occur when forests are logged. We also aim at recording internal variables influencing growth (as reviewed by Palmqvist 2000), such as photosynthetic pigments, efficiency of photosynthesis and thallus mass per area after a sudden transplantation to new environments.…”

CO2 exchange and thallus nitrogen across 75 contrasting lichen associations from different climate zones

“…Some of the unaccounted for variation in NP max might then be related to variation in amount and activity of Rubisco (cf. Palmqvist 2000;MacKenzie et al 2001). Finally, temperature has a large impact on lichen photosynthesis (Kershaw 1985;Kappen 1988) and it is likely that the unaccounted for variation in NP max across the lichens would have been lower if all samples had been measured at their optimal temperature.…”

Nitrogen uptake in relation to excess supply and its effects on the lichens Evernia prunastri (L.) Ach and Xanthoria parietina (L.) Th. Fr.

“…4a) followed the increase in the F v /F m values from 0.67 to 0.74. This probably reflects an annual variation in thallus Chl a concentration and concomitantly in quantum yield efficiency (Mackenzie et al 2001).…”