Low-temperature acclimation of net photosynthesis in the crustaceous lichenCaloplaca trachyphylla

摘要

The seasonal net photosynthetic and respiratory response matrix is presented forCaloplaca trachyphylla(Tuck.) A. Zahlbr. at 7, 14, 21, 28 and 35 deg;C, under 0, 300, 600, 900, and 1200ensp;mu;Eensp;mminus;2ensp;sminus;1illumination, over a full range of thallus hydration, in January, May, and July. The maximum rates of net photosynthesis recorded during the summer period, at 14ndash;21 deg;C, under 1200ensp;mu;Eensp;mminus;2ensp;sminus;1illumination are ca. 3.0ensp;mg CO2ensp;hminus;1ensp;gminus;1. They are interpreted in terms of the thallus temperatures documented during early-morning dew events and during sporadic thunderstorm activity. During winter, net photosynthetic rates at 7 deg;C increase significantly from the summer rates of ca. 2.0ensp;mg CO2ensp;hminus;1ensp;gminus;1to ca. 3.2ensp;mg CO2ensp;hminus;1ensp;gminus;1. This low-temperature photosynthetic-capacity change is shown to be temperature acclimation and it is suggested that the mechanism involves a change in the affinity constant (Km) of ribulose bisphosphate carboxylase. This acclimatory response can be readily induced, or reversed in winter, by air-dry storage at an appropriately high or low ambient temperature. In midsummer, however, comparable storage conditions fail to elicit an acclimatory response. The significance of low-temperature photosynthetic acclimation inC.trachyphyllais discussed in relation to winter snowmelt sequences during chinook conditions in Alberta.